准噶尔盆地吉木萨尔凹陷芦草沟组湖相云质致密油储层特征与分布规律

Characteristics and occurrence of lacustrine dolomitic tight-oil reservoir in the Middle Permian Lucaogou Formation,Jimusaer sag,southeastern Junggar Basin

准噶尔盆地东南缘吉木萨尔凹陷中二叠统芦草沟组新近发现了独特的湖相云质混积岩致密油储层,不同于传统的海/湖相硅质/灰质致密油储层,展示出重要的学科研究意义。本文报道了这类储层的基本特征与分布规律。结果表明,这类储层岩性主要由砂屑白云岩、粉砂质白云岩/白云质粉砂岩和微晶白云岩组成,见少量粉砂岩和凝灰岩;储集空间以次生粒间溶蚀孔隙和部分剩余粒间孔隙为主,微裂缝仅在少数样品中发育。储层含油性与物性呈正相关,据此将储层分为三类:一类储层孔隙度>12%,渗透率>0.1m D;二类储层孔隙度7%~12%,渗透率>0.01m D;三类储层孔隙度以4%~7%,渗透率>0.001m D。前两类是相对优质储层,分布特征表现为南厚北薄,物性南好北差。这种特点受控于沉积相及其物源,南部是主物源区。据此预测了有利储层分布区,其中芦草沟组上甜点段优质储层主要分布在吉32-吉171-吉31井区,下甜点段优质储层主要分布在吉174-吉251-吉36井区。这些认识还可供区域油气勘探参考。

The Middle Permian Lucaogou Formation in the Jimusaer sag of the southeastern Junggar Basin is peculiar at developing lacustrine dolomitic and mixed reservoirs, differing from the conventional marine/lacustrine siliclastic/calcium reservoirs. Thus, the study of the Lucaogou reservoir is of scientific significance. Here we conduct a comprehensive study of the reservoir basic characteristics and occurrence regularities. Results show that the reservoir is composed mainly of dolarenite, sandy dolomite/dolomitic siltstone, and micritic dolomite in terms of lithology. A few siltstone and tufa were also observed. The reservoir space is mainly composed of secondary intergranular dissolution pores and some residual intergranular pores. Micro-cracks were developed only in some samples. The oilness of sample has a good correlation with physical property. Based on this correlation, the reservoir can be divided into three ranks. The first rank has porosity and permeability of 〉12% and 〉0.1mD, respectively. The second rank is 7%~12% and 〉0.01mD, respectively. The third rank is 4%~7% and 〉0.001mD, respectively. Of these three ranks of reservoir, the first two are of relatively good quality. Their occurrence is characterized by thick in the south and thin in the north. The physical property is also better in the south compared with in the north. This is facies controlled and the sedimentary provenance is located in the south. This implies the favorable target areas for exploration. It is in the area along wells J32, J171, and J31 for the upper sweet point. It is in the area along wells J174, J251, and J36 for the lower sweet point. These results can be applied in the practical exploration.