川中气田与苏里格气田“甜点”储层对比研究

COMPARISON OF FORMATION CONDITIONS OF "SWEET POINT" RESERVOIRS IN SULIGE GAS FIELD AND XIANGXI GROUP GAS FIELD IN THE CENTRAL SICHUAN BASIN

四川盆地中部三叠系香溪群与鄂尔多斯盆地苏里格气田主力储层二叠系下盒子组盒8段均具有埋藏深度大、深埋时间长、成岩演化程度高、物性差等特点，属于典型的低孔隙度、低渗透率储层，孔隙度大部分介于4％～6％之间，渗透率一般小于1×10-^-3μm^2，其中都发育有相对优质的有效储层（“甜点”），而且大部分油气都储集在这些“甜点”储层中。通过对这两套储层的形成条件对比分析认为，形成“甜点”储层的主控因素主要是层序地层、有利沉积相带、碎屑颗粒的粒度、有机酸性水的溶蚀以及裂缝的发育程度。研究发现，“甜点”储层均发育在具有块状层理的粗砂岩或中-粗砂岩中，纵向上主要分布在中期基准面旋回的中下部；平面上主要分布在三角洲平原和平原-前缘相带的高能分流河道中；此外，裂缝对致密储层储集能力也具有较大的改善作用。

Both the Triassic Xiangxi Group in the central Sichuan Basin and the eighth member of Permian Xiahezi Formation, the major reservoir of Sulige gas field in the Ordos Basin, are characterized by large burial depth, long duration of deep burial, high level of diagenetic evolution, and poor physical properties. They are all of typical low porosity and low permeability reservoirs, with porosity mostly ranging from 4% to 6% and permeability generally less than 0.1×10-3μm2, and contain excellent effective reservoirs ('sweet point'), in which most of the oil and gas reserves are accumulated. Based on a comparison of the formation conditions between these two reservoir groups, it is believed that the major control factors of the formation of the excellent reservoirs mainly include sequence stratigraphy, favorable sedimentary facies zones, grain sizes, dissolution of organic acidulous water, and development of fractures. Study shows that the high quality 'sweet point' reservoirs are all developed in coarse sandstone and medium-coarse sandstone with massive bedding. Vertically, they are mainly distributed in the middle-lower parts of the middle base-level cycle, while laterally, they are mainly distributed in the delta plain and the distributary channels with high energy in plain-front facies belt. Moreover, the fractures also have relatively large effects on the improvement of the tight reservoirs.