“H2S-related porosity” refers to porosity created in a H2S system where dissolution can be produced by the mixing of waters of different H2S content or by the oxidation of H2S. “Sulfuric acid oil-field karst” refers to a specific kind of H2S-related porosity where carbonate reservoirs of cavernous size have been dissolved by a sulfuric acid mechanism. In a H2S system, porosity can be produced entirely in the deep subsurface and does not have to represent a paleokarst surface or dissolution in the shallow-phreatic or vadose zones.
H2S-related porosity is characterized by the large volume of hydrocarbons it can host, by extensive fracture permeability interconnected with “sponge-work” cavities or caves of tens to hundreds of meters in extent, by porosity related to structural and/or stratigraphic traps, and by the presence of high uranium and/or iron. Possible examples of H2S-generated porosity systems are the Lisburne field, Prudhoe Bay, Alaska, and some of the extremely productive fields of the Middle East.