The Adaptability Of Nitrogen Huff-n-Puff And Its Optimization Parameters In Fault Block Reservoir

Fault block oil fields are widely distributed in eastern China.Their overall recovery efficiency is approximately 25% and still have great potential to improve oil recovery.The structural complexity and reservoir complexity of fault block reservoirs make it difficult for well pattern to control reserves,especially in the late stage of extra-high water-cut development,it is difficult to form injection-production well pattern of extremely complex blocks,high parts of structure controlled by ridges,etc.Due to the lack of effective displacement energy,there are many rich areas of residual oil,how to use this part of residual oil economically and effectively is one of the important directions of reducing cost and improving efficiency of fault block reservoirs.Resulting from nitrogen stimulation effect of Xianhe complex fault block reservoir is quite different;the main mechanisms of nitrogen huff-n-puff in complex fault block reservoir are carried out in this paper by combining oil field static and dynamic analysis,monitoring data analysis and numerical simulation,etc.Mechanisms such as gravity differentiation drive,dilatation energy displacement,and water cut control are three main mechanisms involved during nitrogen huff-n-puff to enhance oil recovery.After that,the sensitivity analysis study of process parameters such as injection rate,injection time and shut-in time that affect nitrogen stimulation operation in fault block reservoirs were carried out,and the optimal range of each process parameter was determined.According to different geological and reservoir fluid parameters,numerical simulation and orthogonal test design are adopted to determine the main controlling factors affecting nitrogen huff-n-puff stimulation process in complex fault block reservoirs.We classified the influencing factors in order of sensitivity: oil saturation,net thickness,water-oil volume ratio,oil viscosity,oil area,permeability ratio,dip Angle,porosity and permeability.Determining the main control factors will help select suitable blocks and Wells for nitrogen stimulation operations.According to the actual well data of an oil field,two Wells from different blocks were selected and the stimulation effect of nitrogen huff-n-puff technology was compared and analyzed.The simulation results proved oil recovery efficiency and the high performance of nitrogen huff-n-puff in fault block reservoir.In terms of enhanced oil recovery,the result of the case1 optimization model shows that the oil recovery factor of the primary production was13.27%,reached 16.68% after a cycle of nitrogen stimulation,and 25.3% after 5 cycles.In case2 well,the oil recovery factor was 17.31% after primary production,38% after a cycle of nitrogen stimulation,and 47.96% after 5 cycles.This provides effective technical support for fault block reservoir to effectively excavate residual oil,reduce cost and increase efficiency.