BASIN AND PETROLEUM SYSTEM MODELING TO ASSESS SEDIMENT CARBON AND HYDROGEN CONTENT REQUIRED FOR BIOGENIC GAS HYDRATE FORMATION

Gas hydrates potentially comprise the largest reservoir of organic carbon on Earth, and have garnered much attention as a potential energy resource. Marine gas hydrate predominantly consists of methane (CH₄) molecules trapped within lattice-like cages of frozen water molecules. Most of this methane is of inferred biogenic origin (i.e., generated via microbial activity). Sedimentary organic matter is the critical feedstock for the methanogens that produce this gas in anaerobic sub-seafloor environments. Thus, an understanding of the minimum amount of this organic material (measured in terms of carbon and hydrogen content—or, total organic carbon (TOC) and the hydrogen index (HI) in the petroleum industry) necessary for methanogenesis to result in appreciable volumes of hydrocarbons is an essential component to understanding the requirements for formation of marine gas hydrate. Numerical modeling (e.g., reactive transport modeling) over the past two decades has suggested minimum requirements of ~0.3–0.5 wt% TOC for the formation of gas hydrate, while earlier work predicted that TOC contents as low as ~0.1–0.2 wt% could produce biogenic gas (albeit in limited quantities). However, hydrogen content (which has been recognized as the limiting reagent in hydrocarbon generation for at least 50 years) needed for biogenic gas generation and gas hydrate formation is much more poorly understood. Furthermore, the minimum organic contents needed for gas hydrate formation have not been investigated via comprehensive basin- and petroleum system-scale computational modeling. Here, we construct a suite of synthetic 2-D basin and gas hydrate system models to investigate minimum sediment TOC and HI contents needed for formation of gas hydrate (at saturations >1%). Results suggest that TOC as low as 0.1 wt% (paired with 100 HI) and HI as low as 50 (paired with 0.2 wt% TOC) may produce biogenic gas hydrate under geologically favorable conditions (e.g., folded, faulted strata).