Extended Reach Drilling Well in China

World Record Extended Reach Drilling and LWD Sonic Tools Confirm Additional Reserves

D Tompkins - Phillips China; Bai X F, K Deepak, D Hill, M Wilger - Anadrill; S Turner - Wireline

Page 16/22/98

World Record Extended ReachDrilling and LWD confirm Additional

Reserves

Dianne Tompkins - Phillips China Inc.Bai Xian Feng, Kajal Deepak, David Hill, Mark Wilger - Anadrill China Inc.

Steve Turner - Wireline & Testing



Page 26/22/98

Abstract

Production from the Xijiang 24-3offshore field in the South China Seaindicated that booked reserves understated theactual amount of oil in place. Revised mapsand seismic interpretations provided theoperator with several promising undrilledlocations. An additional structure to the east,Xijiang 24-1, was also highly regarded as adevelopment project, except it was too smallto justify a platform.

Proving the validity of the new mapswould require drilling additional wells. In anewly discovered prospect, these wouldnormally be vertical delineation wells whichare discarded (P&A’ed) after logging.However, project economics dictated thatevery new well must be able to produce oil tojustify its drilling costs.

The first proposed bottom hole locationwas over 8 km from the platform. Meetingthe objectives of this well required goingbeyond the range of normal developmentdrilling. Ultimately, an extended reach wellwas directionally drilled to a then worldrecord measured depth of 29,000'+ whileusing real time Logging While Drillingservices to provide formation evaluation in atimely and cost effective manner. Thesuccess of this well led to an extension of thedrilling campaign.

Subsequent wells, while not reaching asfar from the platform, utilized LWD sonicand resistivity logging tools to provide realtime seismic correlation, porosity data, andhydrocarbon evaluation. This data allowedthe operator to optimize costs and makedecisions much more quickly.

This paper is a case study of the project,including the economics involved in thedecision making process; the unique drillingrequirements of the extended reach well; thedetails of MWD data transmission at29,000’+; the use of the LWD data on eachwell; and the revision of the seismic and

structure maps based upon the real timelogging data.

Results of the drilling campaign includeincreasing the booked size of the reservoirs,proving the applicability of very long reachdrilling to tap reservoirs far from existingplatforms, and the use of real time LWDlogging tools for cost effective formationevaluation and seismic correlation.

Extended Reach Drilling in China -Figure 1



Page 36/22/98

Introduction

Phillips China Inc. and partners ChinaNational Offshore Oil Company and ShellPectin discovered the Xijiang 24-3 field andset a production platform in 1994. Severalwells were drilled to different producinghorizons and put on production. Outlyingsmaller reservoirs such as Xijiang 24-1 werenot drilled because estimated productioncould not support the cost of setting aplatform or drilling subsea wells.

South China Sea - Figure 2

The engineers and geoscientists involvedin the mapping and delineation of the fieldwere initially conservative in their estimatesof the size of the 24-3 reservoir and theamount of oil in place. This was prudentgiven the large capital investment during aperiod of low product prices.

However, production results up to 1996indicated that booked reserves understated theactual amount of oil in place. This promptedthe reservoir team to review their maps andlook for opportunities to more accuratelydefine the reservoir. Better reservoirdefinition coupled with the right productiontechnology would lead to better recovery andultimately an increased ROI for the project.

Tools commonly used to improvereservoir maps include seismic, reservoirsimulation, log interpretation, and new wells.

Seismic interpretation can be aided by theacquisition of new data and/or newprocessing techniques. Increasing the densityof the seismic lines or using modern surveyequipment can add detail to previousinterpretations (maps). Reprocessing originalseismic data with new inputs or data modelscan sometimes accomplish the same result ata fraction of the cost.

Phillips altered their seismic model forthe area surrounding Xijiang 24-3 andreprocessed the data to determine if the newresults would match the reservoir size thatproduction implied. The revised mapsshowed the team that there were severalpromising undrilled locations.



Page 46/22/98

Proving the validity of the new mapswould require drilling additional wells. In anewly discovered prospect, these wouldnormally be vertical delineation wells whichare discarded (P&A’ed) after logging.However, project economics dictated thatevery new well must be able to produce oil tojustify its drilling costs.

At the same time, operators around theworld (BP - Wytch Farm, Total - Tierra delFuego) were proving that new drillingtechnology called extended reach drilling(ERD) made it feasible to hit targets over 8km away from a surface location. This madethe Xijiang 24-1 reservoir drillable from the24-3 platform.

Xijiang 24-1 field location - Figure 3

The reach of over 8km would be a worldrecord for 6 months until BP at Wytch Farm(Oilfield Review Winter 1997) drilled a10km stepout.

Displacement versus TVD - Figure 4

The first well

Based upon the potential for increasingproven reserves and production, Phillips andpartners decided to drill the A14 well to atarget 8026m from the platform, at a TVD of2950m. The proposed well plan would resultin a 9300m MD well, with most of thewellbore being a tangent section at 80degrees.

Phillips Platform

Structure

Xijiang 24-3

Field

A-14

Well

0 800 1600 2400 3200 4000 4800 5600 6400 7200 8000

3200

2400

1600

800

0

Vertical Section ViewTVD

Vertical Section Departure at 114 deg from (0, 0). (1 cm = 400 meters)

0 4000

-4000

0

Plan View

Scale (1 cm = 2000 meters)

AnadrillSchlumberger

Xijiang 24-3 A14 - Figure 5

A great deal of preparation and planningtook place during the months preceding thestart of drilling. The rig was upgraded to beable to handle the hydraulic and derrickrequirements of drilling to total depth. Thedrilling tools were selected and the loggingrequirements were defined. Casing andcompletion designs were chosen andcontingency plans approved.

Logging While Drilling tools wereselected for initial formation evaluation of thereservoir because they would provide logs incase wireline logs could not be acquired,because they measure the formation beforedamage or invasion, and because they allowthe driller to “see” where the drill string islocated in the geological sequence and thusgives him the chance to quickly alter wherehe is going.

Azimuthal Density Neutron and 2 MHzresistivity gamma ray logs were selected forthe primary LWD tools. This log suite



Page 56/22/98

provides the operator with both porosity andwater saturation, two key components forevaluating a reservoir. The density is also aninput into a synthetic seismic interpretation.The synthetic seismic could be used tocompare to the new seismic maps forcorrelation and confirmation of the seismicinterpretation.

Triple Combo LWD log - Figure 6

On the A14 well the data would becompared while drilling to a synthetic loggenerated by Phillips’ reservoir team. Thislog graphic is similar to what a SchlumbergerGeoSteering Coordinator generates for ahorizontal well.

To drill this type of well to TD thefriction between the drill string and theborehole must be kept as low as possible.This meant the long tangent section had to bestraight and smooth, and the hole had to bekept clean. The dogleg severity needed in thetangent was less than 1 degree per 30m, for adistance of 7000m. To achieve theserequirements meant the drill string needed tobe rotated as much as possible initially, and100% at TD. The ADN was selected as theporosity tool because it could be run withouta stabilizer to minimize drag while stillacquiring a quality density log due to the

acquisition of bottom quadrant density (SPE27226).

The drilling tools selected included adownhole adjustable stabilizer that alloweddirectional drillers to adjust the build or droprate characteristics of the bottom holeassemble without tripping out of the hole.This is not a “rotary steerable” system whichallows 3D steering of the BHA in rotarymode. Instead, the well plan and drilling toolsprovided only a 2D capability at TD.

Measurements while drilling refers to thedirection and inclination sensors that tell thedriller the location of the borehole. The datafrom both MWD and LWD tools are sent tothe surface in realtime by mud pulsetelemetry generated by the MWD tool.Without this data offshore drilling isprohibitively time consuming and expensive.

An ultradeep well such as the A14 poseslarge hurdles for MWD data transmission.The pressure waves attenuate as they travelup the drillstring. The signal loss is a functionof depth, mud properties, and reflections atinner diameter changes in the BHA & rigpiping. Once the signal is too weak to bedetected over the background noise generatedby surface and downhole tools, the realtimeportion of the data is lost. While logging datacan be recovered by tripping the tools to thesurface, the drilling operation is severelyhampered without realtime feedback.Preparation for this job included “gappingdown” the modulator of the MWD tool,proper placement of the signal detectionsensors on the rig piping, daily monitoring ofthe condition of the rig pumps, and closecoordination with the mud engineer to ensuremud properties didn’t inflict too muchdamage to the signal.

The directional plan was therefore acompromise between the geological targetsand drilling practices that assumed most ofthe tools would not work at TD. The uppersand (H5A) was targeted as close to the rigas possible, even though the top of the



Page 66/22/98

structure would be left untouched. The wellplan was to get near the target, and then dropangle in rotary mode at 1.5 degrees per 30muntil TD was reached. This could beaccomplished “blind” if necessary. Themiddle targets (H10B) would be at the crestof the respective sands, while the TD target(H12) would be on the far flank of thereservoir. If the 80 degree tangent inclinationwas held through the reservoir, only a coupleof the targets would be hit.

A14 Formation piercement - Figure 7

First well results

Xijiang 24-3 A14 was successfullydrilled to TD, encountered the predicted paysands, validated the maps and seismicinterpretation, and started production of the24-1 field without the cost or time required toset a platform or subsea template.

The well is still producing 6000 BOPD,with less than 10% water cut, a year aftercompletion. It is the only well on theplatform that does not require artificial lift.

The drilling and logging tools worked asexpected. LWD logs were the only reservoirlogs acquired, and the client is very pleasedwith the data quality. Logs 1 & 2 (shownbehind paper) shows the recorded TripleCombo LWD log presented at the wellsite.Log 3 (full image behind paper) is the ADNimage from one of these intervals. The imageallows the geoscientist to look for unusualfeatures in the formation, perform qualitycontrol of the data, and sometimes toestimate formation dip from the sinusoidalcharacter of the beds. The driller can “see”the effect of certain drilling operations thatcause “corkscrew borehole”.

ADN density image - Figure 8

Realtime data was obtained until the lastfew meters of the well, when targetpenetration was assured and the data becameless critical. Surprisingly, as the well gotdeeper the downhole noise seemed to dropfaster than the MWD signal and signaldetection was fairly routine until the signalstrength dropped below 1 psi. Surface noise



Page 76/22/98

was minimal, as the rig pumps were in verygood condition and the client knew inadvance the importance of helping the MWDengineers in this respect.

The torque and drag were successfullyminimized by keeping the doglegs low andby the use of Oil Based Mud and drill pipeprotectors (a rubber sleeve fitted to the drillpipe).

0

1

2

3

4

5

0 2000 4000 6000 8000 10000

Dogleg Severity versus Depth - Figure 9

Total cost for the A14 ERD well wasapproximately 25 million USD. First oil waspumped in mid 1997, instead of 1999.

Subsequent wells

The subsequent Xijiang 24-3 drillingprogram can be characterized by the A15well, which was proposed as an aggressivestepout well designed to prove the mostoptimistic mapping then available. Thenorthern part of the structure had not beencompletely defined with delineation wellsprior to setting the platform, so the A15would fill in the missing data. Prior todrilling the reservoir team also selected asidetrack location, closer to the platform, thatwould be properly positioned for productionof the oil on the northern flank if the stepoutwas wet.

LWD Sonic was added to the LWDlogging suite because the reservoir teamwanted to continue realtime synthetic seismiccorrelation to the new seismic model in 12_”hole. The data from the Sonic andResistivity/GR tools would be emailed infrom the rig every day and the correlationupdated. Unfortunately no AzimuthalDensity Neutron tool exists for the 12_” holesize Phillips drills.

The Sonic tool measures Delta-Tcompressional of the formation bytransmitting and recording a sonic signalwhile drilling is ongoing. The array of fourreceivers is 10 feet from the transmitter. Thedigitized waveforms from each receiver isrecorded in downhole memory for playbackafter the tool returns to the surface. The tooluses a technique called Slowness TimeCoherence processing to determine Delta-Tcompressional while it is downhole. This isthe value that is transmitted to the surface anddisplayed on the realtime logs.



Page 86/22/98

Second well results

The A15 well was drilled to the targetlocation but unfortunately the maps turnedout to be just a little optimistic. Hydrocarbonswere encountered but not enough of thesands were high enough on structure to havesufficient produceable oil. But because of theinformation gathered, the sidetrack locationwas modified to the most optimumplacement.

The LWD Sonic worked perfectly, butthe realtime use of the information washindered by two factors.

First, the downhole STC processing isrobust (equivalent to the surface processing)but requires preset upper and lower limits inthe downhole tool for accurate realtime Delta-T calculation. This prevents “locking” ontoan incorrect transit time. Unfortunately onthis well, the client estimated the sonic traveltime of the tightest formations at 70 µsec perfoot, when it fact it was actually 50 µsec perfoot. When the tool encountered a formationthat was faster than the preset limit for theSTC processing, the value transmitted to thesurface was incorrect (too slow, or too highporosity). This made the data less valuable,until the tool was pulled above the rotarytable and the recorded waveformsreprocessed at the surface. A subsequent runwith better settings was not attemptedbecause the tool was back in the hole prior todiscovery of the issue.

The second factor that hindered theeffective use of the data was the time spentby the reservoir team each day adding theprevious 24 hour’s data to the model andrecomputing an interpretation. It takes almostas much time and effort to update aninterpretation as it does to do a new one, ifthe analyst is familiar with the field inquestion. This well took about 24 days todrill, so that meant twenty four interpretationsinstead of just one. The reservoir teamsimply became tired of taking valuable timeaway from their other activities to perform

interpretations that in the end were notrequired because the formation top depthswere as valuable to the mapping as thesynthetic seismic.

Phillips saved roughly $1.0MM in rigtime and associated costs because LWD datatold the reservoir team the primary locationneeded to be sidetracked before the wellreached Total Depth. Another benefit in thiscase was the extra time the reservoir teamhad to decide exactly where to place thesubsequent sidetrack.

The interpretation of the A15 logs showsmultiple reservoirs with varying porosities(Logs 4a, 4b, 4c, 4d; 5a, 5b, 5c, 5d). Themost difficult reservoir interpretation isfinding the oil/water transition zone, sincethis usually occurs at a high/low porositytransition. The LWD logs compared verywell with Wireline logs, and the client nowdecides which logging suite to run basedupon the technical and cost factors of thewell.



Page 96/22/98

The Future

Xijiang 24-3 development drillingcontinues a la the A15 well. We have drilledthe A15 and A8 wells, and we will drill theA12 Reentry in June/July. LWD logs arenow chosen on a per well basis, dependingupon the log suite desired and wirelinelogging cost. This normally means LWDResistivity/GR on regular directional wells,plus LWD porosity on highly deviated wells.The GeoSteering Tool will be used on allhorizontal wells, including the next well, theA12 Reentry.

The Xijiang 24-3 field is not as large asthe initial revision of the maps suggested, butit is sufficiently bigger to justify drilling newwells. The production from these new wellswill increase the economic life of theplatform by several years.

Phillips and partners are currentlyevaluating how to produce the remainingreserves from Xijiang 24-1. There are over24 identified sands, with 4 primary zones.The field is best suited to produce from 2horizontal wells and about 4 conventionaldirectional wells.

Extended reach drilling is obviously oneoption being evaluated. Phillips is quiteconfident that they can drill, complete, andproduce the oil with this technique. Theyexpect to get the cost down from $25 millionto about $10 million per well. Drawbacks,however, include loss of slots for Xijiang 24-3 targets, the high cost of ERD, and thegeometry of the target.

Another option being considered byPhillips is letting Schlumberger Solutionsdrill and complete four to 6 subsea wells,with the wellheads near the structure.Drawbacks include an extra 6 months to firstoil, the high cost of subsea workovers, thehigh cost of a pipeline, the problemsassociated with pumping crude from asubsea wellhead to the platform, and the lackof availability of Chinese rigs (compared to

the world class rig they already own on the24-3 platform).

An alternative plan is to put a smallplatform above the subsea template after thewells are drilled from a floating rig. Theproblems with pumping crude areminimized, and workovers can be moreeasily addressed.

A decision is expected June 20th onwhich option to pursue.

Hard at work - Figure 10



Page 106/22/98

Log 1 - Xijiang 24-3 A14 LWD Triple Combo - Recorded Data



Page 116/22/98

Log 2 - Xijiang 24-3 A14 LWD Triple Combo - Recorded Data



Page 126/22/98

Log 3 - Xijiang 24-3 A14 ADN image - Recorded Data



Page 136/22/98

Log 4a - Xijiang A15 Realtime LWD Sonic/CDR log @ 2000m



Page 146/22/98

Log 4b - Xijiang A15 Recorded LWD Sonic/CDR log @ 2000m



Page 156/22/98

Log 4c - Xijiang A15 Recorded LWD Sonic image @ 2000m



Page 166/22/98

Log 4d - Xijiang A15 Wireline log @ 200m



Page 176/22/98

Log 5a - Xijiang A15 Realtime LWD Sonic/CDR log @ 2225m



Page 186/22/98

Log 5b - Xijiang A15 Recorded LWD Sonic/CDR log @ 2225m



Page 196/22/98

Log 5c - Xijiang A15 Recorded LWD Sonic image @ 2225m



Page 206/22/98

Log 5d - Xijiang A15 Wireline log @ 2225m

Documents

Extended Reach Drilling Well in China