黄河口凹陷H－1构造沙河街组混积岩储层控制因素

摘要

黄河口凹陷 H －1构造位于渤南低凸起南侧，其主力储层为一套典型的混积岩。通过对 H －1构造混积岩储层特征及白云岩成因的分析，认为 H －1构造沙河街组混积岩储层储集空间受控于沉积时期的古地理背景、古水质条件与后期的白云岩化程度。古地理背景与古水质条件是混积岩发育的基础，研究区位于扇三角洲前缘侧翼，受到陆源淡水供给与半封闭的微咸水—半咸水湖水的双重影响，发育了由陆源碎屑与生物碎屑滩构成的混积岩。后期白云岩化作用是改善储层的关键因素，等摩尔交代对渗透率的提高以及白云岩化作用引发的选择性溶蚀，对储层物性的改善有很大的影响。混积岩储集性能差异较大，当物源供给的淡水影响较大时，混积岩中碳酸盐以方解石为主，储层较致密；当咸化湖水影响较大时，混积岩中碳酸盐主要为白云石，储层的溶蚀孔隙较发育。化石碎片的背散射图片清晰地证实了混积岩中的白云石是由方解石转化而成。通过对古生物、粘土矿物、古地理背景等资料的分析，认为在伊蒙混层向伊利石的转化过程中产生的 Mg 离子是研究区沙河街组白云岩化作用所需离子的来源之一，亚热带气候条件下半封闭的微咸水－半咸水环境有利于钙质的沉积和 Mg 离子的富集，可为混积岩的白云岩化提供物质基础。研究黄河口凹陷古近系混积岩储层控制因素及优质储层发育规律，对该区中深层油气勘探具有积极意义和参考价值。%H -1 sturcture of Huanghekou Depression,is on the south of Bonan Lower Uplift,in which the main reservoir is diamictite.By analysing the characteristics of diamictite and the origin of dolostones,we be-lieve that the reservoir space of diamictite in Shahejie Formation is controlled by the paleogeographic background of sediment,the paleohydrogeologic conditions and the degree of dolomitization later.Paleogeographic back-ground and paleohydrogeologic conditions are the basis for controlling the formation of diamictite.The research area is located in the fan delta front wing which is affected by both terrigenous fresh water and semi-closed brackish water.Such an environment is beneficial to the growth of diamictite which is made up of terrigenous clastic and bioclastic beach.Dolomitization is the key factor to reform reservoir quality,for the mole-to-mole re-placement of Ca2 + by Mg2 + and the selective dissolution after partly dolomitization both enlarge the porosity or permeability.However,there is a great difference among the diamictite reservoirs.When the fresh water has a greater influence on the sediment,the carbonate in diamictite is mainly composed of calcite and the diamictite under such circumstances has poor reservoir capacity.On the contrary,when diamictite are greatly influenced by brackish water,dolomite occupies the most of carbonate and the diamictite has better reservoir capacity.Fos-sil fragments of back scattering images clearly confirmed the metasomatic origin of dolomite.Based on analysis on paleontology,clay mineral and paleogeographic background data,we found that the Mg2 + which dolomitiza-tion needs is partly from the transformation of illite-montmorillonite mixed-layer to illite.The water environment of sediment for subtropical climate is semi-closed brackish water and such environment is benefit to the deposi-tion of calcium and enrichment of Mg2 +.Meanwhile,the rich Mg2 + can provide material for dolomitization.The research of controlling factors and development law on diamictite reservoir have positive significance on the ex-ploration of deep reservoirs.