Reservoir characteristics and main controlling factors of ultra-deep dolomite in the 4th Member of Sinian Dengying Formation in Penglai area,Sichuan Basin
The Dengying carbonate reservoirs,as one of the primary producing units of ultra-deep hydrocarbon resources in the Sichuan Basin,is required for further studies on their characteristics and controlling factors.This paper focuses on the ultra-deep dolomite of the fourth member of the Dengying For-mation in the recently explored Penglai area of the Sichuan Basin.The study examines the reservoir's petro-logical characteristics,pore spaces,classification of reservoir types,physical properties,diagenetic evo-lution,and the main controlling factors of the reservoirs.The analysis is based on field outcrop profiles,drilling cores,microsections,cathodoluminescence(CL)imaging,scanning electron microscopy(SEM)data,and physical property test results.The findings are as follows:(1)The primary lithologies of the fourth member of the Dengying Formation in the Penglai area include dolo-thrombolite,dolo-stroma-tolite,dolo-spongiomicrobialite,and sand-debris dolomite.The main reservoir spaces consist of primary framework pores and secondary dissolution pores formed by subsequent dissolution processes.(2)Fractured reservoirs,primarily composed of dolo-thrombolite and dolo-stromatolite reservoirs with par-tial bedding pore development,typically exhibit favorable physical properties.The average porosity can ex-ceed 4％,with the average permeability of the former reaching 2.43x10-3 μm2,while the average perme-ability of the latter is only 0.35x10-3 pum2.(3)A comprehensive analysis of diagenetic evolution reveals that the microbial carbonate reservoirs of the fourth member of the Dengying Formation have undergone a sequence of stages:sedimentary-quasi-symbiotic,supergene,shallow-to-medium burial,and deep-to-ul-tra-deep burial stages.(4)Analysis of reservoir distribution patterns in the study area indicates that the reservoir distribution weakens from the platform interior to the platform edge.Overall,the ultra-deep dolo-mite in the fourth member of the Dengying Formation in the Penglai area follows a ternary reservoir model characterized by"sedimentary facies-fault-dissolution."This study provides key insights into the character-istics and controlling factors of the ultra-deep dolomite reservoirs in the Penglai area of the Sichuan Basin,offering significant guidance for future ultra-deep oil and gas exploration in the region.
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