Study On The Geological Characteristics Of The Formation Of The Da'anzhai Section Of The Gongshanmiao Area In Central Sichuan

Exploration and development potential of Daanzhai member tight oil in Gongshanmiao area is very large duo to rich hydrocarbon source and reservoir development,the source-reservoir is "sandwich" type,but for low accumulation degree,low single-well production,complex high-yield well control factors,has a certain exploration risk in areas.Based on drilling,testing data,core observation,sample analysis,in combination with the analysis of field geological survey,seismic,logging data,and in tight oil and gas comprehensive evaluation ideas focusing on oil reservoir geological characteristics of Daanzhai member from source,reservoir,and source-reservior association,figured out high quality hydrocarbon source layer and the high quality reservoir distribution area,revealed the source-relations association,determined high-yield well main control factors,established tight oil accumulation pattern,optimized "sweet spot" blocks,provided the basis for exploration and development.Daanzhai Member is deposited by a large fresh water lake facies,on longitudinal experienced a complete sedimentary cycle with lacustrine transgressive?lake retreat,plane sedimentary facies belt around lake basin center presented a ring belt distribution.Half deep lake subfacies controlled the black argillaceous hydrocarbon source rock distribution,while the high-energy shoal and low-energy shoal controlled shelly limestone reservoir distribution range,in which the reservoir for shoal nuclear microfacies is the better,for shoal edge microfacies is a bit poor.Daanzhai Member has the characteristics of black argillaceous hydrocarbon source rock development,big thickness,high abundance of organic matter,organic matter type of ?1 and?2 type,hydrocarbon source rock thermal evolution in the stage of mature to high mature;oil source correlation by biomarker compound shows that the crude oil and source rock rearrangement hopane content high,rules of hopane content is low,oil and source can be compared,but with the oil of Lianggaoshan Formation and Shaximiao 1 Member have obvious difference,which belongs to self-sourcing self-storing and near-source oil charging pattern.The reservoir rock types of Daanzhai Member are sparry shelly limestone and argillaceous shelly limestone,overall reservoir physical property is of low porosity,low permeability,but local development with high holes.There are three types of reservoir space containing solution cave,matrix pore and fracture,in which fractued-hole type reservoir is the best.The best high quality reservoirs may affected by multiple factors of high-energy shoal,low-energy shoal microfacies,dissolution and fracture,I class reservoirs are mainly distributed in high-energy shoal development zone,and ? class reservoirs are distributed in low-energy shoal development zone.Source-reservoir association of Daanzhai Member in Gongshanmiao area is located in source-reservoir interbed delt in horizontal.In vertical source-reservoir association of the upper Daanzhai Member mainly is source-reservoir interbed type,the secondary lower source-upper reservoir type,and basically upper source-lower reservoir type,part source-reservoir interbed type for the lower Daanzhai Member,overall is good.Fractured-porous(hole)type reservoir is one of the most important controlling factors for high-yield well of Daanzhai Member.The period of hydrocarbon accumulation for Daanzhai Member is many times.At the end of Jurassic,Penglaizhen middle to late,hydrocarbon source rock thermal evolution went into the mature stage,oil and gas can be introduced into reservoir matrix pore,near to the early cretaceous to middle,into the high mature stage,due to the limestone was densification,oil and gas need the late solution pores and cracks can gathered into good reservoir in the period of accumulation,and shaped to Himalayan period.In tight oil and gas evaluation idea,according to the high quality hydrocarbon source layer,the high quality reservoir distribution,source-relations association and fracture development communication situation,formulated the "sweet spot" block evaluation standard,optimized the two "sweet spot" blocks available for drilling,provided the basis for the well placement in the horizontal well volume fracturing process test.