Geochemical characteristics, forming conditions and resource evaluation of oil-cracking gas as exemplified by the platform area of the Tarim Basin

Abstract

Based on the geochemical characteristics of oil-cracking gas and kerogen-cracking gas revealed by simulation experiments and the chemical composition of natural gases in actual gas reservoirs, two kinds of natural gases with different relationships between C2/C3 and C1/C2, C2/C3 and C1/C3, C2/C3 and 100×C1/(C1–C5) were identified in the Tarim Basin, and proposed further by the authors. The relationship charts of C2/C3 and C1/C2, C2/C3 and C1/C3, C2/C3 and 100×C1/(C1–C5) can be used to effectively distinguish oil-cracking gas from kerogen-cracking gas. Petroleum geological analysis of the oil-cracking gas reservoirs showed that the distribution of oil-cracking gas is mostly related with deep-seated faults or faults with a large fault throw, and the burial depth of paleo-oil reservoir is relatively high; crude oil-cracking gas resources have been evaluated by using both forward and inversion methods. The plots of C2/C3 vs. C1/C2, C2/C3 vs. C1/C3, and C2/C3 vs. 100×C1/(C1–C5) were used to distinguish between oil-cracking gas and kerogen-cracking gas, and estimate the mixed ratios of the two kinds of natural gases in the main gas reservoirs of the platform area.