Abstract
Microbial control products for offshore production facilities need to meet stringent product specifications and performance criteria, and must be compatible with infrastructure such as pump capacity and materials of construction. This paper describes the biocide selection process and recommendation for an offshore operation in West Africa.
The chosen chemistries needed to demonstrate robust microbial control under field conditions for top side and downhole protection, as well as pipeline protection. Product specifications such as good chemical stability above 60°C, high flash point, low viscosity, non-corrosive, and low foaming potential also needed to be met. Additional constraints included a defined treatment protocol, and a request that both a glutaraldehyde (GDA) -based product and a tetrakis (hydroxymethyl) phosphonium sulfate (THPS)-based product be recommended.
A wide range of GDA and THPS-based products were tested against planktonic halophilic sulfate reducing bacteria (SRB's) using high throughput testing. No differentiation between products was observed under these conditions. More sophisticated test methods that evaluate kill of sessile bacteria again, showed little differentiation in the short term, but when longer-term control of biofilm regrowth was considered, two GDA formulations performed well. One was ruled out due to its high foaming potential. The leading GDA based formulation (GDA 4) and a non-foaming THPS-based formulation which also met efficacy requirements (THPS B) were further evaluated under conditions simulating microbial corrosion in a pipeline. Both mitigated corrosion relative to an untreated control as indicated by electrochemical monitoring. Corrosivity of the products towards common materials in saltwater was also considered. For Duplex 2205 and stainless steel, no significant corrosion was observed for either neat or use-concentration product. For carbon steel, THPS B showed little variation from the saltwater control while GDA 4 gave marginal protection relative to saltwater alone. Therefore both products were found to suit the requirements of the operation.
This study shows the importance of a holistic approach to microbial control beyond standard planktonic efficacy testing. The selection process should include not only efficacy against relevant microorganisms and conditions, but also evaluation of chemical and physical properties of the product.
