Reservoir Characteristics And Controlling Factors Of Sinian Dengying Formation In Southwestern Of Southern Sichuan Basin

Sinian Dengying Formation,the oldest deep marine carbonate strata in Southern Sichuan Basin,have an exploration history of more than fifty years.In recent years,with many testing wells receiving high yield industrial gas flow increasingly,the exploration of Sinian Dengying Formation has made great progress at the Gaoshiti-moxi structure belt of Leshan-longnvsi palaeo-uplift.What’s more,with well heshen 1 of Hebaochang structure and well jingshi 1 of Jingshi structure receiving industrial gas flow at southern-slope palaeo-uplift,it shows that it has great exploration potential in Southern region of Sichuan Basin.A majority of former domestic researchers on Sinian Dengying Formation were focused on Weiyuan,Ziyang and Gaoshiti etc,whereas the research aimed at Sourthen Sichuan Basin are not thorough enough.Aimed at reservoir characteristics and controlling factors on reservoir development of Dengying Formation in Southwestern Sichuan Basin,guided by theories of sedimentology,reservoir geology and tectonics,and based on analyses of the sedimentary environment and geotectonic background of the Sinian Dengying Formation in whole Sichuan Basin and Upper Yantze Platform,combined with outcrop observation and well logging data,this paper has made a detailed research on stratum and sedimentary facies of the study area.Through the combination of measuring residual thickness on stratum and impression method,the Sinian top’s karst landform before Cambrian depositing in Southern Sichuan Basin is depicted.By outcrop observation,core inspection,thin section analyses as well as physical property statistics,this paper describes reservoir characteristics and diagenetic evolution of Dengying Formation in detail.Based on regional tectonic background,methods of sedimentary-diagenetic evolution process analyses have been employed to find reservoir controlling factors and predict favorable reservoir development zone.Above all,conclusions have been drawn as follows:(1)Each member of Dengying Formation in study area owns segmented feature vertically,which is obvious and easy to divide;Stratum lithology in different area varys a lot on the plane;(2)Dengying Formation,the lithology of which changes little from west to east,derives from upper Yangtze epicontinental deposition,with supratidal and intertidal zone as the main sedimentary microfacies,illustrating that the palaeogeomorphology differs little.(3)Before Cambrian system formed,Moxi-gaoshiti area was karst highland;Laolongba-dawoding area and Gaomuding area were karst platform;Ziyang-weiyuan area and Changning area were karst valley.Meanwhile,the sub sag islocated in Ziyang-weiyuan-changning area was erosion genetic rather than rift genetic.(4)The reservoir rock types are mainly algae dolostone,micritic-powder crystalline dolostone,karst breccias and dolarenite,all of which are deposited in tidal flat environment.The reservoir space are dominated by secondary karst pores and caves,residual pores of botryoidal lace algae dolostone,belonging to fractured-porous or vuggy reservoir type with low porosity and low permeability.(5)Its formation and evolution are controlled by multi-factors,such as sedimentary facies distribution,diagenesis,tectogenesis,paleoclimate and sea level changes.Favorable reservoirs are developed over the top of the 4th member of Dengying Formation and the 2nd member of Dengying Formation,consisting of karst type micritic-powder crystalline dolostone and botryoidal lace algae dolostone separately vertically.However,Karst highland and karst platform are favorable for reservoir development in plane.