Simulation For Radioactive Well Logging In Fractured And Cavernous Carbonate Formation

Carbonate reservoirs with fractures and caves occupy an important position in the world's discovered oil and gas reservoirs,and have great potential for oil and gas development.However,this type of reservoir has diverse reservoir spatial forms,large differences in fracture and hole sizes,and strong heterogeneity.Therefore,it is very difficult to analyze the geophysical characteristics and predict the reservoir.At present,the combination of imaging logging data,core data and conventional logging data is used to evaluate fractures and reservoir grades of fractured-cavity carbonate reservoirs.However,the cost of imaging logging and coring in actual exploration is very high,so it is difficult to perform imaging logging and coring for all intervals of a well.However,when the scale of the karst cave is large,the measurement results are often distorted,and sometimes the core data and complete conventional logging data cannot be obtained.Therefore,in fracture-cavity carbonate reservoirs,further research is needed on the effect of fracture-cavity morphology and its filling form on radioactive logging in conventional logging.The Monte Carlo method is a calculation method based on the probability statistical theory and has a wide range of applications in particle transportation.Based on the application of Monte Carlo method in radiological logging,this paper uses MCNP software to establish a pulsed neutron log model,a compensated neutron log model,and a compensated density log model.Through a large number of particle transport simulation calculations,the study of the relationship between the width and angle of fractures when filling with different substances and the count ratio of near and far detectors for compensated neutron logging and compensation density logging;the corresponding relationship between the size of the cave and the count ratio of near and near detectors when the cave is filled with different substances.Studies have shown that formation water salinity has little effect on porosity and density;while the shape and filling form of fractures and caves have certain effects on porosity and density,and have certain regularity.Through the comparative analysis of the simulation calculation results,it can provide a certain theoretical basis for the pulse neutron logging data,compensated neutron logging data and compensated density logging data in the evaluation and interpretation of fracture-cavity carbonate reservoirs.