An Improved Method to Accurately Estimate TOC of Shale Reservoirs and Coal-Measures

Abstract

Total organic carbon content is the important parameter in determining the quality of hydrocarbon source rocks. To accurately evaluate the TOC parameters of shale reservoirs and coal-measure shale reservoirs, the method to improve the accuracy of a reservoir TOC parameter calculation is investigated using the continental shale A1 well, the marine shale B1 well, and the marine-continental transitional shale C1 well as examples. Each of the three wells characterize a different paleoenvironmental regime. The ∆log R method based on natural gamma spectroscopy logging is proposed to calculate the TOC of shale reservoirs, and the dual ∆log R method based on natural gamma spectroscopy logging is proposed to calculate the TOC of coal-measure shale reservoirs. The results show that the proposed new method can reduce the absolute error by about 0.06~7.34 and the relative error by about 6.75~451.54% in the TOC calculation of three wells. The new method greatly expands the applicability of the ∆log R method and can effectively assist in the exploration and development of shale and coal-measure shale reservoirs.