Evaluation of laboratory techniques for assessing scale inhibition efficiency

Injecting chemical inhibitors is the most common method to mitigate mineral scaling in the oil industry. As such, the effectiveness of the techniques employed to evaluate performance of chemical scale inhibitors and apply the appropriate dosage is a very important aspect to be considered during the design of a scale prevention treatment. In this paper, the kinetics of scale formation and its inhibition are studied using a conventional bottle test, a dynamic tube blocking rig and a recently developed in-situ flow visualization rig. Calcium carbonate scaling brine was prepared at two saturation indices (SI) of 2.1 and 2.8 at 50 °C and run through the rigs at flow rate of 20 ml/min. The conventional polphosphinocarboxylic acid (PPCA) inhibitor was used for the inhibition study at concentration ranging between 0.5 and 10 ppm. The MICbulk determined from bottle test and supported with the in-situ turbidity MICbulk for SI of 2.1 and 2.8 are 1 ppm and 8 ppm respectively. For the same SI values, a considerably lower concentration of PPCA, 0.5 ppm and 4 ppm for the surface inhibition test using the capillary rig were obtained compared to MICsurface of 4 ppm and 8 ppm from the in-situ visualization technique. The surface visualization technique enables the range of concentration of inhibitors at which both bulk and surface scaling are completely controlled to be determined. The different techniques are shown to give complementary information for different stages of crystallization process and inhibition

Surface inorganic scale formation in oil and gas industry: As adhesion and deposition processes

Scale formation on surfaces can normally be divided into two distinct processes: a “deposition process” which refers to the process of heterogeneous nucleation and growth at the asperities of the surface and an “adhesion process” which refers to the sticking of pre-existing crystals, which have nucleated in the bulk solution, and which build up as a layer on the surface. It has been presented in this paper that the surface scale formation rate is more dominantly controlled by the “deposition process” rather than the “adhesion process”. However, the level of agitation could have inverse effects on one process to another. Only a small amount of research has been done to understand the differences of the kinetics of each of these processes. The presented work represents an experimental study of scaling tests to assess the effect of hydrodynamic conditions, using Rotating Cylinder Electrode (RCE), in a complex scaling environment, particularly supersaturated with barium/strontium sulphate and calcium carbonate, on the stainless steel substrate coated with a wide range of different industrial coatings. In addition, the effect of the surface energy and surface roughness on both processes has been studied. The paper provides data that will assist in the understanding of the controlling parameters in scale formation in different conditions, and also describes what characteristics of the surface can make it a good anti-scale surface for inorganic scale; however, the results have showed that merely one parameter cannot assure a surface as a good antifouling surface

Preparation of magnetic carboxymethylchitosan nanoparticles for adsorption of heavy metals ions

The remediation of metal and heavy metal contaminants from water ecosystems is a long-standing problem in the field of water management. The development of efficient, cost effective, and environmentally friendly natural polymer-based adsorbents is reported here. Magnetic chitosan (CS) and carboxymethylchitosan (CMC) nanocomposites have been synthesized by a simple one-step chemical coprecipitation method. The nanoparticles were assessed for the removal of Pb2+, Cu2+, and Zn2+ ions from aqueous solution. Kinetic and thermodynamic models were used to describe and understand the adsorption process of the ions onto the nanomaterials. The interactions between the ions and the biopolymer-based composites are reversible, which means that the nanoparticles can be regenerated in weakly acidic or EDTA containing solution without losing their activity and stability for water cleanup applications

Inorganic mineral precipitation from potable water on heat transfer surfaces

In this study, an experimental approach mimicking processes encountered in electric kettles has been designed toinvestigate the influence of heating and cooling rate, and water composition on the kinetics of inorganic saltprecipitation taking place when water is heated from ambient temperature up to its boiling point. The kinetics ofsalt precipitation in the bulk solution have been monitored through turbidity measurements as well as trackingion concentration throughout the heating/cooling process and the experimentalfindings highlight the criticalrole of the cooling step on the overall amount of salts that precipitate. The presence of magnesium ions in thewater was found to influence the precipitation of calcium carbonate which was found to be the dominant saltcrystallising out of solution; calcium sulphate was not observed

Examining the effect of ionic constituents on crystallization fouling on heat transfer surfaces

The effect of the most abundant constituents in potable water on fouling of aluminium surface has been studied systematically in this work. The role of sodium, chloride, magnesium and sulphate ions and total organic carbon (TOC) on the fouling kinetics and morphology was assessed using a once-through open flow cell. The findings showed that the fouling resistance to heat transfer increases with the concentration of chloride and sodium. A complex influence of magnesium was found on the scaling process, varying between inhibition and promotion of scale formation depending on the concentration. At high concentrations of Mg2+, the formed scale layer consists of needle-like aragonite coated by a crust of magnesium deposits. The inhibitory performance of sulphate SO42− was found to be insignificant when compared with Mg2+ under similar conditions. Even though it is undesirable in potable water, inhibition efficiencies of TOC were 31.3% and 47.9% at concentrations of 2 and 4.3 mg/L respectively. The morphology observations illustrated that the presence of TOC produces a rough scale layer

Controlling the kinetic versus thermodynamic growth of calcium carbonate scale in the bulk and on surfaces

Mineral scale formation and deposition can cause dramatic and unacceptable safety risks and associated operational costs. It is recognized as a major flow assurance problem affecting production in the oil and gas industry. The current models used to predict scale precipitation are solely based upon thermodynamic data without taking into consideration any kinetic aspects of scale induction times or growth rates. The aim of this paper is to investigate the interplay between kinetic and thermodynamic control of calcium carbonate precipitation in the bulk and on surfaces. Standard bulk jar scaling tests were performed over a range of saturation ratios and temperatures. By analyzing bulk precipitation and surface growth experimental data the strong temperature dependence on the rate of surface fouling and a moderate dependency on saturation ratio has been confirmed. The experimental findings of this study suggest that reducing the kinetics of calcium carbonate precipitation in the bulk solution can under some conditions promote surface deposition

Cold rotating finger: Apparatus to study wax deposition under shear

A bench-top Cold Rotating Finger (CRF) is developed to study the effect of fluid shear on wax deposition. An inner rotating cylinder provides opportunity to study wax deposition on surfaces in the region of high fluid shear stress (and laminar/turbulent flows). A model system of linear n-alkane (C20 to C40) dissolved in dodecane to 9 wt% was used for the deposition tests. The bulk fluid temperature was set to 45°C and the temperature of the inner rotating cylinder to 5°C, with wax deposits showing a mass variation less than ~5% at constant rotational speed. The kinetic of wax deposition is non-linear, with an initial rapid deposition (approximately linear) followed by a slower rate as deposit mass tends to steady-state within 30 min. The wax deposit mass is limited by thermal insulation of the cold surface and not wax depletion. As a function of rotational speed, the wax deposit mass is shown to be maximum under static condition and gradually decrease with increasing rotational speed (25 to 500 rpm). The wax deposit morphology is studied by cryo-scanning electron microscopy with the static deposit showing a layered structure (ridges) which diminished at 200 rpm, confirming a denser, less porous deposit. With its simple design and small sample volume, the CRF provides a route to easily study wax deposition under conditions more relevant to the industry scenario

Competitive Adsorption of Interfacially Active Nanoparticles and Anionic Surfactant at the Crude Oil–Water Interface

The interfacial activity of poly(N-isopropylacrylamide) (pNIPAM) nanoparticles in the absence and presence of an anionic surfactant (sodium dodecyl sulfate, SDS) was studied at a crude oil–water interface. Both species are interfacially active and can lower the interfacial tension, but when mixed together, the interfacial composition was found to depend on the aging time and total component concentration. With the total component concentration less than 0.005 wt %, the reduced interfacial tension by pNIPAM was greater than SDS; thus, pNIPAM has a greater affinity to partition at the crude oil–water interface. However, the lower molecular weight (smaller molecule) of SDS compared to pNIPAM meant that it rapidly partitioned at the oil–water interface. When mixed, the interfacial composition was more SDS-like for low total component concentrations (≤ 0.001 wt %), while above, the interfacial composition was more pNIPAM-like, similar to the single component response. Applying a weighted arithmetic mean approach, the surface-active contribution (%) could be approximated for each component, pNIPAM and SDS. Even though SDS rapidly partitioned at the oil–water interface, it was shown to be displaced by the pNIPAM nanoparticles, and for the highest total component concentration, pNIPAM nanoparticles were predominantly contributing to the reduced oil–water interfacial tension. These findings have implications for the design and performance of fluids that are used to enhance crude oil production from reservoirs, particularly highlighting the aging time and component concentration effects to modify interfacial tensions

Scale deposition in the oil and gas industry: From a systematic experimental scale study to real-Time field data

Flow reduction due to scale deposition within the downhole utilities, valve applications, and tubular is recognised as one the major flow assurance problems affecting production in the oil and gas sector. Most of the literatures investigating similar mineral fouling mechanism mainly focused on either a laboratory framework under well controlled conditions or from field conditions with no systematic investigations. The current work bridges between a systematic experimental scale study and field data. The experimental work encompasses an investigation into the effect of the hydrodynamic conditions on the rate of the scale deposits on modified surfaces in a complex scaling environment, where the brine compositions are derived from the field conditions; and the field data includes the rate of scale deposition on the modified surfaces inside the tubing from the formation water. The comparison of these two sets of results facilitates a better understanding of the controlling parameters in scaling formation in both laboratory conditions and field conditions

Wax deposition using a cold rotating finger: An empirical and theoretical assessment in thermally driven and sloughing regimes

Time-dependent wax deposition was studied using a newly-built Cold Rotating Finger (CRF). Wax deposition rates and pseudo-steady state deposit mass values were shown to depend on the CRF rotational speed. Relative to 0 rpm, the wax deposit mass decreased with increasing rotational speed, reducing by 54% at 100 rpm and 82% at 700 rpm. At low rotational speeds, the reduced wax deposit correlated with changes in the bulk oil (To) and wax interface (Ti) temperatures as a function of increasing CRF rotational speed, with the behavior described by a diffusive model which accounted for the CRF fluid motion. The model described the temperature profile in the boundary layer by considering the heat transfer coefficient as a function of the CRF rotational speed, with heat transfer governing wax deposition. Mass transfer was described by Fick's law assuming a linear solubility with temperature and constant diffusivity determined from experimental data at CRF = 100 rpm. The change in heat transfer governed the mass deposited, with deposition at low rotational speeds described by a thermally-driven process. At higher rotational speeds, To was independent of CRF rpm, although the wax deposit mass continued to decrease. Visual assessment of the CRF revealed sloughing at rotational speeds 400 rpm. For high CRF rotational speeds, the molecular diffusion model could not accurately describe the wax deposit mass and was modified to include a sloughing term, , accounting for the wall shear stress, deposit radius and , which was taken to be an adjustable parameter to describe the sloughing intensity