Combination of Inorganic and Organic Geochemistry to Study Mechanism of Carbon Isotope Anomalies of Natural Gas

Abstract

Summary The carbon isotope value of natural gas is the most stable and widely used geochemical fingerprint. It can be used to identify genetic types, source rocks, and thermal maturity of natural gas. If carbon isotope values appear in neither of the positive or negative series, but are arranged in a disordered pattern, it is defined as a partial carbon isotope reversal. The mechanism of carbon isotope reversal is still unclear, which has brought controversy and perplexity to the study of natural gas.The Ordos Basin is China’s main natural gas producing area, and its natural gas production accounts for more than one-third of China’s total. Carbon isotope reversal occurs in the Ordos Basin. Previous studies have focused mainly on organic geochemical characteristics, such as natural gas composition, carbon and hydrogen isotopes, and source rock evaluation. However, very few scholars have studied the inorganic geochemical characteristics of the OMFD to illustrate the carbon isotope anomalies. This study took the inorganic geochemical characteristics of the OMFD as a breakthrough point and combined inorganic geochemical parameters with organic geochemical responses. On this basis, the causes of natural gas carbon isotope anomalies have been studied.