砂砾岩体不同岩相油气充注期储集性能差异及成藏意义--以玛湖凹陷西斜坡区百口泉组油藏为例

玛湖凹陷西斜坡区三叠系百口泉组岩性油藏生、储、盖、运等成藏条件配置优越,有效的侧向及上倾方向圈闭封挡条件为制约油气成藏的关键。在明确泥质含量为影响本区砂砾岩储层储集性能关键因素基础上,以泥质含量为主分类参数,将砂砾岩储层划分为贫泥砂砾岩(泥质含量<5%)、含泥砂砾岩(泥质含量5%~8%)和富泥砂砾岩(泥质含量>8%)三种岩相。早侏罗世的早期油气充注期,上述三种岩相储层均可作为有效储层;早白垩世的主要油气充注期,富泥砂砾岩相储层的储集性能明显变差,成为研究区主要的致密封挡带,而贫泥砂砾岩和含泥砂砾岩仍可作用作为有效储层,且前者的储集性能优于后者。扇三角洲前缘亚相(牵引流)沉积主要对应于贫泥砂砾岩岩相,在油气充注期为有效储层,构成玛湖凹陷西斜坡区百口泉组大面积岩性油藏的主体储集层;扇三角洲平原亚相(牵引流)、砂质碎屑流(重力流)沉积主要对应于富泥砂砾岩岩相,在油气充注期储集性能均较差,主要构成研究区大面积岩性油藏的底部及侧向的致密封挡带,上述两致密封挡带与扇三角洲前缘亚相(牵引流)有效储层配置,共同形成玛湖凹陷西斜坡区百口泉组大型岩性油藏。

Reservoir Property Diversity of Different Lithofacies in Sandy Conglomerate during Oil-gas Injection Period and Reservoir-formation Significance: A Case from Baikouquan Formation in west slope of Mahu depression,Junggar Basin

The reservoir-forming situations of source rocks, reservoir rocks, cap rocks and migration condition in Baikouquan Formation lithologic reservoir, west slope of Mahu Depression, are favorable.The valuable trap sealing condition in lateral and upward direction is the key to reservoir-forming. On the basis of making clear the fact that the mud content is the key factor to the reservoir performance of the sand conglomerate reservoir in this area, this paper divided the sand conglomerate reservoir into three lithofacies: poor-mud conglomerate (mud content<5%), mud-bearing conglomerate (mud content 5%~8%) and mud-rich conglomerate (mud content>8%).During the period of early oil-gas injection in early Jurassic, the three lithofacies above mentioned are all the valuable reservoirs. During the period of main oil-gas injection in early Cretaceous, the reservoir performance of the mud-rich conglomerate is obviously worse, and then the mud-rich conglomerate evolved into the sealing block finally, whereas the poor-mud conglomerate and the mud- bearing conglomerate are still acted as valuable reservoir, with the reservoir performance of the former is better than the latter. Fan delta front sub-facies (traction flow) deposition are mainly corresponding to the poor-mud conglomerate, and acted as valuable reservoir during the period of oil-gas injection, and then acted as the main reservoir in T₁b lithologic reservoir, west slope of Mahu Depression. The fan delta plain (traction flow) deposition and sandy debris flow (gravity flow) deposition are mainly corresponding to mud-rich conglomerate, mainly acted as the sealing blocks in the bottom and the lateral direction of the large lithologic reservoir with the poor reservoir performance. The two sealing blocks mentioned above, configured with the valuable reservoirs in fan delta front sub-facies (traction flow), jointly constitute the large lithologic reservoir in T₁b, west slope of Mahu Depression.