川南地区龙马溪组孔隙特征与页岩气赋存

发布时间：2018-07-22 14:51

【摘要】：下志留统龙马溪组是我国页岩气勘探开发的有利层系之一,认识龙马溪组页岩孔隙演化与页岩气赋存具有理论意义。论文以川南地区龙马溪组为研究对象,就页岩孔隙特征与页岩气赋存等进行了较深入的研究。研究区位于四川盆地南缘,构造相对简单,地层分布稳定。研究目的层龙马溪组页岩有机碳含量较高,平均2.44%;有机质热演化程度高,平均2.90%,处于过成熟阶段。龙马溪组页岩组分以石英、黏土矿物及斜长石占主体;黏土矿物以伊蒙混层与伊利石为主。研究区龙马溪组页岩孔隙以基质孔隙为主,不同矿物组分对页岩孔隙的贡献程度不同,其中单位质量的有机质产生孔隙体积最大,黏土矿物其次,脆性矿物最小。龙马溪组页岩孔隙发育相对稳定,页岩总孔隙体积平均0.0081cm3/g;比表面积平均1.58m~2/g;页岩介孔孔隙优势孔径2~25nm;微孔优势孔径0.3~0.9nm。龙马溪组页岩孔隙符合分形规律,具有自相似性,宏孔孔隙结构较介孔、微孔更为复杂。川南地区马溪组页岩层理发育,平行层理方向页岩初始孔隙度高于垂直层理方向页岩,页岩单位密度层理提供的初始孔隙度约0.14%。随埋深增大,层理对页岩孔隙度的影响逐渐减小,当埋深足够大时(3000m),页岩孔隙度主要是由基质孔隙度提供。龙马溪组页岩平行层理方向初始渗透率总体高于垂直层理方向页岩,且页岩渗透率随有效应力增加呈递减趋势,根据应力敏感程度不同,渗透率变化可分为敏感区、过渡区和不敏感区三个阶段。压力对页岩孔隙变化起到压缩作用,孔隙体积随压力增大总体呈减小趋势。随着埋深增大,页岩吸附气含量整体呈先增大后减小的变化趋势,但在实际地层中埋深较浅的页岩储层由于容易导通地表,形成逸散通道,含气量较低;页岩游离气含量随埋深增大呈先增大后平稳的变化趋势,且储层压力系数越高,游离气含量越大;页岩总含气量随埋深增大总体呈先增大后逐渐减小的变化趋势,相同埋深下,储层压力系数越高,总含气量越大且下降速率越小。在埋深较浅时页岩气以吸附气占主导,埋深较大时,则以游离气占主导。储层压力系数越大,页岩游离气占主导的临界深度越浅。
[Abstract]:The Lower Silurian Longmaxi formation is one of the favorable strata for shale gas exploration and development in China. It is of theoretical significance to understand the evolution of shale pores and the occurrence of shale gas in Longmaxi formation. Taking Longmaxi formation in south Sichuan as the research object, the pore characteristics of shale and the occurrence of shale gas were studied in this paper. The study area is located in the southern margin of Sichuan basin with relatively simple structure and stable stratigraphic distribution. The content of organic carbon in shale of Longmaxi formation is relatively high, with an average of 2.44, and the thermal evolution of organic matter is high, with an average of 2.90, which is in the over-mature stage. The main shale components of Longmaxi formation are quartz, clay and plagioclase, and the clay is mainly composed of Illite and Illite. The shale pores of Longmaxi formation in the study area are dominated by matrix pores, and the contribution of different mineral components to the shale pores is different, in which the pore volume per unit mass of organic matter is the largest, the clay mineral is the second, and the brittle mineral is the least. The shale pore size of Longmaxi formation is relatively stable, the average total pore volume of shale is 0.0081 cm 3 / g; the average specific surface area is 1.58 mm2 / g; the dominant pore size of shale mesoporous is 225 nm; the dominant pore size of micropore is 0.30.9nm. The shale pores of Longmaxi formation accord with fractal law and have self-similarity. The macropore structure is more complex than mesoporous pore and micropore structure. The shale bedding of Maxi formation is developed in south Sichuan. The initial porosity of shale in parallel direction is higher than that in vertical direction, and the initial porosity provided by shale unit density bedding is about 0.14. With the increase of buried depth, the effect of bedding on shale porosity decreases gradually. When the buried depth is large enough (3000m), shale porosity is mainly provided by matrix porosity. The initial permeability in parallel bedding direction of Longmaxi formation is generally higher than that in vertical bedding direction, and the shale permeability decreases with the increase of effective stress. According to the stress sensitivity, the change of permeability can be divided into sensitive areas. Transition zone and insensitive region are three stages. The pore volume decreases with the increase of pressure. With the increase of buried depth, the adsorption gas content of shale increases first and then decreases, but the shallower shale reservoir is easy to lead to the surface of the ground in the actual formation, forming an escape channel and low gas content. The content of shale free gas increases first and then steadily with the increase of buried depth, and the higher the reservoir pressure coefficient, the greater the content of free gas, and the total gas content of shale increases firstly and then decreases gradually with the increase of buried depth. The higher the reservoir pressure coefficient, the larger the total gas content and the smaller the decreasing rate. When the buried depth is shallow, the adsorption gas dominates the shale gas, and the free gas dominates when the buried depth is larger. The greater the reservoir pressure coefficient, the shallower the critical depth dominated by shale free gas.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.13

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