The Study On The Genesis Of Dolomite Reservoirs In Lower Cambrian Xiaoerbulake Formation In Tarim Basin

There are thousands meters of thick dolomite strata in Cambrian in Tarim basin.In 1997,He 4 Well was drilled through the middle and lower Cambrian to explain its high quality reservoir cap assemblage,and uncovered the prelude to the exploration of the subsalt cambrian.However,due to the low degree of early exploration,the accuracy of reservoir research is relatively coarse,the formation of the reservoir is not clear,thus restricting the exploration process from the point to the face.Therefore,this paper took the dolomite reservoir of lower Cambrian Xiaoerbulake Formation in the Tarim Basin as the key and based on the North Tarim Sugaitebulake Formation profile and core hole data,combined with geochemical methods to do a detailed study on the reservoir formation of the lower Cambrian Xiaoerbulake Formation,in order to clarify the formation mechanism and distribution law of dolomite reservoir,and to provide the theoretical basis for the next exploration.This research shows that(1)the study area mainly developed Dolomitic dolomite,Stromatolitic dolomite and Clot dolomite,Shelf rock,bondstone,doloarenite,dolomite and fine dolomite eight lithofacies,based on this attempt,a new classification scheme of dolomite is proposed,which is based on the sedimentation or metasomatism of dolomite;(2)dolomite has various reservoir space,mainly develops intergranular pore/interparticle dissolution pore,intercrystal pore/intercrystal dissolution pore,intraparticle dissolved pore,coelomopore,framework pore,dissolution pore,micropores and cracks,there is a good correlation between lithofacies and petrophysical property,according to the facies belt reservoir types is divided into the margin-shoal reservoirs and the plateform interior reef-shoal reservoirs;(3)dolomite in the study area are mainly formed in penecontemporaneous and early burial period,the main cause is seepage refluction,some parts of dolomite are formed under Sabkha environment,the dolomitization fluid is mainly water,part of dolomite Inherited the penecontemporaneous and early diagenesis in burial environment continue to occur dolomitization,and then the dolomitization fluid is deep groundwater or hot liquid;(4)the study area dolomite has experienced complex diagenesis,dissolution in penecontemporaneous,dissolution in burial environment,dolomitization and cataclasis play a constructive role on the reservoir,and cementation,compaction and pressure solution,recrystallization play a destructive role on the reservoir,recrystallization has two sides;(5)The sedimentary facies has a relatively strong control action to dolomite reservoir,and the porous sediments of high energy reef(mound)flat facies provides the material basis for reservoir development;(6)high frequency sequence is one of the main factors of the dissolution in penecontemporaneous,in a third-order sequence interface,high frequency sequence will transform the regional dolomite reservoir,but the degree of transformation is related to sea level;(7)in the open diagenetic environment,hydrothermal dissolution can form an effective reservoir space,but the formation conditions are relatively harsh,and the scale in crossrange is limited,so that it can only form a reservoir in the local scope;(8)proposed a prediction of the dolomite reservoir distribution in the study area,the margin-shoal reservoirs mainly developed the margin in the north Tarim and the margin of the Lunnan area to Gucheng,the plateform interior reef-shoal reservoirs dolomite reservoir of Tazhong Uplift in the Bachu and developed in the north Tarim plateform.