Description
ABSTRACT
Gas lift is one of a number of processes used to artificially lift oil or water from wells where there is insufficient reservoir pressures to produce the well. The process involves injecting gas through the tubing-casing annulus. Injected gas aerates the fluid to reduce its density; the formation pressure is then able to lift the oil column and forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the producing characteristics of the well and the arrangement of the gas-lift equipment. To enhance the financial revenues this operation has usually always been a subject for optimization to reach the most rewarding design before its operational establishment. Evolutionary approaches have recently been successfully applied to almost every aspect of engineering problems. This study reviews the general facts and ideas related to the gas lift and its optimization and further focus on the application and evaluation of genetic programming for such a purpose. It has been concluded that genetic programming is fully capable in aiding faster gas lift optimizations while is also stable and applicable to a very broad range of operating conditions. The merits and draw backs are finally compared with the neural network approach.
TABLE OF CONTENT
COVER PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
TABLE OF CONTENT
1.0 INTRODUCTION
1.2 BACKGROUND OF THE PROJECT
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 REVIEW OF THE STUDY
2.2 REVIEW OF RELATED STUDIES
2.3 OVERVIEW OF BITTER LEAF
2.4 REFERENCES
CHAPTER THREE
3.0 METHODOLOGY
3.1 INTERMITTENT-FLOW GAS LIFT
3.2 CONTINUOUS-FLOW GAS LIFT
CHAPTER FOUR
4.0 GAS LIFT MECHANISM APPLICATION
4.1 DESIGN METHODS
4.2 DESCRIPTION OF UNLOADING OPERATIONS
4.3 INITIAL INSTALLATION DESIGN CONSIDERATIONS
4.4 ASSUMPTIONS AND SAFETY FACTORS
CHAPTER FIVE
5.0 CONCLUSION
5.1 RECOMMENDATION
5.2 REFERENCES
CHAPTER ONE
- INTRODUCTION
1.1 BACKGROUND OF THE STUDY
The oil and gas industry is a high risk and challenging venture but despite the risk involved in its operations, ranging from the exploration to the production phase; wells are still being drilled and completed for production. Some wells are drilled without hitting the target (oil), some are plugged and abandoned while others are producing successfully till date. Besides, some of these wells completed require an artificial lift at the beginning of the production to lighten the oil due to high fluid density or remove liquid loading in gas wells. Hence, the focus of this paper is to optimize well production from the reservoir to the surface production facilities via gas lift and electrical submersible pump (ESP). This will be achieved by designing a base case and then installing a gas lift and (ESP) to increase productivity index (PI) of the well and ensure longevity of the well conditions. Also, an economic analysis will be performed on the two artificial lift methods chosen for this paper and running sensitivity analysis on different parameters using PROSPER software.
There are different key factors that are considered prior to artificial lift installation in the field which include analysis of the individual well’s parameters and the operational characteristics of the available lift systems. For the different pumps and lift systems available to the oil and gas industry, there are unique operational/engineering criteria particular to each system, but they all require similar data to properly determine application feasibility. Such as the inflow performance relationship, Liquid production rat, Gas-liquid ratio, Water cut, Well depth, Completion type, Wellbore deviation, Casing and tubing sizes, Power sources, Field location, Solids/sand, Reliability, Efficiency, Environmental impact etc. Each of the artificial lift systems has economic and operating limitations that rule out it consideration under certain operating conditions. Some types of lift equipment depending upon the type of installation, can have higher initial costs than others. Gas lift can have a high initial cost for a one or two well system where a compressor must be installed. For a large number of wells, gas lift may become economical. Hydraulic pumping becomes less costly where several well can be operated from a central system.
Clegg (1988) mentioned some economic factors such as: revenue, operational and investment costs as the basis for Artificial Lift selection. He believed that the selected Artificial Lift method could have the best production rate with the least value of operational costs. He also carried out a studied on some operational and designing characteristics of Artificial Lift methods and found that the operational costs and production rate are affected by these factors. Alemi et al. (2010) used “TOPSIS” model to analyzed one of the Iranian oilfields and found ESP pump employment as the optimum artificial lift method. Abdel-Wally et al., (1996) optimized the gas lift process in Gulf of Suez Field, and resulted production increase from 17,000 bbl. /day of oil to 19,000 bbl/day. Ayatollahi et al., (2001) used PVT data combined with fluid and multiphase flow correlations to optimize the continuous gas lift process in Aghajari oil field. From actual pressure and temperature surveys and determining the point of injection, a gas lift performance curve was constructed. In order to determine the optimal gas lift condition, nodal method was used to determine optimum injection depth, optimum well-head pressure, optimum production rate and minimum GOR, electrical power, space, economics etc. which are factors to consider in the selection prior to the installation. Hence, this study presents a sensitivity analysis on these factors for production optimization.
1.2 OBJECTIVES OF THE PROJECT
Thus, this paper is aimed at economic evaluation of electrical submersible pump (ESP) and gas lift selection for production optimization in a GT Niger Delta oil field with an objectives to maximize profit from this oil field on a day-to-day basis. This focuses on:
(1) Building a model using PROSPER software to determine the production potential of both artificial lift methods and the base case “natural flowing well”.
(2) Carry out economic analysis on Gas lift and ESP and also, a cost benefit analysis of changing various components of the system resulting from the optimization exercise.
(3) To develop with time the production forecast of both Gas lift and ESP method and make a comparison with the base case.
(4) To select the best option for the artificial lift method for the case scenarios.
1.3 CHALLENGES OF LIFTING OIL AND GAS FROM THE RESERVOIR
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 is a serious problem in the petroleum and gas industry today. 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 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. In addition, for the fact that artificial lift installed in wells increases the production rate, there are some problems encountered after the installation of these lifting methods to help recover the column of fluid to the production facilities at the surface. Such as flowing pressure and temperature limitation, well depth, production rate, high
1.4 APPLICATIONS OF THE STUDY
Gas lift is particularly applicable for lifting fluids in wells that have a significant amount of gas produced with the crude. Gas compressors are nearly always installed to gather the produced gas and, with only minor changes, can be designed to supply the high injection-gas pressure for the gas lift system. The injected gas only supplements the formation gas and may amount to only a small percentage of the total produced-gas volume. Most continuous-flow wells can be depleted by gas lift because reservoir-pressure maintenance programs are implemented in most major oil fields and many reservoirs have waterdrives.
The flexibility of gas lift, in terms of production rates and depth of lift, can seldom be matched by other methods of artificial lift if adequate injection-gas pressure and volume are available. Gas lift is one of the most forgiving forms of artificial lift because a poorly designed installation will normally gas lift some fluid. The mandrel depths for many gas lift installations with retrievable-valve mandrels are calculated with minimal well information.
Highly deviated wells that produce sand and have high formation-gas/liquid ratios are excellent candidates for gas lift when artificial lift is needed. Many gas lift installations are designed to increase the daily production from flowing wells. No other method is as ideally suited for through-flowline ocean-floor completions as a gas lift system. Wireline-retrievable gas lift valves can be replaced without killing a well or pulling the tubing.
The gas lift valve is a simple device with few moving parts, and sand-laden well fluids do not have to pass through the valve to be lifted. The individual-well downhole equipment is relatively inexpensive. The surface equipment for injection-gas control is simple and requires little maintenance and practically no space for installation. Typically, the reported high overall reliability and lower operating costs for a gas lift system are superior to other methods of lift.
1.5 LIMITATIONS OF THE STUDY
The primary limitation for gas lift operations is the lack of formation gas or an injection-gas source. Wide well spacing and lack of space for compressors on offshore platforms may also limit the application of gas lift. Poor compressor maintenance can increase compressor downtime and add to the cost of gas lift gas, especially with small field units. Compressors are expensive and must be properly maintained. Generally, gas lift is not as suitable as some other systems for single-well installations and widely spaced wells. The use of wet gas without dehydration reduces the reliability of gas lift operations.
Reviews
There are no reviews yet.