鄂尔多斯盆地宜川—黄龙地区马家沟组古岩溶储层特征及形成机理

鄂尔多斯盆地宜川—黄龙地区具备良好勘探潜力，研究其储层主控因素及形成机理对黄龙气田勘探工作具有重要指导意义。以岩芯观察、铸体薄片鉴定、阴极发光及地球化学测试分析为基础，结合钻井、测井资料，研究宜川—黄龙地区马家沟组古岩溶储层基础特征、储层主控因素及形成机理。结果表明:研究区主要发育含膏粉晶云岩、粉晶砂屑云岩及粉—细晶云岩；石膏铸模孔、晶间孔(溶孔)、溶孔及溶缝是最主要的储集空间；储层孔隙度以0.1%～5.0%为主，渗透率以(0.002～0.100)×10^-3 μm²为主，具有低孔低渗—特低孔特低渗特点；有利储层分布受多种地质作用共同影响，含硬石膏结核云坪、白云岩坪及颗粒滩是优质储层发育的物质基础，储层平面分布受控于古岩溶地貌，而垂向分布受控于岩溶旋回，有利储层分布于表生期岩溶垂直渗流带，晚成岩期次生灰化及3期不同组合类型充填作用使有效孔隙锐减，是该区储层物性较差的直接原因。

Characteristics and Forming Mechanism of Palaeokarst Reservoir of Majiagou Formation in Yichuan-Huanglong Area of Ordos Basin,China

The Yichuan-Huanglong area in Ordos Basin has favorable prospect for exploration, which is of great significance for the exploration of Huanglong gasfield to study the main controlling factors and forming mechanism of reservoir. Based on the core observation, casting thin section identification, cathodoluminescence(CL) and geochemical test analysis, combined with the drilling and logging data, the basic characteristics, main controlling factors and forming mechanism of palaeokarst reservoirs of Majiagou Formation in Yichuan-Huanglong area were studied. The results show that the powder crystal gypsodolomite, powder crystal doloarenite and powder-aplitic crystal dolomite mainly develop in the area; the gypsum mold pore, intergranular hole, solution pore and solution fissure are the most important reservoir spaces; the reservoir porosity is mainly from 0.1% to 5.0%, and the permeability is mainly from 0.002×10^-3 μm² to 0.100×10^-3 μm², with low to extra-low porosity and permeability; the distribution of favorable reservoirs is affected by various geological processes, the anhydrite-bearing concretion dolomite flat, dolomite flat and grain bank microfacies are the foundation of development of high quality reservoir, the plane distribution of reservoirs is controlled by the palaeokarst geomorphology, the vertical distribution is controlled by karst cycle, the favorable reservoirs distribute in the vertical permeating belt of the supergene, and the effective porosity is reduced by the dedolomitization in the later stage of diagenesis and three stages of different types of filling, which are the direct factor of poor physical property of reservoir in the area.