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
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.