A STUDY OF THE MICROBIOLOGY AND POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) COMPOSITIONAL PROFILE AND SOURCES IN DRILL CUTTINGS FROM OLOGBO OILFIELD WELLS AT EDO STATE, NIGERIA
Abstract
A study was carried out on the drill cuttings from threedifferent oil and gas wells located at Ologbo Community
at Edo State with respect to their microbiology and
polycyclic aromatic hydrocarbons (PAHs) compositional
profile and sources. Isolation and enumeration of
heterotrophic bacteria and fungi was carried out using
pour plate techniques. pH and electrical conductivity were
monitored using single electrode meters. Polycyclic
Aromatic Hydrocarbon was determined using gas
chromatography, oil and grease concentration was
analyzed using spectrophotometric method. Results of
total heterotrophic bacterial counts ranged between 5.4 x
105 cfu/g at well 2 to 7.23 x 105 cfu/g while the
heterotrophic fungal counts ranged from 3.7 x 104 cfu/g to
3.0 x 105 cfu/g. Total heterotrophic anaerobic bacterial
counts also ranged from 0.8 x 102 cfu/g to 1.7 x 102
cfu/g. The most predominant bacterial isolates were
Clostridium spp. (16.6%) and Mycobacterium spp.
(14.5%). Species of Aspergillus (16.6) and Penicillium
(14.2) also had the highest frequency of occurrence
among the fungi isolates. The pH ranged from 5.42 to
5.78. The highest electrical conductivity value was 383
µS/cm. The range for oil and grease was from 8352 to
9654.61 mg/kg. Of the heavy metals iron had the highest
concentration (126 ppm) while least concentration was
observed in zinc (61 ppm). The 3-ring PAHs had the
highest percentage composition for samples from the
three (3) different wells (53, 73 and 89 for well 1, 2 and 3
respectively). The source identification by isomer ratios of
PAHs revealed that drill cuttings from Wells 1 - 2 were of
pyrogenic origins, while cuttings from well 3 indicated
both petrogenic and pyrogenic origin. It was quite clear
that drill cuttings emanating from Ologbo oilfield wells
were unsafe for disposal and therefore will require a strict
adherence of the procedures and instructions described
for oil drilling exploration and procedure (E and P) waste
management in Nigeria.