ABSTRACT
MIC is currently a prevalent problem in the oil and gas industry due to seawater injection in enhanced oil recovery (EOR). Biocides are often used to mitigate MIC. However, continued biocide dosing leads to resistance by microbes over time. In this work, D-amino acids were used to enhance the tetrakis (hydroxymethyl) phosphonium sulfate (THPS) biocide against a tough field biofilm consortium on C1018 carbon steel coupons. An equi-mass D-amino acid mixture (“D-mix”) of four D-amino acids (D- methionine, D-tyrosine, D-leucine, and D-tryptophan) at a total concentration of 150 ppm (w/w) was tested. D-mix was injected with THPS and EOR chemicals (a polymer, a surfactant, a corrosion inhibitor, and a scale inhibitor) to treat the biofilm consortium and check the compatibility of the chemicals. After a 7-day biofilm removal test, the combination of 50 ppm THPS + 150 ppm D-amino acids achieved one extra log reduction in SRB and GHB sessile cell counts compared with using 50 ppm THPS alone. The combination also achieved lower weight loss and smaller maximum pit depths. The corrosion rates measured from linear polarization resistance were consistent with the weight loss data. The experimental data indicated that D-amino acids were compatible with the EOR chemicals.
INTRODUCTION
Biocorrosion, also known as microbiologically influenced corrosion (MIC) is a major problem in the oil and gas industry.1 Awareness of MIC is increasing in recent years especially after the 2006 Alaska pipeline leak.2 Sulfate reducing bacteria (SRB) often cause corrosion and reservoir souring.3, 4 Other bacteria such as acid producing bacteria (APB) and nitrate reducing bacteria (NRB) may also cause MIC.5 Enhanced oil recovery (EOR) is practiced more often nowadays because of dwindling reserves.6 Seawater injection can bring nutrients and microbes downhole. In the downhole environment, anaerobic microbes, especially SRB flourish. Nutrients and sulfate in seawater can be used by SRB to cause reservoir souring as well as MIC pitting against the downhole tubing.7
