Compensated neutron log responses of cased holes in hydrogen storage strata

This study investigated the compensated neutron log (CNL) responses of cased holes placed in hydrogen storage strata, aiming to quantify the impacts of casing on neutron porosity measurements, with emphasis placed on hydrogen-bearing strata. Using the Monte Carlo numerical simulation method, the models of open and cased holes were constructed to simulate the CNL responses under varying porosity and hydrogen saturation conditions. Furthermore, the relationship between the neutron count ratio from long- to short-distance detectors and the formation hydrogen index (HI) was analyzed. The analytical results indicate that the application of the casing and cement sheath may lead to an underestimation of the apparent HI in the cased hole, with the offset showing a non-linear increase with formation porosity and hydrogen saturation. Based on this, a fitting model incorporating formation porosity, hydrogen saturation, and HI offset was established, yielding a fitting accuracy of 0.9936. Therefore, this model enables effective quantification of the HI offset induced by casing under the condition of varying porosity and hydrogen saturation. Overall, the results of this study can provide a theoretical basis for interpreting the CNL data from cased holes placed in hydrogen storage strata.