查干凹陷下白垩统巴二段储层特征及孔隙演化

Reservoir characteristics and pore evolution of the second member of the Lower Cretaceous Bayingebi Formation in Chagan Depression

为了研究查干凹陷西部次凹巴二段碎屑岩储层特征,分析成岩作用对孔隙度的影响,根据岩心、薄片观察,以及X射线衍射、扫描电镜等储层分析测试资料,建立适合研究区的孔隙度演化定量模型,进而对孔隙演化史进行定量恢复。巴二段储层以长石岩屑砂岩为主,具有"两低一高"的特征,储层物性差,以特低—超低孔、特低—超低渗储层为主,孔隙度为0.17%~15.32%,平均为5.7%,渗透率为0.003 7~162.300 0 mD,平均为3.4 mD,储集空间类型主要为粒间溶蚀孔;巴二段储层经历了早期机械压实、早期碳酸盐胶结、碳酸盐溶蚀和晚期碳酸盐胶结等成岩作用,在埋深为2 100~2 800 m处发育次生孔隙带,现今巴二段大部分处于中成岩A2期。孔隙度演化定量模型计算结果表明:乌力吉构造带巴二段储层原始孔隙度为30.5%,压实作用减孔(使孔隙度减小)19.8%,胶结-交代作用减孔9.7%,溶蚀作用增孔(使孔隙度增加)3.7%,这在一定程度上改善了储层物性(现今孔隙度约为4.8%)。计算结果与实测孔隙度吻合,建立的模型对孔隙演化过程和优质储层预测具有指导作用。

In order to study the characteristics of clastic reservoir and the effects of diagenesis on porosity of the second member of the Lower Cretaceous Bayingebi Formation （Kx b2） in Chagan Depression, a pore evolution model was established based on the data of core, thin section observation, X-ray diffraction and SEM. The reser- voir rock of K1 b~ is mainly composed of feldspar lithic sandstone. The reservoir properties are poor, with ultra- low porosity and ultra-low permeability. The porosity ranges from 0.17% to 15.32% with an average of 5.7%, and the permeability ranges from 0.003 7 mD to 162.300 0 mD, with an average of 3.4 mD. Intergranular dis- solved pores are the main reservoir space. The reservoir of K1 b2 underwent mainly mechanical compaction, early carbonate cementation, carbonate dissolution and late carbonate cementation. Dissolution of carbonate cements, feldspar and rock debris created a secondary pore zone among 2 100-2 800 m, which improves the reservoir pro- perties. The K1 b2 reservoir is mainly at the middle diagenetic A2 stage. The results show that the original porosity of K1 b2is 30.5% in the Wuliji tectonic zone, compaction reduced the porosity of 19.8%, while the cementation reduced porosity of 9.7%, and the dissolution increased porosity by 3.7%, which improves the reservoir properties （the current porosity is approximately 4.8% ）. This result matches well with actual porosity, which has a contribution to cognize pore evolution process and predict high quality reservoirs.