Experimental Research On Reservoir Microstructure And Percolation Characteristics For W Oilfield

W sag is a lithologic hydrocarbon accumulation area dominated by low porosity and low permeability reservoir.Compared with structural reservoir,lithologic reservoir is special and complex because the reservoir zonation is controlled by lithology and physical properties,so the evaluating technologies and methods for microscopic pore structure and flow mechanism are different from those for structural reservoirs.Problems encountered in waterflooding development of low permeability reservoir include mainly rapid drop of the formation pressure,a serious lack of energy,fast oil production decline with a great amplitude,quick rise of injection well pressure,and poor water absorbing capacity,which result in great difficulty in waterflooding.This paper studies Stengel and Aershan reservoirs(glutenite)of low permeability in the blocks of Wells Tai27,Tai53,and Tai17,W oilfield.The study focuses on the microscopic structure and factors influencing waterflooding development.Porosity and permeability,pore types and their characterisitics,and physical properties of the reservoir rock throats are systematically investigated and the petrophysical properties of every block are evaluated in detail using techniques such as conventional physical property,cast thin section identification,mercury injection capillary pressure measurement,and constant mercury injection.The effects of microscopic pore structure and mobile fluid percentage on seepage flow performance of low permeability reservoir fluid and the waterflooding development are studied in depth using nuclear magnetic resonance and mercury injection associatively.Nonlinear seepage theory for low permeability reservoir is established based on the specific presence of actuating pressure in the low permeability reservoir.Mechanism for reservoir damage caused by waterflooding combined with the data of clay mineral analysis,and the sensitivity of reservoir is entirely evaluated,including mobile oil saturation,displacement efficiency,relative oil and water permeabilities,and factors influencing waterflooding development.Development of the low permeability glutenite reservoir of W Oilf ield is extremely difficult due to the low grade of oil reserves.Microscopic pore structure and percolation of the study area of W Oilfield are systematically analyzed in detail for the first time through comprehensive physical simulation.The development potential of the reservoir is reasonably proved,and multiple control factors influencing waterflooding are evaluated comprehensively,which provide technical supports for the understanding of low permeability reservoir and the reasonably efficient waterflooding development.