Tian Wei, Liu Huiqing
College of Petroleum Engineering, China University of Petroleum-Beijing, Beijing 102249, China.
ACS Omega. 2020 Dec 1;5(49):31508-31517. doi: 10.1021/acsomega.0c02980. eCollection 2020 Dec 15.
Shale gas resources are highly abundant in the world. They can provide sustainable energy supply and have the potential to reduce energy prices. Therefore, shale gas has become one of the most important resources for oil and gas exploration and production, especially in North America today. Adsorption and desorption of methane gas are some of the important physical and chemical processes involved in the accumulation, transport, and production of shale gas. The shale matrix will shrink or swell due to the desorption or adsorption of methane gas, which will impact the recovery of shale gas reservoirs. The main purpose of this investigation is to quantitatively ascertain how the adsorption of methane gas affects the volumetric changes of the shale matrix. Based on the adsorption potential theory, a modified Dubinin-Astakhov (D-A) equation was employed to describe the adsorption of supercritical methane gas on shale. Then, a coupled adsorption-strain model was established to investigate the volumetric strain of shale induced by the combined effects of methane gas adsorption and stress compression. The methane adsorption and the induced shale swelling were measured on a black shale sample from the Sichuan Basin at 303.15 K and pressure up to 10 MPa, and the proposed models were employed to interpret the experimental data. The results demonstrate that the proposed models show good applicability and provide a reliable prediction. The swelling moduli of shale samples were obtained by fitting the experimental data using the coupled adsorption-strain model. The results indicate that the swelling modulus of shale in this study is generally greater than that of coal. The calculated ratios of Young's modulus to the swelling modulus do not show great variation from shale to shale in this study, which is similar to coal. This study can be incorporated into the numerical simulation of the production process of shale gas reservoirs.
页岩气资源在全球极为丰富。它们能够提供可持续的能源供应，并有可能降低能源价格。因此，页岩气已成为油气勘探与生产中最重要的资源之一，尤其是在如今的北美地区。甲烷气体的吸附和解吸是页岩气聚集、运移和开采过程中涉及的一些重要物理和化学过程。由于甲烷气体的解吸或吸附，页岩基质会收缩或膨胀，这将影响页岩气藏的采收率。本研究的主要目的是定量确定甲烷气体的吸附如何影响页岩基质的体积变化。基于吸附势理论，采用修正的杜比宁-阿斯塔霍夫（D-A）方程来描述超临界甲烷气体在页岩上的吸附。然后，建立了一个吸附-应变耦合模型，以研究甲烷气体吸附和应力压缩共同作用引起的页岩体积应变。在303.15 K和高达10 MPa的压力下，对四川盆地的一个黑色页岩样品进行了甲烷吸附和诱导页岩膨胀的测量，并采用所提出的模型来解释实验数据。结果表明，所提出的模型具有良好的适用性，并提供了可靠的预测。通过使用吸附-应变耦合模型拟合实验数据，得到了页岩样品的膨胀模量。结果表明，本研究中页岩的膨胀模量一般大于煤的膨胀模量。在本研究中，计算得到的杨氏模量与膨胀模量之比在不同页岩之间变化不大，这与煤相似。本研究可纳入页岩气藏生产过程的数值模拟中。
