Impairment of flow by way of mineral scale formation is a major complication affecting production in the oil and gas industry. Soured reservoirs contain hydrogen sulfide (H 2 S) that can prompt the formation of exotic metal sulfide scales, leading to detrimental fouling that can negatively impact production. The contrast in the mode of precipitation (solid formation from liquid solution) and deposition of both sulfide scale and conventional inorganic carbonate and sulfate scales is herein examined. Design of an experimental rig allowing diffusion of H 2 S gas into the brine phase of a sealed reaction vessel resulted in a realistic representation of scaling processes occurring within sour reservoirs. Multiphase conditions, induced by introduction of a light oil phase to scaling brine within a turbulent regime, aimed to study the effect of oil and water wetting on pipeline fouling. Performance of a range of antifouling surfaces was determined through measurement of scale deposition by gravimetry and microscopy techniques. Under conditions modeled to reflect a typical H 2 S-containing reservoir, the contrasting scaling mechanisms of conventional calcium carbonate (CaCO 3 ) and barium sulfate (BaSO 4 ) scales when compared to lead sulfide (PbS) scale highlighted the critical role of the light oil phase on deposition. While conventional scales showed deposition by both crystallization and adhesion onto surfaces, the thermodynamic driving force for PbS prompted rapid bulk nucleation, with adhesion acting as the overwhelmingly dominant mechanism for deposition. The results showed that the addition of a 5% v/v light oil phase had a profound effect on scale particle behavior and deposition onto antifouling surfaces of varying wettability as a result of two processes. Primarily, the oil wetting of hydrophobic surfaces acted as a barrier to deposition, and second, adsorption of scale crystals at the oil/water interface of oil droplets within a turbulent oil-in-water emulsion resulted in adhesion to hydrophilic surfaces after impaction. It is therefore proposed that sulfide scale, typically deposited in the upper regions of production tubing, is driven by adhesion after formation of a PbS solid-stabilized Pickering emulsion. This contrasts with the commonly held view that metal sulfides precipitate and deposit similarly to conventional scales, whereby salts crystallize both directly upon surfaces and in the aqueous bulk phase as solubility decreases toward the wellhead.

The formation of calcium carbonate scale and the occurrence of CO 2 corrosion are both widespread phenomena observed within pipework during oil and gas production. The most common form of treatment for both processes is the application of chemical inhibition through corrosion and/or scale inhibitors. Surface scaling of pipework rarely occurs in environments where no corrosion exists, yet techniques used to develop and assess the performance of scale inhibitors tend to focus on assessing and reducing solely bulk/surface scaling, without affording consideration towards corrosion, whilst corrosion inhibitors are frequently evaluated in non-scaling environments. Furthermore, both chemicals tend to be evaluated independently meaning that any potential antagonistic effects between the chemicals can go unrecognised. This paper addresses this very issue by presenting a unique setup and methodology to enable the occurrence of scale and corrosion to be monitored simultaneously in a CO 2 -saturated environment in the presence and absence of combined scale and corrosion inhibitors. The test cell focuses on evaluating four key parameters which are quantified either throughout the duration of the test, or from the implementation of post-test surface analysis techniques.The multiple assessment of (i) bulk scale precipitation, (ii) surface scaling, (iii) general corrosion and (iv) localised corrosion permits a full assessment of the chemical blends propensity to mitigate both scaling and corrosion. Non-inhibited tests were initially conducted at 60°C to form a baseline for comparison. Four combined scale/corrosion inhibitors were subsequently used at low concentrations in order to understand their mechanisms and highlight any competitive effect which existed in reducing either scale or corrosion. The results demonstrate that the methodology implemented is effective at assessing the efficiency of combined inhibitors in reducing both corrosion and scale in environments where both processes occur simultaneously. The limitations of conducting solely bulk scaling or corrosion tests in non-scaling environments are discussed relative to the results obtained in this work. The results of each individual inhibitor are discussed and markedly different behaviour is observed according to the concentration administered, as well as the particular blend of chemicals applied.

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Mineral scale formation and deposition in down-hole completion equipment such as subsurface safety valves can cause dramatic and unacceptable safety risks and associated production losses and operational costs. Current scale removal strategies involve both mechanical and chemical technologies, each of them having their own advantages depending on the type of mineral scale and its location. However, these techniques are often costly and of limited efficiency. The current study assesses the ability of a range of chemically and morphologically modified coatings to prevent/reduce mineral scale surface fouling. Building-up on previous work done under static conditions, this paper presents results from scaling tests under laminar and turbulent dynamic conditions using a rotating cylinder electrode under in a complex (mixed) scaling environment (supersaturated w.r.t. calcium carbonate, barium sulfate, strontium sulfate, barium carbonate and strontium carbonate). The study shows that if properly selected, surface treatments represent a promising approach to reduce scale deposition on downhole equipment surfaces that are critical to maintain equipment functionality and thereby well safety barrier integrity. By analyzing the scaling behaviors observed within the set of surfaces tested, suggestions of the controlling factors in anti-fouling on these systems are presented and discussed.

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