页岩气超临界吸附机理分析及等温吸附模型的建立

Mechanisms analysis of shale-gas supercritical adsorption and modeling of isorption adsorption

为认识页岩气吸附机理,抓住页岩气所处超临界态的特点,同时考虑页岩多尺度孔隙空间和黏土矿物与干酪根吸附能力的差异性,理论分析了页岩气超临界吸附机理,同时建立了DALangmuir等温吸附模型。分析表明:低压阶段,甲烷优先吸附在干酪根超微孔表面,以微孔充填形式吸附;高压阶段,甲烷以单分子层形式吸附在中孔和大孔表面。甲烷脱附优先发生在中孔和大孔表面,表现出"吸附滞后"现象。建立的吸附方程拟合结果的R2大于0.995。页岩气吸附方式因吸附剂吸附能力和孔径而异,吸附方式既有单分子层吸附也有微孔充填吸附。吸附滞后现象是吸附剂吸附能力差异性的集中体现。所建模型可反映黏土矿物与干酪根吸附能力的差异及不同孔径吸附状态的差异,模型参数物理意义明确,数据拟合精度较高。

In this paper, the supercritical shale-gas fluid is known at the reservoir pressure and temperature. The mech- anisms of shale-gas supereritical adsorption were analyzed with consideration of the nano-scale pore structure and the difference of adsorption capacity between clay mineral and Kerogen in gas-shale. An alternative adsorption model was proposed combing Dubinin-Astakhov model and Langmuir model. The results show that at low pressure level, methane prefers to adsorb on the super-micro-pore of Kerogen with pore filling. Under high pressure level, methane begins to adsorb on the meso-pore and macro-pore distributed in the clay mineral and Kerogen with single molecular. However, the desorption sequence is reverse as adsorption sequence, in which methane prefers to desorp on the macro-pore and meso-pore. This is why the adsorption hysteresis happens during supercritical gas adsorption. The regression R2 is over 0. 995 using proposed isothermal adsorption equation. The shale gas adsorption pattern depends on both the adsorption capacity and pore diameter of adsorbent, which contains either single layer molecules adsorption or the pore filling. The difference of adsorption capacity is the main reason of adsorption hysteresis happening. The proposed model can handle the difference of adsorbents capacity and different adsorption state. The model parameters own the clear physics mean- ing with excellent fitting accuracy.