Mohd Aji Aminah Qayyimah, Mohshim Dzeti Farhah, Maulianda Belladonna, Elraeis Khaled Abdalla
Universiti Teknologi PETRONAS 32610 Seri Iskandar Perak Malaysia
Universiti Teknologi Malaysia Skudai Johor Malaysia.
RSC Adv. 2022 Jul 15;12(32):20530-20543. doi: 10.1039/d2ra03367d. eCollection 2022 Jul 14.
In shale gas reservoirs, adsorbed gas accounts for 85% of the total shale gas in place (GIP). The adsorption isotherms of shale samples are significant for understanding the mechanisms of shale gas storage, primarily for assessing the GIP and developing an accurate gas flow behaviour. Isothermal adsorption experiments primarily determine the adsorption capacity of methane in shale gas reservoirs. However, experimental data is limited due to the heterogeneous properties of shale and extreme reservoir conditions at high pressures and temperatures. This work discusses the effect of total carbon (TOC), pore size distributions, and mineralogical properties on adsorption capacity. In this study, the gravimetric adsorption isotherm measurement method was applied to obtain the adsorption isotherms of methane on four shale core samples from Eagle Ford reservoirs. Four shale core samples with TOC of 9.67% to 14.4% were used. Adsorption experiments were conducted at a temperature of 120 °C and to a maximum pressure of 10 MPa. The data obtained experimentally were compared with adsorption isotherm models to assess each model's applicability in describing the shale adsorption behaviour. A comparison of these models was performed using fitting and error analysis. It was observed that the calculated absolute adsorption of supercritical methane is higher than the excess adsorption. The percentage of differences between the absolute and excess adsorption is more significant at a pressure higher than the critical methane pressure of 9.6%. Sample EF C has the highest adsorption capacity of 1.308 mg g, followed by EF D 1.194 mg g, EF B 0.546 mg g, and EF A 0.455 mg g. Three statistical error analyses, average relative error (ARE), the Pearson chi-square ( ) test and root mean square error (RMSE) deviation were used to assess the applicability of each model in describing the adsorption behaviour of shale samples. The order of adsorption isotherm fitting with experimental data is Toth > D-R = Freundlich > Langmuir. Error analysis shows that the Toth model has the lowest values compared to other models, 0.6% for EF B, 2.5% for EF C, and 2.2% for EF A and EF D, respectively.
在页岩气藏中，吸附气占原地总页岩气（GIP）的85%。页岩样品的吸附等温线对于理解页岩气储存机制至关重要，主要用于评估原地总气量（GIP）以及建立准确的气流行为。等温吸附实验主要用于确定页岩气藏中甲烷的吸附能力。然而，由于页岩的非均质性以及高压和高温下的极端储层条件，实验数据有限。这项工作讨论了总碳（TOC）、孔径分布和矿物学性质对吸附能力的影响。在本研究中，采用重量吸附等温线测量方法获得了来自伊格尔福特油藏的四个页岩岩心样品上甲烷的吸附等温线。使用了四个总有机碳含量为9.67%至14.4%的页岩岩心样品。吸附实验在120℃温度和最高10MPa压力下进行。将实验获得的数据与吸附等温线模型进行比较，以评估每个模型在描述页岩吸附行为方面的适用性。使用拟合和误差分析对这些模型进行了比较。观察到超临界甲烷的计算绝对吸附量高于过量吸附量。绝对吸附量和过量吸附量之间的差异百分比在高于甲烷临界压力9.6%的压力下更为显著。样品EF C的吸附能力最高，为1.308mg/g，其次是EF D为1.194mg/g，EF B为0.546mg/g，EF A为0.455mg/g。使用三种统计误差分析，即平均相对误差（ARE）、皮尔逊卡方（ ）检验和均方根误差（RMSE）偏差来评估每个模型在描述页岩样品吸附行为方面的适用性。吸附等温线与实验数据拟合的顺序为托特模型＞D-R模型 = 弗伦德利希模型＞朗缪尔模型。误差分析表明，与其他模型相比，托特模型的值最低，EF B为0.6%，EF C为2.5%，EF A和EF D分别为2.2%。
