Monte Carlo Simulation On N-γ Density Logging And Formation Element Logging

D-T/D-D neutron source models are developed according to the neutron spectrum and the neutron angular distribution of D-T/D-D reaction. A standard calibration well model is built. The transports of neutron and y-ray in the well are simulated using MCNP code. Mixed y-spectrum and inelastic y-spectrum in the Nal detector are obtained for the difference distance and the difference formation density. The relationship between the formation density and gamma count is built, through theoretical analysis.For D-T neutron source density logging, the data of the mixed gamma count in the energy range of2.5to4.5MeV as a function of distance is presented.The result show that the detector should be located in the space of20-80cm. The function relationships between the density and the mixed gamma count are presented. The data of the inelastic gamma count in the energy range of1.0to8.0MeV as a function of distance is presented. The result show that the detector should be located in the space of20-40cm or in the neighborhood of80cm. The relationships between the density and the inelastic gamma count can be approximatively expressed as a linear function. For D-D neutron source density logging, inelastic scattering gamma ray can’t reflect the formation density information. The data of the mixed gamma count in the energy range of2.5to5.0MeV as a function of distance is presented. The result show that the Nal detector should be located at a distance of30-80cm from the neutron source. The function relationships between the density and the mixed y count are presented in this paper.Formation elements logging is used to acquire the content of elements and minerals, through recording the gamma ray produced by irradiating the formation with neutrons. To study the analytical methods with neutron-gamma spectrum, Monte Carlo Simulation is applied. Firstly,by using least squares algorithm, capture y-spectrum of a given formation sample is analyzed. Then, the element contents are obtained by oxide closure model. Finally, the minerals contents are abtained by tranforming the element contents. Results contrast with the preset minerals contents, which preliminary validation the effectiveness of this capture y-spectrum analytical method.