Integrated Approach to Determination of Optimal Capacity and Configuration of Booster Compressor Station at Different Realization Stages

摘要

Development of a natural gas field by depletion drive is characterized by a decrease of average formation pressure, bottom hole and wellhead pressures of production wells over time. As a rule, during the initial field development period available formation pressure is sufficient for gas transportation from wellheads to a treatment facility and then to a tie-in to the trunk gas pipeline without using the compressor equipment. However, the formation pressure is decreasing gradually during the whole field life and this in turn leads to a decrease in the entire system "Reservoir - Well - Infield Gas Collection Networks - Gas Treatment Plant". There comes a point of time when the pressure of gas at the gas treatment plant (GTP) inlet becomes insufficient for its treatment and further supply into the trunk gas pipeline under the required pressure and flow rate. Thus, from the point of view of infrastructure development and production technology the process of development of gas and gas condensate fields is divided into two periods: natural pressure and artificial lift production. The difference between these two periods lies in usage of a compressor unit designed for increase of the produced gas pressure to values required both at inlet of the treatment plant (in order to ensure the working parameters of the gas treatment process) and for further supply into the trunk gas pipeline. This unit is called a booster compressor station (BCS). As a rule, it is located at the site adjacent to the GTP site (Figure 1) and is used for the following purposes: 1. Compression of gas for its downstream transportation; 2. Maintaining of the required gas pressure at the GTP inlet. Thus, BCSs are used for extension of the stable gas production period at gas and gas condensate fields where formation pressure is decreased to the point at which pressure in the field gathering main pipeline, at GTP and in trunk gas pipeline restricts flow rates of the wells. In other words, BCS allows to maintain the GTP capacity at the designed level and to increase gas recovery factors as decreased pressure at the BCS inlet may be used for wellhead pressures decrease and increase of flow rates. The BCS service conditions are characterized by the following: continuous change of gas compression rate, flow rate of gas being transferred using one gas pumping unit (GPU) and the BCS, increase of capacity of them at a later stage, necessity of gas supply control and relatively low service life. Typically during the natural pressure drive period around a half of total gas reserves is withdrawn, while field development using the artificial lift allows to recover additional 20% or more of total reserves. This is a significant amount which makes booster compressor stations one of the most important elements of gas production. Installation of BCSs at gas fields is associated with huge capital investments which become comparable with cost of a Gas Treatment Plant as their capacity increases and in most cases it amounts to tens of billions of Rubles. Due to this reason, correct determination of the BCS start-up date and its capacity is one of the most important objectives of gas condensate reservoirs development by depletion.