A biocide evaluation program was undertaken to evaluate the relative risks of microbially influenced corrosion (MIC) in a produced effluent water system for West Kuwait Oil Fields, using a combination of field sampling and laboratory biofouling tests. Bacteria isolated from the field water surveys were used to evaluate remedial treatments such E.S chlorine, chemical biocides and mechanical removal. Recirculating biofouling loops were set up with the effluent water, and inoculated with the bacteria from the system so that an active biofilm was formed on small steel studs. These biofouled studs were then treated with different antibacterial products under various dosage regimes in order to select the most appropriate control regime for the effluent water. The most effective biocides were found to be the glutaraldehyde and a mixed aldehyde with qantemary ammonium and phosphonium compounds.
One of the ways to dispose of the effluent water, that is a by-product of oil production in West Kuwait-Oil fields, is to re-inject it into the oil reservoirs for pressure maintenance. A major Oil Company in Kuwait intends to use this method to enhance its oil production within the next ten years.
Injection of effluent water for secondary oil recovery can encourage the growth of
bacteria, especially as biofilms on pipe wall surfaces. One major problem in water injection systems is the uncontrolled growth of sulphate-reducing bacteria (SRB) which leads to increased corrosion of the process plant as well as creating problems of toxicity and spoilage of the gas and oil. In the reservoir itself, permeability reductions may be caused by growth of bacteria in the pore spaces of the rock leading to reduced recovery efficiency 1-4.
A common characteristic of SRB attack of steel is pitting corrosion, with the ~its being
open and filled with soft black corrosion products in the form of iron sulphides -6 , when the corrosion products are removed, the metal underneath is bright but rapidly rusts on
exposure to air. In aerobic environment, SRB corrosion invariably occurs beneath. deposits of inorganic or organic detritus, microbial slimes, or tubercules caused by the action of the iron-oxidizing bacteria7-8.
Typical electrochemical corrosion would not be expected to occur under anaerobic conditions because the cathode becomes polarized by the build-up of a layer of atomic hydrogen. SRB are potentially able to stimulate the electrochemical corrosion mechanism by a number of possible means, the most widely accepted are: (i) the enzymatic removal of polarizing cathodic hydrogen, (ii) the formation of iron sulphides which are themselves cathodic to steel, (iii) the formation of elemental sulphur upon re¬oxidation of sulphides and (iv) the formation of aggressive iron phosphides by SRB. Although all of these mechanisms may. operate in nature, the production of iron sulphides and cathodic depolarization are the two most important corrosion
mechanisms5-6.
Control of microbes can be effected by chlorination, ozonization, by means of ultraviolet (UV) light and/or organic biocides. A combination of these methods is commonly used to minimize microbially influenced corrosion (MIC) and reservoir souring in oilfield water injection systems. Therefore, in most water injection systems, chemical biocide treatments are employed8 with varying degrees of success9. Great care must be taken in selecting and applying biocides to ensure that they: (a) are compatible with the system (b) can be handled safely and, c) have no environmental impact. Additionally, both batch and low level continuous treatments of organic biocides will ultimately lead to the build¬up of resistant and tol
