The Comprehensive Evaluation Of Low Permeability Sandstone Reservoir Of E₂s₃² In Wa77 Block Of Dawa Oilfield

From the coring observing,the lithology of Wa77 block varies greatly,medium coarse sandstone-fine sandstone-siltstone reservoir are thin interbedded,the thickness of single sand layer is between 0.2-0.3m,and the physical properties are poor,it is a low permeability sandstone reservoir.According to the previous experience,the lithology of the conventional sandstone reservoir was identified by Rt curve.However,the longitudinal bed resolution of the RT curve is bad(only 0.6m)and affected by the surrounding rocks easily,it cannot effectively identify the lithology in this area.Therefore,the comprehensive evaluation of the reservoir is affected.Combined with the drilling coring data,laboratory data,formation testing,pilot production and the well logging information,the areal geological features,sedimentary characteristics,reservoir rock characteristics,pore structure characteristics,reservoir physical properties and reservoir oil-bearing characteristics of Wa77 Block were studied.By screening the sensible logging curves to identify the reservoir lithology and using seismic techniques to predict the distribution of reservoir and combined with the conditions of reservoir capacity for a comprehensive evaluation of the reservoir in this block.This can lay the foundation for reserves submitting and basis for formulating the development plan in Wa77 Block.The recognition and achievements are as follows:(1)Geological features research:By producing a single well synthetic seismogram accurately to calibrate the reflection layer of top and bottom boundary of each stratum on the seismic section.Combining regional geology and stratum development characteristics to determine the structure of the target area is near east-west direction and south inclined monoclinic structure.The fault goes north to the east which is mainly distributed in Shahejie formation to the basement stratum.(2)Sedimentary characteristics research: Lithological features,probability accumulation curve of particle size and characteristics of single well natural potential curve were used to determine the fan delta frontal deposits and the main development of the underwater branch channel sand body.Through analyzing the drilling data and palaeogeomorphic inversion,determined that the source is from the central bulge of the southeast side.(3)Reservoir comprehensive evaluation:Based on the data of core analysis and oil test,the lithology,physical property and oiliness of reservoir are studied and optimum logging curve to identify the lithology of thin interbeddings and then research the lithology and electric property of the reservoir.Through the study of the relationship among the four properties of reservoir,the favorable reservoir is determined.Combined with reservoir prediction technique,the distribution characteristics of reservoir in space are predicted.Combined with reservoir production capacity,and comprehensively evaluates reservoir.(4)The research results of this project are used to calculate the proved reserves and provide basis for the development of programming in Wa77 block.