河控浅水三角洲前缘沉积特征及对岩性油藏的控制——以库车坳陷南斜坡巴西改组为例

Sedimentary characteristics of fluvial dominated shallow water delta front and its control on lithologic reservoir:A case study of Baxigai Formation in south slope of Kuqa Depression

库车坳陷南斜坡白垩系巴西改组已发现2个岩性油气藏,展现出了该地区白垩系岩性油气藏勘探的潜力。为了进一步拓展白垩系巴西改组岩性勘探领域,通过岩心观察、测井相、地震相、砂地比和古地貌等综合分析,明确巴西改组上、中、下3段的物源均来自东南方向的哈拉哈塘南部和英买力南部,沉积体系为河控浅水三角洲。巴西改组中、下段分布在哈拉哈塘东南部,发育河控浅水三角洲内前缘—浅湖亚相,上段在研究区均有分布,为退积型沉积,发育河控浅水三角洲内前缘—外前缘—浅湖亚相。研究区白垩系的构造为南高北低,在南部物源的空间匹配关系下,认为退积型河控浅水三角洲内前缘顶部的席状砂,外前缘侧翼的水下分流河道和外前缘倾末端的席状砂是岩性油气藏勘探的有利相带。巴西改组上段是岩性勘探的首选目的层,英买力南部和yd7—ym46—dh26井环带是其有利地区。该成果可为库车坳陷南斜坡白垩系巴西改组下一步岩性油藏的勘探提供依据。

Two lithologic reservoirs have been discovered in south slope of Kuqa Depression,which shows the great potential of Cretaceous lithologic reservoirs exploration in this area.To further expand the field of lithologic reservoir exploration in Cretaceous Baxigai Formation,based on core observation,well logging facies,seismic facies,ratio of the sand and formation and paleogeomorphology,it is confirmed that the provenance of member U,M and L are from south Halahatang and south Yingmaili.The sedimentary system is fluvial dominated shallow water delta.The member M and L of Baxigai Formation are distributed in the southeast Halahatang,and inner front shallow lacstrine subfacies of fluvial dominated shallow water delta are developed.The member U are distri-buted in the project,which is a retrograde depositional model,inner front-outer front-shallow lacstrine facies of fluvial dominated shallow water delta are developed.The structure of the project is dip northward,and the provenance comes from the south.The sheet sand at the top of the inner front,the underwater distributary channel on the flank of the outer front and the sheet sand at the tip of the outer front are the favorable facies for lithologic reser voir exploration.The south Yingmaili and well annulus of yd7-ym46-dh26 are prospects for Cretaceous lithologic reservoirs exploration in member U of Baxigai Formation.The results can provide a basis for further exploration of Cretaceous lithologic reservoirs in south slope of Kuqa Depression.