Reservoir Reasearch Of Subsalt Dolomite In Keping-Bachu Area,Tarim Basin

Based on the basic research on the carbonate reservoir of the Sholbrak Formation in Keping-Bachu area of Tarim Basin,through core observation,thin section observation,geochemical analysis and simulation experiments,this paper studies Reservoir petrology characteristics,reservoir space types,reservoir properties and lateral distribution characteristics.Through the above work,the following understandings have been obtained:(1)Fine-grained dolomite and silty dolomite are mainly developed in the Sholbrak Formation,and the main reservoir space combination is pore-cavity type,and the reservoir shows quasi-stratiform distribution characteristics in the transverse direction of the central uplift zone;(2)Reservoirs of the Sholbrack Formation are obviously affected by the atmospheric and freshwater dissolution during syngenetic diagenesis,structural fracture and burial dissolution during late diagenesis.Through geochemical analysis,it is confirmed that the diagenetic environment of the reservoir is marine facies,and the later stage is mainly affected by freshwater showering;(3)In the study of the simulation experiment of dissolution,through ion concentration test and sample slice observationit is found that the crystal size,rock structure and mineral composition influence the dissolution process of carbonate rocks.and primary structural fissures,intragranular pore and suture lines are preferentially dissolved.Through energy spectrum analysis and multifractal analysis,it is recognized that the surface elements of carbonate rock are not uniform,affecting the dissolution.The greater the singularity of Ca and Mg elements,the easier the dissolution will occur;(4)During diagenesis,limestone is preferentially dissolved than dolomite,However,the dissolution pore is easy to form in dolomite,and the dolomite has strong compaction resistance,which can well preserve the original pore.Therefore,under burial conditions,dolomite may be easier to form favorable reservoir than limestone,which is consistent with the good dolomite reservoir formed by Sholbrak Formation.