渤海湾盆地东濮地区奥陶系碳酸盐岩成岩作用及对储集层的影响*

随着东濮地区地热勘探的不断深入,现有奥陶系储集层研究精度已不能满足勘探需求。基于露头、岩心、薄片、测录井、碳氧同位素和流体包裹体等手段,结合区域地质背景,深入研究了东濮地区奥陶系碳酸盐岩成岩系统及其对储集层的影响,并进一步预测了有利储集层的分布区。研究表明,准同生和早成岩期发生胶结、压实、准同生白云石化和准同生溶蚀作用,其中胶结、压实作用使储集层原生孔隙度大幅减少;表生成岩期发生风化壳溶蚀作用,对储集层孔隙的增加起决定性作用;中—晚成岩期发生构造破裂、热液溶蚀、压溶、胶结、埋藏白云石化和重结晶作用,其中白云石化、溶蚀和构造破裂作用对储集空间的贡献最大,重结晶作用具有双重性,对粉细晶白云岩起强烈破坏作用。综合研究将研究区划分出Ⅰ类储集层分布区1个、Ⅱ类储集层分布区2个和Ⅲ类储集层分布区2个。其中,颗粒滩、潮坪与断裂发育带、白云石化、准同生溶蚀、风化壳溶蚀、热液溶蚀作用叠合区储集层质量最佳,多为Ⅰ类和Ⅱ类储集层分布区。

Diagenesis and its effect to carbonate reservoirs of the Ordovician in Dongpu area,Bohai Bay Basin

In pace with the intensive exploration of the geothermal resource,the current research level of the ordovician reservoirs in Dongpu area can not meet the exploration demand. Therefore,through the analysis of outcrops,cores,thin sections,loggings,C-O isotopes,and fluid inclusions, this paper documents the diagenesis system and its impacts on the Ordovician carbonate reservoirs in Dongpu area. Furthermore,the current study also points out the areas where develop favourable reservoirs. The results show that cementation,compaction,penecontemporaneous dolomitisation,and penecontemporaneous dissolution occurred in syngenetic diagenesis stage. The cementation and compaction had reduced the primary porosity of the reservoir significantly. Weathering karst developed in the epidiagenetic stage and it played a decisive role for increasing the reservoir porosities. Fracturing,hydrothermal dissolution,pressolution,cementation,burial dolomitization,and recrystallization developed in middle-deep burial diagenesis stage. In this period,the dolomitization,hydrothermal dissolution and fracturing were the most important diagenesis for increasing the reservoir porosities. Meanwhile,the recrystallization has a dual character,which has strong destructive effect on fine crystalline dolomite. By comprehensive study,the current study identifies favourable reservoirs. There are 1 region for developing type Ⅰ reservoir,2 regions for developing type Ⅱ reservoir,and 2 regions for developing type Ⅲ reservoir. The areas that grain bank,tidal flat,superimposed fracture development zone,dolomitization,eogenetic dissolution,weathering karst,and hydrothermal dissolution,are most favourable for developing type Ⅰ and type Ⅱ reservoirs.