Microbial Assessment and Control in Drilling Operations

Formation damage in terms of physio-chemical reactions such as asphaltene deposition, scale precipitation and fines migration for example, is relatively well understood. In contrast to this the effects of indigenous and introduced microbes and their role in oilfield formation damage is less well understood. Oilfield microbes, especially the S.R.B. (sulphate reducing bacteria) have been identified from many oilfields world wide (indigenous) and have been isolated from drilling mud (particularly water based muds) and other down hole chemicals and injection water (introduced microbes). The combination of the various microbial populations often results in the precipitation of insoluble metal sulphides, biopolymer and/or hydrogen sulphide production, with loss in production or injection rates. By utilising bottle tests performed at a range of temperatures up to the actual oilfield reservoir temperature, it is possible to model the microbial formation damage mechanisms using the thermal gradients present in the field. Using this thermal model it is possible to predict where the various microbial formation damage mechanisms, such as hydrogen sulphide production, biopolymer and cell pore blockage, occur in the field area and to predict from the injection water model when the various damage mechanisms will occur in the field. This novel approach using thermal models coupled with microbial bottle and flood tests, and geological interpretative techniques, is the initial step in predicting microbial formation damage in oilfield reservoirs. Introduction Formation damage in terms of physio-chemical reactions such as asphaltene deposition, scale precipitation and fines migration for example is relatively well understood. In contrast to this the effects of indigenous and introduced microbes and their role in oilfield formation damage is less well understood. The presence of microbes in oilfield reservoirs is widely accepted, and have been isolated from oilfield reservoirs world wide (1 & 2). These microbes while often native to the reservoirs can also be introduced as a result of drilling operations and/or water injection (3). The indigenous microbial reservoir populations can be activated by water injection and well chemical squeeze programs resulting in both near wellbore and deep reservoir damage due to microbial/polymer plugging (4) and insoluble metal sulphide precipitation (5). Introduced bacteria from drilling muds, clean up chemicals and completion chemicals can also cause microbial formation damage, which can result in loss of well productivity or injection (6). The production of hydrogen sulphide gas by sulphate reducing bacteria (S.R.B.) both in well and in the reservoir, can cause significant problems due to enhanced corrosion of topside and down hole tubulars, metal sulphide precipitation, health and safety hazards, and increases the refining cost of the oil (7). Temperature is one of the major controls on the growth of bacteria and their by-products. To evaluate the microbial formation damage mechanisms the incubation of preserved core samples from an oilfield reservoir, live drilling mud and injection seawater, in various growth media at selected temperatures was performed. The live reservoir mud and injection seawater was inoculated into growth media at 30°C, 60°C and 90°C. The inoculated core samples, drilling mud and injection seawater subcultures were analysed using dry scanning electron microscopy (S.E.M.) to observe the presence of bacteria, biopolymer and insoluble metal sulphides.

Significant effort around bacteria monitoring has been a focus since July 2016. Water testing program covers all operating areas including southwestern Pennsylvania and Marshall county, West Virginia. The program began with most probable number (MPN); otherwise known as serial dilution testing, for sulfate reducing bacteria (SRB) and acid producing bacteria (APB). Based on the water test results, biocide treatments were performed for selected wells from October 2016. More than 300 horizontal wells from Marcellus formation were tested for SRB and APB by third quarter 2017 and biocide treatments were optimized by the end of 2017. Bacteria DNA testing in the form of next generation sequencing (NGS) and quantitative polymerase chain reaction (qPCR) was performed on selected wells to characterize the microbial consortium present in these samples. Due to the limitations of serial dilution testing and understanding of the bacteria makeup with DNA testing, the program has evolved to utilize fieldwide adenosine triphosphate (ATP) testing and a locked-down biocide treatment procedure. Biocide treatments are prioritized during extended midstream maintenance to minimize downtime and maximize contact time and have shown to be effective for extended durations. To investigate the root causes of bacteria, data science tools are utilized to look at the effect of the completions design and other variables on bacteria during operation. Variables under consideration include biocide type and concentration, fracturing fluid chemical additives, produced water reuse during completions, produced water chemistry, and geologic variation. Initial findings will be discussed and shared with lessons learned from production operations.

Comparative toxicity of drilling muds: role of chromium and petroleum hydrocarbons

Sulfate Reducing Bacteria (SRB) strain form and its sulfate-reducibility was identified after enrichment, separation and purification of SRB from some an-aerobic sludge of a uranium mine. The growth of SRB was stabilized 72 h after inoculation. The influence of inoculation quantity, pH, temperature, SO42- concentration on the growth of SRB was discussed. Sulfate treatment effect with 6.5 g/L SO42- concentration was 51.8 % in 15 days and 69.1 % in 30 days by SRB, respectively. Treatment effect of sulfate was 64 and 83 %, the one of uranium was 60 and 82.3 % from simulated wastewater by SRB and SRB + Fe0, respectively.

Influence of Mg 2+ on the growth and activity of sulfate reducing bacteria

Hydrocarbon-contaminated drill mud waste associated with oil and gas activities constitutes a major risk to the environment, but current conventional treatment methods have not been effective in removing Total Petroleum Hydrocarbon (TPH). In this study, the remedial potential of nutrients addition to stimulate the growth of indigenous microbes was harnessed to treat drill mud contaminated with hydrocarbons as an alternative to the conventional treatment methods. Baseline study of the hydrocarbon contaminated drill mud was carried out to establish the inherent physicochemical and biological characteristics. Homogenized sample of the hydrocarbon contaminated drill mud was inoculated with adequate amount of nutrient and bulking agent into various ratios of contaminated drill mud/nutrients/bulking agent. The specification for each microcosm experiment was 0.2 m × 0.5 m × 1.5 m for depth, breadth and length respectively. The experimental results showed a high TPH level of 8.88 × 105 mg/kg, low nitrogen content of 0.4% and low microbial load of 1.34 × 103 CFU/100ml for the drill mud. TPH degraded sharply, averaging 98% after three weeks and 99.5% after seven weeks augmentation with nutrients. The trends of the other measured parameters supported that the degradation was due to the enhanced microbial activities. The high rate of degradation achieved in this study supports the proposition that bioremediation of drill mud is a feasible approach to effectively remove TPH components from the hydrocarbon contaminated drill mud. This study therefore paves way for scalable studies to be pursued in similar and/or different industrial situations.

In batch and continuous fermentations, the reduction in corrosion of SAE 1018 mild steel and 304 stainless steel caused by inhibition of the reference sulfate-reducing bacterium (SRB) Desulfovibrio vulgaris by a protective, antimicrobial-producing Bacillus brevis biofilm was investigated. The presence of D. vulgaris produced a thick black precipitate on mild steel and a higher corrosion rate in batch cultures than that seen in a mono-culture of non-antimicrobial-producing Pseudomonas fragi K upon the addition of SRB to the aerobic P. fragi K biofilm. In continuous reactors, the polarization resistance RP decreased for stainless stell and increased for mild steel upon the addition of SRB to a P. fragi K biofilm. Addition of either 200 micrograms/ml ampicillin, chloramphenicol, or ammonium molybdate to batch and continuous reactors after SRB had colonized the metal was ineffective in killing SRB, as inferred from the lack of change in both Rp and the impedance spectra. However, when ampicillin was added prior to SRB colonization, the growth of SRB was completely inhibited on stainless steel in continuous reactors. Prior addition of ampicillin was only able to delay the growth of SRB on mild steel in continuous reactors. External addition of the purified peptide antimicrobial agent gramicidin S prior to the addition of SRB also inhibited the growth of SRB on stainless steel in continuous reactors, and the SRB were also inhibited on stainless steel in both batch and continuous reactors by producing gramicidin S in situ in a protective biofilm when the gramicidin-S-overproducing strain Bacillus brevis 18 was used.

Drilling mud is a necessary component of drilling operations. There have been notable attempts to enhance the filtration and rheological properties and increase the cutting carrying capacity of water-based mud (WBM) using nanoparticles (NPs). This study investigates how varying Al2O3 concentrations affect the rheological properties and cutting carrying capacity of drilling fluids. In this study, different drilling muds were produced using bentonite (2.8g) without nanoparticle, 50% bentonite (1.4g) and 50% Al2O3(1.4) and 0% bentonite(0g) and 100% Al2O3 (2.8g). Testing and comparisons were done on the formed mud samples' physiochemical properties, rheology, filtration properties, and cutting carry index (CCI). The Power Law Model was used to define the rheological behavior of the manufactured mud samples, and results showed that all the mud samples were pseudoplastic fluids and remain a preference for drilling fluids because their flow behavior index (n) was less than 1. It was observed that the addition of Al2O3 is directly proportional to the plastic viscosity, apparent viscosity and yield point and inversely proportional to the gel strength of the drilling fluid. The study also shows that the addition of Al2O3 nanoparticle influences the cutting carrying index CCI as the calculated cutting carrying index gives a high cutting carrying index CCI which means that the hole cleaning potential of the drilling mud is good. The study shows that Al2O3 nanoparticles are feasible for use in drilling fluid formulation.

Barite sag poses a considerable challenge in the drilling of high-temperature and high-pressure (HTHP) wells under static and dynamic conditions. Barite particles detach from the base drilling mud during this process. This leads to changes in the weight of the drilling mud, which may result in severe well control problems, including mud loss, borehole instability, and pipe sticking. This study used a synthesized weighing agent comprising combined nano barite (nBaSO4) and nano ilmenite (nFeTiO3), which was subsequently integrated into water-based drilling mud (WBDM) to mitigate barite sagging. The high area-to-volume ratio of the synthesized weighting components necessitates only small quantities of weighting materials to formulate optimal gravity drilling mud. Drilling mud samples were formulated by incorporating different concentrations (0.2, 0.5, and 0.8 lb/bbl) of nFeTiO3 into a base mud consisting of weighted nBaSO4. Static and dynamic tests were conducted at 120 °C and 49 °C, respectively, to assess the sag tendency of the nBaSO4 mud systems and to identify the optimal weight concentration of nFeTiO3 for sag mitigation. The mud systems were measured by measuring the mud pH, density, and rheological properties at 49 °C. A filtration test was performed at 120 °C to determine the influence of nFeTiO3 on nBaSO4 wellbore sealing effectiveness. The research showed that adding nFeTiO3 to nBaSO4-weighted drilling mud made the mud denser and lowered the pH to the best range of 9.5–11.5. Under 49 °C temperature conditions, there was an appreciable increase in the rheological properties of the nBaSO4-based drilling mud with an increasing weight concentration of nFeTiO3. Adding nFeTiO3 to the nBaSO4-based mud resulted in a significant decrease in the sag factor. 0.8 lb/bbl nFeTiO3 effectively inhibited barite drooping under static and dynamic sag conditions, resulting in sag factors of 0.511 and 0.38, respectively. HTHP filtration data demonstrated that nFeTiO3 did not significantly influence the filtration efficiency of nBaSO4. This study found that using combined nBaSO4 and nFeTiO3 could help stop barite sag problems and improve wellbore stability. Deploying this mud under HTHP conditions could be effective, economical, and safe.

Several oilfields undergo to reservoir souring, typically during water injection for secondary recovery, resulted in increasing concentrations of produced hydrogen sulfide (H2S). The main reason for this is the mechanism of generating hydrogen sulfide are the sulfate reducing bacteria (SRB). These bacteria use sulfate (So4) in the injection water as an electron acceptor and use organic acids which exist in formation water as a source of energy and carbon to generate H2S. In addition to that, the issues of health and safety, the existence of H2S decreases the worth of the produced hydrocarbon. The present study includes isolation and enumeration of sulfate reducing bacteria (SRB) from the injection and produced water of Ahdeb oilfield in Iraq by using Most Probable Number (MPN) technique. The Laboratory experimental work for production of sulfide with mix cultures of these bacteria was performed also with sodium lactate as an energy source. The experiments were carried out to determine the concentration of sulfide versus consumption of lactate in vitro. The concentration of sulfide is determined by using spectrophotometer method, whereas; the concentration of sodium lactate is calculated by using high performance liquid chromatography (HPLC) system. The experimental results demonstrates that the most numbers of bacteria in injection water are higher than the number in produced water samples. Whilst, the production of sulfide by SRB presents that inversely correlated to the concentration of sodium lactate. The growth experiments shows that the SRB concentration is increased in areas where the energy source and sulfate have high concentrations. Also, there is a direct relationship between SRB concentration and sulfide production. Therefore, the water injection from these bacteria must be treated before the injection to the reservoir to provide all the condition of SRB growth.

BackgroundAt present, microorganism has been considered as important factors that threaten to buried pipelines with disbonded coatings. Aiming at the problem of unknown corrosion mechanism of sulfate-reducing bacteria (SRB), a series of studies have been carried out in this paper. Spectrophotometer and fluorescent labeling technology are used to study the growth and attachment of SRB in the simulated soil solution. The corrosion behavior of X80 pipeline steel with or without SRB was researched by electrochemical methods such as open circuit potential, dynamic potential polarization curve, and electrochemical impedance spectroscopy. The microscopic morphology of the corrosion products on the surface was observed with a scanning electron microscope (SEM), and the element content of the corrosion products on the surface of the sample after corrosion was observed using X-ray energy spectrum (EDS) analysis.ResultsThe results showed that the growth and reproduction of SRB caused the pH of the soil simulated solution to increase, which may promote the corrosion of X80 steel. In addition, the cathode reaction of X80 steel in a sterile environment is the reduction of H+, and the main corrosion product is iron oxide. When the soil simulation solution contains SRB, the cathodic reaction is controlled by both H+ reduction and sulfide depolarization reactions, and FeS appears in the corrosion products.ConclusionAlthough the life cycle of SRB is only about 14 days, the corrosion of X80 steel is greatly promoted by SRB, and even causes corrosion perforation, which will bring huge economic losses and serious safety hazards.

Radiological survey of the covered and uncovered drilling mud depository

Seawater injection into oil reservoirs for secondary oil recovery is frequently accompanied by souring. Souring causes various problems, such as microbiologically influenced corrosion (MIC) and deterioration of crude oil. Sulfate-reducing bacteria (SRB) are considered to be major players in souring. Nitrate injection has been widely used to control the growth of SRB. The aim of this study was to investigate the changes in the bacterial community in response to nitrate addition to control biological souring. We investigated the effect of nitrate addition in an artificial souring experiment, using diluted crude oil as substrate and electron donor. Desulfotignum sp. was the predominant SRB under all conditions tested. Addition of nitrate at the beginning (N0) repressed the growth of SRB, concomitant with significant growth of the nitrate-reducing bacteria (NRB) Thalassospira sp. Nitrate addition after SRB growth (at day 28, N28) successfully remediated the sulfide produced by SRB, but no significant reduction in sulfate was observed subsequently. In the N28 experiment might be the result of the role of Arcobacter sp., which are nitrate-reducing sulfide-oxidizing bacteria, and/or the ability of Desulfotignum sp. to reduce nitrate and/or nitrite as a stress response. Thus, SRB might persist after nitrate addition, potentially causing subsequent SRB outbreaks

Purpose Bdellovibrio bacteriovorus is a gram-negative predatory bacterium which can potentially inhibit microbiologically influenced corrosion by preying on sulfate-reducing bacteria (SRB). However, no researches about the inhibition are reported according to the authors’ knowledge. The purpose of this paper was to investigate the Inhibition effect of B. bacteriovorus on the corrosion of X70 pipeline steel induced by SRB. Design/methodology/approach The effect of B. bacteriovorus on the growth of SRB was studied by measuring the optical density at 600 nm (OD600) and sulfate concentration in culture medium. X70 pipeline steel was used as the test material to investigate the anti-corrosion effect of B. bacteriovorus on SRB by conducting electrochemical analysis (including Tafel polarization curves and electrochemical impendence spectroscopy) and weight loss measurement. Findings B. bacteriovorus could inhibit the growth of SRB in culture medium by its predation on SRB, which led to decrease of OD600 value and increase of sulfate concentration. The results of electrochemical analysis indicated that B. bacteriovorus had positive inhibition efficiencies on SRB-induced corrosion of X70 pipeline steel. Moreover, corrosion rate of X70 pipeline steel was declined from 19.17 to 3.75 mg·dm-2·day-1 by the presence of B. bacteriovorus. Originality/value This is the first report about using B. bacteriovorus to inhibit the corrosion induced by SRB. Compared to other anti-corrosion methods, the microbial inhibition methods exhibit more considerable application value due to its low cost, high efficiency and non-pollution.

Microbiologically Influenced Corrosion (MIC) caused by the presence of Sulfate-reducing bacteria (SRB) is a big concern in heavy industries. Pipeline infrastructure may experience severe metal loss due to corrosion induced by the species and can potentially lead to catastrophic failure. By studying SRB growth condition, important parameter can be controlled to prevent or slow down a corrosion process. This study discussed on the effect of pH value to the corrosion growth rate on API 5L X70 low carbon steel subjected to outer part of underground pipeline. In this research, the type of SRB that's been used is Postgate C of Desulfovibrio Desulfuricans. There are 80 numbers of samples prepared with various pH value and temperature, which each of the samples contains two coupon steel immersed in the medium together with SRB for 7, 14, 21 and 28 days. The process in determining weight loss is analyzed and the corrosion rate for each steel sample is identified by weight loss. The result is plotted and analyzed, the particular pH values and temperature affect the growth of SRB in the medium where the existence of SRB could accelerate the corrosion rate towards the steel surface of API X-70. The samples are exposed to SRB in days’ time. This experiment aims to determine the optimum temperature for SRB growth and demonstrate the corrosion rate simulation using One-Factor-at-A-Time method (OFAT) method. The consequences of SRB activity, it is shown that pitting corrosion produced on the surface of steel. In fact, the sulphur element is identified as one of the corrosion products due to SRB activity.