IDENTIFICATION OF WELL PROBLEMS USING WELL TESTING (A CASE STUDY OF UMU-N2 WELL OF MIDWESTERN OIL AND GAS COMPANY, KWALE, NIGERIA)
ABSTRACT
Well, tests exist already for a long time. Since the first oil reservoir was discovered, oil companies have always been keen on estimating reservoir properties such as size. Present-day well testing has gone beyond this and its usefulness cannot be overemphasized. This project work is concerned with the use of well testing in identifying well problems. The case under study is the UMU-N2 well of Umusadege field, Kwale. From the analysis of the good test data, it was seen that the well had impairment which was due to reduced permeability and thus, required stimulation for improved recovery of the hydrocarbons present. Also, there was high sand and water production which also reduced the productivity of the well.
TABLE OF CONTENTS
Content
Title
Certification
Dedication
Acknowledgement
Table of contents
List of figures
List of tables
Nomenclature
Abstract
CHAPTER ONE
1.0 INTRODUCTION
1.1 TYPES OF WELL TESTING
1.1.1 PRESSURE TRANSIENT TEST:
1.1.2 PERIODIC PRODUCTIVE WELL TEST:
1.1.3 DELIVERABILITY PRODUCTIVITY TESTS:
1.2 AIMS/OBJECTIVES:
1.3 SCOPE AND LIMITATIONS
1.4 METHODOLOGY
CHAPTER TWO
2.0 Literature review
2.1 Introduction
2.2 Division of Well Testing
2.3 Objectives of Well Testing (Surface Well Testing)
2.4 Objectives of Well Testing (Sub-surface Well Testing)
2.5 Other reasons for Well Testing
2.5.1 Legal consideration
2.5.2 Economic consideration
2.6 Classification of Well Testing
2.6.1 Periodic productivity test
2.6.2 Production or Deliverability test
2.6.2.1 Productivity index test
2.6.2.2 Inflow Performance Relationship (IPR) test
2.6.2.3 Flow after flow test
2.6.2.4 Isochronal test
2.6.2.5 Modified Isochronal test
2.6.2.6 Potential test
2.6.2.7 Pressure Transient test
2.7 Classification of Pressure Transient test
2.7.1 Pressure Drawdown test
2.7.2 Pressure Build-up test
2.7.3 Injectivity test
2.7.4 Fall-off test
2.7.5 Interference test
2.7.6 Multiple rate test
2.7.7 Drill Stem test
2.7.7.1 Drill Stem test tools and technique
2.7.7.2 Drill Stem testing operations
2.7.8 Pulse test
2.8 Flowing Gradient (FG) and Static Gradient (SG)
2.8.1 Flowing Gradient (FG)
2.8.2 Static Gradient (SG)
2.8.3 Complete BHP (Well testing) profiles
2.9 Basis of Well testing
2.9.1 Reservoir Environment
2.9.2 The inner boundary condition
2.9.3 Well bore storage
2.9.4 Skin effect
2.9.5 Induced fracture
2.9.6 Condition around region Two
2.9.7 Homogenous Reservoir
2.9.8 Heterogenous Reservoir
2.9.9 Outer boundary condition
2.9.10 Transient State phase
2.10 Reservoir boundary phase
2.11 Flow regimes
2.11.1 Steady State flow
2.11.2 Unsteady State flow
2.11.3 Pseudo Steady State flow
2.12 Diagnostic analysis
2.13 Difficulties encountered while performing well test
2.13.1 Periodic change of flowrateand pressure
2.13.2 Stabilization period
2.13.3 Fluid Slugging into the separator
2.13.4 Formation Hydrate
2.14 Well problems
2.14.1 Low productivity
2.14.2 Low reservoir permeability
2.14.3 Low reservoir pressure
2.14.4 Formation damage and skin value
2.14.4.1 The concept of damage zone around the wellbore
2.14.4.2 Skin
2.14.4.3 Formation damage skin
2.14.5 Wellbore or Tubing plugging
2.14.6 High viscosity oil
2.14.7 Excessive back pressure on formation
2.14.8 Inadequate Gas lift system
2.14.9 Gas problem in oil wells
2.15 DESCRIPTION OF TERMS
CHAPTER THREE
3.0 Case Study
3.1 Well History
3.2 Production data table
3.3 Production versus Time reading for UMU-N2 WELL
3.5 BHP Graph of Pws versus∆t
3.6 The Graph of log ∆p versus ∆t
CHAPTER FOUR
4.0 Analysis of Data
4.1 Production data analysis
4.2 Analysis of the BHP data
CHAPTER FIVE
5.0 Conclusion and Recommendation
5.1 Conclusion
5.2 Recommendations
References
NOMENCLATURE
Ct=Total compressibility psi-1 (kpa-1)
FE=Flow efficiency (dimensionless)
Net formation thickness, ft, (m)
J=Productivity index, Stb/psi
K=Reservoir rock permeability
M=absolute value of slope of middle time line in psi/cycle
β=Formation volume factor
P*=MTR pressure trend extrapolated to infinite shut-in time, psi
βo=Oil formation volume factor
C= compressibility, psi
Kv=Vertical permeability
Kh=Horizontal permeability
Hp=height of perforation
Ht=Top of perforation
Pi=Original reservoir pressure, psi(kpa)
Pwf=flowing bottom hole pressure
Pws=Shut-in bottom hole pressure psi (kpa)
P1hr=Pressure at 1 hour shut-in (or flow) time on middle-time line (or its extrapolation) psi (kpa)
Q=flow rate, STB/D
r=distance from center of wellbore, ft9m0
re=External drainage radius, ft (m)
ri=Radius of investigation ft
rw=Wellbore radius ft(m)
S=skin factor, dimensionless
T=elapsed time, hours
µ=Viscosity, cp
µo=Oil viscosity, cp
Ø= Porosity of reservoir rock, dimensionless
CHAPTER ONE
1.0 INTRODUCTION
In the petroleum industry, awell test is the execution of a set of planneddata acquisitionactivities to broaden the knowledge and understanding of hydrocarbons properties and characteristics of the undergroundreservoirwherehydrocarbonsare trapped. The overall objective is identifying the reservoir's capacity to produce hydrocarbons, such asoil, natural gasand condensate. Data gathered during the test period includesvolumetric flow rateand pressure observed in the selected well. Well testing can be surface or subsurface testing and each type has its own objectives. A properly designed, executed and analyzed well test usually can provide information about formation permeability, extent of wellbore damage or stimulation, reservoir pressure, reservoir boundaries and heterogeneities etc. Outcomes of a well test, for instance flow rate data andgas oil ratio data, may support thewell allocationprocess for an ongoing production phase, while other data about the reservoir capabilities will support reservoir management. A well is said to have problem when its behavior deviates from the normal production pattern. Typical well problems for producing wells include low productivity, low reservoir pressure, formation damage and skin value, high viscosity oil, wellbore and tubing plugging, high gas- oil ratio etc. Hence, well testing is therefore one of the economic source of valuable information about reservoir properties such as porosity, permeability, fluid viscosity, reservoir limit, drainage volume and vertical permeability orientation etc.
1.1 TYPES OF WELL TESTING
Generally,Well testing can be divided into three types viz:
Pressure transient test
Periodic productive test
Deliverability test
1.1.1 PRESSURE TRANSIENT TEST:This is a means of assessingreservoirperformance by measuring flow rates and pressures under a range of flowing conditions and then applying the data to a mathematicalmodel. During the flow period, thepressure at the formation is monitored over time. Classification of pressure transient test includes pressure drawdown test, pressure build-up test, injectivity test, inference test, fall off test etc. These tests requires higher degree of sophistication and used to determine formation damage or stimulation related to reservoir parameters such as permeability, porosity, pressure, volume etc.
1.1.2 PERIODIC PRODUCTIVE WELL TEST: This is a routine test carried out to physically measure oil, gas and water produced by a particular well under normal producing conditions. It helps to determine the daily production of oil, water and gas. These information serve as an aid in well and reservoir operations and also in meeting legal and regulatory requirements.
1.1.3 DELIVERABILITY PRODUCTIVITY TESTS: This is an intensive oil and gas well test which involves the physical or empirical determination of fluid flow rate versus bottom hole pressure drawdown with a limited number of measurements in order to determine the capability of the well under various degree of pressure drawdown. This test is usually carried out on a newly completed well. Results may be used to set allowable production and in the selection of artificial lift system and production facilities. Classification of deliverability tests include Inflow performance relationship (IPR) test, flow after flow test, isochronal test, Potential test etc.
1.2 AIMS/OBJECTIVES:
To study the various types of well tests carried out in the oil industry and how they can be used in identifying well problems.
To analyze well test data gotten from UMU-N2 well in order to determines its reservoir characteristics by the application of well test knowledge.
To make conclusions on the state of the UMU-N2 well on the basis of data analysis and give possible recommendations.
1.3 SCOPE AND LIMITATIONS
The scope of this project is limited to the data of a particular well test that was carried out on UMU-N2 well which would be used for determining problems and evaluating well productivity.
1.4 METHODOLOGY
Literature review of textbooks, journals, articles etc., and surfing the internet for necessary information.
Obtaining well test data of well UMU-N2 well from the company and carrying out analysis with the aid of mathematical calculations and graphical plots to evaluate the well problems.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION
From the analysis carried out on Umu-N2 well, it was discovered that there was formation damage which has made the permeability inadequate to allow the well to produce at rates high enough for the timely recovery of investment in drilling and completing the well. Also, the high sand and water production is detrimental to high productivity.
5.2 RECOMMENDATION
The formation damage should be removed or repaired. This requires a damage removal technique which is usually matrix acidizing but may occasionally involve hydraulic fracturing
As for the sand production, the wellbore should be cleaned out and the gravel pack re-installed such that it has high integrity.
Excessive water production can be curbed by squeezing off the perforations and re-perforating at a suitable upper interval.
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