Cultures of Clostridium acetobutylicum were used to ferment molasses in the oil wells and produce large amounts of gas and organic acids along with solvent s and surfactants under reservoir conditions. While considerable interest has been devoted to this concept, only a limited amount of field success has been found with this idea. Solvent molecules such as microbially produced aldehydes, ketones, and alcohols dissolve in crude and lower its density. By lowering its density, less energy is required to move a volume of crude oil over a given density. Depending on its chemical makeup, this may also reduce the oil's viscosity.
Porosity is defined as the measure of the void space or storage capacity of a reservoir matrix.
Permeability of a reservoir rock is its ability to transport fluid. Other affects that may be observed are the removal of occlusions from the rock matrix. As these compounds precipitate in the reservoir, they block the pore matrix and impede the movement of oil. Microorganisms that produce significant amounts of acid could be considered for use in increasing porosity by dissolving the rock matrix. Although there have been no successful attempts at demonstrating this technology, it is analogous to what is done by sulfur oxidizing bacteria in releasing the metal component of sulfide ores by generation of sulfuric acid.