Types,Characteristics And Exploration Targets Of Neogene Lithologic And Stratigraphic Traps In The Southwest Of Huizhou

After 40 years of oil and gas exploration,the main exploration targets in southwest of Huizhou area has changed from structural trap to lithologic and stratigraphic traps,and some lithologic oil and gas reservoirs have been found to be contiguous distribution,but types,characteristics,development model and distribution law of lithologic and stratigraphic traps are not clearly understood,which is the key area for the next step of progressive exploration.Based on the well logging,core,mud logging and seismic data,this paper studies the sedimentary facies types,spatial distribution characteristics and control factors of sedimentary characteristics by constructing a high-precision sequence stratigraphic framework of the lower segments of Hanjiang formation and Zhujiang formation in southwest of Huizhou area,summarizes the types and characteristics of lithologic and stratigraphic traps,and clarifies the controlling factors and development law of formation and distribution of lithologic and stratigraphic traps.According to the reservoir forming conditions of the study area,based on the research results of sequence stratigraphy,sedimentary and lithologic and stratigraphic traps in key areas,the characteristics and distribution law of favorable exploration targets are summarized to predict favorable exploration targets.The research results of this paper are as follows:(1)Optimizing the method of standardization of sequence stratigraphy,and by identifying sequence stratigraphic surfaces,dividing system tract types and selecting sequence boundaries,a high-precision sequence stratigraphic framework under the background of complex phase transition in the study area is constructed.(2)The study area develops marine delta sedimentary system and shallow sea shelf sedimentary system.The near-source area is dominated by marine delta deposit and the farsource area is dominated by marine delta front deposit and shallow sea shelf deposit.The sequence is the main factor controlling the development and distribution characteristics of sedimentary facies,and the southern provenance of the lower Zhujiang formation affects the distribution and development of sand bodies in the far-source area.(3)There are five types of lithologic traps in the study area,including distributary channel lateral sealing lithologic trap,delta lobe lateral sealing lithologic trap,regressive delta front sand-body lithologic updip pinch out trap,progressive delta front sand-body lithologic updip pinch out trap,shelf sand ridge lithologic updip pinch out trap,and two types of stratigraphic traps: transgressive unconformity barrier trap and transgressive stratigraphic overlap trap.(4)The formation and distribution of lithologic and stratigraphic traps is controlled by sequence stratigraphy and sedimentary facies:transgressive system tract has good conditions for the formation of lithologic traps.The fourthorder sequence boundary is high-quality caprock.The distribution of lithologic traps in different fourth-order sequences is different.The sequence stratigraphic boundary has an impact on the formation of lithologic and stratigraphic traps.The development characteristics of lithologic traps in different sedimentary facies zones are different.The types and spatial distribution of sand bodies control the types and development sites of lithologic traps.(5)Lithologic traps in near-source areas are usually developed in transgressive system tracts,lithologic traps in farsource areas are usually developed near the boundary of third-order sequences,and stratigraphic traps are developed near unconformable shoreline ravinement surface.(6)The oil and gas in the study area mainly come from the source rocks of Wenchang formation,with large hydrocarbon generation and good migration conditions.The main factor controlling the formation of lithologic and stratigraphic reservoirs is the combination of reservoir and caprock.Based on this principle,two favorable exploration targets are predicted: the lower stratum of ZJ1-5 fourth-order sequence in XJ23-XJ24 structural belt in the near-source area is exploration target,and the ZJ466 sand-body in ZJ4-7 fourth-order sequence in HZ26-8 area and HZ32-2area in the far-source area is exploration target.