A STUDY OF PRODUCTION OPTIMIZATION (A NODAL ANALYSIS APPROACH USING PROSPER)
ABSTRACT
Crude oil production is a major requirement to sustaining the wellbeing of any petroleum company. It entails the effective placement of all facilities and equipment; surface or subsurface in order to achieve optimum volume of crude oil production. This is usually called Production Optimization. In this study, the software PROSPER was utilized to case study wells P-P1 and P-P2. Well P-P1 (short string) and Well P-P2 (long string) were producing at its peak oil rates of 2000STB/day and 2500STB/day at 0% water cut but since then production has been on the decline due to increasing water cut and decreasing reservoir pressure. But to date, Well P-P1 becomes a dead well while Well P-P2 is producing at an oil rate of 1200STB/day at a water-cut of 40%. Thereafter an optimization plan scenarios such as sensitivity runs on the water cut, reservoir pressure and gaslift techniques for the dual string well were simulated in PROSPER and then evaluated. The results of this work suggests that; at present reservoir pressures of 3000psig and 3500psig for Well P-P1 and Well P-P2 with optimum gas injection rates of 3.3MMscf/day and 2.7MMscf/day, the well’s life can be extended to an economical water cut of 90% and 95% respectively. Also, the oil production rates increased from 0STB/day and 1200STB/day at 50% and 40% water cut to about 900STB/day and 1500STB/day for Wells P-P1 and P-P2 respectively.
TABLE OF CONTENTS
TITLE PAGE…………………………………………………………………………i
APPROVAL ....................................................................................................... ii
DEDICATION ............................................................................................. iii
ACKNOWLEDGEMENT ................................................................................. iv
ABSTRACT ............................................................................................. vi
TABLE OF CONTENTS ….……………………...………………………………….vii
LIST OF TABLES .............................................................................. x
LIST OF FIGURES ............................................................................................ xi
CHAPTER ONE ...................................................................................................... 1
1.0 INTRODUCTION .................................................................................................1
1.1 Background of Study ................................................................................... 1
1.2 Statement of Problem ............................................................................................ 2
1.3 Aim and Objectives of Study ........................................................................ 2
1.4 Scope of Study .................................................................................................. 3
1.5 Methodology .................................................................................................3
1.6 Limitations of Study ................................................................................. 3
CHAPTER TWO .............................................................................. 4
2.0 LITERATURE REVIEW ............................................................... 4
2.1 Introduction ...................................................................................................4
2.1.1 Nodal Analysis Theory ......................................................................4
2.1.2 Inflow Performance of a Well .............................................................6
2.1.2.1 Darcy’s equation ................................................................................. 7
2.1.2.2 Productivity Index (PI) ...................................................... 7
2.1.2.3 IPR Curve....................................................................................... 8
2.1.2.3.1 Vogel Equation.......................................................................................... 9
2.1.3 Tubing Performance of a Well ................................................................9
2.1.4 Choke Performance of a Well ................................................................10
2.1.5 Multiphase Flow .....................................................................................11
2.1.6 Overview of Gaslift System ................................................................12
CHAPTER THREE ................................................................................................ 21
3.0 METHODOLOGY OF STUDY .................................................................... 21
3.1 Introduction ............................................................................................21
3.2 Brief Description of PROSPER Tool ....................................................... 21
3.2.1 PVT Data ..........................................................................................25
3.2.2 Equipment Data ..................................................................................26
3.2.3 Inflow Performance Relationship (IPR) Data ...............................................28
3.2.4 Gaslift Data ...............................................................................................29
CHAPTER FOUR ........................................................................................................ 31
4.0 INTERPRETATION, DISCUSSION OF RESULTS AND SENSITIVITY ANALYSIS
FOR WELLS P-P1 AND P-P2 ................................................... 31
4.1 Building a Base Model for Wells P-P1 and P-P2 ..............................................31
4.2 Sensitivity on Gaslift Injection Rates and Water cut ......................................... 39
4.3 Sensitivity on Reservoir Pressure and Water cut ............................................. 40
4.4 Economic Evaluation .............................................................................42
CHAPTER FIVE ........................................................................................................ 43
5.0 CONCLUSION AND RECOMMENDATION .................................................................. 43
5.1 Conclusion ...........................................................................................................43
5.2 Recommendations .................................................................................................44
REFERENCES ..........................................................................................................45
APPENDIX ...................................................................................................... 48 LIST OF TABLES
Table 3.1: PVT data entry……………………………….25
Table 3.2: Downhole equipment data entry…………………….27
Table 3.3: Geothermal gradient data entry……………………28
Table 3.4: PI Entry IPR model data entry…………………28
Table 3.5 Continuous gas lift data entry…………………………...29
Table 4.1a: Showing results of sensitivity on Gaslift injection rates for well P-P1 (short string)……………………………39
Table 4.1b: Showing results of sensitivity on Gaslift injection rates for well P-P2 (long string)……………….39
Table 4.2a: Showing base case forecast results for well P-P1 (short string)……….40
Table 4.2a: Showing base case forecast results for well P-P2 (long string)………..41 LIST OF FIGURES
Figure 2.1: Showing the location of various pressure drop nodes on a well……....5
Figure 2.2: Determination of flow capacity……………………….....6
Figure 2.3: Inflow Performance Relation…………...……………..…7
Figure 2.4: Productivity Index (PI) Curve………………8
Figure 2.5: Effect of tubing size and Finding optimum tubing size………….10
Figure 2.6: Flow regimes in horizontal flow…………………….....11
Figure 2.7: Flow regimes in vertical flow………………………....12
Figure 2.8: General Gaslift system………………..13
Figure 2.9: Estimating optimum gaslift rate…………………….13
Figure 2.10: Gaslift well performance curve………………...........14
Figure 2.11: Gilbert analysis of the System performance for various wellhead chokes...18
Figure 3.1: Flow chart for Systems Analysis using Prosper.......................22
Figure 3.2: Well Completion Status Diagram for Wells P-P1 and P-P2............24
Figure 3.3: Menus and Options in Prosper Main Screen.............................25
Figure 3.4: Deviation survey data............................................27
Figure 4.1a: PVT is matched for Well P-P1 (short string)........................31
Figure 4.1b: PVT is matched for Well P-P2 (long string)..................................32
Figure 4.2: The well deviation survey...................................33
Figure 4.3 Subsurface Equipment design in PROSPER for Wells P-P1 and P-P2..........33
Figure 4.4a: IPR plot for well P-P1 (short string)..................................34
Figure 4.4b: IPR plot for well P-P2 (long string).......................................34
Figure 4.5a: Pressure Transverse for well P-P1 (short string)..................35
Figure 4.5b: Pressure Transverse for well P-P2 (long string)....................36
Figure 4.6a: Gaslift performance curve for well P-P1 (short string).............37
Figure 4.6b: Gaslift performance curve for well P-P2 (long string)................37
Figure 4.7 Pressure Transverse for well P-P1 (short string) under Gaslift...............38
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of Study
Hydrocarbons are produced from wells that penetrate geological formations rich in oil and gas.
The hydrocarbons can flow to surface provided the reservoir pressure is high enough to overcome
the back pressure from the flowing fluid column in the well and the surface facilities. During the
movement or transport of these fluids, the fluids will require energy to overcome frictional losses
in the systems and to lift the fluids to the surface (Golan et.al., 1991). The production rate or
deliverability of a well can often be affected by several components in the system in which energy
or pressure losses occur.
The production optimization of oil and gas wells by NODAL system analysis has contributed to
improved completion techniques, production, and efficiency for many wells as proposed by Gilbert
(1954). He continued his proposal by striking a balance between production deliverability of the
wells and demand which basically is aimed at increasing the rate at which a well flows from the
reservoir without restriction to the surface storage tank(s). Thus, Beggs (1991) stated that
production optimization through nodal analysis is a way of preparing a well for the production of
oil or/and gas from a reservoir to achieve the greatest possible efficiency. Oil and gas production
optimization ensures that wells and facilities are operating at their peak performance at all times
to maximize production (Beggs et al., 1991).
Production system can be divided into main three components. These are inflow (fluid flow
through porous media), vertical well flow (from sand face to the wellhead choke), and flow through
surface facility (Brown and Kermit, 1977). In order to optimize the system, one of these
components must be isolated and evaluated separately. This is performed because the production
rate or deliverability of a well can often be severely restricted by the performance of only one
component in the system. Therefore, well analysis is the most important step to optimize oil
production but before a well can be optimized for effective performance, there is need for a
Production Engineer to;
a) Identify the components in the system.
b) Select one component to be optimized.
c) Select the node location that will best emphasize the effect of change. d) Calculate pressure drop versus rate for all components.
e) Determine the effect of changing the characteristics of the selecting component.
f) Repeat the procedure for each component.
g) Optimize the production system.
Therefore, a Nodal Approach suited for evaluating both flowing wells and wells on artificial lift is
to identify flow restrictions or opportunities to enhance performance (Schlumberger Oilfield
Glossary, 2006). A partial list of possible applications of nodal analysis is given as follows:
a) Selection tubing size and flow line size.
b) Gravel pack design.
c) Surface choke sizing.
d) Subsurface safety valve sizing.
e) Artificial lift design.
f) Allocating injection gas among gaslifted wells.
g) Determining the effect of compression on gas well performance, etc. (PROSPER Manual, 2009).
1.2 Statement of Problem
When the reservoir energy is too low for the well to flow, or the production rate desired is greater
than the reservoir energy can deliver, it becomes necessary to put the well on some form of
artificial lift to provide the energy to bring the fluid to the surface. Hence, one of the challenges
faced in lifting the oil and gas from the reservoir via the production tubing to the surface facilities
is an unnecessary production decline which poses a serious problem to the oil and gas industry
today or inability of the well to flow (expected rate) due to the viscous nature of the fluid. This
decline may be as a result of mismanagement of wells, excessive pressure drops along the
production system, oversized or undersized tubing, and improper perforation method, high water
cut, skin, etc. A change in a single component of the production system may lead to a change in
the pressure drop behavior of the other components since the various components are interactive.
1.3 Aim and Objectives of Study
The quantity of reservoir fluids estimated to be commercially recoverable declines every day, thus
the role of production optimization cannot be overemphasized. Hence, the aim of this work is to
optimize the Wells P-P1 and P-P2 performances in order to maximize the production rates using
PROSPER software. The objectives of this study are;
1. To carry out optimization plan to optimize Wells P-P1 and P-P2 oil productions, by doing
sensitivity runs on the well production system parameters such as the well head pressure,
chokes sizes, tubing sizes, skin, water cut, etc.
2. Finding out the optimum gas injection rates for Wells P-P1 and P-P2, to achieve the
maximum oil production.
1.4 Scope of Study
This study will be conducted on a dual completion well located in the Niger Delta region of Nigeria
and the tool employed for these wells will be carried out using PROSPER (PROduction and
Systems PERformance) analysis software in comparing the productivity of the wells when flowing
naturally and installation of gaslift as a means of production optimization.
1.5 Methodology
The aspect of artificial lift on oil well performance cannot be overemphasized. Therefore the
methods used in this study are as follows:
a) Collection of well and production data from wells P-P1 and P-P2.
b) Building a single well model with the available data.
c) Using prosper to design the gaslift option.
d) Comparing the production rate of the wells using gaslift with that of the naturally producing
wells.
1.6 Limitations of Study
1) Lack of complete field data to give a full scale economic analysis for the optimization plan
of the wells from the subsurface up to the storage tank of the processing facilities so as to
know the profitability of the plan.
2) Inability to optimize the sustainability of the oil production rate of the wells due to non-
availability of a reservoir simulation software like the Eclipse (Schlumberger) software at
the time of conducting this studies.
.