Figure 4
From: Natural gas at thermodynamic equilibrium Implications for the origin of natural gas
Histogram log Q, 87 Offshore Gulf of Mexico Gases [29]. % vol was used to calculate Q, the quotient [(C1)(C3)]/[(C2)2]. Microbial gases have % wt C1 (C1–C4) > 99% and average log Q = 3.1 ± 0.53; δ13C1 average -61.7 ± 7.1, a signature considered biogenic. Only one had δ13C1 below – 50. Non-microbial gases have % wt C1 (C1–C4) < 99% and average log Q = 1.2 ± 0.38. The dark vertical lines indicate approximate thermodynamic equilibrium limits for subsurface conditions [31, 31]. The log Q region marked 'Thermal Cracking' represents the products of thermal cracking based on laboratory experiments [3, 27, 34–36].