Geochemical Characteristics and Gas Source Comparison Analysis of Fault Adjusted Tight Gas Reservoirs

Abstract

Tight gas is an extremely important unconventional oil and gas resource, and its efficient development can effectively alleviate the current tense energy situation. However, the geochemical characteristics and gas source analysis of fault adjusted tight gas reservoirs are currently insufficient. Therefore, based on experimental methods such as tight gas composition and hydrocarbon isotope determination, the geochemical characteristics of typical tight gas reservoirs were analyzed, and discussions were conducted on the genesis of tight gas and source rock properties in the study area. The research results found that the tight gas in the study area is mainly composed of light hydrocarbons, and the tight gas reservoir is an ideal geological body for carbon dioxide geological storage, with an estimated CO₂ burial value of up to 3.43·10⁹ tons. Meanwhile, high-temperature and high-pressure trapping environments can easily cause heavy hydrocarbons in the trap to break down into light hydrocarbons, resulting in a much higher δ¹³-C₁ value in the carbon isotopes of tight gas compared to other carbon isotopes. The light hydrocarbon components of typical tight gas reservoirs are mainly oil associated gas types, while the heavy hydrocarbon components are mainly coal derived gas types. Moreover, the average organic carbon content in the tight gas in the study area is 6.67%, indicating that its source rocks are type I and II-1 kerogen, derived from underlying humic source rocks. Finally, the study found that the δ¹³-CO₂ values of all dense gas samples ranged from 7.85% to 15.3%, and the carbon dioxide concentration was all below 6%, indicating that the source of carbon dioxide in dense gas is a mixed mode.