Multiple linear regression approach for the vitrinite reflectance estimation from well logs: A case study in Sargelu and Naokelekan Formations – Shaikhan-2 Well, Shaikhan oil field, Iraq

The sonic and resistivity logs for Sargelu and Naokelekan Formations in well Shaikhan-2 are utilized to predict vitrinite reflectance values. The precise prediction of vitrinite reflectance can be done based on well logs by applying multiple linear regressions method. This method is an extension from the regression analysis, which incorporates independent values to predict a dependent value. It is expected that both sonic and resistivity log readings in source rock that has reached oil window and hydrocarbons are cooked out of that, to be higher than source rock that is still in diagenesis stage and has not produced any oil and gas. Possible mechanisms to explain decreasing resistivity with increasing maturity include the existence of a conductive petroleum phase (pyrobitumen) and the increase in residual water salinity driven by water vapor solubility in the produced gas. The best matching between the vitrinite reflectance measured from the cutting samples and the vitrinite reflectance predicted from the log data in the well Shaikhan-2 has achieved.