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 three different 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 ìS/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.

Keywords: : drill-cuttings, muds, microbial qualities, PAHs, heavy metals.