Experimental Study On Relationship Between Oil-water Relative Permeability And Resistivity Of Matrix-conducting Shaly Rock

In recent years,low resistivity reservoirs with a certain reserve have been discovered in many oil fields in the world,and considerable economic benefits obtained.The exploitation value and potential of low resistivity reservoirs are revealed out.However,there are still many difficulties and challenges in the exploration and development of low resistivity reservoirs,such as the evaluation of producing fluid properties and productivity prediction of matrix-conducting low resistivity reservoirs containing pyrite grains.The more complex pore structure characteristics and conductivity laws increase the difficulty of log evaluation,water production rate calculation and productivity prediction of matrix-conducting low resistivity reservoirs.As a key parameter of water production rate calculation and productivity prediction,the oil-water relative permeability is usually calculated by empirical formula method.This method has problems such as strong experience and poor generality.Therefore,in this paper,a model is established to calculate the oil-water relative permeability in complex reservoirs accurately from the resistivity parameters which can effectively reflect the conductive path of movable water and obtained easily.In addition,it can describe the rock seepage law with complex micropore structure characteristics.Twenty-eight matrix-conducting shaly sand samples are manufactured with pyrite,illite,and quartz grains at high temperature and pressure.On this basis,a set of simultaneous measurement scheme for oil-water relative permeability and resistivity from steady-state method and related other experiments for matrix-conducting shaly rock samples are proposed.Porosity-permeability experiments,nuclear magnetic resonance experiments(NMR),simultaneous measurements of relative permeability and resistivity from steady-state method,and mercury injection experiments are carried out on the original samples in turn.X-ray diffraction whole rock analysis experiments are carried out on the parallel samples to ensure the consistency and integrity of the experimental data of each rock sample.The experimental study on the relationship between oil-water relative permeability and resistivity of matrixconducting shaly rock shows that the water-phase relative permeability decreases as resistivity index increases.And the water-phase relative permeability decreases with the decrease of porosity and permeability as well as the increase of clay content and pyrite content.The oilphase relative permeability decreases with the decrease of resistivity index,i.e.(1-1/I).And the oil-phase relative permeability increases with the decrease of porosity and permeability as well as the increase of clay content and pyrite content.Based on the experimental study on the relationship between oil-water relative permeability and resistivity,and the similarity of water and electricity flow,rock seepage law can be better described by rock resistivity parameter reflecting the conduction paths of the movable water.Bending capillary,unequal radius capillary and convergent-divergent unequal radius straight capillary are used to describe seepage and conduction paths of the rock with different micro-pore structures.Combining Darcy's law and Poiseuille's equation with conductivity theory such as equivalent rock element model,three models of oil-water relative permeability and resistivity are established for both matrix-conducting shaly rock and shaly sands.The validity of the models is proved by theoretical analysis and boundary condition test.Three kinds of general resistivity models are established to describe the conductive law of complex rocks with conductive particles,non-conductive particles and dispersed clay,based on the conductivity differential equation,generalized Archie equation and the combination of the two equations.Theoretical analysis and experimental validation show the resistivity model based on combination of general Archie and difference equation is the best to describe the conductive law of matrix-conducting shaly rock.On this basis,two methods for calculating resistivity of hypothetical clean rock with only movable fluid pore are established.The resistivity correction method considering the effect of particle and fluid shape is selected to determine the resistivity index of hypothetical clean rock with only movable fluid pore in the relative permeability model.Finally,the models established in this paper are verified by the experimental data of relative permeability and resistivity combined measurements of matrix-conducting shaly rock with different mineral components and contents.It is proved that the models can effectively improve the accuracy of oil-water relative permeability and make up for the deficiency of empirical formula.The research results in this paper are of great application value for the accurate evaluation of producing fluid properties and the improvement of accuracy of productivity prediction of matrix-conducting low resistivity reservoirs.