Research On Application Of Electric Potential Method Monitoring The Residual Oil Inoilfield

The oil and gas reservoir are having sharp reduction, which are exploited easilyand of relatively simple type, with large-scale and in-depth development of oil andgas fields. Increasing production of oil and gas depends mainly on the search for newcomplex reservoir and improve the oil recovery of the old oil fields. Since the1990s,the remaining oil and water flooding on the direction and the leading edge are a hotresearch topic in the oil and gas field development work, they are also about theimportant issues of the International Conference. The new methods and newtechnologies of predicting distribution of remaining oil are in urgent need of researchand development. In the article, there are also brief introductions on several othercommonly used residual oil monitoring methods: seismic techniques, tracermonitoring methods， well logging reservoir description method，and elaboratingtheir respective strengths and weaknesses. Compared with those methods, thepotential method has lower cost, higher efficiency, and dynamic monitoring could beimplemented in this method. The method is based on the law principles ofmise-a-la-masse method and the basic theory of the underground dynamicconductor. To make quantitative and qualitative judgments on the distribution ofresidual oil and the flow of working fluid through studying the change of surfacepotential after injecting the working fluid. In other words, the injected working fluidreduce the resistivity of target layer during injecting working fluid, that leads torelatively large differences to the resistivity of surrounding rock medium.In the method of numerical simulation, the total potential is divided into thenormal potential and abnormal potential, we got the normal potential based onpotential formula of the point current source, and the equations of the abnormalpotential using finite difference method. We applied the incomplete Choleskyconjugate gradient method to solve large sparse linear equations and got theexpression of the abnormal potential to eliminate the singularity near the power source. There are discussions on the boundary conditions of total potential, normalpotential and abnormal potential. Based on forward numerical calculation method，inverse problem was linearized, and then applying the smoothness constraint leastsquares method for the calculation of inversion problem, However, by applying thereciprocity principle, the partial derivatives can be very efficiently obtained withouthaving to directly solve the matrix equations a number of times. The basic idea isdescribed in Tripp et al.（1984） and is known as the sensitivity theorem. Accordingto the above algorithm, we simulated three power supplying ways: surface-surface,borehole-borehole, surface-borehole. From the forward and inversion model,weknow that electric potential method has high detection ability on the target body inmodel when surface-borehole power supplying way was used, no detection abilitywhile the other two power supplying ways.There is an experiment in the Zhongyuan Oilfield to verify that potentialmethod’s result is correct. Some blocks of the Zhongyuan Oilfield have entered thehigh water cut stage, the reservoir’s physical properties, pressure field and oil-waterproportion have been changing, and it is not clear about the distribution of residualoil, and exploiting the oil fields more and more difficult. Because of those difficulties，we apply the potential method in these blocks, we got the apparent resistivitycontour maps drawn according to the test data, and they are compared with thesaturation of contour map, we got this conclusion that the potential method can beused for monitoring residual oil. In addition, we also carried out test in the WindyCity Oilfield in Xinjiang using ring measured net. Potential monitoring results werecompared to determine the direction of the proliferation and migration law of thesteam, and we get satisfactory results.