Sedimentological Research On The Carbonate Reservoir Of Chihsia And Maokou Formation In Northwest Sichuan

Around the world nearly half of the oil and gas resources had been found in the foreland basin and had a great potential.While the oil and gas are very common in marine carbonate of Mesozoic located in Longmenshan nappe tectonic belt,Indicates has a potential and exploration prospect.Since than the mechanism and origin of Chihsia and Maokou formation reservoir of middle Permian is very necessary,Especially the research of basin-mountain coupling effect and evolution history and distribution pattern is benefits to optimize the exploration targets and favorable area.Based on the analysis of the domestic and overseas research situation of carbonate reservoir,,according to the theory of carbonate reservoir sedimentology,reservoir geology,sequence stratigraphy,geochemistry and sedimentary dynamics,geotectonics and other multi-disciplinary theory,then combining with the measured geological section,drilling core description,logging data and seismic data,we achieved the folling results about the reservoir sedimentology of Chihsia Formation and Maokou formation of the Sichuan basin:(1)The Permian stratigraphic classification scheme system in northwest sichuan is reclassified,and Chihsia formation divided into two segment and Maokou is four in this research,there have a typical facies from the shallow to deep sea,such as the combination facies of open platform,platform margin,ramp of front platform and basin.(2)The carbonate platform sedimentary system in this research area is further divided into such subfacies as open platform,platform margin,ramp of front platform and baisn,based on the plane distribution rule of Permian sedimentation is summarized through stratigra phic correlationand sedimentary facies analysis,which esablished the sedimentary model of “ shelving rimmed carbonate platform”,then the plane distributive maps of sedimentary facies of Chihsia and Maokou formation are drawn for predicting reservoir.(3)The early dolomite predicted tobe the recrystallization of the fine dolomite under the e ffect of hydrothermal fluid as the thickening and geothemal gradient rise,which formed the typical minerals such as the saddle dolomite,and the origin of Chihsia and Maokou formation dolomite is buried dolomization and tectonic hydrothermal dolomization superpos ition reconstruction(4)The results of origin research about carbonate reservoir shows that: under the effect of regional tectonics many structural fractures are not associated with the strata depth,but the joint occurrence of fractures is good consistency with the regional teconic stress direction,indicate the tectonic uplift and later relaxation are major factors for Chihsia and Maokou formation carbonate fractures reservoir.(5)The intracrystalline pore and fissures constitutes the reservoir space of Chihsia and Maokou formation is especially low pore and low permeability reservoir in northeast of Sichu an,Lithologically,the resevoir formation is composed mainly of crystalline(aplite,medium,co arse and saddle)dolostone forming a typical fractured-porous reservoir.(6)The carbonate reservoir of Chihsia and Maokou formation is mainly distributed in the platform margin facies,and the lithology of reservoir is granular grain limestone in the early stage,then the contemporaneous,shallow burying,medium burying and deep burying process gradually transition,and the dolomitization transformed the reservoir storage space,ch anged the original rock fabric,improved the dissolution fluid space,while the celestine,silicati zation and asphalt filled the few spaces,in general the dolomitization,dissolution,fracturation plag a important role in the forming high quality reservior.