Evaluation of pore structure in low permeability reservoirs based on common well logs

The pore structure of low permeability reservoirs has important influences on the porosity,permeability and oil productivity.It is a hot point in the low permeability reservoir study.Most of the pore structure studies are focused on laboratory test methods and new well logging technologies.A method of evaluating the reservoir pore structure of low permeability reservoirs is urgently needed.In this study,the low permeability reservoir of Cretaceous in the Tanan depression is taken for example.The thin slices,porosity and permeability tests,capillary pressure test are in combination with the well logs.Reservoir Quality Index is chosen to realize the common well logs interpretation of pore structure parameters(average radius of pore and throat,replacement pressure)indirectly.The pore structure types of the reservoir are evaluated with these parameters.In the study area,there develop the reservoirs with four types of pore structure including the pore-connection type,pore semiconnection type,fracture and microfracture type and tight type.The first and second ones are the main types.The storage space type,the capillary pressure curve and the porosity and permeability properties of each reservoirs are different.Analysis of the well testing sections for Well W30 and Well W49 show that the pore structures of the reservoir controls the oil productivity of low permeability reservoirs in the study area.