苏里格气田马家沟组膏模孔型储层特征及成因

Characteristics and Genesis of the Gypsum-mold Type Reservoir of the Majiagou Formation in the Sulige Gas Field

含“膏模”孔泥粉晶云岩是鄂尔多斯盆地马家沟组上组合地层重要储集岩类型,其形成时间和成因对于该类型储层的认识具有重要意义。研究利用苏里格东区丰富的取芯资料,根据岩芯、薄片等观察手段,结合常规物性测试分析,综合研究含“膏模”孔型储层特征及其成因。结果表明,“膏模”孔主要发育于泥粉晶白云岩中,位于向上变浅序列中部,常可见未充填-半充填型与全充填型两类。储层特征方面,该类储集岩主要发育“膏模”孔充填残余孔、渗流粉砂间微孔和基岩晶间溶蚀微孔3类储集空间,物性测试显示储集性能优越,平均孔隙度可达5.34%,平均渗透率为1.02 mD。纵向沉积序列显示“膏模”孔发育受沉积旋回控制,旋回中部“膏模”孔内存在溶蚀,内为云质渗流粉砂充填,旋回顶部具有暴露特征,且可见下一次海侵泥质灌入岩溶系统内,各类特征均指示“膏模”孔形成与准同生期岩溶相关,即“膏模”孔形成于准同生期,而非传统认识的表生阶段。

Gypsum-mold-bearing micrite dolomite is an important reservoir type in the upper Ordovician Majiagou Formation in the Ordos Basin,and its formation time and genesis are important for the understanding ofthis reservoir type.In this research,based on the abundant core data ofthe study area,using the analysis of conventional physical properties and observation methods such as core,thin sections,the characteristics ofthe reservoir containing“gypsum-mold”and its genesis are comprehensively studied.The results show that the“gypsum-mold”is mainly developed in the micrite dolomite,which is located in the middle part ofthe shallowing upward sequence,and the two types of non-semi-filled and fully-filled types are often seen.As a reservoir,that mainly develops three kinds of reservoir spaces:residual pores in gypsum mold and interbedded pores in bedrock.The physical property test shows that this reservoir has superior performance,whose average porosity is 5.34%,and the average permeability is 1.02 mD.The dolomitic seepage silt similar to the composition ofthe bedrock is filled in the“gypsum-molds”.The vertical sedimentary sequence shows that the development of the“gypsum-mold”is controlled by sedimentary cycles,the top of the cycles is characteristic of exposure,and the karst system can be seen poured with mud from the next transgression,all indicating that the formation of the“gypsum-mold”is related to the eogenetic karst,that is,the pore is formed in the early diagenetic stage,not the epigenetic stage of traditional understanding.