Investigation Into the Dominant Factors of Gas Recovery in High-Temperature and High-Pressure Gas Reservoir

With the exploration and development of gas reservoirs moving into deeper formation, high temperature and high pressure (HTHP) gas reservoirs have gradually become one of the research focuses. However, there is still lack of enough experience and systematic understanding of the development principles of HTHP gas reservoirs with different petrophysical characteristics to clarify the development strategies. This paper established a model of HTHP gas reservoir to investigate the effects of the major development and geological factors on gas recovery factor and stable production period, such as reservoir permeability, water aquifer, stress sensitivity, and gas production rate, figuring out the sensitivity of each factor to gas recovery factor. Then a RBF neural network algorithm was employed to predict the gas recovery factors of HTHP gas reservoirs with different gas production rate in the Yinggehai Basin in the South China Sea, and then effective development approach for HTHP gas reservoirs was proposed. The research results showed that reservoir permeability had the highest impact on gas reservoir recovery, followed by water body multiples and permeability stress sensitivity, while gas production rate came in last. The development of medium and high permeability gas reservoirs was different from that of low and ultra-low permeability ones. As the permeability and stress sensitivity increased, the recovery factor of medium and high permeability gas reservoirs changed slightly, which was more affected by water aquifer. However, that was not the case in low and ultra-low permeability gas reservoirs. For medium and high permeability gas reservoirs with weak water aquifer, it was proposed to improve the gas production rate to enhance the development economics. For low and ultra-low permeability gas reservoirs with strong stress sensitivity, it was proposed to control the gas production rate to weaken the permeability damage and increase the stable production period in addition to the methods such as long horizontal wells, branch wells, and fracturing acidification. The research results could provide an effective guidance for the development of HTHP gas reservoirs.