School of EngineeringCOURSEWORK SUBMISSION SHEET

All sections except the “LATE DATE” section must be completed and the declaration signed, for the submission to be accepted.Any request for a coursework extension must be submitted on the appropriate form (please refer to http://www.rgu.ac.uk/academicaffairs/quality_assurance/page.cfm?pge=44250), prior to the due date.

Due Date Date Submitted For official use only5 November 2010 4 November 2010 LATE DATE

MATRIC No. 1010207

SURNAME Hermani

FIRST NAME(S) Arief Budiman

COURSE & STAGEMSc Drilling & Well Engineering

Full Time /Part-Time/ODL

MODULE NUMBER & TITLE ENM200 Subsurface

ASSIGNMENT TITLE

2(a) Drill Stem Testing

2(b) Reservoir Properties of Carbonates Sedimentary

Rocks

LECTURER ISSUING COURSEWORK Brian Cronin

I confirm: (a) That the work undertaken for this assignment is entirely my own and that I have not made use of any unauthorised assistance.

(b) That the sources of all reference material have been properly acknowledged.[NB: For information on Academic Misconduct, refer to http://www.rgu.ac.uk/academicaffairs/assessment/page.cfm?pge=7088]

Signed ………………………..................................... Date ......................................................

Marker’s Comments

Marker Grade

Coursework Question 2(a)

Drill Stem Testing

In petroleum exploration it is essential to determine the commercial viability of a potential reservoir.

This can be performed with a series of tests. There are 4 major classes of tools & techniques to

evaluate a formation, namely mud logging, coring & core analysis, wireline logging and drill stem

testing (Jorden and Campbell, 1984).

Drill Stem Testing (DST) is one of the methods to determine the production capability of a well. It is

conducted to determine the reservoir characteristics i.e. probability and pressure of a reservoir. In

principal, it is a flow experiment on an isolated area of interest in a formation. Normally carried out on

exploratory wells or temporary completions, it is performed by acquiring formation samples which will

be analyzed based on the liquid content, flow rate, pressure and temperature. It can also be

conducted during actual drilling operations. DST data will assist on the development of the production

facilities required, estimating or/ and reducing the development cost as well as the safety of advance

drilling. This will also help in the plan to accelerate the production schedule and maximize the

reservoir life span. Generally there are 2 applications of DST, namely Cased Hole (with casing) or

Open Hole (without casing, more economical). Diagram 1 show the basic setting for DST. Below is a

table listing the basic equipment in DST and its’ description:

No Equipment Description

1 Drill String A hollow pipe with valves in it to allow flow of the formation fluid. The

valves are controlled from the surface to minimize wellbore effect.

2 Packers Inflatable/ expanding rubber seal that act as plugs.

3 Test Tree/ Choke A combination of valves that controls the flow of the formation fluid.

Table 1: Basic Equipment in Drill Stem Testing

As an alternative to utilizing hydrostatic head to control the well as in normal drilling, DST works on

mechanical system which controls the fluid flow. Formation fluid is obtained through the drill string

instead of the annulus. Initially the test string is lowered with deflated packer(s) and closed valves.

Once it reaches the zone of interest, the packer(s) will be inflated until it seals off the area in between

the casing/ wellbore wall and the drill string wall. This will restrict the formation fluid flow into the

annulus and only allows it to flow into the drill string through perforations around the drill string. Next

the valves in the string are opened and the test tree/ test choke is operated to initiate the fluid flow.

Typical DST is split into 4 periods (Schubert, 2010). Please refer Diagram 2 for the pressure vs. time

analysis:

1. Pre-Flow Period (approximately 5 – 10 minutes)

This period is to bring down the pressure to well bore pressure and remove any supercharge

caused by mud infiltrating the hole during the drilling process.

2. Initial Shut-In

This cycle allows the formation to recover from the pressure surge and let the pressure build

back to the true static pressure.

3. Main Flow (approximately 1 hour)

This is an extensive production phase where large samples of fluid is captured and analyzed for

water content, gas bubble, bust pressure and temperature.

4. Final Shut-In (approximately 24 hours)

In this stage the formation pressure is recorded within a predetermined interval. Data acquires at

this point will approximate the permeability, degree of formation damage during drilling and the

size.

Research based on the data gathered in DST will help in the assessment on the further progress

either for potential production or abandonment of the well. DST may also be combined with other test

method such as gamma ray logging. Since the control of the formation fluid is done manually by the

use of chokes and valves, for safety reasons, proper planning and precaution need to be in place prior

to execution.

Diagram 1: Basic Setting of Drill Stem Testing in an Open Hole ( Schubert, 2010)

Drill StemPackers

Area of Interest

Area of Interest

Fluid Flow

Perforations

Graph 1: Standard Pressure vs. Time during DST (Jorden & Campbell, 1984)

References

JORDEN, J.R., CAMPBELL, F.L., 1984. Well logging I: rock properties, borehole environment, mud

and temperature logging. New York: American Institute of Mining, metallurgical & petroleum

engineers.

SCHUBERT, J.J, 2010. Drill stem testing. [online]. College Station, Texas: Texas A&M University.

Available from http://webcache.googleusercontent.com/search?

q=cache:sV26Xi3xU80J:www.pe.tamu.edu/schubert/public_html/DOE_SLB%2520short

%2520course/22.3%2520Drillstem

%2520Testing.ppt+drill+stem+test&cd=11&hl=en&ct=clnk&gl=uk&client=firefox-a. [Accessed on 23

October 2010].

WIKIPEDIA, 2010. Drill stem test. [online]. San Francisco: Wikipedia Foundation Inc. Available from

http://en.wikipedia.org/wiki/Drill_Stem_Test. [Accessed on 24 October 2010].

SCHLUMBERGER, 2010. Oilfield glossary. [online]. Houston: Schlumberger Limited. Available from

http://www.glossary.oilfield.slb.com/Display.cfm?Term=drillstem%20test. [Accessed on 23 October

2010].

Bibiliography

KOHLHASS, C.A., 1980. Drill Stem Testing. In: Society of Petroleum Engineers (SPE), SPE reprint

series book no: 14 pressure transient testing method. Dallas, Texas: SPE. pp 314-318.

Montgomery, J.M., 2010. Drillstem testing and sampling of deep Frio and Wilcox reservoirs.

Duncan, Oklahoma: Halliburton Services Research.

BC F

Time

Pre

ssur

eA D E G

H

I

A – DTS tool is lowered to holeAB – Increasing pressureB – DST tool is at area of interest, packer(s) inflatedC – Valve inside drill stem is opened, fluid starts filling drill stemCD – Pre-flow periodEF – Well shut-in for pressure build upGH – Main Flow PeriodHI – Final shut-inI – Packer(s) deflated, DST toll removed

RITCHIEWIKI, 2010. Drill-stem testing. [online]. Kelowna: Equipment, specifications, information and

photos. Available from http://www.ritchiewiki.com/wiki/index.php/Drill-stem_Testing. [Accessed on 23

October 2010].

Coursework 2(b) – Petroleum Geology

Reservoir Properties of Carbonates Sedimentary Rocks

While there are reservoirs that are made from highly fractured igneous and metamorphic rocks, which

are not likely and in smaller scale, most reservoir rocks are made of sedimentary rocks. There are 3

basic types of sedimentary rocks: 1. Clastic/ detrital (made from rock debris e.g. sandstone &

mudstones); 2. Biochemical (produced by organism e.g. limestones) and; 3. Chemical (precipitation

of chemical solutions e.g. dolostones)

Carbonate sedimentary rock formed more than 50% of the world’s oil and gas reservoir (Roehl &

Choquette, 1985). It has distinctive features that characterized it from other sedimentary rocks.

Basically made up of more than 50% of organic matters, it is mostly originated intra-basinal. Majority

of carbonate sedimentary rocks are in the form of two types of rocks:

1. Limestones which are composed mostly of calcite or high magnesium calcite, and

2. Dolostones which are composed mostly of dolomite.

Carbonate Rocks Mineralogy

1. Calcite Group Minerals – Includes Calcite (CaCO3), Smithsonite (ZnCO3), Magnesite

(MgCO3), Otavite (CdCO3) and Siderite (FeCO3).

2. Dolomite Group Minerals – Includes Dolomite (CaMg(CO3)2) Ankerite (CaFe(CO3)2)

Kutnohorite (CaMn(CO3)2)

3. Aragonite Group – Includes Aragonite (CaCo3), Witherite (BaCO3), Strontianite (SrCO3) and

Cerussite (PbCo3).

Grains Types

Fossil (Full or pieces of skeleton of organisms) - Sizes vary from granule to fine sand depending

on the organism and scale of damage throughout deposition.

Ooids (coated grains) - A spherical sand size particle with concentric or radial internal formation.

The centre is usually made of quartz or other carbonate particles. It is covered by deposits of

chemical precipitated calcite.

Peloids (by product pellets) - Spherical accumulation of microcrystalline calcite of coarse silt to fine

sand size. Comes from the excrement pellets of burrowing benthic organisms which consist of

microcrystalline calcite.

Aggregates & Inter-clast - Debris of earlier created limestone or partly lithified limestones. Mostly

originated from within the basin of deposition. Aggregates consist of several carbonate particles

cemented by microcrystalline cement or bound by organic matter (Tucker, 1981).

Matrix/ Cement

1. Micrite – Fine grain carbonate mud that gives dull opaque appearance on most limestone.

2. Sparite – Coarse grain calcite crystals from digenesis.

Porosity & Permeability

Vuggy/ vugular, less homogeneous and irregular as carbonate can undergo dissolution/ re-

precipitation even in low acidic environment. Normally is very high in porosity and permeability.

Classification

Folk Classification (primarily used in laboratory works)

This type of classification divides carbonates into 2 groups:

i. Allochemical - Grains that originated from other sources (depositional effects) similar to

detrital grains in clastic rocks.

ii. Orthochemical – Carbonates that crystallize in place.

Diagram 1: Folk Classification of Carbonate Rocks (Nelson, 2000)

Dunham Classification (widely used)

This classification segregates the rock based on the texture and grain size and divides grains into 2

broad groups as in the diagram below:

Diagram 2: Dunham Classification of Carbonate Rocks (Nelson, 2000)

Structure

Arrangement varies between bedding planes (cross, graded, imbricates), current and wave structures

(ripples, cross laminar), dunes, hardground surface (horizons of synsedimentary) and tepees (Tucker,

1981). Stratifications may not be as obvious as in sandstones since it is lack in contrasting colours. It

may contain irregular discontinuity or non-structural fracture called stylolite. This is due to insoluble

residue or insoluble organic material in the build up of sedimentation.

Main Depositional Environments and Facies (Press et al., 1995)

Continental-shelf/ carbonate platforms or shelters – Warm shallow seas joined to continents or

epeiric seas (partially or fully covering continents).

Shoreline intertidal flats – Areas that are flooded during high tides and uncovered during low tides.

Deep ocean floor – Only in shallow part of deep sea unless it is saturated with highly excessive

organic activity and organism remains are buried considerably quick. This is due to the high rate of

dissolution in this type of area. Unsaturated area is insufficient for sedimentation.

Continental non-marine lagoon – High carbonate water content area located behind barriers.

Normally has excessive organism constituent which will assist in precipitation of carbonate by removal

of CO2.

Most of the petroleum reservoir in the world is made up of carbonate sedimentary rock. These types

or rock are mostly formed in-situ. Its elements depend highly on organic activity and are very sensitive

to post-deposition alterations. Water body’s temperature, salinity and depth need to be in the “just

right” condition for deposition and sedimentation to occur.

References

ROEHL, P.O., CHOUQUETTE, P.W., 1985. Carbonate petroleum reservoirs (casebooks in earth

sciences). Berlin, Heidelberg, New York, Tokyo: Springer-Verlag.

TUCKER, M.E., 1981. Sedimentary petrology: an introduction to the origin of sedimentary rocks.2nd

ed. London: Blackwell Science.

NELSON, S.A., 2000. Carbonates and other rocks. [online]. New Orleans: University of Tulane.

Available from http://www.tulane.edu/~sanelson/geol212/carbonates.htm. [Accessed on 23 October

2010].

PRESS, F. et al., 1995. Understanding earth. 4th ed. New York: W.H. Freeman and Company.

Bibliography

LYNN, S.F., 2000. Carbonate sedimentary rock classifications. [online]. Harrisonburg, Virginia: James

Madison University. Available from http://csmres.jmu.edu/geollab/fichter/SedRx/Carbonate.html.

[Accessed on 23 October 2010].

KIRKALDY, J.F., 1963. Minerals and rocks in colour. Stockholm: Blanford Press.