No abstract

Manganese- and iron-oxidizing bacteria (MFOB) are widely implicated in microbially influenced corrosion, often in association with sulfate-reducing bacteria (SRB). Traditionally MFOB have been assigned a passive role in the corrosion process, promoting differential aeration cells, and providing oxygen depleted conditions conducive to the growth and corrosive attack of SRB. Recent work, summarized in this article, demonstrates that manganese biofouling alters the electrochemical behavior of stainless steel (SS), and suggests that MFOB are more active in localized corrosion than traditionally held. The paper discusses the chemistry and potentially corrosive impact of manganese and iron oxides on SS, explores the possible relationship between MFOB and SRB, and proposes a model to describe the synergistic influence these organisms may exert in the corrosion process.

The noble shift in open-circuit potential exhibited by microbially colonized stainless steel (ennoblement) was investigated by examining the relationship among surface colonization, manganese deposition, and opencircuit potential for stainless steel coupons exposed to batch cultures of the manganese-depositing bacterium Leptothrix discophora. Open-circuit potential shifted from ؊100 to ؉330 mV SCE as a biofilm containing 75 nmol of MnO x cm ؊2 formed on the coupon surface but changed little further with continued MnO x deposition up to 270 nmol cm ؊2. Increased open-circuit potential corresponded to decreasing Mn(II) concentration in solution and to increased MnO x accumulation and attached cell density on the coupon surfaces. MnO x deposition was attributable to biological activity, and Mn(II) was observed to enhance cell attachment. The experimental results support a mechanism of ennoblement in which open-circuit potential is fixed near ؉350 mV SCE by the cathodic activity of biomineralized MnO x .

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A high pressure, water jet drilling system has been developed using a new force system to concurrently drill a bore hole and place a metal tube in the bore hole. The first commercial application has been horizontal radials for shallow heavy oil reservoirs. Many radials may be placed at the same elevation. Logging, and completion techniques have been developed.