Adsorption and desorption mechanism and development practice of shallow normal pressure shale gas in Nanchuan area
Exploration and development of shallow normal pressure shale gas in China is still in the exploratory stage.Currently,multiple shallow shale gas wells in the Sichuan Basin and its periphery have encountered gas bearing layers with good shows,which reveals the significant exploration and development potential of shallow shale gas.However,the shallow normal pressure shale gas is mainly in the occurrence state of adsorbed gas,and its exploration and development face such problems that adsorption and desorption rules are not understood clearly and there is no targeted production technology.Taking the normal pressure shale gas field in the Wulong Block of Nanchuan area of Chongqing as the research object,this paper selects several core samples taken from different burial depths in the Wulong Block to carry out shale reservoir evaluation and indoor isothermal adsorption experiments.Based on the isothermal adsorption curve,a adsorption and desorption model of shallow shale gas is established,and the desorption of adsorbed gas is divided into three stages.Finally,the adsorption and desorption mechanisms of shallow normal pressure shale gas in the Wulong Block and the influencing factors are clarified.And the following research results are obtained.First,the isothermal adsorption curve of shallow normal pressure shale gas shows a"┌"type characteristic,and as the reservoir pressure decreases,the desorption rate suddenly changes from slow desorption to rapid desorption.Second,the"sensitive desorption pressure"corresponding to the inflection point of desorption rate can be obtained by deriving the curvature of the desorption efficiency curve.The sensitive desorption pressure of shallow normal pressure shale gas outside the Sichuan Basin is generally in the range of 1.8-2.5 MPa.Third,the flowing pressure reducing desorption test in Well PD1HF shows that after the bottomhole flowing pressure is reduced to below 2.5 MPa through artificial lifting,the adsorbed gas is desorbed and released rapidly,and the well productivity is more than 5 times the original one,marking a significant breakthrough in the productivity of shallow normal pressure shale gas wells.In conclusion,the clarification of the adsorption and desorption characteristics of the shallow normal pressure shale gas in the Wulong Block of Nanchuan area and its successful development practice are of great guiding significance for promoting the beneficial development of shallow normal pressure shale gas in this area and the development of similar shallow normal pressure shale gas in China.
国家科技期刊平台
NSTL
万方数据
维普
