Research On Log Evaluation And Method Of Cased Water Flooded Reservoir In X Oilfield Based On Numerical Simulation

In order to improve the production of water flooded reservoirs,researchers at home and abroad currently use neutron lifetime logging technology to interpret and evaluate the remaining oil saturation of water flooded reservoirs.X Oilfield is facing a critical moment of stable production during the medium to high water cut period.Due to different water injection production methods,complex changes have taken place in the properties of underground fluids and stratum structure after water flooding.It leads to difficult selection of interpretation parameters and correction of influencing factors,and low interpretation accuracy of water flooded layers.Based on neutron logging,this paper starting from the theory and principle of neutron lifetime logging technology,and comprehensively applying Monte Carlo numerical simulation method to solve the random sampling problem of particles in nuclear logging.The different response laws of neutron logging are studied,and the spatial response distribution characteristics of thermal neutrons are determined through simulation.The lateral and longitudinal detection ranges of neutron lifetime logging technology are obtained.Combined with the measurement characteristics of the azimuth gamma imaging logging tool,the imaging law of the deviated well formation based on the principle of neutron lifetime logging is studied and determined,and can be further extrapolated to the imaging monitoring of remaining oil saturation.Through simulation of its influencing factors,it is found that the fluctuation error of the counting rate during logging and the borehole environment have a small impact on its measured values,while the reservoir characteristics have a large impact.It indicates that the framework,shale,formation water salinity,and oil saturation are highly correlated with saturation interpretation,and based on this,it is proposed to establish porosity capture cross section charts for qualitative identification of water flooding levels under different formation water salinity.According to the complexity of interpretation of remaining oil saturation in water flooded reservoirs,by establishing a reservoir model consistent with the threedimensional stratigraphic structure and matching neutron lifetime logging tools,the actual logging results can be basically approached.The theoretical accuracy and error range of residual oil saturation interpretation for simulated formations were analyzed,and a interpretation method for calculating residual oil saturation based on the formation capture section of the volumetric model was determined.Conduct physical property research,saturation logging technology comparison,and applicability analysis of logging tools on the target block to determine that the measurement results of the saturation logging tools applied in X Oilfield are available.In qualitative identification and quantitative evaluation of water flooding in T area,it is found that the genesis of its low resistivity is a favorable factor for saturation logging interpretation.Moreover,the effect of identifying the degree of water flooding in highly mineralized reservoirs using the porosity capture cross section plot is significantly better than that using the porosity resistivity plot.The calculation models for porosity,shale content,and remaining oil saturation were established using open hole data and production data from X Oilfield.Combining the water production rate and water saturation data from core analysis,the water flooding classification criteria were determined.Using a multiple linear regression model optimized based on particle swarm optimization(PSO)to optimize interpretation parameters,the goodness of fit of the multiple linear regression model was improved from0.8215 to 0.8973,with a significant improvement effect.The results show that the remaining oil saturation interpretation results obtained by using the optimized interpretation parameters for logging evaluation of remaining oil saturation,combined with the potential layer identification chart established by production data,have a high coincidence rate with production verification data.Based on the response laws and influencing factors of neutron logging determined by numerical simulation,this paper provides a certain reference value for the research and correction direction of neutron lifetime logging,and obtains a qualitative identification chart from a theoretical perspective.The error of residual oil saturation interpretation based on formation capture cross section of volume model is revealed from the interpretation of residual oil saturation in simulated formations.In the interpretation of water flooded zones in X Oilfield,the comprehensive evaluation method of determining the legal identification of the plate and calculating the remaining oil saturation has a good effect.This method can be used to guide the field work of production interpretation,with high universality and popularization value,and can provide a new solution for the interpretation and evaluation of water flooded layers.