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Design of a continuous gas lift system to initiate production in a dead well

Tetoros Ioannis

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Summary

Artificial lift systems are among the most widely used production technologies in global oil and gas operations. Wells that cannot produce liquids to the surface under their own pressure require lift technologies to enable production. Some liquid wells need lift assistance from the beginning and almost all require it sooner or later. The majority of the producing wells worldwide currently use artificial lift.One of the most popular artificial lift methods applied in the oil industry, in order to enhance oil recovery, is the gas lift method. Its main principal is the injection of gas in the well to reduce the average density of the fluids produced from the reservoir, hence the weight of the fluid column. As a result, the declined reservoir pressure is sufficient to lift the fluids up to the surface.The present MSc thesis is based upon a fictitious onshore well named A-1, in the Alpha field. Due to the field’s declined pressure (3,844 psi) and the increasing water cut (20.3%), production may seize in the upcoming months.The main task is to design a gas lift system which will not only assist production during the current operating conditions, but also in future unfavorable situations where according to the reservoir forecasting, water cut is expected to increase up to 50% and reservoir pressure will drop down to 2,850 psi. The procedure of designing an optimized gas lift system in PROSPER is thoroughly described.The main idea behind the design process was to recomplete the well once to ensure that the project will be economically viable and, on the other hand, maximized production was achieved during all operating conditions. Minimum oil production rate was set at 2000 bopd.A continuous gas lift system design was carried out, based on the worst case scenario. Side pocket mandrels for the unloading process were set at certain depths, according to the calculations. Then, the rest of the cases, with lower water cut levels and higher reservoir pressure, were adapted to the initial side pocket mandrel spacing plan. Results showed that in all cases, the system was capable of delivering oil rates well over the minimum requested rate. Initial tubing diameter was also varied to ensure production optimization. The lowest oil rate achieved is 3,300 stb/day and the best rate is obtained at current operating conditions and is equal to 8,593 stb/day. Stability analysis of all designs indicated stable gas lift systems for all cases. The predicted production levels showed that the existing completion plan can serve for even worse scenaria in terms of system productivity.

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