Gravity Flow Sedimentary Characteristics Within High-frequency Sequence Framework And Favorable Reservoir Controlling Factors Of Chang6 Oil Formation In Huaqing Area

In recent years,marine deep-water gravity flow exploration shows huge proved reserves,deep-water gravity flow deposition has become the focus of researchers and attracted people's attention.Gravity flow deposits rich in oil and gas resources,both marine gravity flow sand bodies and continental lake basin gravity flow sand bodies are good reservoirs.Previous studies on gravity flow mainly focused on marine basins.There are many similarities between continental lake basin gravity flow deposition and marine gravity flow deposition,but the research on continental gravity flow deposition should be different from marine gravity flow due to the difference of tectonic background.Chang 6 member in Huaqing area is typical deep-water gravity flow deposit,this paper is based on the theoretical basis of sedimentology,sequence stratigraphy and reservoir geology,this paper studies the high-frequency sequence,sedimentary microfacies and reservoirs of Chang 6 oil formation in Huaqing area,the following main understandings are obtained:(1)Based on outcrop,core,well logging and other data,combined with previous studies,Chang 6 oil formation in Huaqing area is a transgressive half cycle of third-order sequence,Chang 6 and the overlying Chang 4+5 oil formation are a complete third-order sequence.High-frequency sequences are identified by combining Fischer diagram,logging curve wavelet transform analysis and spectrum analysis.Three third-order sequences(pss1-pss3),seven fifth-order sequences((1)-(7))and more than 50 sixth-order sequences can be identified in Chang 6 member.The high-frequency sequence framework in Huaqing area is built,then the development characteristics of strata within the high-frequency sequence framework are studied.(2)Based on the data of core,thin section,scanning electron microscope,cathodoluminescence,X-ray diffraction,12 lithofacies types of Chang 6 member in the study area are identified,including pebbly sandstone lithofacies(LF1),mudstone tearing debris sandstone lithofacies(LF2),pure sandstone lithofacies(LF3),pebbly mudstone lithofacies(LF4),massive mudstone lithofacies(LF5),sandstone mudstone couplets lithofacies(LF6),normally graded sandstone lithofacies(LF7)Inversely graded sandstone lithofacies(LF8),inversely to normally graded sandstone lithofacies(LF9),sliding sandstone lithofacies(LF10),slump sandstone lithofacies(LF11),slump mudstone lithofacies(LF12)and six types of lithofacies associations,namely,sliding-slump and sandy debris flow lithofacies superimposed associations(LA1),multi period sandy debris flow superimposed lithofacies associations(LA2),sandy debris flow and argillaceous debris flow superimposed lithofacies associations(LA3),sandy debris flow and turbidite superimposed lithofacies associations(LA4),sliding-slump and turbidite superimposed lithofacies associations(LA5),multi period turbidite superimposed lithofacies associations(LA6).On the basis of lithofacies division,the sedimentary microfacies are identified,the distribution characteristics of sedimentary microfacies within high-frequency sequence framework in Huaqing area are studied,and the gravity flow sedimentary model is built.(3)Arkose sandstone and lithic arkose sandstone are mainly developed in Chang 6 reservoirs,with intergranular pores and feldspar dissolved pores being extremely developed.The reservoir has experienced four diagenesis types: compaction-pressure dissolution,metasomatism,dissolution and cementation.On the whole,the reservoir has reached to phase A of medium diagenesis.Based on the data of high-pressure mercury injection,constant velocity mercury injection,nano CT and nitrogen adsorption,pore throat characteristics of the reservoir are described by multi-scale and full-scale diameter.The reservoirs have the similar characteristics as type II and III high-pressure mercury injection curves,type III constant velocity mercury injection curves.Nano pores are mainly mesoporous(4)The reservoir genesis in the study area is complex,which is mainly controlled by tectonism,high-frequency sequences,lithofacies,sedimentary environment and diagenesis.On the basis of the comprehensive analysis of various control factors,the distribution law of favorable reservoirs is analyzed.On this basis,the next exploration direction is analyzed and the favorable areas are predicted.