ASSESSMENT OF SAFE AND COST EFFECTIVE METHODS TO MAXIMIZE PRODUCTION (PROFITABILITY) FROM A GAS-LIFTED FIELD

ABSTRACT

 The intent behind this study was to optimize the Gas Lift System in order to achieve the target of maximizing the oil production from the four oil wells. To accomplish the optimization process, hurdles or constraints associated were addressed efficiently which resulted in effective outcome. Initial gas injection rates and oil production rates were analyzed by using Well Flo3.8.7 and maximum economic waters cuts were calculated for each well. Increasing water cuts is one of the major constraint that limits the injection gas volume which needs to be optimized and this constraint was addressed by calculating the optimum gas injection rates for all wells using Well Flo3.8.7. The overall comparison between the initial conditions and optimized conditions for all wells were presented in order to provide a clear picture of optimization in terms of oil production and maximum economic water cut. The results for total increase in all production were found to be 25954stb/day and initially it was 19099stb/day. The maximum economic water cut has been improved from 52% to 78%. The second major constraint is the ability of compressor to handle the optimized gas lift volumes and to deliver these gas volumes at sufficient discharge pressure for effective gas lift process, which were addressed by making use of HYSIS simulator. A model of three stage compression system is run in HYSIS simulator by using the designed capacity of compressor in terms of volume and discharge pressure to validate the design ratings and the load of compressor was also calculated at these conditions which includes power consumption by each compression stage and respective inter stage coolers. Another model is run in HYSIS simulator for compression train and the results for the optimum injection gas lift rates (23.8 MMSCFD) were used as an input in this model and hence an optimized model of compression train was obtained which could handle the optimized gas lift volumes at sufficient discharge pressure (3100 psig). In the end the total power consumption for both models was compared together and small increase of 253 KWH were observed which is acceptable in terms of increase in oil production.

CHAPTER 1

INTRODUCTION

1.1   Background of Project

 Gas lift is a type of artificial method that is currently being used in most of the oil field across the world and the reason behind that is its wide range of applications and particular characteristics which includes flexibility in the production rates of oil and depth which makes it superior over other artificial lift methods, gas lift method is applicable and suitable for the highly deviated wells in which dog leg severity is extremely high and it can handle sand production unlike ESP because of the absence of any moving mechanical equipment. The effective designing of gas lift system is very important so that the gas lift system should adhere and cop up with the changing conditions of reservoir. Pressure depletion can cause reservoir compaction and water injection is used as a remedial action for maintaining the reservoir pressure but with the passage of time problems occurs such as increased water cuts which will increase the hydrostatic head pressure in the tubing resulting in decreased production rates and in efficient gas lift operation. To address these problems, compression unit of the gas lift system should be capable of delivering an increased volumetric capacity of gas at sufficient discharge pressures. A multi stage compression unit can deliver the discharge pressures that are sufficient for well kick off if required as well as for normal continuous gas lit operations. Use of electrical motors as prime movers provides a great amount of flexibility to the compressors in terms of the operating parameters that are flow rate and discharge pressure by using variable speed drive (VSD) motors. Optimization of current units to achieve the targets is an effective tool that saves cost and time both and this technique enables to use the current asset potentials and it also plays a vital role and help exploration & production companies for making correct procurement decisions for new equipments.

1.2   Problem Statements

With the passage of time, it is the advent phenomenon that the water cut in production tubing will increase due to the injection of water for pressure maintenance of the reservoir and a completion using an aid of gas lift process will surely face problem in this scenario. These problems will result in the lower flow rates of oil which will make the gas lift process ineffective. The problems that need to be addressed and solvedinclude:

• Increased injection rates of lift gas required because of the increasing hydrostatic head of the column of the fluids present in the tubing that consists of oil and water so more volume of lift gas is required in order to achieve maximum production. This lift gas injected rate should be optimum because injection more from an optimum rate will cause decrease in production due to gas slippage effect. Therefore for the lift gas requirements need to be recalculated in order to achieve maximum production by choosing the accurate and optimum injectionrates.

• How to optimize the compressor unit in order to accommodate the increased injection rates of lift gas that is essential to lift the fluid from the well at economically optimum rates and at the same time maintains the pressure of the lift gas which should be sufficient for effective gas lift process. Optimization of gas lift operation must be acceptable which implies that the difference between the total power requirements at design capacity and at optimized conditions should be in acceptableranges.

1.3   Objectives

1. To analyze the initial gas injection rates and oil production rates, To Calculate maximum economic water cuts by using Well Flo3.8.7.
2. Tocalculatetheoptimumliftgasinjectionrates,Optimizedoilproduction rates and improved maximum economic water cuts by using Well Flo3.8.7.

3. To optimize the compression system which enables the existing compression unit to accommodate the increased gas lift injection volumes (13.8 MMSCFD) and sufficient discharge pressure (3100 psig) for continuous gas lift operation by using HYSIS simulator. The approach that was followed, relates to Charles Law that is reduction in pressure causes increasing in volume. Power calculation and comparison for the optimization of compression system is mandatory to establish by using HYSIS simulator.

1.4   Scope of Study

Optimization is the key for achieving efficiency by making use of available resources. Optimization of gas lift system in terms of increase oil production has accepted a wide range of significance in oil and gas industry. Optimum gas injection rates are calculated to insure maximum oil production and sensitivity analysis of water cuts is conducted which yields the maximum economic water cut for enhancing the cumulative oil production. The optimized gas injection volumes at sufficient pressure are provided by compression unit. The need to optimize the available compression unit is to obtain lift gas which will eliminate the need to add another compression unit which is more costly than the whole gas lift system. Simulation of compression unit involves the feed properties input and required discharge pressure, based on the available margin of the machine molar flow rate of lift gas (23.8 MMSCFD) has been handled at a discharge pressure of 3100 psig. The required power to handle increased gas volumes calculation gave a clear picture for the acceptability of optimizing the system, as small increment in power has been observed. The whole work conducted not only removed the need for capital investment but also, enhanced and increased the total output of all wells.

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