Prediction of Low-Maturity Gas Accumulations: Application to the Eastern Mediterranean “Biogenic Play”

Abstract

SUMMARYBiogenic gas is becoming increasingly important as an exploration target in the petroleum industry because it occurs in geologically predictable circumstances and in large quantities at shallow depths as free gas or gas hydrates. As accumulations of biogenic gas result in a subtle synchronization between early generation and early trapping, we integrated a macroscopic model of microbial gas generation within a 3D basin and petroleum system forward simulator.

Mechanisms of Methane Hydrate Formation in Geological Systems

“…Sizable biogenic gas reserves thought to be sourced from beneath the BHSZ have recently been discovered, suggesting that microbial biogenesis extends to significant depths (Albalushi et al, 2016;Skiple et al, 2012;Steinberg et al, 2011). Better models to describe microbial processes are necessary to understand this system (Schneider et al, 2016).…”

“…On the other hand, other studies suggested that increasing temperature at depth may increase the reactivity of the remaining organic matter, thus extending the depth range of microbial methanogenesis (Burdige, ; Gu et al, ; Malinverno & Martinez, ; Wellsbury et al, ). Incubation experiments conducted at different temperatures show microbial methanogenesis rates that peak at 30°–45°C (Belyaev et al, ), and this temperature effect has been included to estimate microbial gas generation in commercial accumulations (Katz, ; Schneider et al, ). A similar temperature dependence of microbial methanogenesis has been used by Frye () to evaluate in‐place gas hydrate resources on the northern GoM continental slope.…”

Evolution of the Percolation Threshold in Muds and Mudrocks During Burial

“…Methane release to the water column on the southern Brazilian margin has similarly been tied to glacially mediated changes in ocean circulation and temperature (Portilho-Ramos et al, 2018). At the same time, recently discovered large, recoverable accumulations of microbial gas in the eastern Mediterranean Sea (Needham et al, 2017) require that the microbial gas, which is generated in the upper few hundred meters of marine muds below the seafloor (Schneider et al, 2016), does not accumulate to sufficient concentrations to flow and leak at the seafloor. Higher gas mobility thresholds would seem to be necessary for microbial gas to be transported and concentrated at depth.…”

“…Gas fields offshore Israel and Egypt include a significant component of microbial gas, which is interpreted to come from source rocks as old as the Cretaceous (Feinstein et al, 2002). Since these gases would have been generated at relatively low temperatures (40-80 °C) corresponding to the upper kilometer or so of sediments (Schneider et al, 2016), some mechanism is necessary to transport this gas to its current depth of >4 km below seafloor in many fields (Feinstein et al, 2002;Nassar et al, 2012;Needham et al, 2017). A large percolation threshold would aid in this process, as gas saturations less than about 20% (Figure 2b) would be carried down with host sediments during burial.…”

Prediction of Low-Maturity Gas and Heavy Oil: Biogenic Gas and Biodegraded Oil Modeling

“…Furthermore, it has been applied in the offshore Lebanon in order to check the viability of a biogenic gas system Schneider et al, 2013 The mass balance calculations provided by the model show that the biogenic gas generation is limited to areas where the active source-rocks remained in the oil window. Besides, the kinetics of oil expulsion versus secondary cracking in the source-rocks drive the composition of the gas (biogenic vs. thermogenic) in the shallow (< 2000 m) reservoirs.…”