Reservoir Characteristics And Controlling Factors Of The Sinian Dengying Formation In Western Yibin Area,Sichuan Basin

Based on the cores data,casting thin sections,scanning electron microscopy,cathode luminescence,physical parameters,logging interpretation results and seismic data of the Sinian Dengying Formation,guided by the theoretical methods of sedimentology,reservoir geology and tectonic geology,this thesis mainly studies stratigraphic distribution,sedimentary facies evolution and reservoir characteristics with the aim of controlling factors in the western area of Yibin,southwestern Sichuan Basin.The detailed research has obtained the following understandings:The Dengying Formation in the western Yibin area develops 4 members with thicker strata,and the thickness of each section in different areas changes greatly.The formation thickness of the 1^st and 2^ndmember is generally stable,while of the 3^rd and 4^th member gradually gets thinner to the east and completely denuded in the Changning area.The sedimentary environment of the Dengying Formation in the study area is restricted platform,which develops two sedimentary cycles from low to high sea level,including dolomite flat,algae flat and gypsum flat microfacies.The Dengying Formation reservoirs are developed in the 4^th and2^nd Member.The types of reservoir rocks are mainly micritic-powder crystalline dolomite and algal dolomite;the types of reservoir space are diverse,mainly including dissolved pores,intercrystalline pores and fractures,mostly filled by dolomite and asphalt.There are two reservoir types,micro-fracture-intergranular pore type and fracture-dissolved pore type,both with low-porosity and ultra-low permeability.The average porosity of the4^th Member reservior is 1.87%,which is less than that of the 2^nd Member with an average porosity of 1.98%.The development of the Dengying Formation reservoir is controlled by sedimentary facies,diagenesis,palaeogeomorphology and tectonic movements.Sedimentary facies provide a material basis for the development of reservoirs,and the algae flat microfacies which deposit high-porosity algal dolomite are the favorable facies.Diagenesis plays a decisive role in the reservoir capabity.In particular,supergene karstification is the most important mechanism leading to the reservoir development,and dolomite cementation is the main reason for reservoir damage.The karst development is controlled by palaeogeomorphology.The karst uplands and karst slopes of the northwestern study area are conducive to reservoir development.Tectogenesis lift up the strata forming unconformities,and multi-stage fractures formed by the influence of Yanshan and Xishan movements effectively improve the reservoir performance.