涠西南凹陷流三段储层成岩相分析与甜点储层预测

Diagenetic facies analysis and sweet point reservoir prediction for the 3rd Member of Liushagang Formation in the Weixinan Sag

根据岩心、铸体薄片、扫描电镜、阴极发光、X衍射等资料并结合物性资料,对北部湾盆地涠西南凹陷流三段储层的储层特征、成岩作用特点进行了研究。结果表明研究区压实作用强烈是储层致密化的主要原因。胶结作用对储层有一定的破坏作用,但是早期碳酸盐胶结、自生高岭石有利于优质储层的发育。溶蚀作用是优质储层发育的基础,破裂作用改善了储层的渗流能力。在成岩作用研究的基础上,根据成岩作用的强度及特殊成岩矿物,划分了五类成岩相。其中,弱压实弱胶结相物性最好,中等压实中等溶蚀相、强压实中强溶蚀相物性次之,压实充填相和碳酸盐致密胶结相物性最差。通过成岩相的测井响应分析,识别了单井-剖面-平面的成岩相。预测研究区东部辫状河三角洲浅埋藏储层、西北部扇三角洲和西南部扇三角洲的水下分流河道中厚层砂砾岩体储层为甜点发育区。

Data from cores,casting thin sections,scanning electron microscopy,cathodoluminescence and X-ray diffraction are applied to study the petrological characteristics and diagenesis of the reservoirs of the 3rd Member of the Liushagang Formation in the Weixinan Sag of Beibu Gulf Basin.Special attention is paid to diagenesis and its evolutionary stages.It is found that strong compaction is the main reason for density and tightness increase of the sediments.Cementation seems to have certain negative impact to reservoir properties,but the early carbonate cementation and authigenic kaolinite always have close connections with high-quality reservoirs.Dissolution is a basic process for enhancement of reservoir qualities,and fractures may improve the permeability of reservoir rocks.According to the intensity of diagenesis and the composition of diagenetic minerals,five types of diagenetic facies are qualitatively recognized.Among them,the diagenetic facies of weak compaction and weak cementation are the best for hydrocarbon accumulation,followed by the medium compaction and medium dissolution facies,and the strong compaction and medium to strong dissolution facies.The compaction and filling facies and the densely carbonate cemented facies are listed the worst in quality.Five types of logging curves are selected to define and describe the diagenetic facies.With the spatial distribution of diagenetic facies,it is recognized that the shallow buried deltaic reservoirs in the east of the study area,and the thick conglomerate reservoir of underwater distributary channel facies in northwest and southwest fan deltas are the sweet points of reservoirs in the study area.