THE ROAD AHEAD TO REAL-TIME OIL AND GAS RESERVOIR … · THE ROAD AHEAD TO REAL-TIME OIL AND GAS RESERVOIR MANAGEMENT* R. G. SMITH and G. C. MAITLAND² Schlumberger Limited, Sugar

THE ROAD AHEAD TO REAL-TIME OIL AND GAS

RESERVOIR MANAGEMENT*

R. G. SMITH and G. C. MAITLAND²

Schlumberger Limited, Sugar Land, Texas, USA² Schlumberger Cambridge Research, Cambridge, UK

The aim of this paper is to provide a vision of how the processes and materials used toextract hydrocarbons from underground reservoirs might evolve over the next decadeor so, in order to stimulate and provide signposts for the research and development

which is needed to meet the industry’s future needs. The target is to double the recovery ofhydrocarbon in place from today’ s typical values of 30±40%. This will require real-timereservoir management, for which the ability to simulate, monitor and control all the keyprocesses that take place within the reservoir and production system is a fundamentalrequirement. A particular emphasis is placed on the role to be played by chemical and processengineering. Existing exploration and production practices are summarized and possiblescenarios described for the way in which the enabling technology and engineering mightevolve. This is done by presenting a series of technology roadmaps and cartoon futurescenarios for four technology packages that together have the potential to enable a new era inproductivity. Oil and gas wells can be likened to high pressure, high temperature tubularreactors, whose geometry and sophistication is becoming increasingly complex. It is envisagedthat the oil reservoir of the future will evolve towards a subterranean factory of interconnectingdrainholes, whose overall ef® ciency in producing saleable products will be determined by theway that its individual production units are deployed and coupled in the light of market needs.Linked to improved understanding of the regional geology, optimising the downhole factoryproductivity will enable the operators to reduce signi® cantly their investment risks andsubstantially increase worldwide recovery rates.

Keywords: oil® eld; reservoir management; process optimization and control; ¯ ow simulation;porous media; complex ¯ uids; multiphase ¯ ow; sensors; smart materials

INTRODUCTION

The aim of this review is somewhat different than thosenormally commissioned for this Journal. The topic is thescience and engineering of hydrocarbon recovery processesand, whilst providing a summary of existing practices, themain aim is to provide a vision of how these practices mightevolve over the next decade or so. It is hoped that this willprovide a stimulus for both academic research and enhancedcollaboration between universities, the service sector and oilcompanies to enable such a vision to be achieved and evensurpassed.

The scenario on which this picture of the future is basedassumes that, as for the past decade, hydrocarbon prices willremain relatively low for some time into the future. Theconsequence of this is that, with new reserves beingdiscovered in increasingly dif® cult to exploit locations(deep water, cold climates etc.), the only way for oil and gasextraction to remain economically viable is to maintain andreduce the lifting costs by the development of increasinglycost-effective new technology. After a decade when oilsupply has signi® cantly exceeded demand, these curves are

now converging, and at some stage will undoubtedly cross.Estimates of when this will occur vary (3±10 years) alongwith those for the total recoverable reserves in place (850±2000 Bbbl) [1 bbl = 159 l] and when global productionof conventional oil will start to decline (2010±2030)1 .However, the bottom line is that recovery cost andef® ciency will continue to be strong drivers throughoutthis evolution. Consumption up to the end of 1997 was 900Bbbl and the most optimistic of models predicts thatconsumption will exceed reserves in place by 2012.

In this context, the major drivers for oil® eld technologyfall into ® ve main categories:

· Optimizing the costs and ef® ciency of well construction± Introducing surface to reservoir drainholes in the most

cost-effective manner

· Maximizing well productivity± Optimizing the connectivity of individual wells to the

producing reservoir

· Managing reservoirs to optimize the overall recovery± Optimizing the placement/treatment of wells and ¯ uid

drainage patterns

· Ensuring environmental compliance and best practices± Adopting a proactive approach to minimizing environ-

mental impact

539

0263±8762/98/$10.00+0.00� Institution of Chemical Engineers

Trans IChemE, Vol 76, Part A, July 1998

* This paper is based on a presentation made by Reid G. Smith at a RoyalSociety of Edinburgh Foresight Forum on 17th April 1997.

· Being able to operate in increasingly extreme conditions± Coping with the extremes of water depth, climate,

reservoir depth, location access, etc. that are characteristicof almost all new reserves discoveries.

A simply stated but challenging goal that emerges fromthese drivers is to increase recovery by a factor of twoÐfrom the current typical levels of 30±40% towards 60±80%or beyond. The authors take the view that to reach thistarget will require Real-time Reservoir Management.(Reservoir Management has been de® ned by Al-Hussainyand Humphreys2 as `the marshalling of all appropriatebusiness, technical and operating resources to exploit areservoir optimally from discovery to abandonment . . .’ .) Toachieve this, the ability to simulate, monitor and control inreal time all the key processes that occur within the reservoirand production system is a fundamental requirement. Thesetechnologies are at the heart of Chemical and ProcessEngineering; we aim to demonstrate that whilst mechanical,electrical and electronic engineering advances will continueto be key to meeting the technical challenges that lie aheadin extracting hydrocarbons from the earth, the techniquesof process automation, optimization and control that arecommonplace in the chemical and process industries havea major role to play in the evolution, or even revolution, ofthe industry. In many ways, an oil well is nothing morethan a high temperature, high pressure (HTHP) tubularreactor, in both its constructionand productionphases, and areservoir is an underground factory whose overall ef® ciencyin producing saleable products is determined by the way thatits individual production units are deployed and coupled inthe light of market needs. Linked to improved under-standing of regional geology, optimizing the downholefactory productivity will enable the operators to reducesigni® cantly their investment risks and substantiallyincrease worldwide recovery rates.

It is worth pointing out that in setting the goal ofincreasing reservoir recoveries to 80%, we are not enteringthe realms of enhanced or tertiary oil recovery (EOR). Thisregime is concerned with extracting oil that is trappedwithin the ® ne capillary structure of a porous reservoir, andrequires technology that addresses the additional capillarypressures that arise at the pore level (microns) in suchcircumstances3 . The increase from 40% to 80% recoverycan by and large be addressed by improving the globalsweep, or conformance control, of the reservoir byrecognizing that it is highly heterogeneous at the cm scaleor above, both through permeability contrasts and theexistence of natural fractures and faults. It is this regime thatis the target of what is usually termed today Improved OilRecovery or IOR4 , and it is within this context that thispaper is written.

The approach we take is to examine four areas of oil® eldtechnology that are on the critical path towards achievingthis goal. For each we describe a `Technology Roadmap’ Ðthe way aheadÐ which charts the possible evolution of thescience and technology that needs to be developed andintegrated to reach this new era in reservoir productivity.The roadmap method has been popularized by Motorola5 asan orderly process for developing a picture of futuretechnology, together with a projection of its evolution overtime. It was originally intended as a practical tool toencourage business managers to give proper attention

to their technological future. It also provides a means ofcommunicating to engineers and marketing personnel whichtechnologies will be requiring development and applicationfor future products.

The process starts by stating a clear overall target, basedon product market, competitive or technology trends. Forthe upstream exploration and development sector of theindustry, we are suggesting doublingeconomic hydrocarbonrecovery. Armed with such a target, developing the roadmapis an iterative brainstorming process, often involvingpeople from a variety of functions (e.g. R&D, manufactur-ing, marketing, business). The fact that roadmap timeframes tend to extend well beyond conventional businessand product planning horizons adds to the challenge.Another bene® t of the process is that it forces theparticipants to be explicit about their assumptionsÐ tomake clear the problems that must be solved to reachthe target, the order in which they will be solved, and theexpected interim results.

The process has been adopted by the US semiconductorindustry overall, where it has been used to provide acommon visionÐ a framework to guide R&D for all sectorsof the US semiconductor technology baseÐ industry,universities, and government organizations6 . The overalltarget was established by extending historic trends fordynamic random access memory (DRAM) bit count by afactor of four every three years until 2010; this implies64 Gb/chip in 2010. From that follow the requirementsfor supporting technology to enable such devices to bedesigned, manufactured, and tested.

In describing how current approaches might evolve or bereplaced, we show how each of these supporting technologypackages might change the nature of the surface anddownhole hardware employed, and the way the reservoir ismanaged, through a series of cartoons. These demonstratehow implementing a process/systems engineering approachto exploiting the reservoir can respond to the various driversand constraints mentioned earlier. We should emphasizethat the roadmaps and cartoons do not represent the R&Dstrategy of Schlumberger. Meeting the challenges describedhere7 requires an overall industry effortÐ building on thework of operators, service companies, suppliers, academics,SME’ s, and government.

THE RESERVOIR MANAGEMENT PROCESS

For many years, the dream of the oil company operatorshas been to integrate the data, interpretations, models,simulations, and effects of development and productiondecisions in such a way as to optimally deplete the reservoiraccording to a business model and economic constraints.The basic steps are shown Figure 1.

A central step in reservoir management is the develop-ment of a reservoir model that can be used in mapping thedistribution of ¯ uids, identifying unswept reservoir volumesand developing production strategies, including placementof in® ll wells, design of injection and production pro-grams (such as extended well testing), and targeting ofhorizontal and multilateral (multiple wells from the sameprimary wellbore, possibly with further branches and sub-branchesÐ see later section on Well Construction) wells.The model must capture reservoir geometry, internalarchitecture, rock properties and their variability, ¯ uid

540 SMITH and MAITLAND


content and distribution, ¯ uid properties and producibility.Key elements of the ¯ ow simulation include the ¯ uidmechanics of multiphase ¯ uids in complex porous andfractured media, the thermophysical properties of hydro-carbon ¯ uid/aqueous salt solution mixtures and theirvariation with temperature/pressure and their thermody-namic phase behaviour under reservoir and productionconditions. The overall objective of building the model isreduced reservoir uncertainty in a broad sense, fromprospect appraisal to production extension. This is a keyto exploration risk reduction and to optimum reservoirmanagement.

Not shown in the ® gure, but underlying all elements ofthe process, is the Data Management system responsiblefor all data involved in reservoir management. Ef® cientdata management and software integration are of primeimportance throughout. They often limit the practicality ofiterative, detailed reservoir model development and `whatif ’ scenario planning.

In what follows we touch on many of the boxes shownin the Figure, including the extremely important ® eldÌmplementation’Ð taking action based on the data,modelling, and simulation. Given this is the reservoirmanagement process of today, what technology advancescould result in substantial improvement? We discuss thisunder four headings, key technology highways on our routeto doubling recovery:

· Reservoir modelling

· Well construction

· Well productivity optimization

· Reservoir management

RESERVOIR MODELLING: TOWARDS THESHARED EARTH MODEL

In obtaining suitable models of the reservoir, the focus istechnology aimed at risk reduction by acquiring new data,enabling fuller use of acquired data and improving reservoirmodeling and simulation. The roadmap for this domain isshown in Figure 2. As for each roadmap, Figure 2 has atime axis proceeding from left to right. On the left-handside, labelled `Today’ , we show the current state of the art inthe industry. On the right-hand side, labelled `Long Term’ ,

we indicate the possible state of the technology and practiceover, perhaps, a 10 year period. Also shown are some`Near Term’ milestones. The arrows indicate evolution ofthe individual elements. Along the time axis is shown theoverall targetÐ doubling economically viable hydrocarbonrecovery. If today the goal is 30±40%, not unrealistic forNorth Sea reservoirs, then the long-term goal is 60±80%recovery. In other reservoirs, the economically viablenumbers may be much lower, but the goal of doublingrecovery remains.

The roadmaps emphasise the broad technologies andengineering issues that are the key stepping stones toprogress. They do not show all the detail, such as technicaloptions, decision points, critical success factors, requiredcore competencies etc. that are needed to de® ne a speci® cplan of action. They are the framework within which themore detailed technologies we describe, and those whichthe community has yet to develop, ® t together and act as aguide to the capabilities and timing required of these newtechnologies.

Existing TechnologyÐ Coarse Reservoir Model

In today’ s oil® elds, the reliability of reservoir simulationand production forecasting is often limited by the accuracyof the reservoir model. Many failures in pilot and ® eld-wideIOR projects can be attributed to the poor quality of thereservoir model used to simulate the process; the decisionto go ahead with the project had been based on overlyoptimistic forecasts of reservoir performance, which mainlyresulted from an inadequate description of reservoirheterogeneity. We have what is termed a coarse reservoirmodel.

With present industry techniques, reservoir models aretypically built by ® rst delineating major horizons and faultsfrom surface seismic data (see Figure 3 on colour insertbetween pp 542 and 543). Most would argue that 3D seismicimaging has had a major effect on the upstream business inrecent years8 . On the other hand, while steady progress hasbeen made to reduce acquisition costs, much remains to bedone, especially for land and shallow water seismics.

Reservoir geometry and properties are then de® ned at aresolution much ® ner than seismic through use of well-logdataÐ see Figure 4 on colour insert between pp 542 and

541THE ROAD AHEAD TO REAL-TIME OIL AND GAS RESERVOIR MANAGEMENT


Figure 1. Key inputs and basic steps of the overall Reservoir ManagementProcess.

Figure 2. Reservoir modelling roadmap; the time scale proceeds from leftto right and covers, say, a ten year period.

543. Electrical, acoustic, gamma ray and other radiationprobes9 are being deployed with increasing resolution,acquisition ef® ciency, depth of investigation and reliabilityto map out the rock and ¯ uid features away from a drilledwellbore. These data are already routinely transmitted bysatellite to remote of® ces in real-time. Well test data canhelp de® ne reservoir characteristics further from the well-bore. In recent years, there has been much effort devoted toextended well testing/early production systems. An exampleis the BP Machar ® eld in the UK North Sea.

Geology is only handled in an ad hoc way (e.g. byspecifying a statistical correlation distance parameter) giventhe limited geological information available and there isonly loose integration of the various data inputs to themodel. Many software packages are available, at differentscales of integration1 0 .

Near Term

Improved MeasurementsIn the near term, we can expect improvements in existing

measurements, as well as introduction of new measure-ments. A number of approaches are being explored forimproving the de® nition of seismic data. Some efforts areaimed at improving resolution from the current 20±100 m.Others are aimed at elucidation of ¯ uid contacts, as well asrock and ¯ uid properties. In addition, there is much activitysurrounding 4D, or time-lapse, data. One recent exampleof this is the BP-Shell Foinaven ® eld, West of Shetlands,where periodic seismic surveys combine data from conven-tional towed streamers and a seismic monitoring system,consisting of a sea-bed mounted array of permanent sensors.In Foinaven, where each well represents a large investmentin drilling, completion, and subsea infrastructure, 4Dseismic may permit the operator to reduce the number ofwells necessary to access the oil, resulting in a substantialreduction in development costs.

Another example of the use of the technique is by Statoilin the N Sea Gullfaks ® eld1 1 . In Figure 5 (see colour insertbetween pp 542 and 543) a comparison of seismic imagesacquired in 1985 (left) and 1995 (right) shows the reservoirchanges that have occurred as this ® eld has been produced.Overall, oil has been replaced by water in the lower, westernsections of each fault block. This indicates a relativelysmooth sweep. In some areas, however, such as in thenorthern part of the middle fault block, oil and gas appear tobe in a separate compartment that has not been tapped. Anassessment of actual drainage patterns is helping Statoilreservoir engineers optimize the management of reserves.

In addition, we can expect improved measurements (e.g.NMR, optical logging, ¯ uorescence) and deep measure-ments, for both cased-hole and open-hole applications.For instance, NMR1 2 is used to deduce permeability, free-¯ uid porosity, the porosity irrespective of the lithology, anda new petrophysical parameterÐ pore size distribution.These parameters will help interpreters locate by-passedoil, predict overall productivity and make completiondecisions. We can also expect new measurements, perhapsinvolving chemical/biochemical sensors and nanotechnol-ogy, aimed at improved characterization of the localchemical nature of the reservoir and its ¯ uids.

An area which complements attempts to improve theresolution of seismics data where near-term developments

are feasible is by extending log measurements away fromthe borehole, in freshly drilled wellbores and in those thathave been cased with a steel lining. In addition, as morewells are drilled with multiple laterals, cross-well measure-ments are likely to make a comeback in the guise of cross-lateral measurements (e.g. electromagnetic, acoustic). Newpermanent sensors will be installed within wells for bothproduction monitoring and formation evaluation.

Tools for the GeologistIn parallel, new tools will be developed for the Geologist.

These will include new measurements and/or applica-tions (e.g. paleo-magnetism, geochemistry, age, deposi-tional environment, sequence stratigraphy). Today, buildinga reservoir model is a time-consuming and dif® cult process.However, we can see the beginningsof CAD-like systems toassist geologists in building and re® ning models. Thesesystems include geoscience extensions to the traditionalgeometric and topological representations of mechanicalCAD.

Advances in IT, speci® cally 3D graphics and webbrowsers, are leveraged to provide the geologist with anew tool kit to sit on top of an integrated data managementsystem1 3 . The geologist is able to see all of the oil ® eld data(thin sections, cores, borehole images, seismic amplitudes,etc.) at their true scale and in their correct spatial context.By using an online archive of geological knowledge, he isable to make a 3D interpretation of the geology of the oil® eld and to view this interpretation in the context of thedata. The interpretation may then be exported to support¯ uid ¯ ow simulation, well planning, etc.

New tools for basin geology modelling are also ofinterest. They perform mathematical simulation of physicaland chemical geological processes at the scale of thesedimentary basin. The modelling entails the prediction ofthe deposition and burial history of rocks, their temperaturehistories, the location, amounts, type, and timing ofhydrocarbons generated and the location, amounts, type,and timing of accumulations and losses. Questions that maybe answered by basin simulations include: when didstructures ® ll and with what, how likely is it that spillagehas taken place, what are the most crucial parameters tothese assessments, and is it possible to determine theseevents better? In the near term, we can expect improvementsto be made to the current 1D modelling capability, and tosee these systems integrated with the CAD-like and othermodelling systems.

Integrated SoftwareThere are in fact two integration problems that need

addressing. First, how to design software frameworks so thatfuture applications can be folded into an existing ensemblein a seamless and straightforward manner. Second, how tointegrate the measured and interpreted geoscience data fromthe point of view of the reservoir physics and chemistry,across a great variety of scales.

The former, software problem is likely to be solvedbefore the geoscience problem since integration of diversepackages is a central problem facing the entire softwareindustry, rather than a problem unique to the oil industry.However, there is a piece the oil industry must addressby itselfÐ the design and evolution of a standardMultidisciplinary Data Model, i.e. one which is able to



integrate data as diverse as seismic, real-time drilling, andproduction data. Immersive visualization, or virtual realityinteraction, is another technique that is likely to prove apowerful aid in enabling the models to be used bygeneralists. The ability of reservoir managers to roamthrough the producing and evolving reservoir, taking real-time production decisions, is an enticing prospect.

Long TermÐ Integrated Reservoir Model

The end goal is development of the technology necessaryto enable use of a single, integrated reservoir model,commonly called the `Shared Earth Model’ . It is `the onemodel for all data’ (geometric, geological, geophysical,petrophysical, geochemical, reservoir, ¯ uid ¯ ow, ¯ uidphysics...). It must be both veri® able and predictive andbe capable of capturing the reservoir architecture, the ¯ uidhighways, barriers, and contacts, together with rock and¯ uid types and properties.

Time-lapse measurements will include 4D seismic data,but will include a variety of other data as well. For instancemore proactive, interventional characterization procedures(such as advanced, smart tracer techniques) will bedeveloped to complement methods which simply monitorthe naturally evolving reservoir. Eventually 5D data couldbecome the norm, with the dimensionality increased toinclude a dimension spanning different data types. A centralfocus of current research is methods for better constraining4D reservoir modelling by more complete assimilationof measurements across many scales, consideration ofrealistic geological discontinuities and early incorporationof dynamic data. The objective is twofold:

(a) to make better use of all available data and(b) to decrease signi® cantly the time it takes to obtain a¯ uid ¯ ow simulation model that ® ts the data and can be usedfor prediction.

Progress here is vital to enabling practical reservoir modelsto be built and updated in an iterative manner to aidproduction decisions. Models obtained by direct inversionof such data combinations, rather then by ® tting andextrapolation, are likely to prove a key element.

Alongside the improved models of reservoir structure andpermeability maps, and the provision of techniques tomonitor ¯ uid movements within the reservoir for bothmodel calibration and validation purposes, there are greatchallenges for the ¯ uid mechanicians. The techniques formodelling the ¯ ow of multiphase ¯ uids in heterogeneousporous media must keep pace with the level of detail andcomplexity with which the matrix permeability distribu-tion will be capable of being speci® edÐ or plausiblegeostatistical stochastic realizations developed. Today, avariety of upscaling techniques are used to coarsenpermeability data, speci® ed or constructed with high spatialresolution, to the lower resolution that present day ¯ owsimulators can handle. While single phase ¯ ow permeabilitycan be upscaled with some con® dence, methodology forupscaling a two-phase ¯ ow description is still a topic ofactive research.

The speed, accuracy and spatial resolution of thesimulation will need to meet the demands of real-timeapplications and of using 4D data from a range of sourcesto update and re® ne the integrated model. There will

therefore be much scope for methodology development.Today, streamline-based ¯ ow simulation methods areadvocated as a means to speed up simulations, by effec-tively adapting the computational grid to the permeability® eld and ¯ ow solution. It is clear that there are manyfurther advances to be made by exploiting the possibilitiesof solution-adaptive geometry, physics and discretisation.Improved models for ¯ uid thermophysical properties atreservoir conditions will also be needed; for example, asgreater chemical detail is sensed and simulated, we mustre-think the degree to which species can be lumped togetherand treated as a single effective component.

Figure 6 (see colour insert between pp 542 and 543) is acartoon illustrating the impact of reservoir modelling in theera of the Shared Earth Model. We see an engineer incoveralls virtually immersed in the dataÐ the virtualreservoir. Another geoscience specialist colleague or clientis sitting in an of® ce distant from the reservoir,also immersed in the data, relayed by satellite. The analystswork with the parts of the reservoir which have alreadybeen illuminated. This information is relayed and pre-sented as ìmmersive visualization’ in the of® ce environ-ment. Ghostly manifestations of the illuminated parts of thereservoir ¯ oat in the remote of® ce and surround the analyst.Over time, the detail will increase, as will the level ofillumination and colouring/texturing representing reservoirparameters.

A large rig in the corner has drilled (unsuccessfully) a partof the earth `cube’ . The track of the well has illuminated thatpart of the cube in a pale, cylindrical zone represent-ing Logging/Measurements-While-Drilling (LWD/MWD)data. Above the reservoir top are icons representingdifferent sorts of `shared earth model’ dataÐ a 2-D graphfor petrophysical modelling, a couple of ray paths and atrace for seismic modelling and acquisition, a 3-D graphfor a classi® cation system, a strip of well log, etc. Each iconemits a `glow’ which illuminates the reservoir. The logilluminates a strip where the well would have passed, theseismic rays illuminate concentrated spots at the point ofre¯ ection and a `curtain’ of light where they pass vertically,and the graphs cast a wide but pale light.

There are clearly areas of dark `gloom’ around the cubewhere no light has yet been thrown. The illuminated partsof the reservoir are reproduced in the of® ce. A randomlyorganized set of surface sensors communicate to a centralpoint. These could be permanent seismic-while-drillinggeophones or any other wireless sensors.

WELL CONSTRUCTION: TOWARDS RESERVOIRPLUMBINGÐ OPTIMAL ACCESS TO THE

UNDAMAGED RESERVOIR

In addition to these important data and simulation issues,there are two major `® eld implementation’ issues. The ® rstof these is how we construct the well; the roadmap in Figure7 illustrates an anticipated evolution of the Well Construc-tion Process.

Existing TechnologyÐ Improving Drilling Ef® ciency

A major advance over the past 10±15 years has been thedevelopment of ¯ exible advanced drilling technologies,including steerable downhole motors, MWD and LWD,



which have enabled directional drilling to become routine1 4 .Vertical wells (of which typically 25 would be required toproduce, say, 50,000bbl of oil per day, along with perhaps15,000bbl of unwanted water) have given way to deviatedand horizontal extended-reach wells within the reservoir,see Figure 8 on colour insert between pp 542 and 543,whose productivity is typically about ® ve times that of avertical well due to the increased production contact areawith the reservoir (only 5 would be required to produce thesame 50,000 bopd, along with only, say, 5,000bbl of water).

Figure 9 (see colour insert between pp 542 and 543)shows the state of the art for extended-reach drilling (ERD)today. This shows the envelope, in terms of true verticaldepth vs. horizontal departure, of what can be considered as`standard’ vs àdvanced’ technology. It can be seen thatsome of the most challenging wells have been drilled in theUK; in 1997, BP drilled a then world-record 10.5 kmextended-reach well from their Wytch Farm facility inDorset out underneath Poole harbour, combining highproductivity with low (offshore) environmental impact1 5 .

Today, the main goal is to improve drilling ef® ciency,assuming the reservoir model indicates correctly where weshould drill. Another advance has been the use of coiledtubing1 6 (steel hose-pipe, typically 4±6 cm in diameterwhich can be reeled down a well from a truck, removingthe need for a full (expensive) drilling rig). This is usedboth for drilling new wells, and so-called re-entry drilling1 7

whereby old, unproductive wells can be given a new leaseof life by drilling sidetracks into pockets of the reservoirrevealed as oil/gas-bearing by improved reservoir modelsand characterization. Underbalanced drilling1 8 is anotherway in which the drilling process is being modi® ed to takeinto account the overall targetÐ enhanced productivity. Bychanging from the traditional overbalanced scenario,whereby the wellbore pressure exerted by the drilling ¯ uidexceeds the rock pore ¯ uid pressure in order to avoidpremature production of ¯ uids (and possible blowouts), tocontrolled underbalanced conditions (with a `shut-in’ well)potentially prevents the invasion of damaging solids andchemically-incompatible ¯ uids from the drilling ¯ uid inthe wellbore into the reservoir, avoiding so-called `forma-tion damage’ and maintaining reservoir productivity atits incipient level. Such technology, whilst bene® cial inprinciple, is not straightforward to apply in practice,requiring highly accurate pressure monitoring and control

in both the reservoir and the wellbore, and is an area whereprocess enhancements will undoubtedly bring bene® ts inthe near to mid-term.

All these technologies are being applied regularly insome parts of the world to improve productivity via in® lldrilling and reduce reservoir formation damage by thedrilling ¯ uids used to create the well. For example, it hasbeen reported recently1 9 that Saga and Statoil plan toemploy Coiled Tubing Drilling (CTD) in the Snorre andGullfaks ® elds. Saga believes that by drilling multilateralhorizontal wells it may be able to recover an additional7.6 m bbl of oil if successful. Likewise Shell have reportedsigni® cant production enhancements by the use of hori-zontal drilling, percussion drilling, CTD and underbalanceddrilling in Oman2 0 .

Much of the cost of constructing a well lies in thedowntime that arises from drilling problems, such aswellbore instabilities and drillstrings or logging toolsbecoming stuck in the hole. So much effort has and isgoing into ensuring reduced risk and unplanned time byimproved, real-time decision-making aids that anticipateand diagnose problems, and appropriate corrective action,before they become criticalÐ these take the form of bothplanning aids and so-called smart alarms.

For example, effective geosteering of horizontal wellscan be aided by 3D geological models which help locatewells by avoiding faults and tapping high porosity zones.Figure 10 (see colour insert between pp 542 and 543)depicts Seismic-While-Drilling2 1 Ð imaging, using the drillbit as a seismic source, with geophones on the surface or seabottom offshore. As the drill bit approaches an over-pressured zone, which represents a potential gas kick orblowout hazard, the driller can see what is happening on theVSP (vertical seismic pro® le) image. The technique enablesmore accurate placement of the drill bit on the originalsurface seismic image. Several operators in the Far Easthave used the technique to save a steel casing string, andthus effect a substantial cost saving.

3-Dvisualizationis beginningtobeused tounderstandwhatis happeningin the vicinityof the drill bit. In the future,we canexpect new forms of visualization and virtual reality, coupledwith new measurements, to permit the driller to understandwhat is ahead of, around, and behind the bitÐ the lattercapability to identify incipient wellbore stability problems.Tomorrow’ s driller will be able to draw upon remote experts,also immersed in the data, in case help is required.

Figure 11 (see colour insert between pp 542 and543) shows fracture orientation and aperture visualizedwith an ultrasonic imaging tool. Breakouts (stress-relateddamage in the plane of least horizontal stress) are seen onopposite sides of the borehole. There has been much writtenover the past years on the subject of wellbore stability2 2 andsome operators have made substantial progress in combat-ting the problem (e.g. the highly faulted and fracturedCusiana ® eld in Colombia). Unfortunately, today this workis of most use in guiding drilling strategies on the next wellto be drilled in an area, rather than for real-time guidance.However, research shows promise in real-time problemidenti® cation from real-time wellsite data, diagnosis of rootcauses, and suggestions for remedial actions. Over time, weexpect to see improved measurements and understandingof the underlying mechanical and chemomechanicalmechanisms2 3 result in closed-loop approaches.



Figure 7. Roadmap illustrating the possible evolution of the WellConstruction Process.

Near-Term: Reduce Rig Cost

In the near term, there are efforts ongoing in the industryaimed at reducing the cost of drilling rigs. The `standard’well construction platform of tomorrow will consider theoverall process, including directional drilling, wirelinelogging, the subsequent completion phase, etc. It willprovide increased levels of integration, including physicalspace and networks.

Eliminating the marine riser2 4 , the heavy ¯ uid return pipejoining the seabed to the sea-level platform, is one way toreduce the necessary deck load capacity, and therefore theweight, of a well construction platform. Conoco and Hydrilare exploring a riserless drilling concept which employs a3000ft ¯ exible lightweight umbilical for mud returns, andchoke/kill well control safety operations. Elimination ofmarine risers is seen as an issue that will take on increasingimportance as drilling operations move to ever deeper waterin the future. Wells in the Gulf of Mexico are currentlybeing drilled in 1000 m of water; drill-ships and platformsto drill in even greater depths (>2500 m) are planned forthe year 2000.

Simultaneous operations are another way to improveef® ciency and lower cost. For example, Shell has recentlyreported2 5 that Coiled Tubing Drilling was used in the NorthSea to sidetrack an existing well through the completion,while the rig was drilling a conventional sidetrack. A relatedapproach to improving rig ef® ciency for workover opera-tions is to use multipurpose service vessels which reducelogistical complexity, improve operational ¯ exibility andef® ciency, and decrease time spent waiting on weather.Using the same equipment (pumps, mixers, etc.) for severaltypes of operation or ¯ uid (e.g. drilling, cementing) is alsohelping to reduce rig costs and size.

Automation offers a number of potential advantages,including improved performance, improved safety bymoving people out of a dangerous environment, andreduced cost by reducing the necessary crew. A BPinvestigation2 6 into cost drivers for well construction inthe Ula Gyda Asset identi® ed offshore personnel as thebiggest single cost driver, accounting for around 50% ofdrilling expenditure. The report concludes that a worldwidereduction of just 1 person per rig could result in annualsavings of $10M in drilling expenditure.

Near-Term: Reduce Time to Top-of-Reservoir

In the near term also, the industry will concentrate onthe ® rst stage of drilling, i.e. performance drilling fromsurface to top of reservoir (where the metric is cost per unitdistance).

New Bits, Motors and Drilling FluidsSteerable downhole motors1 6 have enabled substantial

achievements in horizontal drilling. In the coming years,we expect that non-steerable motors will also see increasinguse as performance aids for getting down to the reservoir,even in the vertical section, as well as drilling inside it.

The nature of the drilling ¯ uids can also make majorcontributions to reducing drilling times and costs. Oil andsynthetic-based (invert emulsion) muds still have severaladvantages over water-based ¯ uidsÐ inhibition of water-swellable shale wellbore stability problems, high lubricity

in deviated ERD wells, low ® ltercake sticking riskÐ butare increasingly being ruled out by tighter environmentallegislation, led by offshore locations like the North Seaand the Gulf of Mexico. Whilst great progress has beenmade in recent years in ® nding water-based ¯ uids which cancompete on performance 23, there is still some way to go.The advent of horizontal wells, deeper hotter wells etc. hasput additional challenges on drilling ¯ uid performance,requiring faster gelation on cessation of ¯ ow, improvedrheology for effective cuttings transport and hole cleaningand the ability to maintain rheology and low ¯ uid loss topermeable formations at increasingly high temperaturesand pressures. Current temperature requirements extend to350°C and are expected to rise further over the next decade.

All this demands increasingly smart and responsive¯ uids, and an enhanced understanding of structure-propertyrelationships for complex ¯ uids built from polymer/colloid/surfactant and other self-assembling building blocks. Thisrepresents an exciting challenge for materials chemistry.Here too simulation can aid experiment to ® nd optimalsolutions more ef® ciently. Figure 12 (see colour insertbetween pp 542 and 543) demonstrates the use of moleculardynamics simulation in search of new polymer-basedaqueous drilling ¯ uids. The rectangular, evenly spacedslabs are layers of montmorillonite, a swelling clay found inmany chemically-reactive shales. In the example shown, thepolymer chains anchor onto the clay surface to bind thelayers together as well as forming a partial barrier to waterinvasion. Such simulations have proved highly effective inidentifying the most appropriate chemical structures,reducing the number of potential additives that need to bescreened experimentally, accelerating development timesand reducing costs.

Eliminate Connections and TripsA central problem today is that, overall, too much time

is consumed on non-drilling activities. It is not unusual to® nd that only 30% of the total time available is spent indrilling. Another 30% may be spent in trippingÐ taking thedrillstring in and out of the hole in order to insert a casing/liner, to log or carry out other operations. Whilst greatprogress has been made making measurements whiledrilling, a long term goal must be to carry out as manyother operations as possible while drilling, leading to asingle, uninterrupted, continuous well construction opera-tion. Replacement of the current 4±5 section telescopicwell2 7 by the monobore well, from surface to reservoir,should offer many advantages in terms of cost (time andmaterials) and producibility (size determined by thereservoir capability and production needs rather than bythe number of sections of telescopic wellbore required tomaintain hole stability in weaving between the variousgeophysical constraints of rock strength and pore pressure,using today’ s intermittent and sequential technology). Toachieve this will require the development of continuousdrillpipe, new drilling techniques, ways to line the boreholecontinuously while drilling etc., which present excitingchallenges in mechanical and process engineering and inmaterials science. Such processes will involve simultaneousmechanical, ¯ uid mechanical and chemical operations andtheir successful deployment will require good processmodels and appropriate downhole sensors and smartalarms for real-time monitoring and control. The separate



¯ uids used in today’s well constructionÐ drilling, cement-ing, completionÐ will need to be replaced by multifunc-tional, smart, responsive well construction ¯ uids whoseproperties can be locally optimized at different stages ofthe operation.

A number of projects have begun to address these issues.Experiments have been carried out with a number ofalternative lining technologies, including expandable steeltubulars2 8 and downhole cross-linkable resin sleeves2 9 ,which aim to save one or more casing strings, the ® rststep towards the monobore continuously-lined hole. Themajor impact of coiled tubing for drilling and otheroperations has already been mentioned; further progresscan be expected in reeled systems generally3 0 , particularlyfor well lining.

As simultaneous operations for well construction becomethe norm, a continuation can be expected of current trendsin logging measurementsÐ less wireline logging and moreformation evaluationwhile drilling. Tools will be developedwhich are capable of looking ahead and around the bit andso becoming an active part of the real-time trajectoryselection process; current resistivity-at-the-bit images3 1 areearly examples of this.

Accelerate Learning CurveÐ Integrated, Multi-disciplinaryTeams

Key to improving performance is accelerating orsteepening the learning curve: taking advantage of allinformation available from across the organization, includ-ing that available from the ® rst well drilled in an area, tocompress the learning time. Currently, it typically takes5±10 wells drilled in a new area to optimize the process.If an approach based on smarter real-time measurementsand better information management and interpretation issuccessful in the extreme, the second well drilled becomesas ef® cient as the nth well. Furthermore, the learning isthen robust with respect to changes in the team, theenvironment, etc. It is well understood that multi-disciplin-ary integrated teams with aligned goals are vital to thisimprovement. Over time we expect non-traditional drillingtechnology, such as data mining, virtual reality, globalcommunication, and `push’ technology (webcasting) willplay a strong role as well. Imagine replacement of isolatedspecialists by multi-disciplinary teams taking immediateadvantage of the best knowledge and experience availableworldwideÐ drillers become knowledge workers.

Long Term: Deliver Optimal Access to UndamagedReservoir

The second stage of drilling is drilling in the reservoir,where the metrics are number of barrels produced and pro® tper barrel. The end goal over the long term is not simplydrilling `deeper and cheaper’ , it is delivering optimal accessto the undamaged reservoir, a properly placed drainagesystem capable of producing to the maximum.

Productivity/Economic SteeringProductivity Steering or Economic Steering means that

the future driller will have the capability to `steer ineconomic space’ . Imagine an alarm that lights up whenthe well has been drilled long enough to achieve the ROItarget. BP has used an early version of this idea at Wytch

FarmÐ a `Cumulative Productivity Index (PI)’ approach tode® ning the length of horizontal sections1 5 .

Install Reservoir PlumbingWe can expect well construction to evolve into something

that looks much more like installation of reservoir plumbing(or keyhole surgery). One can imagine a small number ofconduits to surface, with many complex laterals, which areanalogous to the plumbing of a city. The overall designproblem must determine the optimal number, location, andmakeup of laterals. The reservoir characterization/model-ling and drainhole creation processes hence becomeintimately related and inter-dependent. The CAD tech-niques developed for process engineering should ® ndincreasing application here.

New logging-while-drilling tools which permit the drillerto see ahead and around the bit will have major applicationsonce in the reservoir, enabling him or her to optimizetargeting and minimize undulations in horizontal laterals.The `piping’ may be conveyed with tractors, moles, orrobots. It could also be installed via coiled tubing jettingto achieve ultra-short radius drainholes, kicked off in thereservoir. All these prospects come under what Shell intheir vision of the future32 term `Smart Wells’ .

Closed-Loop Drilling Process ControlReal-Time Shared Earth Model Update

All this is moving towards the capability to implementclosed-loop drilling process control. The reservoir and thedrainhole creation process become suf® ciently well charac-terized and monitored for the whole activity to be underreal-time automatic control. Key here is the linkage to theShared Earth Model for

(a) continuously monitoring of where we are in thereservoir versus where we want to be;(b) updating the model (including the overburden) as newdata are acquired, and(c) modifying the well plan and trajectory to optimizereservoir drainage.

Putting this all together, the scenario shown in the cartoon ofFigure 13 (see colour insert between pp 542 and 543) can beenvisaged. The same illuminated areas remain fromFigure 6. Contours on the surface of the reservoir illustratezones interpreted as being of economic interest. A simplemulti-lateral well has been drilled, around which anilluminated halo sheds more light (from LWD/MWD logdata acquired during drilling). A third lateral is being drilledby a signi® cantly smaller rig than in the ® rst cartoon. Thecountryside encroaches on the rig, and nearby are surfacefacilities to deal with production from the evolving drainagesystem. Whereas the ® rst rig in Figure 6 had severalsatellite sites (mud tanks, MWD shack, driller’ s hut, engineroom, etc.), the second is much smaller and has only oneroom attachedÐ generally illustrating the merging ofdisciplines (e.g., mud 1 cement), and use of the samemechanics for all functions.

Smart drilling technology is also involved in guidingrapid, accurate, controllable installation of the drainagesytem. This is illustrated by a cruise missile seeking out aproductive/economic target ahead. The missile is ìllumi-nating’ the reservoir as before (illustrating the data beingacquired). Behind the missile, in the hole made by it, is a



double ended, wheeled, `crawler’ with a spraying headon the front coating the well bore with a new boreholelining material and a ¯ ame thrower at the back, baking thematerial. A tributary pipe or valve is being installed onthe liner behind the crawlerÐ `reservoir plumbing’ .

The mission control room receives data from the missileand other sensors and sends instructions back. The reservoiris becoming increasingly well lit and the room full ofvisualization is becoming more complete with its coloured-textured virtual image of the reservoir, on an increasinglycomplete volume. We also see a drilling supervisor on thesurface, with the learning curve for the area in evidence.

WELL PRODUCTIVITY OPTIMIZATION:TOWARDS LIFETIME OPTIMAL PRODUCTIVITY

INDEX, FLUIDS, AND DATA DELIVERY

Now we move on to the second crucial operational step:having created the optimum well structure and connectivityto the reservoir, ensuring that production from the reservoircontinues to be optimal throughout its lifetime, respondingto changes both in the downhole environment as thereservoir evolves during production, and in hydrocarbonrequirements at surface, the marketplace. The roadmap forhow this Well Productivity Optimization stage might evolveis shown in Figure 14.

Existing Technology

On the left-hand side, we show today’ s state of the artfrom two points of view: Drilling and Completion, andMonitoring and Treatment.

Drilling and CompletionWe have already referred to the key role played by the

choice of drilling ¯ uid and drilling practice (overbalancedvs underbalanced) in the reservoir for minimizing perme-ability impairment, particularly for open-hole completions(where a casing is not cemented in place and subsequentlyperforated with explosive charges, but the hole simplysupported by a slotted liner or porous screen). Drilling ¯ uidsvary from the simple to the complex3 3 ,3 4 , presenting drillerswith signi® cant choice and the need for appropriate ¯ uidselection and management. Fluids engineering, adopting a

holistic approach which includes ¯ uid mixing, placement,monitoring, modi® cation, recycle and disposal in addition tothe chemistry and physics of ¯ uid design, will become anincreasingly important aspect of well and reservoir opera-tions. Progress has already been made towards this goal3 5

but much remains to be done. Designing the ideal ¯ uid isa complex optimization, varying with the nature of theformation, well trajectory, drilling practice and the comple-tion. Unfortunately, it is still true today that manymechanisms underlying ¯ uid functional properties andtheir interaction with rock materials are not well understood.Much ¯ uid selection is based on experience, and often on apartial view of the hydrocarbon extraction chain, rather thana holistic approach that combines management of previousdata (èxperience’ ) with composition-structure-propertyrelationships and design constraints imposed by thereservoir model and the well construction strategy.

A signi® cant problem with poorly consolidated forma-tions is the production of sand alongside the ¯ uids3 6 .Current practice is to diagnose potential sanding zonesand to use completions that prevent sand from enteringthe well. Two commonly used options are gravel packs,which create a ® ne porous ® lter adjacent to the wellborewall, and frac&pack, whereby short fractures (usuallyless than 30 m long and up to 3 cm wide) are created byapplying hydraulic pressure through the perforations withhigh viscosity ¯ uids carrying (in this case high) concen-trations of sand or ceramic particles (`proppant’ ). Theshort, wide fractures become packed from tip to wellborewith proppant which subsequently acts as a near-wellborescreen.

The completion must be designed to optimize productiv-ity given the nature of the reservoir, ¯ uids in place,geometry of the well, etc. Productivity analysis software,based on nodal analysis techniques, is commonly availablefor predicting the ¯ owrate/ pressure drop characteristics of agiven completion scenario.

Monitoring and TreatmentToday, the common practice is only to monitor ¯ uid

production at surface from co-mingled wells; the ¯ ow fromindividual branches of multilaterals is not measured.Typically, to understand accurately the composition ofthe ¯ ow produced by an individual well requires installationof a separator. Three-phase (oil-gas-water) meters are stillin their infancy; key issues are cost and the ability to dealwith a wide range of ¯ ow rates and amounts of gas.

Downhole production logging tools are becomingincreasingly sophisticated in their ability to measure bothindividual phase ¯ owrates and the structure of the multi-phase ¯ ow3 7 , but they are still used relatively infrequentlycompared to surface monitoring because of the high costinvolved. A key reason behind the expense of downholemeasurements is the need for re-entry. Production loggingin long horizontal wells3 8 may entail up to 10 days of coiled-tubing time, an expensive operation. As with diagnosisof a production problem (low oil production, unacceptablyhigh water entry), so with the corresponding treatmentsdesigned to increase productivity3 9 , such as fracturing,matrix acidizing or reperforation. These too involveexpensive re-entry operations and the combined cost ofdiagnosis/treatment must be amply compensated for byimproved production to justify their implementation.



Figure 14. Roadmap showing the possible evolution of Well ProductivityOptimization.

Near-term: Tools for Lifetime Optimization

In the near term, we foresee the development of toolsfor lifetime optimization of well production. Drilling andcompletion ¯ uids will become better matched to reservoirproperties. (Figure 15Ð see colour insert between pp 542and 543Ð shows the importance of engineering drilling¯ uids solids particle size for optimum pore bridging andexternal cake building4 0 .) This presumes the accuratecharacterization of mud/completion ¯ uid damage; todaythe industry does not have a tool for measuring the damagedone to the reservoir by the well construction ¯ uids. Aproper measure would help with reservoir characterizationand in characterizing the real value brought by the drill-in¯ uid engineering.

Surface Monitoring and Downhole SensorsThe intensive effort on three-phase metering should

lead to economical and robust meters in the relatively nearterm. New downhole sensors are being developed for bothcased and open-holes, to monitor the evolving state of thereservoir and production. Permanent sensors are alreadybeing deployed4 1 . For instance, Statoil have installed apressure monitoring system in the Gullfaks and Veslefrikk® elds; data recorded by permanent gauges is transmittedby satellite to oil company of® ces for use in reservoirmodelling. The problems to be solved in this area are many,including power, telemetry, and miniaturization. It isalso interesting to conjecture that autonomous vehiclesÐrobotsÐ may some day query and service the sensors.

Downhole Separation and DisposalA signi® cant part of oil recovery costs arise from the need

to separate oil from produced water on surface. A growingtarget is to only return selected hydrocarbon to surface byimplementing downhole separation procedures4 2 , andreinjecting the unwanted water or gas into the reservoir,preferably in a manner which aids the reservoir pressuriza-tion and sweep ef® ciency for further secondary recovery ofoil. The challenge here is to transfer water/hydrocarbonseparation processes, standard within the petrochemicalsand other process industries, into compact, cost-effectivedevices capable of operating deep within the wellboreplumbing network. Coupling to the reservoir model is ofcourse essential for planning the location of disposal wellsto optimize the bene® ts of reinjection. All this will helpreduce the environmental footprint of the extractionoperation, both in terms of returned ¯ uids and externalfacilities.

Long-term: Deliver Optimum Productivity Index, Fluidsand Data over Well Lifetime

Universal Non-Damaging Drilling FluidThe long-term goal is to deliver the optimum Productivity

Index (bbl/day/psi/ft), ¯ uids and data to the surface overthe lifetime of the well, delivering to the surface only the¯ uids that are wanted. Delivery to the surface of datathat will assist in reservoir management is also extremelyimportant. As already anticipated, we may expect to seeùniversal’ non-damaging well construction ¯ uidsÐperhaps adaptive ¯ uids that are able to match theircharacteristics to drilling and reservoir conditions, which

may be linked to measurement and adaptive controlsystems, either at surface or downhole.

Low Cost/Impairment Sand ControlImprovements in sanding prediction procedures3 6 will be

exploited through the development of selective treatments.Rather than simply preventing sand reaching the wellbore,methods need to be found to consolidate weak producingformations whilst maintaining their producibilityÐ eitherthrough maintaining their intrinsic permeability or intro-ducing alternative high permeability pathways through theconsolidated rock.

Downhole Completion ControlToday, what downhole control there is over production

from individual laterals is quite simple. Typically, mechan-ical intervention is required to exert control. In the long-term, we can expect much more factory-like control inthe subsurface, with instrumented completions enablingthe branches and sub-branches of the drainage system to beshut-in or brought on stream through valves operatedremotely by Production Control.

Suite of Cost-Effective TreatmentsIn order to maintain the well productivity at high levels,

it will be essential to have accurate diagnosis proceduresfor the cause and location of production problems, be theyan overall decline in produced ¯ uid rates or increasingamounts of unwanted water or gas. This will requireaccurate and localized production logging and formationdamage monitorsÐ permanent sensors within the well andthe reservoir. The appropriate treatment procedure will beselected on the basis of technical match to the diagnosis andits cost-effective impact on the well productivity, throughlinkage back to the reservoir production models.

The suite of available treatment procedures will beexpanded from those currently available in various ways.New fracturing ¯ uids will be developed which deliver 100%retained permeability within the fracture and can operateover wide ranges of formation permeability and reservoirtemperature. New matrix treatments will be developedwhich replace the existing unfriendly acid ¯ uids4 3 by newmilder and selective solvents, which remove drilling andproduction damage to restore or enhance reservoir perme-ability. The creation of scale through the precipitation ofnormally insoluble salts like barium sulphate and calciumcarbonate in the near wellbore formation and the productiontubulars has a major impact on well production. Scalecontrol is today effected by injection of precipitationcontrol agents into the reservoir4 4 ; their release is controlledover a period of several months by adsorption and slowdissolution processes within the reservoir45, but the periodbetween treatments (costly both in the materials used andthe production interruptions they cause) is still quite short,typically 6±18 months. In time, scale treatments will bedeveloped that last for years; the challenging target forcurrent research is a single treatment that lasts the lifetimeof the well.

Water control, or conformance control4 6 as it is increas-ingly widely called, is a technology that is cruciallydependent on good problem diagnosis in order to matchthe treatment to the root cause . . . water can enter a wellborefor a wide variety of reasons, some associated with the



integrity of the near-wellbore zonal isolation, others withthe detailed topology of the reservoir and the placement ofthe well within it. Potential solutions include fracturing,shutting-in existing wells and drilling alternative laterals,local drainholes and gel injection.Gel treatments4 7 have hadmixed success to date, mainly because of uncertaintiesin exactly where to inject the gelling ¯ uid or to what depthand due to the lack of control over exactly where the gel¯ ows to in the reservoir before it sets. Sometimes oil zonesbecome blocked as well as water zones or improvements inoil productivity are transient as injected water eventuallybypasses both the gel barriers and the oil. In the future,smart conformance control systems will be introduced thatare relatively insensitive to the detailed reservoir topo-graphy for their effectiveness and selectively enable theproduction of oil. The ultimate goal, of course, will be toproduce only oil into the wellbore, transferring downholeseparation from the current target, the wellbore, back intothe reservoir.

Another issue for cost-effective treatments is zonalisolation. In long horizontal wells with open-hole comple-tions, it is currently not easy to isolate the section of thewell responsible for unwanted ¯ uid entries, as it is forconventional cemented and perforated wells. If it provesnecessary to seal off the well from its toe up to the positionof entry, then a large fraction of the productive area of thewell will be lost. So increasing efforts will be requiredto develop systems which can isolate problem sections ofa well, enable a local treatment to be carried out (gelinjection, matrix treatment, fracturing, etc.) and then restorethe whole of the well back to full productionat its original orenhanced level. An example of an early approach to this isthe use of new types of settable thixotropic ¯ uids to placeannular packers (sealing plugs) to give local zonal isolationin slotted liner completions4 8 Ð see Figure 16.

Linkage with Shared Earth ModelIn addition to the crucial role played by the shared earth

model in selecting and optimizing well treatments, therewill be a signi® cant market niche for software toolsdesigning intelligent completions, using simulation todetermine for each case the optimum type, number, andplacement of sensors and controllers in laterals and atbranch points. As with all of the software components inthese roadmaps, ease of use and the capability for seamlessintegration with other software will be as important as therobustness and accuracy of the underlying algorithms.

The picture of well operations that emerges from this isshown in Figure 17 (see colour insert between pp 542 and543). Here the original multilateral has grown additionalbranches. One multilateral branch has a circumferentialpressure sensor and a ¯ owmeter and can be controlled by avalve (`sensor like’ ® ttings on the pipes). A downholeseparator is shown with three units: one separates oil andwater, one feeds water to a well branch in contact with theaquifer (downhole disposal) and the third one sends the oilonward to surface in the well. Other multilateral branchescould be drilled into another zone (aquifer for disposal, gasfor lift, etc.).

Sensors in each of the branches continue to send dataabout the well to surface production control. A new sensoris being installed in one of the branches. The sensorsinclude cross-lateral sensors (e.g. acoustic or chemical or

electromagnetic). Signals travel between branches and tothe surface (up and down).

On the surface, two characters also have access to theshared earth model to devise appropriate treatments. Anultra-short radius drainhole is being drilled via coiled-tubingjetting. The reservoir illumination is getting better in theregion of the downhole sensors (time-lapse pressure data).Data acquisition from the permanent sensors is shown byradar/sonar-like pulses around the sensor. The re® nery/factory has moved to surround the rig and wellhead, whichoccupies a smaller area, surrounded by trees.

REAL-TIME RESERVOIR MANAGEMENT:TOWARDS THE RESERVOIR AS A FACTORY

Figure 18 shows the ® nal roadmap, illustrating how,once we have the means to optimize the reservoir



Figure 16. (a) Typical production problems encountered in horizontal wellscompleted with uncemented slotted liners to maximize ¯ uid production.Initially the produced ¯ uid is mainly oil, but eventually the entry ofunwanted water or gas, through fractures or faults or high permeabilitystreaks in the reservoir can make production uneconomic. The unwanted¯ uid entries can only be sealed off by ® lling the wellbore with, e.g. cementfrom its toe up to the entry point, resulting in loss of a large portion of thewell’ s producing area. (b) One way to treat the problem is to place chemicalplugs behind the slotted liner, one on each side of the water or gas entrypoint. These isolate this small section of the well to enable cement or othersealing ¯ uid to be pumped into the fracture/fault to seal off the unwantedentry, without losing production from the downstream section of the well.

model, well construction and well productivity, we mightevolve towards the ultimate goal of real-time reservoirmanagement.

Existing Technology and Practice

On the left-hand side, we consider today’ s approach toReservoir Management from two points of view: FlowSimulation and Reservoir Treatment Selection (i.e. what canbe done in the ® eld to improve recovery and productionrate). We have already discussed the state of the art andimprovements expected in measurements and reservoir(Shared Earth) models on previous roadmaps.

Flow SimulationToday, primary well placement is determined on the

basis of reservoir characterization linked to ® eld-widesimulation9 ,4 9 and a knowledge of the drive mechanismÐgravity, solution gas, water in¯ ux or compaction. Thecoarse reservoir model is the basis of ¯ ow simulation andsingle-phase upscaling is standard, being supported byseveral software packages.

Reservoir Treatment SelectionBy contrast with the global character of ¯ ow simulation

for well placement and sweep, treatment selection (e.g.stimulation) is largely based on identifying individual wellsas candidates using criteria linked to Net-Present-Valueanalysis4 9 . Commercial software exists for simulation,candidate recognition, and treatment design. For instance,plots of horizontal permeability across a ® eld can be used toidentify the best candidate wells for matrix acidizing.Figure 19 (see colour insert between pp 542 and 543) showsa Net-Present-Value analysis for a fracturing job, and howthe bene® ts vary with formation permeability and fracturedepth.

A variety of treatment/¯ uid design packages exists,though these are usually used prior to a job rather thanfor real-time optimisation and control. They requiresolid mechanics models of the reservoir rock, ¯ uidmechanics models of the ¯ uid placement and modules forvariation of ¯ uid properties with well and reservoirconditions. It is expected that such process and ¯ uidmodels for all these operations will become increasingly

re® ned and user-friendly over the coming years, as bothimprovements in the underlying physics and availablecomputer power are exploited to produce real-time inter-active software.

The task of producing accurate and speedy simulations ofreservoir treatment processes is perhaps even morechallenging than for reservoir simulation since here,unlike in production ¯ ows, the injected ¯ uids are non-Newtonian, sometimes viscoelastic and have properties thatmay vary with time or with chemical environment. In thisarea, there are great possibilities for pore-scale simulationsto be combined with simulations on the reservoir scale, so asto capture the consequences of complex small-scale ¯ owprocesses on the behaviour of the reservoir as a whole.While the multiphase extension of Darcy’ s law may beadequate for simple oil-water production ¯ ow displace-ments, there is little doubt that this description will proveinadequate when we come to simulate treatment ¯ ows inwhich viscous forces and evolving ¯ uid properties arecentral to the functioning of the process.

Near-term: Reservoir Optimization

In the near term, the industry is moving towards asituation where data from a variety of sources and length-scales (near-wellbore to full reservoir) will be integratedto give enhanced reservoir models. Risk analysis anduncertainty management will also be incorporated andcombined with the reservoir models for design of multiple-well treatment-optimization programs, where `treatment’may include in® ll and lateral well placement.

Increasingly sophisticated production monitoring tech-niques and software will provide the data and `glue’necessary to allow reservoir models to be updatedperiodically as the ® eld is produced. The parallel develop-ment of multilateral drilling and completion technology,together with increasingly selective treatment methodolo-gies, will enable this improved reservoir characterization/simulation capability to be exploited to the full. Multi-disciplinary teams which cross both technical specialitiesand the technical/marketing/business boundaries are anincreasingly key part of this holistic approach.

For instance integrating surface network simulators withreservoir simulators will enable production managers tominimize capital investment in surface facilities, optimize¯ ow, and ® ne-tune ® eld planning. Multiple well treatmentoptimization packages will be developed which couplereservoir simulators to economic and business models toevaluate the relative merits of alternative treatmentscenarios. Uncertainty analysis and risk management willbe increasingly integrated into the decision processes.

IT has already had a major impact on the practice of allphases of geoscienceÐ geology, geophysics, petroleumengineering, reservoir engineering, and data management5 0 .As in many industries, it is also beginning to have an impacton the ® nancial, business, and operational aspects of theE&P sector. Many companies are struggling to implementbusiness software packages across their product lines andgeographic areas; business software developers have by andlarge not had the experience to consider the global reachof the oil industry, with its abundance of transnationaloperations, currencies, and so on. So, though the potential ishigh, much remains to be done here too.



Figure 18. Roadmap for the possible evolution of Reservoir Management.

Long-term: Real-Time Reservoir Management

In the longer term, we can expect major advances inpermanent sensors, together with advances in computational,communications, SCADA (supervisory control and dataacquisition) and simulation technology. In conjunction withthe advances in reservoir models and ¯ uid mechanicalsimulation discussed earlier, these will enable continuouslyupdated ¯ uid-movement maps and an integrated package forreal-time reservoir control. Coupled with further advances indrilling, completion, and treatment technology, this will leadto automatic generation and analysis of well placement andtreatment scenarios and will enable production decisions tobe optimized in the context of operator business goals. By thispoint, geoscience, process engineering and business softwareare seamlessly integratedÐ business simulation is linkedwith reservoir simulation.

Achieving the long-term goal requires effective integra-tion of data, software, responsive mechanical and ¯ uidtechnology and multi-disciplinary teams. Putting this alltogether, we see real-time reservoir management as thenorm. For example, one can envisage scenarios where cross-lateral measurements are being made with permanentsensors. As water enters the lowest of the lateral branches,and reaches a critical control valve, this lateral is closed into minimize water production. At a later stage, decisionsmight be taken to reverse the process and inject waterinto an already ¯ ooded lateral to displace oil towards otherarms of the reservoir drainage system. Reservoir treatmentand intervention only become necessary once optionsinvolving manipulation of the existing underground net-work have been exhausted.

And so in Figure 20 (see colour insert between pp 542 and543) we reach the ® nal cartoon of how an oil® eld locationmight look in the real-time reservoir management era. Theseparator is still downhole, but the surface facilities havealso slipped below ground level. At the surface now is apetrol station; a highway leads to the station whereprocessed products are delivered after downhole processing.The countryside is only marginally impacted by the facilitywhich is part of a small conurbation. Apparently, we nowhave a pore to pour operation.

The last trace of local `mission control’ is an aerial inthe woods sending data back to the immersive visualizationroom, now occupied by a business manager analysinggraphs (backed up by a ® nancial specialist and a geosciencespecialist, although the latter has slipped into the back-ground). Feedback communication from the immersivevisualization lab to the wellhead control, a valve system atsurface, and a valve downhole emphasize the fact thatsimulation is in the loopÐ the reservoir simulation is goingon all the time, rather than as discrete runs.

The reservoir is now brightly illuminated and thevisualization is very detailed and complete. At this point,we have a reservoir `factory’ ; its individual pipelinereactors, each producing hydrocarbon product with ayield and purity that vary with time but in a way that canbe closely monitored and controlled, are operated as anintegrated system. The data are comprehensive and clear;the management task is fed by the data update.

CONCLUSION

This review has attempted to summarize existing practice

in the hydrocarbon recovery (exploration and production)sector of the oil industry, and to suggest possible scenariosfor the way that the enabling technology and engineeringmight evolve over the next 10±20 years. We have done thisby presenting technology roadmaps and cartoon futurescenarios for four technology packages that together havethe potential to enable a new era in productivity. It isenvisaged that the oil reservoir of the future will evolvetowards a subterranean factory, consisting of an inter-connecting network of individual production units (wells ordrainholes) which deliver only saleable hydrocarbon tothe surface. This hydrocarbon production system will beclosely monitored in situ and controlled from a remotenerve-centre which has responsibility for controlling andoptimising production from many geographically dispersedassets. The reservoir (or system of reservoirs) will beexploited using a systems engineering approach, into whichbusiness considerations are seamlessly integrated, to ensurethat the individual production units are deployed andmodi® ed in a way that optimizes the cost, amount andnature of produced hydrocarbon required to match marketneeds and business strategy. Proactive, real-time reservoirmanagement will become the norm.

Such a summary must inevitably be incomplete andselective, but it is hoped that the major targets have beenidenti® ed and that ways in which the process engineeringand chemical technology communities, in particular, cancontribute to shaping the future of the industry are clear.Achieving the goals described will require an overallindustry effortÐ building on the work of operators, servicecompanies, suppliers, SMEs, academics and government.Hopefully this paper will stimulate further dialogue andcollaboration between all these groups to develop atechnical agenda that turns the vision of real-time reservoirmanagement into a reality.

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ACKNOWLEDGEMENTS

The authors thank Schlumberger Oil® eld Services for permission topublish this review, and gratefully acknowledge the assistance of all theirmany colleagues in Schlumberger who provided information and ideas thathave been incorporated into the paper.

ADDRESS

Correspondence concerning this paper should be addressed toDr G. C. Maitland, Schlumberger Cambridge Research, High Cross,Madingley Road, Cambridge CB3 0EL, UK.

The manuscript was received 10 June 1998 and accepted for publication.



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THE ROAD AHEAD TO REAL-TIME OIL AND GAS RESERVOIR … · THE ROAD AHEAD TO REAL-TIME OIL AND GAS RESERVOIR MANAGEMENT* R. G. SMITH and G. C. MAITLAND² Schlumberger Limited, Sugar