常规取心过程中页岩含气量解吸测定分析及建议

Analysis and recommendations for shale gas content measurement during conventional coring

我国页岩气储层埋深大,普遍采用常规取心方式。根据页岩储层条件及孔隙结构分析,解吸法可以更为准确的测定页岩含气量。统计发现,页岩气与煤层气在累计解吸气量与解吸时间的关系中比较一致,在解吸速率和解吸时间的关系中存在较大差距,因此,采用回归法计算损失气的方法不能在页岩气解吸中盲目使用,需谨慎选择稳定解吸点计算损失气。分析认为,通过三阶温度解吸分步骤计算损失气能够完善整个测定过程;同时,针对不同压力条件地层,损失时间的计算要根据实际储层压力、泥浆压力、大气压力进行计算,保障常规取心过程中损失气及页岩含气量的准确性。

The burial depth of shale gas reservoirs is big in China, the conventional coring method is used commonly. Desorption measurement can determine the gas content more accuracy through the analysis of shale reservoir's conditions and pore structure. It can be found from the statistics that the relationship of cumulative desorbed gas content and desorption time of shale gas and coalbed methane is consistent, however the relationship of desorption rate and desorption time for them is quite different. The regression method for the calculation of lost gas can't be adopted blindly in shale gas desorption, and it is needed to select the stable gas desorption data carefully. It can be concluded from the analysis that the whole measurement process can be improved by calculating the lost gas stepwise based on third-stage desorption temperature. Meanwhile, for different formation pressure, lost time should be calculated based on the actual reservoir pressure, mud pressure and atmospheric pressure so that the lost gas content and shale gas content in conventional coring process can be calculated more accuracy.