Print this pageSome of the world's most productive oil reserves, termed oil-field karst, are found in carbonate rocks with significant secondary porosity created by acidic porewater solutions. These acids include microbially-produced sulfuric acid derived from the oxidation of reduced sulfur compounds. Sulfidic groundwater cave systems were used in this study to investigate the potential for porosity enhancement by microorganisms. In actively-forming sulfidic caves, notable rock corrosion was found on non-submerged, cave-wall surfaces where extensive microbial biofilms and acidic conditions existed. Chemoautotrophic, sulfur- and thiosulfate- oxidizing bacteria were isolated from four sulfidic caves. Sulfuric acid produced by the microorganisms grown under laboratory conditions enhanced carbonate dissolution more rapidly than abiotic processes alone. Preliminary results from ribosomal DNA extraction and sequencing indicate that the isolated bacteria are novel strains of Thiobacillus, a genus associated with low pH environments such as acid mine drainage. These results support the hypothesis that sulfur-oxidizing microorganisms can cause sulfuric acid dissolution of carbonate host rocks and enhance of secondary subsurface porosity.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid