PNNL

Abstract

To understand the conditions under which microorganisms exist in deep hydrocarbon reservoirs, sidewall cores were collected from a natural gas-bearing formation, 2800 m below the surface in Taylorsville Basin, Virginia. Data from chemical and microbial tracers and controls indicate that the interiors of some sidewall cores contained microorganisms indigenous to the rock formation. The cultured microorganisms were composed primarily of saline-tolerant, thermophilic fermenting, Fe(lll)-reducing, and sulfate-reducing bacteria (I to 10(4) cells/g). The physiological capabilities of the cultured microorganisms are compatible with the temperature (76 degrees C), pressure (32 MPa), and salinity (approximate to 0.8 wt.% NaCl equivalent) in the sampled interval. The petrological data indicated that the strata contain intercrystalline pores of micrometer size, that occur between late diagenetic cement in siltstone and within cross-cutting, mineralized fractures in shale. These pores made up only 0.04% of the rock volume, were mostly gas-filled, and were interconnected by pore throats with diameters 0.1% of the viable bacteria. The recovery of living bacteria from such an austere environment represents one of the most remarkable examples of microbial survival yet reported.