Rock types and sedimentary facies division scheme of the Sinian Dengying Formation dolomite in the Sichuan Basin and its periphery
The Sinian Dengying Formation in the Sichuan Basin shows immense potential in natural gas exploration,but there are more disputes on the rock classification of dolomite and the interpretation of sedimentary environment,which is not beneficial for the precise characterization of the distribution of sedimentary facies and favorable reservoir belts,restricting the subsequent petroleum exploration and development.In this paper,the lithofacies and sedimentary environments in the Sichuan Basin and its periphery are analyzed systematically based on outcrops and wells.Based on the types of the dolomite determined,sedimentary facies are identified using the lithological combination method,and then the scheme proposed in this paper is compared with the lithology and sedimentary facies division schemes proposed in previous studies.Finally,a set of dolomite rock type and sedimentary facies classification scheme suitable for oil and gas exploration and sedimentological research is established.The following results are obtained.First,based on texture genesis,the Dengying Formation dolomite is divided into two categories,including sixteen subtypes of six types.The first category is the dolomite with original sedimentary texture,including granular dolomite,micritic dolomite and microbe(algae)bounded dolomite,which are divided into nine subtypes.The second category is the dolomite reworked from protolith through diagenesis,including grape-like dolomite,breccia dolomite and crystalline dolomite,which are divided into seven subtypes.Second,in the dolomite of the study area,two facies belts are identified,i.e.,platform margin facies and restricted platform facies,which are divided into seventeen microfacies of eight subfacies.The platform margin facies consists of three subfacies,i.e.,microbial(algal)mound,intermound/shoal bottomland and shallow shoal,which are subdivided into eight microfacies.The restricted platform facies consists of five subfacies,i.e.,microbial(algal)mound,intermound/shoal sea,shallow shoal,intraplatform bottomland and lagoon,which are subdivided into nine microfacies.Third,in comparison with the restricted platform facies,the platform margin facies is characterized by higher mound/shoal proportion,greater single-layer thickness and superposed occurrence.Fourth,the growth sequence of mound base-mound core-mound flat-mound cap reflects the whole growth-drowning cycle of a microbial mound,and the mound base-mound core-mound flat sequence corresponds to meter-scale shallowing-upward cycle of subtide-intertide-supratide.It is concluded that the mound/shoal microfacies division scheme proposed in this study improves the theoretic foundation of sedimentary environment interpretation in this area,and has strong applicability to petroleum exploration.
万方数据
维普
