川东北元坝地区侏罗系大安寨段黑色页岩沉积及储层特征

Sedimentary and Reservoir Characteristics of Black Shale in the Jurassic Da’anzhai Member in the Yuanba Area of Northeastern Sichuan

摘要: 侏罗系自流井组大安寨段是现阶段四川盆地湖相页岩勘探开发的热点层位，本文通过岩石观察与特殊元素测井分析，场发射扫描电镜观察、岩石孔隙度实验、X射线全岩衍射(XRD)、低温氮气吸附以等实验分析，对川东北元坝地区侏罗系大安寨段二亚段湖相页岩的沉积环境及储层特征进行系统分析，研究结果显示：大安寨段页岩Sr/Cu介于2.50~8.34之间，Sr/Ba介于0.15~0.47之间，V/(V+Ni)在0.65~0.79之间，指示温暖、潮湿环境及缺氧的淡水湖盆沉积，发育滨湖、浅湖、半深湖3种沉积沉积相，发育层状泥岩夹介壳灰岩、砂–灰–泥三元混积、纹层–层状泥岩夹介壳灰岩、厚层状灰泥混积等四种岩性组合。页岩矿物类型以粘土矿物、石英、方解石为主，含少量长石、白云石以及黄铁矿；孔隙类型以无机孔隙发育为主，尤其是粘土晶间孔隙，有机质孔隙含量相对较少。纹层–层状泥岩夹介壳灰岩相及层状泥岩夹介壳灰岩相因“源–储”配置良好，具有高脆性、高孔隙度及高含气量特点，同时页理缝及介壳纹层发育，成为大安寨段开发的主要层段。

Abstract: Da’anzhai member of Ziliujing Formation in Jurassic is a hot zone for lacustrine shale exploration and development in Sichuan Basin at present. In this paper, through rock observation and logging analysis of special elements, field emission scanning electron microscope observation, rock porosity experiment, X-ray whole rock diffraction (XRD), cryogenic nitrogen adsorption and other experimental analysis, the sedimentary environment and reservoir characteristics of lacustrine shale in the second sub-member of Jurassic Da’anzhai Member in Yuanba area, northeast Sichuan Basin were systematically analyzed. The research results show that: The Sr/Cu, Sr/Ba, and V/(V+Ni) of the Da’anzhai Member shale range from 2.50 to 8.34, 0.15 to 0.47, and 0.65 to 0.79, indicating the warm and humid environment and anoxic freshwater lacustrine sedimentary facies, shallow lacustrine sedimentary facies and semi-deep lacustrine sedimentary facies. There are four lithologic assemblages: bedded mudstone intercalated shell limestone, sand-lime-mud ternary mixing, laminated-bedded mudstone intercalated shell limestone, thick bedded plaster mixing. Shale minerals are mainly clay minerals, quartz and calcite, with a small amount of feldspar, dolomite and pyrite. The pore types are mainly inorganic pores, especially intergranular clay pores, while the content of organic matter pores is relatively small. Laminate-bedded mudstone intercalated limestone facies and bedded mudstone intercalated limestone facies have the characteristics of high brittleness, high porosity and high gas content due to their good source-reservoir configuration. At the same time, cleavage fractures and intercalated laminae are developed, which become the main strata in the Development of Da’anzhai Member.