川南地区龙马溪组页岩有利储层发育特征及其影响因素

下志留统龙马溪组是四川盆地南部重要的烃源岩和页岩气勘探层位，为查明其有利储层的发育特征及其影响因素，通过对昭通、长宁、威远地区7口页岩气井的钻井岩心观察及野外露头地质调查，结合岩石薄片鉴定、扫描电镜观察、比表面积测定以及岩石物性等分析结果，明确了该区龙马溪组页岩地层展布、岩性组合、矿物组成、储集空间类型等特征：①龙马溪组页岩在地层发育、岩性组合及富有机质程度上具有很强的各向异性，有效页岩储层以高有机质层段为主；②页岩储层具有高成岩作用、高热演化程度特点，发育无机物质孔、有机物质孔和微裂缝等储集空间类型；③对页岩气储集有贡献的主要是黏土矿物层间孔和有机质孔，孔径分布在50 nm~2 μm，其形成与黏土矿物和有机质的含量、成岩作用及有机质热演化作用有关。在此基础上，分析认为：页岩沉积环境、矿物组成、有机质含量是影响页岩储集能力的重要因素，有机物质富集有利于页岩气的生成与吸附，脆性矿物的存在提高了储层的脆性，有利于储层的增产改造。

Favorable reservoir characteristics of the Longmaxi shale in the southern Sichuan Basin and their influencing factors

Important source rocks were found in the Lower Silurian Longmaxi Fm which is also regarded as a shale gas exploration target in the southern Sichuan Basin. In order to understand its favorable reservoir characteristics and their influential factors, we observed the cores of 7 shale gas wells in Zhaotong, Changning and Weiyuan areas and made geologic investigation of outcrops. In addition, we also collected various data such as thin section test, SEM, specific surface area measurement and physical properties analysis. All these data were integrated to study the distribution, lithology combinations, mineral composition and reservoir space types of the Longmaxi shale in the study area. The following conclusions were obtained. First, the Longmaxi shale is strongly anisotropic in formation development, lithologic assemblage and organic abundance. The effective shale reservoirs are dominated by shale intervals with a high organic content. Second, the shale reservoirs are featured by high diagenesis, high thermal maturity, and multiple reservoir space types including inorganic pores, organic pores and microfractures. Third, the interlayer pores of clay minerals and organic pores with diameters in the range of 50 nm 2 μm are effective for shale gas storage and their formation is controlled by the content of clay minerals and organic matters, diagenesis and ther mal evolution of organic matters. It is concluded that sedimentary environment, mineral composition and organic content are the major factors influencing shale reservoir quality, that the enrichment of organic matters is favorable for the generation and adsorption of shale gas, and that a high content of brittle minerals is favorable for reservoir stimulation.