During off-shore oil drilling, penetration of the oil-bearing rock strata releases the
pressure of the gases dissolved in the oil. This energy and that of the formation water drive
the crude oil from the rock reservoir up to the storage tanks on the platform or in the
derrick legs. This initial flow rate diminishes rapidly and as a consequence a considerable
proportion (20 to 30 %) of the crude oil remains in the reservoir adsorbed to the rock pore
walls. This loss of oil is unacceptable and in order to maximize the profit from industrial
exploitation secondary oil recovery is used.
Secondary oil recovery consists of injecting, under pressure, large amounts of filtered sea
water into the oil reservoir. This water displaces residual oil which is still bound in the
rock after the fall-off in the initial well pressure. As rock strata vary in permeability, such
injection water may fail to penetrate and flush oil from the denser layers. In principle this
problem can be overcome by the addition of a viscous compound to the injection water
which can block the more porous strata.The biopolymer xanthan has been recommended
for this purpose at a concentration of ca 0.1 % w/v.
Xanthan is a high molecular weight polymer commercially produced from the plant
pathogen Xanthomonas campestris. It consists of a linear backbone of β glucose residues
-similar to cellulose-with trisaccharide side chains of:
1) acetylated mannose
2) glucuronic acid
3) pyruvylated mannose.
Although this molecule is not attacked by SRB, it was thought that other heterotrophic
organisms associated with them in the marine environment could degrade xanthan to the
lower molecular weight compounds used by SRB. Therefore we investigated the effect of
xanthan addition on the degradation rate of organic matter, electron transport system
(ETS) activity and on SRB development in marine sediments.
ETS ACTIVITY
Degradation of organic material in a sediment occurs by aerobic respiration, in the
presence of oxygen and by fermentation/ anaerobic respiration in its absence. As fermentation end products are respired somewhere in the system (e.g; by SRB), xanthan
decomposition can be considered to occur via aerobic and anaerobic respiration (Vosjan,
1982). All respiring organisms possess a respiratory chain and the quantity of electrons
passing along the electron transport system per unit of time is a useful measure of the rate
of respiration. ETS activity can be measured using the artificial electron acceptor INT
(2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride) which is reduced to
INT-formazan. The quantity of this can be determined by its absorption at 490 nm. As a
large abundance of electron donors (NADH, NADPH and succinate) are used in the
assay the rates obtained give the metabolic potential of the sediment (Vosjan, 1982).
MATERIALS AND METHODS
Intertidal sediment from the River Forth estuary (S.E. Scotland) was collected at low tide
using Perspex core tubes. The top 10 cm of a series of cores were combined and carefully
mixed, to avoid as far as possible, the inclusion of air. Homogenized sediment was
distributed in 17 g amounts into sterile 28 ml bottles and the following additions made (2
ml) :
612
pressure of the gases dissolved in the oil. This energy and that of the formation water drive
the crude oil from the rock reservoir up to the storage tanks on the platform or in the
derrick legs. This initial flow rate diminishes rapidly and as a consequence a considerable
proportion (20 to 30 %) of the crude oil remains in the reservoir adsorbed to the rock pore
walls. This loss of oil is unacceptable and in order to maximize the profit from industrial
exploitation secondary oil recovery is used.
Secondary oil recovery consists of injecting, under pressure, large amounts of filtered sea
water into the oil reservoir. This water displaces residual oil which is still bound in the
rock after the fall-off in the initial well pressure. As rock strata vary in permeability, such
injection water may fail to penetrate and flush oil from the denser layers. In principle this
problem can be overcome by the addition of a viscous compound to the injection water
which can block the more porous strata.The biopolymer xanthan has been recommended
for this purpose at a concentration of ca 0.1 % w/v.
Xanthan is a high molecular weight polymer commercially produced from the plant
pathogen Xanthomonas campestris. It consists of a linear backbone of β glucose residues
-similar to cellulose-with trisaccharide side chains of:
1) acetylated mannose
2) glucuronic acid
3) pyruvylated mannose.
Although this molecule is not attacked by SRB, it was thought that other heterotrophic
organisms associated with them in the marine environment could degrade xanthan to the
lower molecular weight compounds used by SRB. Therefore we investigated the effect of
xanthan addition on the degradation rate of organic matter, electron transport system
(ETS) activity and on SRB development in marine sediments.
ETS ACTIVITY
Degradation of organic material in a sediment occurs by aerobic respiration, in the
presence of oxygen and by fermentation/ anaerobic respiration in its absence. As fermentation end products are respired somewhere in the system (e.g; by SRB), xanthan
decomposition can be considered to occur via aerobic and anaerobic respiration (Vosjan,
1982). All respiring organisms possess a respiratory chain and the quantity of electrons
passing along the electron transport system per unit of time is a useful measure of the rate
of respiration. ETS activity can be measured using the artificial electron acceptor INT
(2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride) which is reduced to
INT-formazan. The quantity of this can be determined by its absorption at 490 nm. As a
large abundance of electron donors (NADH, NADPH and succinate) are used in the
assay the rates obtained give the metabolic potential of the sediment (Vosjan, 1982).
MATERIALS AND METHODS
Intertidal sediment from the River Forth estuary (S.E. Scotland) was collected at low tide
using Perspex core tubes. The top 10 cm of a series of cores were combined and carefully
mixed, to avoid as far as possible, the inclusion of air. Homogenized sediment was
distributed in 17 g amounts into sterile 28 ml bottles and the following additions made (2
ml) :
612