基于竞争吸附的页岩气藏提高采收率机理

Mechanism of Enhanced Gas Recovery in Shale Gas Reservoirs Based on Competitive Adsorption

为研究注CO_2提高页岩气藏采收率的机理以及确定合理的注入参数,以页岩吸附解吸实验为基础,对比了页岩自然降压开采和在不同注入压力、注入速率下注CO_2开采页岩气藏的实验结果,研究了降压开采和注CO_2开采2种方式下CH_4的采气速率和采收率的变化。结果表明,在相同实验条件下,CO_2吸附能力最强,CH_4次之,N_2最弱,N_2解吸能力最强,CH_4次之,CO_2最弱;3种气体的等温解吸曲线相对于等温吸附曲线均存在一定的滞后,CO_2的滞后现象最为明显;降压开采的采收率较低,注CO_2可以有效提高CH_4的采气速率,延长稳产时间,使累计产气量快速增长;在一定注入压力和注入速率范围内,CH_4采收率随着CO_2注入压力和注入速率的增加而增加,但其增加幅度因岩心孔隙度和渗透率的不同而有所不同。

In order to study the mechanism of injecting CO2 to increase the recovery of shale gas reservoirs and determine reasonable injec⁃tion parameters,the experimental results of the production of shale gas reservoir developed by natural pressure drop and by injecting CO2 at different pressure and rates were compared based on shale adsorption and desorption experiments,and the changes in CH4 production rate and recovery factor under the two methods were studied.The results show that under the same experimental conditions,as to adsorption ca⁃pacity,CO2 is the strongest,followed by CH4,and then N2,while as to desorption capacity,N2 is the strongest,followed by CH4,and then CO2.Compared with the isothermal adsorption curves,the isothermal desorption curves of the three kinds of gas are hysteretic to a certain extent,and the hysteresis of CO2 is the most obvious.The recovery factor of shale reservoirs developed by natural pressure drop is low,while CO2 injection can effectively increase the production rate of CH4,greatly prolong stable production and increase cumulative gas pro⁃duction.Within certain ranges of injection pressure and injection rate,the CH4 recovery increases with the increase of CO2 injection pres⁃sure and injection rate,but the increment varies with core porosity and permeability.