富有机质页岩气藏多尺度传质实验模拟研究

发布时间：2018-06-01 11:34

本文选题：页岩 + 多尺度　；参考：《西南石油大学》2016年硕士论文

【摘要】：页岩孔隙结构复杂,既有纳米级的有机质粒内孔隙、粒间孔隙,还发育微米级裂缝,孔喉直径非常小,渗透率极低。同时,吸附气和游离气共存,游离气储集在孔隙空间中,吸附气储集在有机质和黏土矿物中。页岩富含有机质且非均质性强,气体传质机制复杂,传质过程具有多尺度性。因而,研究页岩多尺度孔隙结构中的气体传质,对于明确产气机理和优化产能模型都具有重要意义。选择四川盆地东部龙马溪组黑色页岩为研究对象,以实验模拟气体多尺度传质过程为核心,结合页岩矿物组成和有机质特征,在页岩孔隙结构分析基础上,设计并开展了低速渗流实验、压力衰减实验和压力脉冲实验,模拟页岩多尺度孔隙结构(基块、天然裂缝、人工裂缝)下的气体传质过程,并研究其多尺度传质特征。分析表明,龙马溪组页岩矿物组成主要为石英、黏土矿物和长石,而黏土矿物组成以伊利石、伊／蒙间层矿物和绿泥石为主。有机碳含量平均为3.06%,有机质成熟度平均为2.91%；高压压汞测试出页岩平均孔径为232.2nm,纳米级孔隙占页岩孔隙的80%,存在大量的介孔和宏孔。低温氮气吸附测试出平均孔径3.528-5.619nm,纳米级孔隙形态多以狭缝状和墨水瓶状为主；有机质纳米级孔隙的孔径为10-300nm。设计并开展了低速渗流实验研究气体传质的渗流过程。实验采用三类岩样(人工裂缝、天然裂缝和基块)代表页岩不同尺度的孔隙流动空间,分析出孔隙尺度对滑脱效应影响的强弱次序为基块天然裂缝人工裂缝；确定了页岩滑脱渗流通道尺寸为126.00-229.66nm,通过Kn数确定了渗流过程气体传质方式主要滑脱流和过渡流。设计并开展了压力衰减实验模拟页岩气在多尺度孔隙结构(基块、天然裂缝、人工裂缝)中的扩散行为。分析出纳米级孔隙扩散过程约占整个扩散阶段的90%；纳米级孔隙扩散过程的甲烷扩散系数的数量级为10-12cm2/s,气体传质方式主要为努森扩散；吸附气向干酪根扩散过程的甲烷扩散系数的数量级为10-17cm2/s,气体传质方式主要为表面扩散。设计并开展了压力脉冲实验模拟气体在页岩基块中的多尺度传质行为。阐述了压力脉冲实验的设计思路,划分了渗流阶段与扩散阶段,解释了在吸附过程中气体吸附量跃变的原因；分析出岩样在不同孔压下渗透率与绝对渗透率的误差范围小于7%；大颗粒形成的孔隙中甲烷扩散系数的数量级为10-1cm2/s,小颗粒形成的孔隙中甲烷扩散系数的数量级为10-13cm2/s；大颗粒中的扩散在扩散过程中占据主导地位,随着孔压的增大,小颗粒中的扩散对整个扩散过程的贡献也在逐步增大。分析了压力脉冲实验与压力衰减实验气体扩散过程的扩散系数差异,总结了三种实验分析方法的特点和适用范围。
[Abstract]:The pore structure of shale is complex. There are organic plasmid pores intergranular pores and micrometer fractures. The pore throat diameter is very small and the permeability is very low. At the same time, adsorption gas and free gas coexist, free gas is stored in pore space, adsorption gas is stored in organic matter and clay mineral. Shale is rich in organic matter and strong heterogeneity, gas mass transfer mechanism is complex, mass transfer process is multi-scale. Therefore, the study of gas mass transfer in shale multi-scale pore structure is of great significance for the determination of gas production mechanism and optimization of productivity model. The black shale of Longmaxi formation in the eastern Sichuan Basin is selected as the research object. Taking the experimental simulation of gas mass transfer process as the core, combining the mineral composition of shale and the characteristics of organic matter, the pore structure of shale is analyzed. Low velocity seepage experiments, pressure attenuation experiments and pressure pulse experiments are designed and carried out to simulate the gas mass transfer process in shale multi-scale pore structure (base block, natural fracture, artificial fracture), and to study its multi-scale mass transfer characteristics. The analysis shows that the shale minerals of Longmaxi formation are mainly composed of quartz, clay and feldspar, while the clay minerals are mainly composed of Illite, Illite / Mengjian and chlorite. The average content of organic carbon is 3.06, the maturity of organic matter is 2.91, the average pore size of shale is 232.2 nm by high pressure mercury injection, and the pore size of nano-scale is 80% of the shale pore, there are a lot of mesoporous and macropores. The average pore size was 3.528-5.619 nm by nitrogen adsorption at low temperature, and the pore size of nano-pore was mainly slit and ink bottle, while the pore size of organic matter nano-pore was 10-300 nm. The flow process of gas mass transfer is studied by low speed seepage experiment. Three kinds of rock samples (artificial fracture, natural fracture and base block) are used to represent pore flow space of shale on different scales, and the order of influence of pore size on slippage effect is analyzed as artificial fracture of base natural fracture. The size of shale detachment flow channel is 126.00-229.66nm, and the gas mass transfer mode is determined by Kn number. The diffusion behavior of shale gas in multi-scale pore structure (base block, natural fracture, artificial fracture) was simulated by pressure attenuation experiment. The results show that the nano-pore diffusion process accounts for 90% of the whole diffusion stage, and the methane diffusion coefficient of the nano-scale pore diffusion process is in the order of 10-12 cm ~ 2 / s, and the gas mass transfer mode is mainly Knudsen diffusion. The diffusion coefficient of methane from adsorbed gas to kerogen is in the order of 10 ~ (-17) cm ~ (2) / s, and the gas mass transfer mode is mainly surface diffusion. The multi-scale mass transfer behavior of gas in shale block was simulated by pressure pulse experiment. The design idea of pressure pulse experiment is expounded, the seepage stage and diffusion stage are divided, and the reason of gas adsorption jump in adsorption process is explained. The results show that the error range between permeability and absolute permeability of rock samples under different pore pressures is less than 7. The order of magnitude of methane diffusion coefficient in the pore formed by large particles is 10 ~ (-1) cm ~ 2 / s, and the order of magnitude of methane diffusion coefficient in pores formed by small particles is 10 ~ (-13) cm ~ 2 / s. Diffusion in large particles dominates the diffusion process. With the increase of pore pressure, the contribution of diffusion in small particles to the whole diffusion process increases gradually. The difference of diffusion coefficient between pressure pulse experiment and pressure attenuation experiment is analyzed, and the characteristics and applicable range of three experimental analysis methods are summarized.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TE37

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