塔中地区志留系层序、沉积和油气分布规律

塔里木盆地塔中地区志留系沉积环境为潮控滨岸带,主要发育潮坪沉积体系,这在柯坪塔格组表现得尤为突出.在低缓地形背景下发育的柯坪塔格组潮坪沉积环境可分为潮间带和潮下带,发育泥坪、混合坪、砂坪和潮道沉积相.根据层序地层学理论,综合研究野外露头、测井、地震等资料,将塔中地区志留系划分为5个三级层序,每个层序均由海侵和高位体系域两部分组成.由于潮坪沉积的特殊性,每个层序均由1个完整的旋回构成.结合试油资料对塔中11油藏的塔中11井、塔中11-1和塔中117井进行分析,发现在层序的高位体系域中富集油气,而且在SQ1中富集油,在SQ2中富集气,形成低孔低渗油气藏.形成储层的潮道和砂坪沉积具有较好的储集物性,其上覆泥坪形成有效遮挡的盖层,这些是形成油气藏的根本原因,直接原因是高位体系域中的储层比海侵体系域中的储层更靠近盖层.

Stratigraphical sequence, sedimentary characteristics and reservoir distribution of the Silurian in central Talimu Basin

The Silurian in this area is tide-controlled coastline sedimentary environment and here mainly developed the tidal flat depositional system.This is especially true of Kepingtage Formation.The tidal flat depositional environment in Kepingtage Formation includes intertidal zone and subtidal zone,in which developed mud flat,mixed flat,sand flat and tidal channel facies.The Silurian in this area is divided into 5 third-order stratigraphic sequences by comprehensively studying outcrop,logging and seismic data based on sequence stratigraphic theory.Every sequence is made up of transgressive systems tracts and highstand systems tracts.Because of the particularity of tidal flat sedimentation every sequence forms a cycle.According to the analysis of the production testing data of Tazhong11,Tazhong11-1 and Tazhong117 wells,it is held that there is oil and gas enrichment in the highstand systems tracts(HST),oil is rich in SQ_1 while gas is rich in SQ_2,and the oil and gas reservoirs with low permeability and low porosity are formed.The tidal channel and sand flat facies form the reservoirs with better physical property and their overlying formations which are made up of mud flat form effective barriers.These are the fundamental reasons for the formation of the oil and gas reservoirs,and the direct reason is that the reservoirs in HST are closer to the caps than those in transgressive systems tracts.