Application of Fingerprinting Bacteria DNA in Crude Oil For Evaluating the Reservoir

Chegenizadeh, Negin; Hayatdavoudi, Asadollah; Chistoserdov, Andrei; Boukadi, F.

In early 80's, while reassessing some old rocks and gravel pack sands from a well, Hayatdavoudi noticed some sludge 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 thought of abandoning the field and consequently stopped all Workover measures. The owner stated that there was no more oil left in the reservoir. This observation and the previous ones in early 70', in addition to later laboratory studies, suggested the existence of bacteria in the oil. In the current study we implemented a novel, sensitive technique for bacterial DNA fingerprinting; that is, denaturing gradient gel electrophoresis of PCR amplified 16S rRNA genes. This approach allowed us to identify and classify bacteria found in the oil and enabled us to evaluate the application of our technique to evaluate both conventional and unconventional reservoirs.

To prove the hypothesis that bacteria were present in oil, we requested an operating company to provide us with 6 samples taken from 2 separate wells, but drilled in the same reservoir or at least the operator thought both wells were drilled in the same reservoir. We implemented our procedure of fingerprinting bacteria DNA as follows: (1) DNA extraction from oil, (2) DNA concentration, (3) Making 0.7% and 1% Agarose gel, (4) Electrophoresis of total DNA isolated from oil, (5) PCR amplification of 16S rRNA gene fragment from DNA isolated from oil, (6) Running gel on the PCR product, (7) Running Denaturing Gradient Gel Electrophoresis (DGGE), and (8) Cycle Sequencing DNA.

The result from DNA concentration by our technique proved the existence of the bacteria DNA in all crude oil samples, which was not possible to find previously. Furthermore, upon classifying the bacteria we found the origin of the crude oil produced from each well. Based on our results, we found that Well A drained oil from a buried forest, fresh water environment, whereas Well B drained oil from a very shallow marine environment. From results, we concluded that, first these two wells are not drilled in the same reservoir as the property owner thought, second the reservoirs are under-drilled, and third it is estimated that there may be enough oil left in both reservoirs to be drained by one or more wells.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013