Mixed metal oxide (MMO) is widely used as anode material for the cathodic protection of storage tank bottoms due to its advantages such as low consumption rate long service life and ideal current distribution. However with the elapse of service time the MMO CP systems have been found with such issues as low polarization level and uneven potential distribution threatening the operation safety of storage tanks. In this study numerical modeling and subscale experiment were chosen to clarify the main factors responsible for the aforementioned issues. The results indicated that the inadequacy of polarization and the lack of uniform potential distribution were related to a combination of multiple factors including the anode-to-tank bottom distance the impressed current level and the number of drain points. On the basis of these systematic analyses this paper conclusively proposes certain design principles and maintenance suggestions for the cathodic protection system of tank bottoms.  

The oil and gas industry’s efforts to characterize microbial communities in oilfield process fluids has shed increasing light on the influence of bacteria and archaea on hydrocarbon production. Notably topside or downhole water contamination by prokaryotes such as sulfate-reducing bacteria acid-producing bacteria and/or other halophiles can negatively impact asset integrity and reduce the quality and/or quantity of produced oil and gas. Molecular microbiology methods have contributed to our understanding of these complex processes by providing unprecedented resolution of resident microbial communities. However a lack of methodological consistency among industry and academic laboratories studying microbiological processes in oilfield systems has precluded the industry’s ability to discern broad cause-and-effect trends or compare results across laboratories. For example there exists no standard primer set for 16S rRNA gene amplicon sequencing agreed upon by the oil and gas community.Recently Dow Microbial Control and The Ohio State University partnered to perform a comprehensive microbial audit of multiple unconventional upstream operations. Over the course of the audit samples were systematically taken during drilling throughout completions and periodically over the first year of production. Produced water samples were submitted for whole-genome metagenomic sequencing and assembly with near-complete genomes for input microbes and reservoir-colonizing microbes subsequently resolved. By creating this genome-resolved metagenomic dataset we removed the PCR bias of any given 16S primer set allowing for comparison and curation of common 16S rRNA gene primer sets and elucidation of the most appropriate sequencing methodology for oilfield samples. Ultimately the use of validated molecular microbiological methods among the oilfield industry will more quickly advance our understanding of microbiological processes in these systems.

Stainless steel UNS S17400 (17-4PH) has been successfully used in oilfield services outside the traditional NACE MR0175/ISO 15156 limits for permanent equipment. The exact operational envelops of 17-4PH (HH1150), including the tensile threshold stress, sour gas partial pressure, temperature, and exposure time that enable the crack-free usage of 17-4PH (HH1150) are not well established. For service equipment, NACE MR0175/ISO15156 currently provides exemptions from the tight environmental restrictions of permanent equipment, but instead limits the maximum applied stress to a debatable 60% of the specified minimum yield strength (SMYS). In this investigation, the sulfide stress-corrosion cracking of 17-4PH is revisited through 51 new NACE TM0177 Methods A tests conducted over 240 hours minimum (480hrs in certain cases). Under unrestricted sour gas partial pressures, the threshold tensile stress below which cracking does not occur is between 45% and 60% of the SMYS at ambient temperature. Alloy 17-4PH is also less susceptible to sulfide stress cracking as temperature increases from 70°F (21°C) to 350°F (177°C). Risk of sulfide stress cracking is also greatly mitigated when delta ferrite is controlled. With reduced delta ferrite, as provided by two out of three tested heats, and reverted austenite promoted by both chemical composition and longer aging treatments, no cracking is seen at 60% stress level up to 45psi H2S (0.31MPa); at 45% stress level, this value is increased to 120psi (0.83MPa) based on newly-collected test data.