Fouling+In+Industry

=Introduction: = In the offshore oil and gas industry fouling is an inevitable problem that will occur on all exposed surfaces. Fouling can occur on the inside of your pipes when the brine being transported experiences a decrease in solubility. This usually occurs when the brine is supersaturated and undergoes a temperature or pressure change, when being brought to the surface. Also, biological fouling can occur on the exterior of your equipment whether it’s the pipes that transport the oil or the vessels used to transport the oil back to shore for revenue.

=Biological-Fouling: = Biological fouling occurs when algae and other living organisms attach onto the outside material forming a biological film layer (protein layer). This first step is referred to as the micro-fouling stage. Once the biological film has been formed larger sea life such as barnacles, mussels, and seaweed can attach, onto the protein layer, forming a biological scale. This second step is referred to as the macro-fouling stage. The build up of this type of scale can drastically increase the weight of the structure and decrease the hydrodynamics of oil carrying vessels. The U.S. Navy found that biological fouling can account for up to a 40 % increase in fuel consumption and a 10% speed reduction on their vessels; as a result, costing more money to operate. The United States Government spends upwards of 5.7 billion dollars to remedy biological fouling each year. Some of the remedies include spraying antifouling coatings onto the metal surfaces to prevent the protein layer from adhering to the metal surface. One of the major problems encountered with this technique is that the use of chemicals such as TBT (tributyltin) are extremely toxic to the marine life, resulting in many abnormalities or even death of the marine life. The only real eco friendly method to remove biological fouling is to mechanically scrape the barnacles, mussels, and seaweed off annually.



=Scaling: = The second type of fouling the oil and gas industry faces is scaling. Scaling occurs in the inside of the pipe causing a reduction in pipe diameter; as a result, reducing the flow rate of the oil to the surface. Scaling occurs when a saturated brine undergoes a temperature or pressure change causing the solubility to decrease, which results in the precipitation of solid crystals. Some of the common scales that form in the offshore oil recovery process are barium sulphate (barite), calcium carbonate (calcite), strontium sulphate, and magnesium sulphate. The removal process for these types of scales is extremely costly and very difficult to do.

Scaling affects the profitability of oil and gas operations in a number of different ways. The table below outlines some of the ways that scaling impacts the profitability of the oil and gas industry:



As the table above indicates, chemical inhibition is a common cost factor regardless of where a scale problem manifests.


 * Scaling Has a Knock-On Effect on Profitability**

The potential for lost oil and gas production revenue manifests in many forms where scaling problems are endemic. When water is injected downhole for reservoir pressure maintenance or disposed of into deep well-accessed saline aquifers, the conditions are perfect for scale formation. Steep pressure and temperature gradients are present - serving as thermodynamic energy wells. These extreme conditions also promote the supersaturation of water with the dissolved ions that form the building blocks of scale crystals. Due to the large localized pressure differential, scale forms in the perforated interval of the wellbore where direct communication to the subsurface geological formation of interest exists.

Where water is being injected downhole to maintain reservoir pressure (a scenario known as a waterflood in industry parlance), the loss of a single injection well due to scale formation will result in a loss of local reservoir pressure support. The loss of this single injector well will also result in a breakdown of the larger overall water injection pattern that drives the oil in the reservoir in a piston-like manner from injectors towards producer wells. This breakdown of the overall waterflood pattern-drive mechanism can result in premature water breakthrough at some of the producer wells.

Water breakthrough is an irreversible condition resulting from a permanent change in the relative permeability of the reservoir rock. The costs of disposing of the produced water at a watered-out well include the variable (fuel, trucking, chemicals) and fixed (equipment, facilities) costs of treating the produced water-oil emulsion. There is also a significant loss of revenue from the decreased oil production at the watered-out well. The water that is produced from this watered-out well will need to be treated and transported to a disposal or injector well. Since the closest injector well is out of service due to scaling problems, it may be necessary to truck the water farther afield where existing water flowlines are not available.


 * Barite Scale Presents Special Challenges**

Once formed, Barite scale is particularly expensive to treat due to its insolubility in acid solutions. As such, mechanical removal is frequently used where Barite scales are present. Unlike acid treatment, mechanical removal always requires an associated production shutdown. Many surface process facilities have regularly scheduled production turnarounds during which mechanical scale removal can be performed safely and cost-effectively. A production shutdown can also be scheduled for a producing wellbore, although it is far more common to take at least one unplanned shutdown before a scheduled maintenance program is intiated for a typical wellbore. Due to the increasing scarcity of oil and gas resources, it is becoming more and more frequent to have scaling occuring in remote and deep offshore wellbores. The costs associated even for a planned service outage for an offshore production facility are much higher than those for a land-based facility. Of course, it follows that for remote offshore wells, no cost will be spared to prevent a scaling problem from leading to a workover situation.

Much of the industry research into scaling has consequently been focused on finding novel and more effective chemical approaches to the inhibiton of Barite scale. If Barite scale can be prevented from occuring in the first place using chemical inhibitors, then the need for mechanical scale removal with its associated costs and lost production can be alleviated to a great extent. Chemical scale inhibitors are generally classified by the mechanism that they employ to ihibit scale. The two main scale inhibitor classes are the nucleation inhibitors and the crystal growth inhibitors.

The use of chelating agents such as EDTA and DPTA have also been shown to be effective at removing existing Barite scales by incorporating the Barium atom into a stable, acid soluble metal ion complex that can then be removed using convential acid treatment techniques. Some other chelating agents alse exist that form stable water insoluble metal complexes with certain scale cations. Once formed, these water insoluble metal complexes can be removed from suspension using flocculating agents.

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