Methods for the evaluation of water saturation considering TOC in shale reservoirs

Water saturation is one of the most important parameters in petroleum exploration and development. However, its calculation has been limited by the insufficient logging data required by a new technique that further influences the calculation of the free gas content. Total organic carbon (TOC) is comprehensively considered in this study because it can indirectly control the gas content and saturation. After analyzing the relationship between TOC, core water saturation and conventional water saturation, two new methods are proposed to improve the accuracy of water saturation estimates: the TOC correction method and water saturation difference method, in which Archie water saturation, modified total shale water saturation, and TOC are integrated. According to the case studies, the water saturation results from these two methods in shale reservoirs with different lithology are consistent with those from core analysis. It is concluded that these two methods can quickly and effectively evaluate the water saturation of shale reservoirs.