鄂尔多斯盆地庆阳气田二叠系山西组1段层序结构与沉积演化及其控制因素

Sequence architecture,sedimentary evolution and controlling factors of the Permian Shan-1 Member,Qingyang gas field,southwestern Ordos Basin

庆阳气田是鄂尔多斯盆天然气增储上产的潜力区,二叠系山西组1段(山1段)为其主力产层,然而其沉积演化及其控制因素等方面的认识依然不清,制约着气田的勘探开发。综合利用三维地震、测井、岩心及分析化验等资料,应用测井小波变换、INPEFA技术及Fischer图解等分析方法,对庆阳气田山1段沉积层序发育演化及其对古地貌、古水流流向和湖平面变化的响应关系开展了系统性研究。结果表明:山1段可划分为一个三级层序,由完整的水进—水退旋回构成,内部进一步划分出低位体系域、湖侵体系域及高位体系域,可识别出浅水三角洲以及湖泊等沉积体系。Fischer图解表明山1段的湖平面经历过“快速上升—缓慢下降”的变化过程,内部伴随着次级的湖平面振荡。“PA(进积—加积)—R(退积)—AP(加积—进积)”叠加序列的转变响应着沉积相的迁移演化及可容空间的变化。低位域时期,在沉积前微古地貌与沉积期古水流流向的耦合作用下,古地貌斜坡区三角洲砂岩储层广泛发育,是后期勘探开发的潜在有利区。

The Qingyang gas field in the Ordos Basin is the most promising for reserve growth and production addition,with the first member of Permian Shanxi Formation(Shan-1)being the main pay zone.However,a lack of understanding to the sedimentary evolution and controlling factors of the member hinders further exploration and development of the field.A systematic study was then carried out on the development and evolution of sedimentary sequences of the member as well as its response to palaeogeomorphology,paleocurrent and lake level changes based on analyses of 3D seismic,logging,core and test data through logging wavelet transform,INPEFA and Fischer plots.The results show that the member contains a third-order sequence of a full transgressive-regressive cycle.The sequence can be further divided into the low stand,transgressive and high stand system tracts.Depositional systems are recognized to be shallow-water deltas and lacustrine systems.Fischer plots reveal that the lacustrine level change during deposition of the member experienced a rapid transgression to a slow regression,accompanied by the secondary lake-level fluctuation.The stacking succession recording PA(progradation to accretion)to R(retrogradation)then to AP(accretion to progradation)corresponds to the migration and evolution of sedimentary facies and the changes in accommodation space.The delta sandstone reservoirs,widely developed in ancient landform slope area during the low stand system tracts,are considered the potential targets for exploration and development of gas in the field.