ABSTRACT
This research work is aimed at determining the most economical means of estimating the quantity of hydrocarbon saturations in a particular reservoir and the evaluation of oil ultimate recovery using the recovery factor (RF) equations that have been developed. In order to achieve this aim, a model called Area-depth concept model was developed using Agbara oil well reservoir in Niger-Delta as a case study. This model is an extension of the existing volumetric model which has been found insufficient in the evaluation of reservoir viability. The method considers a reservoir as an enclosed volume element and to planimeter the isopachous or horizon map drawn from a reservoir cross-section. The integral of the reservoir volume was taken and the values of bulk gas sand volume, Vg, and bulk oil sand volume, VO, were analytically estimated from the cumulative bulk volume plot (CBV plot). Using the collected field data and the necessary related petro-physical parameters, the stock tank oil initially in place (STOIIP) in the reservoir and the recoverable quantity were analytically estimated from the CBV Plot. In this study, an evaluation of actual log readings from Niger-Delta were collected and used to calculate the connate water saturations in order to determine the productive oil zones in a reservoir by using Achie’s Equations. Equilibrium initialization algorithm was also used to determine pressure gradient in a particular reservoir . The research also covered the basic economic measures that are related to oil production. Considering the related petrophysical parameters involved in the evaluation, the reservoir was found to contain an oil deposit of 295.8 x 106 stock tank barrel (stb). The amount recovered for a case where there is a strong aquifer influx was 153.82 x 106 stb. The amount of recovery for a case where there is no aquifer influx was 136.1 x 106 stb. These results showed that the reservoir investigated was economically viable. It is hoped that this study will be helpful for efficient, quick collection, processing and interpretation of drilling data to analytically give the accurate estimation of recoverable hydrocarbon in a particular reservoir in order to achieve optimum yield.
TABLE OF CONTENTS
Title page i
Approval page ii
Acknowledgement iii
Abstract iv
Table of contents v
List of figures viii
List of tables ix
List of symbols x
CHAPTER ONE
1.0 Introduction 1
1.1 Objectives of the Study 2
1.2 Significance of the Study 2
1.3 Limitations of the Study 2
1.4 Methodology 3
CHAPTER TWO
2.0 Literature Review 5
2.1 Background of the Study 5
2.2 Petrophysical Evaluation 9
CHAPTER THREE
3.0 Research Methodology 33
3.1 Area-Depth Concept Model 33
3.2 Modification of Formula for Estimation using Volumetric Method 36
3.3 Mathematical Analysis of Reservoir Geometry by Area-Depth
Concept Model using Horizon or Isopachous Map 36
3.4 Assumptions in the Application of Area –Depth Concept Model 38
3.5 Limitations of Area- Depth Concept Model 38
3.7 Calculation of the Cumulative Bulk Volume From
The Area-Depth Graph 40
3.8 Petrophysical Data of the Agbara Oil Well Reservoir 43
3.9 Model For Estimation of Oil Ultimate Recovery from the Reservoir 45
3.9.1 Parameters for Recovery Factor Derivation 47
3.9.2 Saturation and Sweep Efficiencies 48
3.9.3 Analysis of oil Ultimate Recovery Using Results from
the Area-Depth Concept Model (cbv – dept plot) 51
3.9.4 Archie’s Law 53
3.9.5 Formation Factor and Archie’s Equation 53
3.9.6 Archie’s Water Saturation Equation 54
3.9.7 The Ratio Method 56
3.9.8 Using Archie’s Equation to Determine Water Saturations 58
3.9.10 Equilibrium Initialization Algorithm for Determining
Pressure in a reservoir 62
3.4.1 Basic Economic Concept of Reservoir Management 65
3.4.2 Definitions of selected economic measures 65
3.4.3 Evaluation of Economic Measures in Relation to Oil Production 65
3.4.4 Evaluation of NPV and Breakeven Oil Price 66
3.4.5 Analysis of Capital Expenditure, Operating Expenditure
and Discount Rate 66
CHAPTER FOUR
Results and Analysis 69
CHAPTER FIVE
5.0 DISCUSION 74
5.1 Exploration Economics 75
5.2 Specific Cost breakdown of an offshore Exploration Well 76
5.3 Analysis of the Economic viability of Agbara oil well reservoir
using the total cost expenditure 78
5.4 Formation Evaluation 78
5.5 Well Test Analysis 79
5.6 Importance of Well Test Analysis 80
5.7 Common Types of Reservoir 81
5.8 Application of Fluid Pressure To Determine Gas Oil Contact(GOC),
Gas Water Contact(GWC), Oil Water Contact(OWC) 82
5.9 Pressure and Temperature Gauge Placement 83
5.9.1 Gauge Performance Check 84
5.9.2 Pressure Programming and Interpretation for RFT Analysis 85
5.9.3 Laboratory Analysis of Oil Samples 86
CHAPTER SIX
6.0 CONCLUSION 87
6.1 RECOMMENDATIONS 88
References
Appendix
CHAPTER ONE
1.0 INTRODUCTION
Generally, the major oil companies maintain their own research and development (R&D) records and also, nurture in-house technological and engineering skills acquisition schemes. For this reason, some companies see the core activities needed before oil exploration as unrealistic if carried out, externally.
They now preserve only what is essential to evaluating the cost of exploration from a particular reservoir.
These core activities include the formation evaluation technique, which is applied to determine hydrocarbon saturation in a given reservoir, the determination of oil- in- place (OIP) or stock Tank Oil initially in Place (STOIIP) and the application of ultimate Recovery Factor (URF), based on analysis of some petrophysical parameters using current technology.
This research work gives attention to determining the most economical means of estimating the percentage of hydrocarbon saturation in a particular reservoir, and its recovery factor. A model called, Area – Depth concept model was developed to analytically estimate the quantity of crude oil deposits in a reservoir, using Agbara oil well reservoir as a case study. The basic economic measures that are related to oil production were evaluated. In this research, Archies’ Law was applied in the determination of water saturations at different zones in a particular reservoirs based on the log data of the petrophysical parameters from the Agbara oil well reservoir, in the Niger-Delta basin. This helps to determine the productive oil zones by estimating the percentage of hydrocarbon saturations in the reservoir. This study would help reduce considerably the overall cost involved in executing recovery process from a particular reservoir in order to achieve optimum yield.
There is no doubt in the fact that the world has consumed approximately 40 percent of the estimated recoverable reserves, i.e. more than one- third of the easily recoverable reserves have been found and consumed (Stela Shamon,1998).
When 50 percent of recoverable reserve is reached, production will inevitably go down because of the difficulty of extracting the rest. The only hope of extending the world’s oil reserve is to make a quantum leap in production from 35% to 60%.
1.1 OBJECTIVES OF THE STUDY
- To estimate the quantity of recoverable hydrocarbon in a reservoir and evaluate the recovery factor, by using the related petrophysical parameters.
- To improve the efficacy of volumetric method in reservoir evaluation by using the area-depth concept model.
- To determine the productive oil zones in a particular reservoir , by the use of Archie’s equations.
4 To develop initialization algorithm for determination of
pressure gradient in a reservoir.
5 To evaluate the basic economic measures in relation to oil production.
1.2 SIGNIFICANCE OF THE STUDY
The significance of this research work will include:
- Provision of a background for easy interpretation of resulting drilling data before and during exploration.
- Reduction in the overall drilling costs from a reservoir.
- Improvement on the quality and quantity of crude oil recovered from a particular reservoir
- Reduction in the cost of energy to consumers
1.3 LIMITATIONS OF THE STUDY
- First, it would be impossible within the short time frame of this study to conduct extensive oral or written interviews outside Port Harcourt
- Secondly, time factor would also not permit to deal exhaustively with the issues of management views arising from the first constraint.
- Thirdly, the values of the petrophysical parameters from log readings used for these evaluations are only dependent upon the precision and accuracy of the instrument used.
1.4 METHODOLOGY
The information for this study will be obtained from the following sources;
- Publications such as: Learned journals ,Internet and Seminars.
Research findings from Schlumberger oil services Ltd and Chevron Nigeria Ltd, in Port Harcourt.
Data collected from actual drill samples during fieldwork was used for the analysis of formation evaluation. They were collated and analyzed. These data include the petro-physical parameters like porosity, permeability, resistivity, shaliness, lithology and formation temperature. These data would be used to evaluate the viability of a reservoir, by the use of formation factor and Archie’s Equation. Also, information on economic and management considerations would be obtained from interviews and observations during a visit to some selected companies in the Niger- Delta area.
The processes, economics and management of enhanced drilling techniques are pre-requisite for the actualization of these objectives.
Formation evaluation (Otherwise referred to as log Interpretation) is the process whereby physically measurable properties are translated into petrophysical parameters of interest. Some of the major petro-physical parameters that would be used in this research work, to determine and evaluate the viability of a crude oil reservoirs are as follows:
- Resistivity (R) :- The reluctance of a unit volume of formation (matrix + fluid) to the flow of electrical current
- Porosity (ø):- This is the percentage of void space in a unit volume of rock.
- Hydrocarbon saturation (S): This is the percentage of pore space filled with hydrocarbons (gas or oil).
- Permeability (K):- This is the measure of the specific flow capacity or ease with which fluid flows.
- Lithology (L):- This is the study of rocks to determine their character and composition
- Shaliness (Vsh):- The fraction of a very fine grained detrital sedimentary rock composed of silt and clay. It is the volume of shale in a particular rock formation.
- Water saturation (Sw)-: The percentage of the porous fraction of formation that contains water.
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