Characterization Of Reservoir Heterogeneity And Petrophysical Facies Under Sequence Framework

As the largest oil and gas bearing basin in China,the Tarim Basin is a large reservoir of oil and gas exploration,and Donghe sandstone,a typical representative of the marine clastic rock,is one of the most important objects in the exploration and development of oil and gas.In this paper,the Donghe sandstone in the block Ka-1 of the Tarim Basin is studied.The heterogeneity of the reservoir under sequence framework and the study of rock physical facies are carried out through the core observation and combined with the normal thin sections,casting thin sections,scanning electron microscopy,cathode luminescence analyses,mercury injection capillary pressure analyses and conventional logging data.The paper has obtained the following achievements and recognition:1.We made clear the formation of Donghe sandstone unit and determined the development era.On the basis of the systematic combing of the Donghe sandstone division and evolution,combined with the previous research results of spores fossils,five lithostratigraphic units are divided according to the lithologic section: the lower sandstone section,the middle mudstone section and the upper sandstone section(the above three units are equivalent to the traditional Donghetang formation,or the Donghe sandstone section),the gravel and the lower mudstone.The section(formerly divided into the Early Carboniferous Bachu formation),collectively known as the "Donghe sandstone",is different from the previous understanding of the Early Carboniferous products of the gravel and lower mudstone segments.2.The sequence stratigraphic framework of the Donghe sandstone is constructed.Depending on the field outcrop,core observation,logging curve and seismic data to identify and divide the key sequence of sequence,the Donghe sandstone is divided into 6 three sequence sequences,that is,the sand body is divided into 6 stages,from lower to SQ1-SQ6,and Q1-SQ3 corresponding to the lower sandstone section,the middle mudstone section and the upper sandstone section of the Donghetang formation.SQ4-SQ6 corresponds to the gravel and sandstone section of Donghe formation.In the study area,Ka-1 block is affected by structural factors,and only develops SQ4-SQ6,that is 3 stages of sand bodies.3.we have made clear the types,characteristics and evolution of sedimentary facies in sequence framework.Through the study of 7 types of facies markers,such as rock color,lithofacies,sedimentary structure,granularity,profile structure,log facies and seismic facies,two types of sedimentary facies are divided in Ka-1 block.It is considered that SQ4-SQ5 mainly develops shore bank deposits and SQ6 mainly develops continental shelf deposits,indicating that the Donghe sandstone sink is deposited with the development of different sequences.The accumulating area gradually expands from west to east,so as to establish the sedimentary model of Ka-1Donghe sandstone.4.we compared the three stage sandbody heterogeneity characteristics in the sequence framework.By analyzing the macro heterogeneity(inhomogeneity in layer,interlayer heterogeneity and plane heterogeneity)and microscopic heterogeneity in each period,the heterogeneity of SQ4-SQ5 sand body is weaker than SQ6,and SQ4 is the weakest.The optimum range of sand body in sequence framework is clarified,and it is revealed that reservoir heterogeneity is controlled by sedimentation,diagenesis action and tectonic factors,and the main factors are sedimentary and diagenesis.5.We use petrophysical facies to predict high-quality reservoirs in the study area for the first time.In the range of sand body optimization,based on the factors of heterogeneity control,the lithology and lithofacies of the Donghe sandstone in the study area are named and divided under the principle of lithology,lithofacies,diagenesis and tectonic facies,and 8 petrophysical facies are obtained.The petrophysical facies of Donghe sandstone reservoir are quantified to solve the problem of lithologic identification and reservoir division of non coring drilling,and a reliable basis for finding high quality reservoir development sites is provided.6.Through the division and comparison of petrophysical facies in the study area,according to the physical characteristics,the medium compacted medium cemented strong dissolution phase-the fine sand rock phase-no fissure facies(I type),medium compaction medium cemented strong corrosion phase-the shoreline beach bar fine sand facies-fractured facies(II type),strong pressure medium cemented medium corrosion facies-shore bank dam The medium-coarse sand facies-non fractured facies(III type)are divided into dominant lithofacies,mostly developed in the SQ4 sequence,concentrated in the beach bar facies area,and the sequence framework controls the dominant petrophysical facies,and the sedimentary facies are the material basis of the dominant petrophysical facies,and the dissolution is the key to the formation of the dominant petrophysical facies.Cracks are complementary to the formation of dominant rock physical facies.Combined with the characteristics of this area,we summed up the logging identification marks of the dominant petrophysical facies,which provided theoretical guidance for the study of petrophysical facies in similar areas.