M. M. Al-Darbi

Biodegradation of Natural Oils in Seawater

Abstract Spills of non-petroleum hydrocarbons including vegetable oils and fish oils are of environmental concern because of their potential to cause serious effects on marine life and coastal environments. Biodegradation by indigenous microorganisms is an important and potentially ubiquitous process affecting both the chemical composition and physical properties of contaminant oils. Data on the environmental persistence of non-petroleum oils is now required for risk assessments and decision making by spill responders. This article investigates the biodegradability of various vegetable and fish oils under the influence of natural bacteria in seawater. The influence of nutrients and microbial environment on changes in bacterial numbers and the extent and rate of degradation for various test oils (olive, mustard, canola and cod liver oils) were studied over time. Time-series visual and microscopic observations were made to characterize physical changes in the residual oils, formation of floating and precipitate particles, oil droplets and dispersion. The biodegradation process was significantly influenced by environmental conditions, with a higher rate and extent of biodegradation observed in seawater amended with nutrients and wastewater that contained elevated numbers of bacteria and nutrients. It was observed that different oils respond in different rates and extents to biodegradation depending on their stability, viscosity and compositions. All results clearly revealed a significant response of the oil-contaminated samples to both the seawater and wastewater environments. Observations on changes in the physical properties of the residual oil may be important in the context of oil spill response strategies. For example, simple physical recovery methods may be used to recover polymeric lumps at the sea surface.

Control of Microbial Corrosion Using Coatings and Natural Additives

One of the major concerns in the oil and gas industry is corrosion. Microbial-influenced corrosion (MIC) can be defined as the deterioration of metals by natural processes directly or indirectly related to the activity of microorganisms. MIC affects many industries, such as petrochemical, ships and marine structures, power generating, aircraft fuel systems, waste water facilities, cooling water systems, process industries, paper mills, and water supply and distribution systems. In this study, the influence of sulfate-reducing bacteria (SRB), grown in a lactate/ sulfate culture medium, on the corrosion of both uncoated and coated mild steel was evaluated in the presence and absence of natural additives. To achieve this, an oilbased coating (alkyd) was used with and without the addition of natural additives to protect mild steel in a sulfate-reducing bacteria environment. Another objective of this study was to investigate the effects of SRB and/or their metabolites on the used coatings and the adverse effects of those coatings and additives on biofilm formation and bacteria growth rate. In this paper, 2 natural additives were identified for effective MIC protection. Natural products were selected based on the environmental appeal of the products. Two additives, derived from olive oil and Manhaden fish oil, were found to be effective in reducing MIC. In general, 2-3% of a natural additive was deemed adequate for effective MIC protection. Bacteria populations were counted at the beginning and at the end of the tests using the plate count method. After immersing the different coupons for 3 months in the SRB medium, it was noticed that the number of bacteria and their colonies were highly affected by both the environment and the used coating systems. A series of corrosion tests was performed to study the effectiveness of various natural additives. Visual observations, scanning electron microscopy (SEM) analyses, and computer image analyzer techniques were used to study the effects of SRB on the different coupon surfaces. It was observed that the presence of coatings inhibited both the biofilm growth and biocorrosion effects. The results revealed that the addition of some natural additives improved the protection ability of commercial coatings, with the best result with Manhaden fish oil.

A New Theory and Methodology for Modeling Sand During Oil Production

This article considers the problem of depletion-induced sand production during oil production. The whole process of sand production is considered and different mechanisms of sanding are addressed. The problem of sand production costs the oil and gas industry hundreds of millions of dollars per year. An accurate method for predicting sand production can help engineers design well completions that maximize petroleum production while minimizing sand-related problems. In this article, sanding mechanisms during depletion are reviewed with a view to developing guidelines for new tests. These triaxial tests capture the essence of physics that prevails in field scale. A material model is presented for simulating the behavior of the formation against the applied loads, particularly in aged reservoirs. Finally, a model for numerical simulations of these experiments is presented. This model can be used for scaling-up laboratory results. The numerical model is used to evaluate field performance under a series of conditions. The numerical analyses confirm the proposed model and scenario as is explained. We also evaluate the effect of cohesion and friction angle and initial cap pressure on the depletion at the time of failure. The phenomenon of the pore collapse is modelled by using Mohr-Coulomb and considering the strain softening/hardening cap model.

Deflection Criteria for Numerical Assessment of the Sand Production Potential in an Openhole Completion

An elastic-plastic three-dimensional fully coupled model is proposed to model shear and tensile-induced sanding and consequently estimate volume of sand production. The problem is of significant interest to industry since a good estimation of wellface failure and therefore sand production helps the completion engineer to best design downhole completions. Such a design would not only maximize flow rate but also minimize cost of completion. In this investigation, a numerical analysis by using the finite difference method was performed. An elastic-plastic analysis by using the Mohr-Coulomb model was conducted. This model is indeed considered to be the most useful model for geotechnical analysis. For the purpose of this study, the openhole case was considered to have had large deformation and large plastic strains in order to determine the wellface failure and therefore sand production. Effective stress distributions around a wellbore were investigated. Based on this investigation, an effective way to model depletion-induced sanding is proposed. The effects of cohesion, friction angle, and modulus of elasticity as well as reservoir pressure on the critical bottom hole pressure were examined. The results show that the cohesion and the variation in friction angle affect the critical value of drawdown, the effect of the former one being more significant than the latter. Moreover, the modulus of elasticity and reservoir pressure affect the critical value of drawdown significantly. At higher values of the modulus of elasticity, however, the effect of the modulus of elasticity tapers off and a further increase in its value does not affect the critical value proportionally. The effect of the reservoir pressure on acceptable drawdown value indicates the effect of reservoir depletion on the potential of sand production.

The Inhibitive Characteristics of Mixed Inhibitor Combinations Under Heat and Mass Transfer Conditions

Oil and gas production operations are characterized by the inevitability of numerous technical problems related to the nature of the products and effluents. Moreover, these problems change gradually and require a periodic adjustment of the solution. One of the major concerns in the oil and gas industry is corrosion. Corrosion can be defined as the destruction or deterioration of material because of a reaction with its environment. In this paper the inhibitive characteristics of mixed inhibitor combinations on mild steel, under controlled conditions of heat and mass transfer, have been investigated using a rotating cylinder electrode system. Potentiostatic polarization experiments were carried out in both inhibited and uninhibited brackish water solutions under isothermal and heat transfer conditions. The optimum concentrations of the inhibitors used were estimated under the isothermal and dynamic conditions. Under isothermal conditions, the limiting current density values of oxygen reduction in the brackish water followed the Eisenberg equation. The presence of heat transfer enhanced the oxygen transfer rate over and above the value under isothermal conditions. The corrosion potential, passivation potential, and passive current density values, were a complex function of temperature, flow rate, and heat transfer. The anodic current density values increased with increases in temperature, flow rate, and the presence of heat transfer. The mixed inhibitor combinations showed high protection efficiency under the studied heat and mass transfer conditions.