Study On Logging Evaluation Method Of Polymer Flooding Unconsolidated Sandstone Reservoir Parameters In Offshore X Oilfield

Residual oil development in the middle and late stages of oilfield development is of great significance,and polymer flooding is one of the effective methods.The main hydrocarbon-bearing target bed in this oilfield is the lower part of the Paleogene Dongying Formation,and the reservoir belongs to a large river delta sedimentary complex.The natural rock samples provided by Haihai X Oilfield were measured experimentally,and the variation law of resistivity of these samples under three different displacement modes of oil flooding,water flooding and polymer flooding was investigated.The variation law of resistivity with the increase of water saturation was summarized,which laid a foundation for the reasonable interpretation of water flooded zones in oil wells in the area.After reservoir flooding,reservoir physical properties change and logging curve response characteristics change.It is necessary to re-study curve response characteristics in order to find interpretation methods to re-interpret.For this oilfield,the response characteristics of log curves of original reservoir,water flooding and polymer flooding are studied respectively by using sub-well analysis technology.The salinity of polymer injection solution is 9568 ppm and that of original formation water is 6071 ppm.The resistivity decreases after water flooding,and the stronger the water flooding degree,the more the decline,the lower the resistivity value after polymer flooding.The curves of SP,gamma,neutron and density have little change trend,and the response mechanism of logging curve is analyzed according to the change trend of curve response characteristics.Considering the influence of shale and oil and gas on density curve and neutron curve,the model of shale content and porosity is established by eliminating the influence of shale and oil and gas by iteration method.The relationship between irreducible water saturation and permeability with shale content and porosity is found by using core physical experiment data.The model of irreducible water saturation and permeability is established by using shale content and porosity.Aiming at the difficult problem of calculating the resistivity of mixed liquid in water flooded zone,the improved model of parallel resistivity of mixed liquid and the conductivity model of water ion in mixed liquid formation are validated by core data.The method of simultaneous calculating water saturation and resistivity of mixed liquid is established by simultaneous calculating Archie resistivity equation and resistivity equation of mixed liquid.Based on the establishment of pore,permeability and saturation models,a complete set of point-by-point continuous logging interpretation methods for reservoir parameters of polymer flooding is formed.The average absolute errors of porosity and shale content are 1.03% and 2.05% respectively,and the average relative errors of water saturation and permeability are 7.17% and 32.71% respectively.It shows that the interpretation parameters are of high accuracy.It can be seen that the interpretation method has certain reliability and validity.