涠西南凹陷X油田中块渐新统储层碳酸盐胶结物特征及孔隙演化模式

为了寻找南海北部湾盆地涠西南凹陷开发有利区，指导剩余油挖潜，以X油田中块渐新统涠洲组三段 (E3w3) 碎屑岩储层碳酸盐胶结作用为研究重点，并以凹陷中心和断裂附近为两大主体区域开展研究工作，通过粒度分析、薄片显微镜下鉴定、阴极发光、扫描电镜、岩芯常规物性分析及单井成岩作用数值模拟等技术手段，深入研究了碳酸盐胶结物类型、含量及分布特征，明确了涠洲组碎屑岩储层孔隙演化模式。结果表明，研究区涠洲组储层碳酸盐胶结物以方解石和白云石为主，主要形成于成岩作用早期阶段。受断裂分布和热流体活动影响，在平面和垂向上，碳酸盐胶结物分布特征具有明显规律性。断裂附近区域储层中碳酸盐胶结物更为发育，其损失孔隙占比约22.6%，占总胶结物损失孔隙度的67.0%；洼陷中心区储层中碳酸盐胶结较弱，其损失孔隙占比约7.9%，占总胶结物损失孔隙度的39.9%。因此，洼陷中心弱胶结作用区碎屑岩储层储集物性较好，可作为油气藏开发有利区的首选目标。

Carbonate cement characteristics and porosity evolution model of the Oligocene reservoir in the middle block of X Oilfield in Weixinan Sag

To search for favorable development areas and guide the exploration of remaining oil of Weixinan Sag in Beibu Gulf Basin, South China Sea, this research focused on the carbonate cementation of the third member of the Oligocene Weizhou Formation in the middle block of X Oilfield (E3w3) between two main areas in the sag center and near fault, respectively. The type, content, and distribution characteristics of carbonate cements of the clastic rock reservoir in the E3w3 were quantitatively analyzed by means of laser particle size analysis, slice microscopic identification, cathode luminescence, scanning electron microscopy, conventional physical property analysis of core, numerical simulation of diagenesis of single well, and the porosity evolution modeling. The results show that, the carbonate cements of the reservoir are mainly of calcite and dolomite, which is mainly formed in the early stage of diagenesis. Under the influence of fracture distribution and thermal fluid activity, the distribution of carbonate cements in horizontal and vertical directions showed obvious regularity. The carbonate cement near fault was more developed, the porosity loss was 22.6%, which accounted for 67.0% of the total porosity loss caused by cementation, while those in the sag center were weaker, being 7.9% and 39.9%, respectively. The clastic rock reservoir of weak cementation area in the sag center showed better physical properties, and thus can be used as a target of favorable area for oil and gas reservoir development.