Investigating the Effect of Gamma Ray Source Activity on Down-hole Nuclear Density Tool’s Reading Using Simulation by MCNP Code

Developing well logging methods will increase the applications of logs related to all the other geology sciences. Well logging curves introduce the essential information to evaluate reservoir characterizations, rock type and also formation fluid properties quantitatively. One of the most important parts of drilling and completion operations which affect making decision about the future planes is based on how logging data is acquired and interpreted precisely and completely. Litho-density logging tool is a nuclear tool measures formation density and indicating its lithology. Therefore the accuracy of tool measurements is significant. Cs137 is the radioactive source inserted in the tool for downhole measurements. Formation density and lithology are measured by gamma ray Compton scattering and photoelectric absorption phenomena respectively. In this approach, simulation of density tool using MCNP code is discussed to figure out the effect of radioactive sourcechr('39')s activity on the output of energy spectrum belongs to shale, sandstone and limestone formations with known densities. The energy spectrum results affect the accuracy of measurements due to either increase or decrease in source activity.