Geochemical Characteristics And Geological Significance Of Oil And Gas Fluid Yang Ba Sinian Section In North Sichuan Area

In this paper,the Sinian Dengying Formation in Yangba section of northern Sichuan is taken as the research object.The process of formation and destruction of oil and gas reservoirs was dynamically restored by the inclusions and isotopes of pores,holes,seam mineral,the evolution history of source rocks,the tectonic evolution history,and the characteristics of asphalt.The main understanding is as follows:The Sinian reservoirs are dominated by confined plateau dolomites,and the main lithologies are grain dolostones and algal dolomites.The pore type of the reservoir is a fracture-hole type,which is a low-porosity and low-permeability reservoir with an average face ratio of 1.15%.The main distribution of the face ratio of the Dengying 2 segment is 0.5% to 3% with an average of 1.41%.The major distribution of the face ratio of the Dengying 4 segment is 0.1% to 2% with an average of 0.85%.The face ratio of the top of the Dengying 2 segment and the Dengying 4 segment is relatively high,which is related to the leaching of atmospheric fresh water.Dissolution and tectonic fracturing are the main reservoir pore constructional effects,while compaction,pressure dissolution and silicification are the main reservoir pore destructive effects.The main filling minerals in reservoir pores,holes and seams are dolomite,quartz and asphalt..The order of filling is first-generation columnar dolomite,second-generation fine-coarse-grain dolomite,third-generation pore-filled bitumen,fourth-generation fine-coarse-grain dolomite,fifth-generation quartz,sixth Age-filled asphalt,which correspond to the first phase of brine filling,the second phase of brine filling,the first phase of oil and gas filling,the third phase of brine filling,the fourth phase of brine filling,the second phase of oil and gas filling.The mineral filling sequence and the fluid filling period were the complete records of the reservoir-forming process of the Yangba section in northern Sichuan.There are three major inclusions in the reservoir,which are fluid inclusions in the second generation and fourth generation dolomite in the window of the oil generation and fluid inclusions in the fifth generation quartz in the window of the gas generation.The peak temperature of homogeneous temperature of inclusions on the fourth generation dolomite inclusions is concentrated at 100 ~ 120°C,while the fifth generation quartz inclusions are concentrated at 180~200°C.According to the characteristic peak analysis of laser Raman spectrum,the main components of inclusions are methane and hydrogen sulfide.The results of the isotope analysis of the pores,holes,and seam-filled minerals show that the Sinian exogenous fluid comes from the source rock of the Qiongzhusi Formation,and the hydrocarbon-rich fluids migrate from deep to shallow through the unconformity to the reservoir.Analysis of the sources of asphalt filled in holes shows that the third generation of asphalt is caused by the biodegradation of the first-stage ancient reservoir when it was destroyed at the end of the Caledonian period,and the sixth generation of asphalt is the thermal pyrolysis of petroleum in the second stage of ancient reservoirs.The main source rocks of the Sinian Dengying Formation is Qiomzhu Formation,and the shale in Dengying 3 segment and the dolomites of the Dengying 2 segment also have some potential for hydrocarbon generation but is not a main source rock.The Qiongzhusi Formation and the Dengying Formation are "side-by-side storage" type source rock and reservoir combination.The evolution of oil and gas accumulations has undergone the primary formation of paleo-reservoir,the destruction stage,the paleo-reservoir re-formation phase,the formation phase of the paleo-gas reservoir,the paleo-gas reservoir destruction stage.