Description

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 analysis of the well 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.

Cover Page

Title page

Declaration

Certification

Dedication

Acknowledgements

Abstract

Table of Content

List of Figures

List of Tables

Chapter One: Introduction

1.1 Background to the Study

1.2 Statement of the Problem

1.3 Objectives of the Study

1.4 Significance of the study

1.5 Scope of the Study

1.6 Limitations

1.7 Operational Definition of Terms

Chapter Two: Literature Review

2.1 Conceptual Review

2.2 Theoretical Framework

2.3 Empirical Review

2.4 Gap in Knowledge

CHAPTER THREE

3.0 methodology

3.1 study area

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, a well test is the execution of a set of planned data acquisition activities to broaden the knowledge and understanding of hydrocarbons properties and characteristics of the underground reservoir where hydrocarbons are trapped. The overall objective is identifying the reservoir’s capacity to produce hydrocarbons, such a soil, natural gas and condensate. Data gathered during the test period includes volumetric flow rate and 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 and gas oil ratio data, may support the well allocation process 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      BACKGROUND OF THE STUDY

In the petroleum industry, a well test is the execution of a set of planned data acquisition activities to broaden the knowledge and understanding of hydrocarbons properties and characteristics of the underground reservoir where hydrocarbons are trapped. The overall objective is identifying the reservoir’s capacity to produce hydrocarbons, such as oil, natural gas and condensate. Data gathered during the test period includes volumetric flow rate and 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 and gas oil ratio data, may support the well allocation process 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.

1.2     Statement of Problem

The use of transient well testing for determining reservoir parameters and productivity of horizontal wells has become common because of the upsurge in horizontal drilling. Initially, horizontal well tests were analyzed with the conventional techniques designed for vertical wells, but the problem with the conventional method is low pressure. During the last decade, well testing method was introduced to overcome the low pressure problem and have been presented for the pressure behavior of horizontal wells and used frequently to estimate horizontal and vertical permeabilities of the reservoir, wellbore skin, and reservoir pressure.

1.3      Objectives of the Study

1. To study the various types of well tests carried out in the oil industry and how they can be used in identifying well problems.
2. 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.

1.4     significance of study

This study shall serve as means of exploring and finding out a field potential, it presents a way to understand the various characteristics of a well. Reservoir properties like permeability, wellbore dia. meter and horizontal well length are known through well test simulation and further studies on it are used to predict the behaviour of the well during its productive life.

Also, the study shall serve an approach in which a test model is built by an engineer by integrating many disciplines and a field schedule done in order to reproduce the testing data and then sensitivity analysis

1.5     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.

1.6     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.

1.7 Operational definition of terms

Oil Well: An oil well is a boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas may be termed a gas well.

Petroleum Reservoir: A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations.

Hydrocarbon: A hydrocarbon is any of a class of organic chemicals made up of only the elements carbon (C) and hydrogen (H). The carbon atoms join together to form the framework of the compound, and the hydrogen atoms attach to them in many different configurations.

Skin due to partial penetration: When a well does not fully penetrate the formation, or the perforations do not open up the whole formation, the reservoir fluid has to flow vertically with the flow lines converging near the penetrated area at the wellbore. The convergence of the flow lines near the wellbore cause an additional pressure drop near the wellbore, an effect similar to that caused by wellbore damage. The effects of partial penetration are accounted for by treating it as a skin effect called skin due to partial penetration (spp). This skin is always positive and typically varies from 0 to 30. It is a function of the height of the perforated interval (hp), the distance from the top of the zone to the top of the perforations (htop), and the horizontal to vertical permeability ratio ( k h /k v ). The height of perforations or perforated interval (hp) is that portion of the net pay (h) that is open to flow into the wellbore either through partial penetration of the wellbore, or incomplete perforation. Normally, in order to maximize production, the entire net pay (h) is open to flow into the wellbore (fully penetrated, hp = h). In some cases, it is necessary to perforate so only a portion of the net pay (h ) is open to the wellbore in orderto minimize coning effects. This perforated interval is judiciously placed a certain distance from the top of the zone to the top of the perforations (htop ).The perforated interval has a maximum value dependent on the net pay ( h) and the net wellbore inclination ( s) . Top of Zone to Top of Perforations (htop ) In a partially penetrated well  is the distance from the top of the zone to the top of perforations. When a formation is only partially penetrated, the location of the perforated interval has an effect on the skin due to partial penetration (spp). Thus we could have the same net pay (h) and the same perforated intervals, but because these perforated intervals are located at different locations they will have different skin effects due to partial penetration. The horizontal-to-vertical permeability ratio represents the contrast in permeability between the horizontal and vertical planes within a formation (anisotropic permeability). This ratio is applicable when dealing with partially penetrated or horizontal wells and directly affects the skin due to partial penetration (spp). It typically ranges in value from 0.1 to 1000. For example, in a well with partial penetration the fluid has to travel vertically because the whole of the net pay (h) is not open to the wellbore as shown below. This vertical component of flow calls into play the vertical permeability, in addition to the horizontal permeability. A large horizontal-to-vertical permeability ratio implies a relatively low vertical permeability, which creates a larger pressure drop near the wellbore due to the vertical component of flow. Thus, this increase in pressure drop near the wellbore is represented as an increase in the skin due to partial penetration (spp).

Radius of investigation: Radius of investigation represents how far into the reservoir the transient effects have traveled. A pressure transient is created when a disturbance such as a change in rate occurs at a well. As time progresses, the pressure transient advances further and further into the reservoir. This concept is not theoretically rigorous, but is adequate for practical purposes. Theoretically, when a pressure disturbance is initiated at the well, it will have an immediate effect, however minimal, at all points in the reservoir. At a certain distance from the well, however, the effect of the disturbance will be so small as to be unmeasurable. The furthest distance at which the effect is detectable is called the radius of investigation. There is a time t when the pressure disturbance reaches the distance ri (radius of investigation).

STIMULATION: Oil well stimulation is the general term describing a variety of operations performed on a well to improve its productivity.it can be conducted on old wells and new wells alike; and it can be designed for remedial purposes or for enhanced production. Its main two types of operations are matrix acidization and hydraulic fracturing. Matrix acidization involves the placement of acid within the wellbore at rates and pressures designed to attack an impediment to production without fracturing or damaging the reservoir (typically, hydrofluoric acid is used for sandstone/silica-based problems, and hydrochloric acid or acetic acid is used for limestone/carbonate-based problems). Hydraulic fracturing, which includes acid fracturing, involves the injection of a variety of fluids and other materials into the well at rates that actually cause the cracking or fracturing of the reservoir formation.

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 intergrity.
• The excessive water production can be curbed by squeezing off the perforations and re-perforating at a suitable upper interval.