Abstract
The existence of deep marine hypersaline anoxic basins (DHAB) has been well-documented starting with the MedRiff Project in the Eastern Mediterranean. We suppose that there is analogy between the recent and ancient DHABs. This premise allows us to hypothesize that some methane accumulations in geological reservoirs may have been generated by historical euryhaline bacteria. The extreme life conditions of the bacteria and the facieses, as found in currently existing supersaturated salt brines DHABs, may have also existed in the geological past. Since salt basins overlap some of the most productive gas provinces, this article aims to introduce a new approach to salt and methane generation. It highlights the need to reconsider the classical approach to salt and methane generation due to new observations. Hereby we describe a new mechanism for DHAB generation due to membrane polarization. These phenomena generate a surface on which seawater of normal salinity meets the underneath brine of high salinity, and there is no diffusion between them. Hence we presume that non-crystalized, over-pressured, salty brine is the appropriate material to trap and host methane. Following overburden by deposited basin sediments, this viscous, gas-saturated brine can be an engine for diapir formation, which is prior to the crystalline phase. This new idea redefines our search for salt and methane deposits yet it requires further research and consideration, along with the new approach of salt diapir formation in specific salt basins.
Highlights
Prior to the installation of a proper ventilation system in Wieliczka Salt Mine (Poland), skilled workers were responsible for burning off the methane that would accumulate in the ceilings of the mine chambers
Borin et al (2008) mention that methanogenesis greatly exceeds sulphate reduction in most of the saline layers in Urania deep marine hypersaline anoxic basins (DHAB) where extremely high bacterial abundance varies from layer to layer
In geological timescale the thickness of such buried DHABs may be higher than the actual brines, because it depends on the basin filling rate
Summary
The first recorded firedamp explosion occurred on 9 September 1664 in Hallstatt (Austria), in a salt mine and not in a coal mine (Harris, 1908). Prior to the installation of a proper ventilation system in Wieliczka Salt Mine (Poland), skilled workers were responsible for burning off the methane that would accumulate in the ceilings of the mine chambers. Nowadays salt mines are equipped with extensive ventilation systems to prevent similar firedamp explosions. It is wellknown that numerous hydrocarbon accumulations are connected to salt basins. It is crucial to understand the deposition and generation of evaporites, how the subsequent deformation history can influence salt basin petroleum systems (Thomas, 2008). Arrhenius & Lachman (Arrhenius & Lachman, 2003) point out that no large-scale salt deposits are being formed under current geological conditions
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