Study On The Neutron Porosity Correction Method For D-T Source Lwd Measurement

With the extensive application of high-angle wells,horizontal wells and directional wells in the exploration of complex oil and gas fields,LWD has become an important method for geological evaluation of complex oil and gas reservoirs.Neutron porosity as a basic parameter of geological evaluation,is sensitive to environmental factors.Therefore,it is important to survey on the accuracy of neutron porosity measurement in order to evaluate the geology of complex reservoirs,improving the correction method of LWD neutron porosity results.The Monte Carlo numerical simulation method is used as the main technical means for nuclear logging principle,instrument structure design,and logging response research.It has the advantage that overcoming the limitations of time and space and other factors,which has been widely used in the qualitative research of logging response.Due to the lack of a benchmark experiment,conventional Monte Carlo simulation results can hardly reflect the specificity of actual instruments and formation conditions.In order to satisfy actual quantitative experimental requirements,it is necessary to calibrate actual LWD results to adjust MCNP model,which can both guarantee the accuracy of simulation results and complete actual quantitative research.This paper is based on the process of neutrons and the distribution of neutrons.Monte Carlo numerical simulation method was used to study the neutron porosity instrumental detection characteristics of different neutron sources,and the detection advantages of D-T source were compared.Survey on the influence of environmental factors,determining the neutron porosity response rule of different environmental factors,and it is proposed that the measurement results of LWD neutron porosity be corrected.In order to determine the D-T source neutron porosity correction method,MCNP benchmark experiment was conducted for the actual D-T source neutron porosity instrument of CNPC Well Logging Company Limited.Combining the D-T source neutron porosity instrument measured response and Monte Carlo numerical simulation method to fine equivalent Monte Carlo calculation instrument model parameters.Finally,the source distance of near and far detectors in equivalent Monte Carlo model was determined as 35.2 cm and 68 cm.The equivalent Monte Carlo calculation model was used to simulate the neutron porosity response of D-T source LWD instrument whiledrilling dimensions is 4.75 in,6.75 in,and 8in.The correction formulas of different environmental influence factors were determined,and the correction chart of different environmental influence factors was also established.Finally,based on the CIFLog software development platform to program the correction module of D-T source neutron porosity.Through data loading,visual porosity calculation,and correction of environmental influence factors to realize the rapid correction of D-T source LWD neutron porosity data,which is significant technical support for the data processing of D-T source LWD neutron porosity instrument and formation parameter evaluation.