The influence of intense weathering on the evaluation indexes of hydrocarbon source rocks: A case study of Carboniferous-Permian Strata of Ejin Banner and its neighboring areas

Based on a comparative study of the hydrocarbon source rocks evaluation indexes of organic matter abundance, type and maturity between samples from four shallow drill holes and outcrop samples of Permian Maihanhada Formation, Aqide Formation and Haersuhai Formation, and between core samples of XT9 well and outcrop samples of Ganquan Formation of Dahulishan section, the authors hold that the influence range of intense weathering on the source rocks evaluation indexes of organic matter abundance and normal type (H/C-O/C) is over 50m, and the extents of influence on various evaluation indexes are somewhat different.The influence on TOC is minimum, the influence on the potential hydrocarbon generation amount is maximum, and the influence on the biomarkers indexes is comparatively insignificant. On such a basis, organic matter types of outcrop samples can be effectively divided. The influence range of intense weathering on the vitrinite reflectance (Ro) is less than 10 m.