Study On The Genesis And Heterogeneity Of Low Permeability Reservoir In Block Fan29 Of Daluhu Oilfield

The ever-increasingly severe situation of oil exploration and development in the world raises people's awareness of the importance of low permeability reservoirs.It is of great significance to study their genesis and heterogeneity characteristics for the efficient oil and gas exploitation.Based on the analysis of the core data,logging data,previous research results and microscopic data of Block Fan29 in the Daluhu Oilfield,this paper describes the petrological characteristics of reservoir rocks,and presents the facies characteristics in single well chart,well correlation profile,and planar facies distribution map.Then thin sections are observed under the microscope to further identify the formation mechanism and controlling factors of low permeability reservoirs.The core and logging data are fully employed to calculate the reservoir physical parameters,analyze the type and distribution of interlayers,characterize the planar distribution of sand body as well as porosity and permeability,and delineate the macroscopic heterogeneity.Eventually,thin sections are combined with mercury injection data to analyze the pore characteristics and describe microscopic heterogeneity.The reservoir sand body of Block Fan29 mainly consists of sublacustrine fan deposits,including subfacies of middle fan,outer fan and lacustrine shale,with the middle fan subfacies dominating.Braided channel microfacies in the middle fan subfacies is the most extensive,which is the product of vertical accretion.Sand bar,braided channel and lobe-shaped sand body are favored for the oil and gas accumulation due to their good physical properties.It is found that sedimentology,diagenesis and tectonic commonly contribute to the formation of the low permeability reservoir in Block Fan29,among which sedimentology plays the main role.In terms of diagenesis,compaction and cementation deteriorate the physical properties of reservoir,while dissolution improves them.Natural fractures produced by tectonism have dual effects on reservoir physical properties.Characterized by the middle porosity and low permeability,reservoirs in Block Fan29 have strong heterogeneity within inner layers and interlayers on the microscopic scale in the plane.The 4~3 single layer has relatively good physical properties due to its relatively weak heterogeneity,and thus serves as the main reservoir.