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 gravel-pack 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.