A new algorithm for evaluating reservoir density based on X-ray logging technology

Highlights: • A reservoir density detection method that does not require mud cake correction is proposed. • The Newton iteration method is applied to the inversion of the formation and mud cake parameters in real-time. • Using the Monte Carlo simulation, the response database of photons with respect to various parameters is established. Rock density is an important parameter to provide critical information for evaluating both conventional and unconventional reservoirs. During the drilling process, it's a huge challenge to eliminating the negative effects of irregular mud cake formed in drilling fluid deposition to evaluating reservoir information accurately. However, the calibration of density measurement by correction charts would usually generate large errors, and the parameters that need to be corrected are often unpredictable. Therefore, based on the X-ray density logging technology, while eliminating the radioactive hazards of the isotope gamma source (¹³⁷Cs), a new method is proposed to address the problem through the energy spectrum information from four detectors. Theoretically, this method would analyze the role of X-rays in the dual media of formation and mud cake and then integrate the energy spectrum information from four detectors, while using Newton iterative inversion to invert the parameters about formation and mud cake. As a result, the evaluation of reservoir parameters can be achieved without correcting the mud cake. In verifying the effectiveness of this method, a simulation example shows the high accuracy of X-ray density inversion for multiple parameters. This research provides an X-ray density inversion algorithm to realize the simultaneous calculation of formation and mud cake parameters, which is of great significance for guiding hydrocarbon exploration and production.