The Study On Well Logging Evaluation Method Of Salty Water Flooded Reservoir In W Oil Field

The water-cut increases rapidly in W oil field in the west of the South China Sea,and partial blocks of it are in the middle or high water-cut stage.It's found that the self-potential log isn't a general and effective well logging technique in the research area,so the self-potential log can't be used to calculate the formation resistivity with mixed fluid in water flooded reservoir.Besides,a lack of complete logging evaluation system of salty water flooded reservoir will lead to the restriction of development processes,so this paper will focus on the study on well logging evaluation method of salty water flooded reservoir in W oil field.Based on the W-S model and Archie's formula,the numerical simulation formulas proved that the cementation exponent and saturation exponent would increase with the increase of the conductivity of formation water respectively.Through the error analysis,it was found that the impact on the result of the water saturation of the dynamic cementation exponent and saturation exponent can be ignored.Through the changing mechanism study of geological parameter of water flooded reservoir,three influence factors which includes the medium-stronger velocity sensitivity,the exceeding mass concentration and median grain diameter of suspended solids and the scaling cause by the incompatibility of injected water and formation water,were found to be result in the worse pore structure,obvious decreased permeability and remaining oil saturation distributing in lager pore-throat.Based on the oil saturated formation resistivity and the water saturated formation resistivity inversed by the material balance method of variable multiple injected water,the study provide two techniques to identify the salty water flooded layer qualitatively,including the comparison between the real formation resistivity and two inversed formation resistivity,and two rates of resistivity change calculated by the inversed oil saturated formation resistivity and water saturated formation resistivity to identify the water flooded layer.After relevant reservoir parameter interpretation models were established,the material balance method of variable multiple injected water was used to achieved high-precision formation mixed fluid resistivity,water saturation and water cut by adaptive and iterative regression algorithm,which achieves the quantitative evaluation of salty water flooded reservoir finely.Besides the water-cut criterion,two rates of resistivity change,calculated by the inversed oil saturated formation resistivity and water saturated formation resistivity,were used to establish the fine logging interpretation chart of division criterion of water flooded in the study.Finally the combination of qualitative identification method and quantitative recognition method were applied to evaluate the salty water flooded and water flooded finely in W oil field,which was a complete set of logging data processing and comprehensive interpretation system.The real logging data processing of eighteen wells employing this system showed that the interpretation precision of the water flooded reached more than 88 percent,and a very ideal geologic result had been achieved.