Diagenesis Characteristics and System for Dolostone in Feixianguan Formation of Northeast Sichuan

Through the comprehensive study of the texture-genetic classification,diagenetic manners and evolution stages,trace element characteristics of Fe,Mn,Sr,and isotopic geochemistry characteristics of C,O and Sr of Feixianguan Formation,Lower Triassic in Northeast Sichuan,four diagenetic systems were divided in the dolostone of Feixianguan Formation according to hydrological system,which were pore brine of the penecontemporaneous stage,compaction hot brine of the early and middle diagenetic stages.The character and source of dolomitic fluids of various diagenetic stages and system had certain familiarity and inheritance features of development and evolution,but the interaction process between fluid and rock,diagenetic manners and characteristics of product and assemblage were different respectively.So the diagenetic systems and manner of diagenesis,which are related to the reservoir development closely,are mainly the burial dolomitization and dissolution of multiple-stage.According to the temporal-spatial accordance and matching relations of reservoirs and oil-gas accumulations in different diagenesis systems,four controlling factors of high-quality dolomite reservoirs were concluded:(1) the regional distribution and size of reservoirs were controlled by oolitic shoal microfacies;(2) high-quality reservoirs were based on the burial dolomitization of early and middle diagenetic stages;(3) the distribution of reservoirs was expanded and their quality was improved by burial dolomitization of the late diagenetic stage;(4) tectonic disruption,TSR and dissolution were the key to forming highly-efficient oolitic shoal gas reservoir which contained acid gas rich in H2S and CO2.