Fingerprinting Bacteria DNA in Crude Oil for Reservoir Characterization
Authors: Carpenter Chris 
Published: February 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 166087, ’Application of New Fingerprinting of Bacteria DNA in Crude Oil for Reservoir Characterization - Part II,’ by A. Hayatdavoudi, N. Chegenizadeh, A. Chistoserdov, F. Boukadi, and R. Bajpai, University of Louisiana at Lafayette, prepared for the 2013 SPE Annual Technical Conference and Exhibition, New Orleans, 30 September-2 October. The paper has not been peer reviewed.

In the early 1980s, while the authors of the original paper were reassessing some old gravel-pack sands from a well, some sludge was noticed in the samples. The sludge had plugged formation and the gravelpack pores. The permeability was so low that the owner of the oil property considered abandoning the well and consequently stopped all workover measures, concluding that there was no more oil left in the reservoir. The scenario suggested the existence of bacteria in the oil. In the current study, a novel, sensitive technique for bacterial deoxyribonucleic acid (DNA) fingerprinting is implemented.

Introduction

To find bacterially induced chemical changes in oil, the research team in the first of two complete papers (only the second part is summarized here) compared the chromatograms of six carefully sampled oils obtained from two wells. The oil samples were taken directly from two wellheads without disrupting the production from the naturally flowing wells. To obtain a representative oil sample from each perforation interval, three samples were taken at different time intervals approximately half an hour apart. The distance between tops of producing intervals was approximately 3,000 ft, and the wells were designated Well A and Well B. The operator believed the two wells produced oil from the same reservoir. Despite their effective use as a tool in oil fingerprinting, chromatographic fingerprints of oil samples raised more questions than the team expected. Actually, in view of the well-known fact that oil reservoirs provide a favorable ecosystem for the growth of bacteria colonies, the precise role of bacteria in modifying the oil chemical compounds or creating new compounds could not be ascertained by use of the chromatograms.

The bacterial growth indigenous to the reservoir is attributable to the abundance of nutrient, whether inorganic, organic, or a combination of both. To survive, the bacteria must adapt to conditions in which they find themselves. The process of adaptability of bacteria to their surroundings (i.e., reservoirrock minerals and reservoir fluids as nutrients under reservoir conditions) can and will change rock petrophysical properties such as zeta potential; rock wettability; relative permeability; and permeability to water, oil, gas, or other flowing fluids. Generally, the bacteria in the water phase of petroleum reservoirs possess the ability to modify the surface chemistry of rock minerals and to extract or to concentrate metal and nonmetal ions.

Molecular-biology techniques have only recently been used for exploring for oil reservoirs. Recent achievements in molecular biology have extended the understanding of the role of microbial transformation and maturation of petroleum compounds under certain pressure and temperature windows and have enhanced our ability to investigate the microbial communities in petroleum-impacted ecosystems. The analyses mostly have focused on identifying the diversity of microbial species present in or on the seeps, seabed, gas vents, and reservoir waters by use of microbial 16S rRNA, a ribosome (a ribonucleic acid found in all microorganisms since the beginning of life on the planet). To identify a microorganism, its 16S-rRNA sequence information is checked against the 16S-rRNA sequence data available in the GenBank database. 16S-rRNA gene information is available for microorganisms found in different parts of the world and great distances apart such as North Sea, South American, and Asian oil fields. By use of these free gene databases, microorganisms most closely related to those which have been found in oil or gas reservoirs can be identified accurately.