Sedimentary Facies And Reservoir Characteristics Of Permian Qixia Formation, Southwestern Sichuan Basin

This paper takes the Qixia Formation of southwestern Sichuan basin as theresearch object, guided by multi-disciplinary theory of sedimentology and petroleumgeology, adequately applying with field outcrops, drilling section, well logging andseismic section, with sedimentary evolution–lithofacies paleogeography evolution–reservoir evolution as the main line, combining outdoor macro geological observationand indoor micro analysis, sedimentary facies and characteristics of reservoir weresystematacially researched.Southwestern Sichuan basin deposited huge thick marine carbonate sediment inQixia period. Through the research of sedimentology sign, paleobiology sign and logfacies sign, the sedimentary facies of researched area can be divided into open sea(inter-bank sea) and inner platform bank subfacies, and the characteristic of eachsunfacies and microfacies were took a deeper research. On the basis of the connectioncomparison of wells and profiles, the temporal and spatial distribution of thesedimentary facies and vertical evolution characteristics of paleogeograhpy had beenanalysed systematacially. The results showed that the inner plateform banksdeveloped in the second section of Qixia Formation were much more than thatdeveloped in first section; meanwhile, the banks in the south and west parts of studyarea were much more developed than that in the north and east parts.Through theanalysis of vertical evolution of sedimentary facies, Qixia formation was divided intotwo sedimentary cycles. Taking the cycles as unit, lithofacies paleogeography mapswere produced, and the result showed that most of the research area was covered byopen sea subfacies in the first cycle of Qixia period, while in the second cycle ofQixia period, the area of Yaan-Emei-Shawan and Zigong are covered by banksubfacies.According to the lithology characteristic and kinds of test and analysis results, itindicates that the characteristics of reservoir rocks and reservoir space in research area.Resevoir rocks mainly included dolomitic limestone, limy dolostone andpowder-macrograin crystal dolostone; Reservoir space was comprised ofintercrystalline pore, intercrystalline corroded pore/intergranular corroded pore andcorroded cave. Through the relationship of these pores and caves, reservoirs could be divided into slit-pore style, slit-cave style, pore style and cave style, and the mostimportant reservoirs were slit-pore style and slit-cave style.Through the comparation of physical parameter from different reservoir rocks,we found that: macrograin crystal dolostone has a very good physical property, and itowned a reservoir with high porosity and permeability, however, dolomitic limestoneand limy dolostone have a reservoir with poor physical property. Combining withprevious research and regional structure, we discovered that: there were three factors,which included sedimentary facies, diagenesis and fracturing action, affected thedevelopment of reservoirs. Sedimentary facies were the material basis of reservoir,and it decided the temporal and spatial distribution of earlier reservoir; diagenesisdecide the quality of reservoir; fracturing action made reservoir own fracture, andimproved the capacity.