All aspects of oil and gas (O&G) production, processing, transportation, and storage are subject to problems related to the presence and activities of microorganisms. Such microbiologically-related problems include biofouling (slimes), deposition, and microbiologically influenced corrosion (MIC). These problems often compromise the function and integrity of system components by reducing porosity (and, therefore, production rates), plugging equipment, souring, and initiating or accelerating corrosion.
Why O&G Facilities Experience Microbiologically-Related Problems O&G facilities are susceptible to microbiologically-related problems where there is long-term exposure of metals to MIC-related microbes—including aerobes, slime formers, iron-related bacteria, anaerobes, organic acid-producing bacteria, and sulfate-reducing bacteria (which produce corrosive sulfides and consume hydrogen)—which are found both in water and in hydrocarbons carrying even small amounts of entrained water, water, nutrients (principally the hydrocarbons themselves), and corrosive ions such as chloride. The conditions required to get rapid corrosion in internal portions of most O&G facilities usually only occur in small portions of the facilities where water, microbes, nutrients, and salts accumulate, such as at low points in pipelines and bottoms of tanks.
External corrosion of O&G facilities, including pipelines and storage tanks, occurs because coatings have developed holidays and disbondments. When these areas of disbondment come into contact with soils that contain microbial, chemical, and conductivity conditions permissive of microbial colonization of the pipe under the disbonded coating, MIC can rapidly develop. Cathodic protection (CP) is ineffective in controlling this corrosion since the corrosion is occurringunderthe disbonded coating and, therefore, isshieldedfrom CP. The occurrence of MIC and its severity is determined largely by local conditions, which can change within a space of inches.
Microbiologically-Related Problems Experienced in O&G Systems O&G systems may experience a variety of microbiologically-related problems. Many times these problems occur simultaneously in an affected system and may not affect all systems uniformly due to differences in local environmental, operational, chemical, and biological factors. Microbial problems may include:
1. Reduced porosity in production and storage zones—and, thereby, production rates—due to microbial biomass and biofilms.
Biofilms (also called slimes), which are formed by microbial communities—in most cases composed of many different types of microbes (e.g., aerobic, slime-forming, anaerobic, acid-producing, iron- and manganese-depositing bacteria, molds, and sulfate-reducing bacteria)—attach to surfaces in contact with non-treated or inadequately treated waters. Biofilms are an early indicator of microbial activity.
2. Plugging of process and filtration equipment—including those in service stations, vehicles, and boats and ships—due to biofilms and deposition.
Over time, biofilms grow in thickness and areal extent. They mature by collecting more types of microbes (and, therefore, more biochemical reactions) and non-biological materials (e.g., sand, debris, organic and inorganic materials) and form deposits which can break off of the pipe surface and plug system components. Discrete deposits are a clear indication of microbial activity.
3. Souring of production and storage zones as a result of contamination during drilling and completion (especially when polymers with improper biocides or insufficient levels of biocides are used) or through use of materials added to enhance production, such as water and other materials.
Metabolic by-products are produced by microbes which exist in soils, water, and other materials encountered during the drilling and completion phases or through use of materials (e.g., water) to enhance production. Microbial metabolic by-products—such as acids, hydrogen, carbon dioxide, sulfides, and ammonia—can cause souring and accelerated MIC-type corrosion. These metabolic by-products are indicators of microbial activity.
4. Compromised system component integrity in production equipment, pipelines, processing equipment, and storage tanks in processing and distribution facilities due to under-deposit pitting type corrosion.
Once deposits are established, and given the right environmental conditions, microbial metabolic by-products—such as organic and inorganic acids, hydrogen, carbon dioxide, sulfides, and ammonia—accumulate within the deposits due to the activities of microbes and other chemical reactions. These metabolic by-products corrode the underlying metal and often lead to rapid under-deposit pitting-type corrosion beneath the deposits. This type of corrosion is a telltale sign of MIC. Microbes can both initiate corrosion and accelerate any existing corrosion.
5. Component failures due to under-deposit leaks.
Once corrosion and MIC advance to the stage of under-deposit pitting corrosion, the metabolic by-products in deposits corrode the underlying metal until leaks develop under the deposits. Pinhole leaks are another telltale sign of MIC.
6. Damage to coatings and destruction of underlying metal due to microbial activities.
Microbes enter holidays in protective coatings in pipes and storage facilities. Once established, microbial production and accumulation of corrosive materials under the coating (and next to the metal surface) causes further disbonding of the coating, allowing damage to the coating and underlying metal to spread and proceed at very rapid rates. The disbondment acts to trap and concentrate microbes and corrosive materials next to the metal surface, causing even faster corrosion to occur. Since this occursunderthe coating, the site is not protected by cathodic protection and cannot be treated using corrosion inhibitors and biocides. These problems can occur on the inside or outside of equipment.
Materials Affected Most metals and alloys, except titanium, are affected by microbial problems, including MIC. Since the majority of O&G components are made of carbon steel, these components are susceptible to MIC.
Systems Affected The following O&G facility systems are all potentially susceptible to biofouling, deposition, and MIC:
End-use (ships, boats, over-the-road carriers)
Whether this “MIC potential” progresses to rapid and severe MIC-type corrosion depends on local conditions—even in the same “system”—over time.
Diagnostic Products for O&G Industry Systems BTI Products offers test kits designed specifically for diagnosis of microbial problems in O&G industry systems. Our test kits provide microbiological, chemical, and site-specific information important in diagnosis of microbial and other problems and in the design of treatment and prevention strategies. BTI Products and its many O&G clients use BTI Products test kits to investigate MIC and design effective treatment programs. In fact, BTI Products test kits were used in Gas Technology Institute (GTI, formerly the Gas Research Institute) investigations of MIC and microbially-influenced souring (MIS) for over 14 years.
BTI Products kits can be used foralltypes of samples—including those containing water, particulates, corrosion products, hydrocarbons, and/or other materials. BTI Products test kits are designed to test for MIC-related microbes in samples from freezing to boiling temperatures and from a wide variety of salinities (from fresh water to sea water or production brines). They can be used to test for MIC-related microbes in almost all real-world samples and, most importantly, can be used by untrained industry personnel, on-site, to obtain accurate and pertinent data quickly and inexpensively.1
It is very important that proper methods be used to assess chemical and viable MIC-related microbes at sites which are most likely to have conditions conducive to microbial growth and corrosion. Proper sampling locations for various O&G facilities, methods of testing and assessment, and protocols for selecting treatment methods and monitoring are provided in GTI publications prepared by BTI and BTI Products.2
BTI Products test kits have been used to investigate MIC in O&G facilities for GRI, GTI, numerous O&G companies, and other industrial and government clients. BTI Products MICkits® were used byallparties in investigations of pipeline leaks at Prudhoe Bay, AK because the parties agreed that BTI Products test kits were most appropriate to the investigations.
Recommended Diagnostic Test Kits
MICkit® 3to test internal portions of O&G facilities for microbes involved in biofouling, deposition, and MIC
MICkit® 4to test locations using cathodic protection or coatings for chemistries important in corrosion diagnosis and treatment
MICkit® 5to test external portions of O&G facilities for microbes involved in biofouling, deposition, and MIC
MICkit® Comprehensiveto test external portions of O&G facilities for microbes and chemical parameters involved in biofouling, deposition, MIC, and other forms of corrosion
MICkit® Pipe Inspection Kitto physically inspect pipes in systems that have tested positive for MIC-related bacteria and/or systems with a history of leaks/failures
Diagnostic & Mitigation Services for O&G Industry Systems BTI Products can also assist in evaluation of samples, test data, field-site investigations, and design and implementation of mitigation measures. BTI Products performs and supports research and testing programs related to causes, prevention, and treatment of microbial problems for individual clients.
Scott, P.J.B. and M. Davies. 1992. Survey of field kits for sulfate reducing bacteria. Materials Performance, May, 64-67.
Pope, Daniel H., and Rebecca Pope. 1999. Topical Report: Diagnosis, Treatment and Monitoring of Microbiologically Influenced Corrosion in the Natural Gas Industry. Chicago: Gas Research Institute.
Further Reading For more detailed information on MIC in O&G facilities, please refer to the following publications:
Pope, Daniel H. 1999.Diagnosis and Treatment of Microbiologically Influenced Corrosion in Natural Gas Industry Facilities. Chicago: Gas Research Institute.
Pope, Daniel H., and Alan Morris. 1994.GRI Field Guide 1994, Microbiologically Influenced Souring (MIS): Assessment of MIS in Natural Gas Storage Fields. Chicago: Gas Research Institute.
Pope, Daniel H. 1992.GRI Field Guide 1992, Microbiologically Influenced Corrosion (MIC) II: Investigation of Internal MIC and Testing Mitigation Measures. Chicago: Gas Research Institute.
Pope, Daniel H. 1992.Topical Report: State-of-the-Art Report on Monitoring, Prevention and Mitigation of Microbiologically Influenced Corrosion in the Natural Gas Industry. Chicago: Gas Research Institute.
Pope, D.H., O. Siebert, and D. Jackson. 1990.GRI Field Guide 1990, Microbiologically Influenced Corrosion (MIC): Methods of Detection in the Field. Chicago: Gas Research Institute.
Pope, D.H., D.M. Dziewulski, T.P. Zintel, and O. Siebert. 1988.Guide to the Investigation of Microbial Corrosion in Gas Industry Facilities. Chicago: Gas Research Institute.