Theoretical Analysis of Gravity-Controlled Waterfloods.
ABSTRACT
The concept of dump flooding is to flow water from a high-pressure aquifer zone to a low-pressure oil-producing zone by the natural force of gravity through a well connecting the two zones to enhance oil sweep into a producing well.
The research described is aimed to find solutions to one of the flaws in dump flooding that is, the inability to quantify the rate of water injection from a high-pressure aquifer zone to a low-pressure oil-producing zone.
Theoretical dump flood equations were developed for evaluating the rate of water injection from an aquifer into various types of oil reservoirs.
Two cases were considered in the development of the rate of injection equations, which were; water from a finite aquifer injecting into a finite oil reservoir and water from an infinite aquifer injecting into a finite oil reservoir.
In each case, the theory is applied to an undersaturated oil reservoir as well as an oil reservoir with a gas cap. A simple single-well model was built using Excel Spreadsheet to solve the rate of injection equations by Bisection iteration technique.
Graphical sensitivity analysis ascertained in both cases that, the rate of water injection increases as the productivity index increases at constant time intervals, however, there is a decline in the rate of injection for constant productivity index as time increases.
In conclusion, the rate of water injection recorded in both cases higher values in the finite oil reservoir with gas cap compared to the finite undersaturated oil reservoir because a large amount of water goes into compressing the gas cap gas. The boundary pressure in the finite aquifer zone depletes much faster compared to the infinite aquifer zone.
TABLE OF CONTENTS
Page
ABSTRACT i
DEDICATION ii
ACKNOWLEDGEMENTS iii
TABLE OF CONTENTS iv
LIST OF FIGURES vii
LIST OF TABLES x
CHAPTER 1 INTRODUCTION 1
1.1 Motivation 1
1.2 Objectives 2
1.3 Methodology 2
1.4 Scope and Limitation of Work 2
1.5 Organization of Work 2
CHAPTER 2 OVERVIEW OF GRAVITY WATERFLOODING (DUMP FLOODING) 4
2.1 Definition of Dumpflooding 4
2.2 Review of Dumpflooding 5
2.2.1 Advantages of Dumpflooding 6
2.2.2 Disadvantages of dump flooding 7
CHAPTER 3 DUMP FLOODING FLOW MECHANISMS 9
3.1 Downward Flow Mechanism 9
3.2 Upward Flow Mechanism 10
3.3 Pressure Drop in the Wellbore 11
3.4 Material Balance Equation (MBE) for Reservoir Boundary Pressures 12
3.5 Solution Gas Drive Reservoir 13
3.5.1 Undersaturated Oil Reservoir 13
3.5.2 Oil Reservoir with Gas Cap 14
CHAPTER 4 APPLICATION OF DUMPFLOOD THEORY 15
4.1. Case 1: Water from a Finite Aquifer Injecting into a Finite Reservoir 15
4.1.1 Undersaturated Oil Reservoir 15
4.1.2 Oil Reservoir with Gas Cap 16
4.2 Case 2: Water from an Infinite Aquifer Injecting into a Finite Reservoir 16
4.2.1 Undersaturated Oil Reservoir 16
4.2.2 Oil Reservoir with Gas Cap 17
4.3 Application of Bisection Method for Solving Fluid Rate Transfer 17
CHAPTER 5 DISCUSSIONS AND ANALYSES OF RESULTS 19
5.1 Sensitivity Analysis for Case 1: Finite Aquifer Injecting into Finite Reservoir 19
5.1.1 Undersaturated Oil Reservoir 19
5.1.2 Oil Reservoir with Gas Cap 20
5.1.3 Comparing Case 1a & 1b: Undersaturated Oil Reservoir vs. Oil Reservoir with Gas Cap 21
5.2 Sensitivity Analysis for Case 2: Infinite Aquifer Injecting into Finite Reservoir 21
5.2.1 Undersaturated Oil Reservoir 21
5.2.2 Oil Reservoir with Gas Cap 22
5.2.3 Comparing Case 2a & 2b: Undersaturated Oil Reservoir vs. Oil Reservoir with Gas Cap 23
5.3 Sensitivity Analysis of Cases 1 & 2 24
5.3.1 Case 1a & 2a: Comparing Undersaturated Oil Reservoirs 24
5.3.2 Case 1b & 2b: Comparing Oil Reservoirs with Gas Cap 24
5.4 Conclusions and Recommendations 25
NOMENCLATURE 26
REFERENCES 28
INTRODUCTION
The technique of injecting water into an oil-producing reservoir for either pressure maintenance or secondary recovery is a well-established process.
In an effort to reduce and reverse the declining pressure and increase oil recovery, a method of replacing the voidage created by the volume of oil extracted from the reservoir is required.
The sources of water available for injection purposes are; produced water, seawater, aquifer water, and freshwater, however, the economics associated with the injection project usually dictates which source should be used. The source of water used is dependent on the quality and quantity of water available.
This work deals with what is probably the cheapest method of injecting water into an oil reservoir, that is, gravity waterflooding (also known as dump flooding). The terms dump flooding and gravity waterflooding will be used interchangeably.
The concept of dump flooding is to flow water from a high-pressure aquifer zone to a low-pressure oil-producing zone by the natural force of gravity through a well connecting the two zones to enhance oil sweep into a producing well.
REFERENCES
Davies, C.A., “The Theory and Practice of Monitoring and Controlling Dumpfloods”, paper SPE 3733, presented at the European Spring Meeting of the Society of Petroleum Engineers of AIME, Armsterdam, The Netherlands, 16-18 May 1972.
Rawding, J., Al Matar, B.S., and Konopczynski, M.R., “Application of Intelligent Well Completion for Controlled Dumpflood in West Kuwait”, paper SPE 112243, presented at the SPE Intelligent Energy Conference and Exhibition, Armsterdam, The Netherlands, 25-27 February 2008.
Quttainah, R., and Al-Hunaif, J., “Umm Gudair Dumpflood Pilot Project: The Applicability of Dumpflood to Enhance Sweep & Maintain Reservoir Pressure” paper SPE 68721, presented at the SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, Indonesia, 17-19 April 2001.
Yao, C.Y., Hill, N.C., and McVay, D.A., “Economic Pilot-Floods of Carbonate Reservoirs using a Pump-Aided Reserve Dumpflood Technique”, paper SPE 52179, presented at the SPE Mid-Continent Operations Symposium, Oklahoma City, Oklahoma, 28-31 March 1999.
Koot, L.W, and Konopczynski, M.R., “Single Well Combination Oil Production/Water Dumpflood Apparatus and Methods”. Patent Application No.: US 2003/0066649 A1, 10 April 2003.
6 Dake, L.P., “Fundamentals of Reservoir Engineering”, Elsevier Development in Petroleum Science, The Netherlands, Vol 8, 1978, pp. 71-79.
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