页岩气高压吸附特征及其对储采规律的影响

针对目前页岩吸附等温线测试温度、压力通常未达到储层温压条件这一问题，设计了页岩高温高压吸附等温线测试方法，研究了储层温度、压力条件下页岩吸附等温线特征，以实际页岩岩心为例计算了游离气和吸附气随压力的变化规律，并采用全直径页岩氦气和甲烷控压生产实验研究了吸附气对产气特征的影响。结果表明：视吸附量先随压力增大而增大，到达峰值之后视吸附量随压力的增大而减小；在低压条件下，采用Langmuir外推计算的吸附气量与高压实验计算的吸附气量相差不大；而在高压条件下，采用低压Langmuir理论推算总含气量高估9.2%；低于临界解吸压力时，吸附气解吸附使得单位压差产气量增加；高于临界解吸压力时，吸附气对单位压差产气量几乎没有影响；开发初期，低于临界解吸压力范围较小，吸附气对产气量贡献较小，尽可能动用游离气是高效开发的关键。

High pressure adsorption characteristics of shale gas and their impact on the law of reserve-production

Presently, the testing temperature and pressure of the shale adsorption isotherm cannot usually reach that of the reservoir. To solve this problem, the high temperature/high pressure test methods were designed, and the characteristics of shale adsorption isotherm under reservoir temperature/pressure were analyzed. In addition, variations in free and adsorbed gas with changing reservoir pressure were calculated in accordance with the actual shale core model; the effect of adsorbed gas on the characteristics of gas production was also studied by examining the pressure controlled production of helium & methane using whole diameter shale core. Results show that gas adsorption by visual assessment increases initially with increasing pressure and decreases after peak. It is found that under low pressure conditions, gas adsorption calculated by Langmuir extrapolation is close to that of high pressure experiments; but under high pressure conditions, total gas content calculated by low pressure Langmuir theory is overvalued by about 9.2%. Moreover, below the critical desorption pressure, desorbed gas causes gas production to increase per unit differential pressure; while above the critical desorption pressure, adsorbed gas hardly affects gas production. During the early development, reservoir pressure ranges slightly below the critical desorption pressure so that the adsorbed gas contributes very little to gas production. Therefore making full use of free gas is key to high efficiency reservoir development.