A Novel Method for Calculating Irreducible Water Saturation of Tight Gas Reservoir

Abstract

Summary The complex pore structure of tight gas reservoir makes it difficult to accurately calculate the irreducible water saturation. In order to solve this problem. A novel method for calculating irreducible water saturation is proposed in this paper. Firstly, based on the morphology of NMR T2 spectrum and the value of irreducible water saturation, T2 spectrum is divided into three types. Secondly, the Gaussian distribution function is used to fit (NMR) T2 spectrum, and the fitting parameters are extracted, which are classified by decision tree algorithm, and the actual T2 spectrum classification standard is established. Thirdly, the capillary pressure curve (CPC) was fitted by variable scale power function (VSPF) respectively. Finally, taking the minimum root mean square error (RMSE) between the irreducible water saturation measured by 21 NMR experiments and the corresponding irreducible water saturation under each cumulative contribution rate of permeability (CCROP) as the objective function, the CCROP and irreducible water saturation is determined. The core experimental results show the irreducible water saturation calculated is in good agreement with the core experimental results, which verifies the accuracy of this method. The results for logging data are compared with NMR experimental data to verify the practicability and effectiveness of this method.