Iron Sulphide (FeS) Scale Prediction-Modelling Development and Experimental Methodology Design

Iron sulphide (Fes) scale is widely present in both oilfield and geothermal systems and causes a range of production and Health and Safety problems. Although substantial progress has been made, continued efforts are needed to precisely understand and predict FeS scaling. The aim of this work is to present a simple robust model for FeS scale experiments in the laboratory. This model predicts saturation ratios (SRs) and masses of the formed iron sulphide scale, final solution compositions and final pH levels, for specific lab experiments. This model is verified by comparing results with carefully designed experiments which are monitored by a range of analytical experimental techniques, e.g., ICP-OES, ESEM/EDX and XRD (explained in the text). These analytical methods allow us to analyse for all the components present, such as initial and final [Fe2+], aqueous [H2S] levels etc, and they also give direct information on the morphology of any precipitates formed, either as crystalline or amorphous solids. Experiments were performed in an anaerobic chamber since we were using iron (II) ions (Fe2+) from both iron (II) chloride tetrahydrate and also ammonium iron (II) sulphate hexahydrate. The latter, known as Mohr salt, is thought to be a more reliable source of Fe2+. In fact, we found different crystallographic types of FeS scale precipitate from each of these 2 irons (II) salts. In addition, we observed that when FeS particles are precipitated from the solution, then under some circumstances some FeS particles can remain in colloidal suspension. This has implications for the level of measured "[Fe2+]" by ICP which measures the total Fe in solution, i.e., the free Fe2+ ions as well as any suspended colloidal FeS. The results show that there is a quantitative agreement between the experimental results and the predictions of the model in determining final pH of solution, final [Fe2+] and mass of FeS precipitate. However, it was also noted in some cases where discrepancies occurred - e.g., in [Fe2+] level - this may be ascribed to the colloidal nature of FeS scale. The information presented in this study will help production chemists to understand the chemical formation of FeS in laboratory testing, and this will assist in the selection and design for future scale inhibitor treatments.</p

Coupled Adsorption/Precipitation Modelling of Phosphonate Scale Inhibitors in a Batch Reactive System

Scale inhibitor squeeze treatments are one of the most common ways to prevent scale deposition. The mineral scale will be inhibited if the concentration of the scale inhibitor (SI) in the produced water is above a certain threshold, known as the Minimum Inhibitor Concentration (MIC), which is controlled by scale inhibitor retention. Therefore, accurate modelling of the SI retention through adsorption (Γ) and precipitation (Π) is critical to the successful design and implementation of squeeze treatments. In this study, an equilibrium model has been developed to simulate the coupled adsorption-precipitation (Γ/Π) of phosphonate scale inhibitors in reactive formations, such as carbonates, in the presence of calcium and magnesium cations. In this approach, the scale inhibitor (SI) was considered as a poly weak acid that may be protonated (HnA), resulting in the complexation with Ca/Mg ions, leading to the precipitation of SI_Ca/Mg complexes. All these reactions occur in an integrated system where carbonate system reactions and adsorption of the soluble species are occurring in parallel. In the adsorption process, all the SI derivatives remaining in the solution, including free and complex species, are considered to participate in the adsorption process, described by an an adsorption isotherm model (e.g., Freundlich). For the precipitation part, the model considers the following reactions: (i) the carbonate system, (ii) SI speciation, considered as weak polyacid, HnA, (iii) the SI-metal (Ca and Mg) binding complexes, and (iv) subsequent precipitation of the SI-Ca/Mg complex. The system charge balance and the mass balances for calcium, magnesium, carbon, and SI are considered, to numerically equilibrate the system (excluding the adsorbed species), by solving a determined set of non-linear equations numerically. Following the algebraic reduction of the equations, the system is reduced to three non-linear equations that may be solved by the Newton-Raphson method. The precipitation of the SI-Ca/Mg is modelled in the equilibrium model based on the solubility of SI in the solution, determined from the lab experiments. The reliability of the proposed model was established by comparison with experimental results from a previous study (Kalantari Meybodi et al., 2023) on the interactions of DETPMP in a Calcite/brine (containing free Ca/Mg) system, where the final concentration of SI, Ca2+, Mg2+, CO2 and pH were compared. The modelling showed good general agreement with the experimental results, and a further sensitivity analysis was performed to examine the behaviour of some uncertain parameters, such as the stability constant of complexes.</p

The Effect of pH and Mineralogy on the Retention of Polymeric Scale Inhibitors on Carbonate Rocks for Precipitation Squeeze Treatments

Abstract The bulk "apparent adsorption" behavior (Γapp, vs. Cf) of 2 polymeric scale inhibitors (SI), PPCA and PFC, onto carbonate mineral substrates has been studied for initial solution pH values of pH 2, 4 and 6. The 2 carbonate minerals used, calcite and dolomite, are much more chemically reactive than sandstone minerals (e.g. quartz, feldspars, clays etc.) which have already been studied extensively. In nearly all cases, precipitates formed at higher SI concentrations were due to the formation of sparingly soluble SI/Ca complexes. A systematic study has been carried out on the SI/Ca precipitates formed, by applying both ESEM/EDX and particle size analysis (PSA), and this identifies the morphology and the approximate composition of the precipitates. For PPCA, at all initial solution pH values, regions of pure adsorption (Γ) ([PPCA] &amp;lt;100ppm) and coupled adsorption/ precipitation (Γ/Π) are clearly observed for both calcite and dolomite. PFC at pH = 4 and 6 also showed very similar behavior with a region of pure adsorption (Γ) for [PFC] &amp;lt; 500ppm and a region of coupled adsorption/precipitation (Γ/Π) above this level. However, the PFC/calcite case at pH 2 showed only pure adsorption, while the PFC/dolomite case at pH 2 again showed coupled adsorption/ precipitation at higher PFC concentrations. For both SIs on both carbonate substrates, precipitation is the more dominant mechanism for SI retention than adsorption above a minimum concentration of ~100 – 500 ppm SI. The actual amount of precipitate formed varies from case to case, depending on the specific SI, substrate (calcite/dolomite) and initial pH (pH 2, 4 and 6). Although the qualitative behavior of both PPCA and PFC was similar on both carbonate substrates, the apparent adsorption of PPCA was higher on calcite than on dolomite; PFC apparent adsorption was higher on dolomite than on calcite. It is discussed in the paper how these observations are related to the reactivity of the different carbonate minerals, the resulting final pH (which affects the dissociation of the SI), Ca-SI binding and the solubility of the resulting complex.</jats:p

A bilayer microarray patch (MAP) for HIV pre-exposure prophylaxis: the role of MAP designs and formulation composition in enhancing long-acting drug delivery

Microarray patches (MAPs) have shown great potential for efficient and patient-friendly drug delivery through the skin; however, improving their delivery efficiency for long-acting drug release remains a significant challenge. This research provides an overview of novel strategies aimed at enhancing the efficiency of MAP delivery of micronized cabotegravir sodium (CAB Na) for HIV pre-exposure prophylaxis (PrEP). The refinement of microneedle design parameters, including needle length, shape, density, and arrangement, and the formulation properties, such as solubility, viscosity, polymer molecular weight, and stability, are crucial for improving penetration and release profiles. Additionally, a bilayer MAP optimization step was conducted by diluting the CAB Na polymeric mixture to localize the drug into the tips of the needles to enable rapid drug deposition into the skin following MAP application. Six MAP designs were analyzed and investigated with regard to delivery efficiency into the skin in ex vivo and in vivo studies. The improved MAP design and formulations were found to be robust and had more than 30% in vivo delivery efficiency, with plasma levels several-fold above the therapeutic concentration over a month. Repeated weekly dosing demonstrated the robustness of MAPs in delivering a consistent and sustained dose of CAB. In summary, CAB Na MAPs were able to deliver therapeutically relevant levels of drug.<br/