基于分子模拟的页岩气吸附微观机理研究

Adsorption is the main speciation of shale gas, and adsorption property and action law is an important prerequisite for the effective exploitation of shale gas. At present, the mechanism of microscopic adsorption of shale gas is not yet clear, in addition, The prediction model of shale gas adsorption with different mineral composition and organic matter in shale was not established. The project will adopt Elemental analyzer、Field emission scanning electron microscope and X ray diffraction methods, research shale pore structure distribution, construct micro pore model which can reflect the characteristics of pore structure of shale; based on the micro pore model as the foundation, using the grand canonical ensemble Monte Carlo simulation method, the adsorption behavior of methane in the pores of shale is simulated , the quantitative relationships is found between the shale gas adsorption capacity and total organic carbon content, pore size, water content, reservoir temperature and pressure factors, burial depth. Adsorption prediction model for different minerals and organic matter in shale is established; Finally, based on the mineral composition and organic matter of shale, a new model for predicting shale adsorption is established. The experimental test and prediction models adsorption gas are compared, fitting the model. The micro mechanism of shale gas adsorption will be revealed. The research results of this project are of great significance to the development and improvement of shale gas adsorption mechanism, and also provide a solid theoretical basis for the efficient development of shale gas reservoirs.

吸附态是页岩气的主要赋存形态，明确页岩吸附性能及作用规律是页岩气有效开采的重要前提。目前，关于页岩气微观吸附的机理尚不明确，且未建立考虑页岩不同矿物组成和有机质的页岩气吸附预测模型。本项目拟采用元素分析仪、场发射扫描电镜和X射线衍射的方法，研究页岩微观孔隙结构分布，构建能反映页岩孔隙结构特征的不同矿物和有机质微观孔隙模型；以所建微观孔隙模型为基础，运用巨正则系综Monte Carlo方法，模拟甲烷在页岩纳米孔隙中的吸附行为，研究页岩吸附气量与总有机碳含量、孔隙大小、含水率、储层温度和压力、埋藏深度等因素的定量关系，建立页岩不同矿物和有机质吸附预测模型；最后，根据页岩矿物组成和有机质，建立新的页岩吸附预测模型，将实验测试吸附气量与预测模型进行对比，拟合所建模型，揭示页岩气微观吸附机理。本项目研究成果对发展和完善页岩气吸附机理具有重要意义，也为页岩气藏高效开发提供坚实的理论基础。

随着当前能源消费的迅速增加，常规天然气资源短缺，很难满足日益增长的能源需求。页岩气作为一种非常规天然气，具有资源潜力大和低碳排放等优点，已成为全球油气资源勘探开发的焦点和热点。因此，深入研究页岩气的吸附机理和开采方式，对缓解我国能源对外依存度，提高页岩气采收率具有重要意义。.本项目的主要研究内容包括以下4个方面：（1）陆相页岩储层矿物成分分析；（2）页岩高压等温吸附实验研究；（3）页岩吸附分子动力学模拟；（4）建立页岩最大吸附气含量预测模型。.通过本研究，获得以下重要结论和关键数据：.（1）鄂尔多斯盆地长7段陆相页岩主要矿物为石英，含量为32-75%，平均为45%；黏土为次要矿物，含量为15-34%，平均为24%；斜长石含量为10-27%，平均为18%。.（2）开展了5块岩心的高压等温吸附实验，研究表明：随着压力增加，CH4吸附量增加，当压力大于21MPa时，CH4吸附量达到平衡；随着压力增加，CH4/CO2二元混合气体绝对吸附量增加，随着CO2含量增加，气体绝对吸附量增加；随着温度增加，CH4吸附量降低。.（3）建立了石墨、伊利石、高岭石、石英和蒙脱石的分子模型。研究表明：当压力一定时，气体的吸附量随着温度的升高而降低；温度一定时，吸附量随着压力的升高而增加。低压下吸附量：石墨>伊利石>高岭石>石英>蒙脱石，而高压下：伊利石>高岭石> 石英> 石墨片层>蒙脱石，高压下吸附量规律与低压下存在差异。.（4）通过多元回归分析法，以最大吸附气量为因变量，以黏土矿物和有机质组成为自变量，建立了陆相页岩最大吸附气量预测方程。预测结果表明：新建模型的预测值与实际值误差绝对值最大为2.801%，最小为0.0583%，平均为1.0615%，证明了新建模型具有较高的精度。.本项目通过实验测试、分子模拟和理论计算，建立了一套系统评价陆相页岩吸附机理、吸附影响因素、吸附微观机理和吸附量计算的方法，为后期陆相页岩储量计算和日产气量预测等研究提供了依据和科学基础。