Favorable Main Controlling Factors Of Paleogene Wenchang Formation In The Southwest Of Huizhou Sag Of Zhuyi Depression

Huizhou depression is one of the most hydrocarbon-rich depressions in the east of the south China sea.Due to the influence of paleogene burial depth and low porosity and low permeability of reservoir,huizhou sag oil field is mainly found in neogene Marine strata.With the deepening of exploration in paleogene in recent years,commercial or potential commercial discoveries have been made in structures such as hz19-1,hz19-2,hz25-4 and hz25-7,revealing good exploration potential of paleogene in huizhou depression.However,the wenchang formation in huizhou sag has a large burial depth,strong reservoir heterogeneity,unclear understanding of diagenesis and reservoir characteristics,and no in-depth analysis of the main controlling factors of favorable reservoirs has been made,which restricts further oil and gas exploration in this area.The study survey of previous research achievements of predecessors,with sedimentary petrology,reservoir physics,oil and natural gas geology,lithofacies paleogeography theory as the foundation,adopted from the cm level-millimeter-micron level of core observation to thin section microscopic identification and scanning electron microscopy(sem)analysis of the combination of macro and micro experiment means,on the basis of mudstone vitrinite reflectance,fluid inclusion cervix temperature,carbon and oxygen isotope determination of advanced testing methods,such as system of wenchang group in the studied area sandstone sedimentary characteristics,petrological characteristics,reservoir characteristics,diagenesis characteristics are analyzed and summarized,The main controlling factors of the sandstone reservoir of wenchang formation in the study area are clarified.Fan-delta facies and lacustrine facies are mainly developed in wenchang formation of huizhou sag.The sandstone of wenchang formation is dominated by lithic arkose,which is characterized by "rich feldspathic and poor lithic",with medium component maturity and low structure maturity.The reservoir space of the wenchang formation is diverse,mainly composed of granular pores,with many extra-large pores and small throat channels,and low porosity and permeability.It is a low-porosity and ultra-low-permeability reservoir.At present,the sandstone of wenchang formation has evolved to the stage of meso-diagenesis A,and its diagenesis is relatively complex,mainly including destructive diagenesis(compaction,cementation)and constructive diagenesis(dissolut ion,hydrocarbon filling and fracture),and the main autologous mineral precipitation mechanism has been clarified.According to establish reservoir classification evaluation standard,wenchang group of favorable reservoir porosity lower limit is 12%,the lower permeability of 3 md,comparative analysis on the different types of reservoir favorable reservoir characteristics as follows: the sedimentary environment of distributary channel,mouth bar and high-energy environment,igneous rock debris content in rock is high,low content of cement and mixed base,sorting roundness are better,the coarse grain size,early hydrocarbon filing.