High performance maleic acid based oil well scale inhibitors—Development and comparative evaluation

Asymmetrical Dependence of {Ba2+}:{SO4 2-} on BaSO4 Crystal Nucleation and Growth in Aqueous Solutions: A Dynamic Light Scattering Study

The impact of solution stoichiometry, upon formation of BaSO₄ crystals in 0.02 M NaCl suspensions, on the development of particle size was investigated using dynamic light scattering (DLS). Measurements were performed on a set of suspensions prepared with predefined initial supersaturation, based on the quotient of the constituent ion activity product {Ba²⁺}{SO₄ ^2-} over the solubility product K _sp (Ω_barite = {Ba²⁺}{SO₄ ^2-}/K _sp = 100, 500, or 1000-11,000 in steps of 1000), and ion activity solution stoichiometries (r _aq = {Ba²⁺}:{SO₄ ^2-} = 0.01, 0.1, 1, 10 and 100), at circumneutral pH of 5.5-6.0, and ambient temperature and pressure. DLS showed that for batch experiments, crystal formation with varying r _aq was best investigated at an initial Ω_barite of 1000 and using the forward detection angle. At this Ω_barite and set of r _aq, the average apparent hydrodynamic particle size of the largest population present in all suspensions increased from ∼200 to ∼700 nm within 10-15 min and was independently confirmed by transmission electron microscopy (TEM) imaging. Additional DLS measurements conducted at the same conditions in flow confirmed that the BaSO₄ formation kinetics were very fast for our specifically chosen conditions. The DLS flow measurements, monitoring the first minute of BaSO₄ formation, showed strong signs of aggregation of prenucleation clusters forming particles with a size in the range of 200-300 nm for every r _aq. The estimated initial bulk growth rates from batch DLS results show that BaSO₄ crystals formed fastest at near-stoichiometric conditions and more slowly at nonstoichiometric conditions. Moreover, at extreme SO₄-limiting conditions, barite formation was slower compared to Ba-limiting conditions. Our results show that DLS can be used to investigate nucleation and growth at carefully selected experimental and analytical conditions. The combined DLS and TEM results imply that BaSO₄ formation is influenced by solution stoichiometry and may aid to optimize antiscalant efficiency and regulate BaSO₄ (scale) formation processes.

Development and Performance Evaluation of Scale-Inhibiting Fracturing Fluid System

The injection water and formation water in the Mahu oil field have high salinity and poor compatibility, which leads to scaling and blockage in the formation or fracture propping zone during production. In this paper, a scale-inhibiting fracturing fluid system is developed which can prevent the formation of scale in the reservoir and solves the problem of scaling in the fracture propping zone at the Mahu oil field. Firstly, based on scale-inhibition rate, the performances of six commercial scale inhibitors were evaluated, including their acid and alkali resistance and temperature resistance. Then, the optimal scale inhibitors were combined with the fracturing fluid to obtain a scale-inhibiting fracturing fluid system. Its compatibility with other additives and scale-inhibition performance were evaluated. Finally, the system’s drag-reduction ability was tested through the loop friction tester. The results showed that, among the six scale inhibitors, the organic phosphonic acid scale inhibitor SC-1 has the best performance regardless of high-temperature, alkaline, and mixed scale conditions. In addition, SC-1 has good compatibility with the fracturing fluid. The scale-inhibiting fracturing fluid system can effectively prevent scaling inside the large pores in the propping zone, and a scale-inhibiting efficiency of 96.29% was obtained. The new fracture system maintained a drag-reduction efficiency of about 75%, indicating that the addition of the scale inhibitor did not cause a significant influence on the drag-reduction efficiency of the fracturing fluid.

Calcite Scale Inhibition Using Environmental-Friendly Amino Acid Inhibitors: DFT Investigation

Scale prevention is a long-term challenge. It is essential for ensuring the optimum utilization of oil and gas wells and minimizing economic losses due to disruptions in the hydrocarbon flow. Among the commonly precipitated scales is calcite, especially in oilfield production facilities. Previous studies on scale inhibitors have focused on investigating the performance of several phosphonates and carboxylates. However, the increased environmental awareness has pushed toward investigating environmental-friendly inhibitors. Research studies demonstrated the potential of using amino acids as standalone inhibitors or as inhibitor-modifying reagents. In this study, 10 amino acids for calcite inhibitors have been investigated using molecular simulations. Eco-toxicity, quantum chemical calculations, binding energy, geometrical, and charge analyses were all evaluated to gain a holistic view of the behavior and interaction of these inhibitors with the calcite {1 0 4} surface. According to the DFT simulation, alanine, aspartic acid, phenylalanine, and tyrosine amino acids have the best inhibitor features. The results revealed that the binding energies were -2.16, -1.75, -2.24, and -2.66 eV for alanine, aspartic acid, phenylalanine, and tyrosine, respectively. Therefore, this study predicted an inhibition efficiency of the order tyrosine > phenylalanine > alanine > aspartic acid. The predicted inhibition efficiency order reveals agreement with the reported experimental results. Finally, the geometrical and charge analyses illustrated that the adsorption onto calcite is physisorption in the acquired adsorption energy range.

Development of a Unique Organic Acid Solution for Removing Composite Field Scales

Removal of oil field scales commonly requires low pH acid, which may cause many issues under downhole conditions. Because of the deposition of different scale types and the economic effect, there is a need to develop a remedial descaling fluid that can be effectively used to remove different types of scales at a different position in the well. This paper provides a new scale dissolver that is noncorrosive and has high scale dissolution performance for composite scales. This study shows a series of comprehensive experimental lab tests as scale characterization, equilibrium brine compositional analysis, fluid compatibility and stability, solubility test, precipitation tendency for the dissolved solids, corrosion test, and core flooding. The scale samples contain magnetite, kaolinite, calcium carbonate, and sulfate scales. The results showed that the dissolution rate was higher than 74% for composite field scale samples after 6 h at 70 °C, while the new dissolver completely dissolved the two samples at 100 °C after 5 h. The new dissolver outperformed the common commercial dissolver used in the oil and gas industry. The new dissolver has a pH of 9 and showed safe use regarding the precipitation of dissolved solids that can be produced during the scale treatment and a low corrosion rate of 0.063 kg/m² at 6.9 MPa and 100 °C for 6 h. Also, the new dissolver was tested through core flooding for Indiana limestone and showed core permeability enhancement; the treatment with the new dissolver enhanced the core permeability from an initial value of 0.67 milliDarcy (mD) to record 1.29 mD.

A Review of Green Scale Inhibitors: Process, Types, Mechanism and Properties

In the present time, more often, it has been seen that scaling has grown as widely and caused problems in the oilfield industry. Scaling is the deposition of various salts of inorganic/organic materials due to the supersaturation of salt-water mixtures. Many works have been proposed by researchers using different methods to solve the problem, of which scale inhibition is one of them. The scale inhibitors, particularly for antiscaling, have derived from natural and synthetic polymers. Among different polymers, inorganic and organic compounds (polyphosphates, carboxylic acid, ethylenediaminetetraacetic acid (EDTA), etc.) can effectively manage the oilfield scales of which many are toxic and expansive. Scale inhibitors of alkaline earth metal carbonate and sulfates and transition metal sulfide are commonly used in oilfield applications. Scale inhibition of metallic surfaces is an essential activity in technical, environmental, economic, and safety purposes. Scale inhibitors containing phosphorus appear to have significant achievements in the inhibition process despite its toxicity. However, phosphorus-based inhibitors can serve as supplements prompting eutrification difficulties. Besides these increasing environmental concerns, green scale inhibitors are renewable, biodegradable, and ecologically acceptable that has been used to prevent, control, and retard the formation of scale. Considering the facts, this review article summarized the concept of scale, various green scale inhibitors, types, mechanisms, comparative performance, significance, and future aspects of green scale inhibitors, which will shed light and be helpful for the professionals working in the oil and gas industries.

Characterization of scale deposition in oil pipelines through X-Ray Microfluorescence and X-Ray microtomography

The formation of scales consists in one of the most relevant problems in the oil prospecting field and occurs when incompatible types of water (injected sea water and formation water) are mixed in the reservoir, unavoidably undergoing chemical interaction followed by mineral precipitation. In this work, scale samples extracted from obstructed oil pipes were characterized through X-Ray Microfluorescence and X-Ray microtomography by analyzing their elemental and structural composition. Different types of scale were found according to their elemental distribution (mainly BaSO₄ and CaCO₃) and to the way that they were deposited inside the pipes. The results of both techniques provided data that can be used to optimize the prevention and removal methods of such materials from pipes and equipments used in oil facilities.

Molecular Modeling Study toward Development of H2S-Free Removal of Iron Sulfide Scale from Oil and Gas Wells

A common problem that faces the oil and gas industry is the formation of iron sulfide scale in various stages of production. Recently an effective chemical formulation was proposed to remove all types of iron sulfide scales (including pyrite), consisting of a chelating agent diethylenetriaminepentaacetic acid (DTPA) at high pH using potassium carbonate (K₂CO₃). The aim of this molecular modeling study is to develop insight into the thermodynamics and kinetics of the chemical reactions during scale removal. A cluster approach was chosen to mimic the overall system. Standard density functional theory (B3LYP/6-31G*) was used for all calculations. Low spin K₄Fe(II)₄(S₂H)₁₂ and K₃Fe(II)(S₂H)₅ clusters were derived from the crystal structure of pyrite and used as mimics for surface scale FeS₂. In addition, K₅DTPA was used as a starting material too. High spin K₃Fe(II)DTPA, and K₂S₂ were considered as products. A series of K _m Fe(II)(S₂H) _n complexes (m = n-2, n = 5-0) with various carboxylate and glycinate ligands was used to establish the most plausible reaction pathway. Some ligand exchange reactions were investigated on even simpler Fe(II) complexes in various spin states. It was found that the dissolution of iron sulfide scale with DTPA under basic conditions is thermodynamically favored and not limited by ligand exchange kinetics as the activation barriers for these reactions are very low. Singlet-quintet spin crossover and aqueous solvation of the products almost equally contribute to the overall reaction energy. Furthermore, seven-coordination to Fe(II) was observed in both high spin K₃Fe(II)DTPA and K₂Fe(II)(EDTA)(H₂O) albeit in a slightly different manner.

Assessment of novel maleic anhydride copolymers prepared via nitroxide-mediated radical polymerization as CaSO4 crystal growth inhibitors

Calcium sulfate is one of the dominant scales which, unlike carbonate scale, are not easily removable by acid. To inhibit CaSO₄ scale formation in artificial cooling water systems, well-defined low molecular weight maleic anhydride and n-alkylacrylamide copolymers (YMR-S series) were synthesized via nitroxide-mediated radical polymerization initiated by benzoyl peroxide in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy at varying concentrations. These polymerizations exhibit living polymerization characteristics; that is, they show linear growth in chain length as a function of monomer conversion, and have narrow molecular weight distributions. Resultant polymers were characterized by means of ¹H-NMR and ¹³C-NMR. The inhibition behavior of these YMR-S series polymers against CaSO₄ was evaluated using the static scale inhibition method and a dynamic tube block test. The inhibition ability on the CaSO₄ scale is 99.5% with 9 ppm dosage level at pH 10.45 and temperature 70°C. Scanning electronic microscope analysis proved the morphological changes of the CaSO₄ scales due to the strong inhibition action of YMR-S polymers. It is also observed that the antiscaling effect of the copolymers greatly depends on the molecular weight, and the optimum range is below 20,000 and approximately in the range 500-2000.

Acrylic Acid-Allylpolyethoxy Carboxylate Copolymer Dispersant for Calcium Carbonate and Iron(III) Hydroxide Scales in Cooling Water Systems

A novel environmentally friendly type of calcium carbonate and iron(III) scale inhibitor (ALn) was synthesized. The anti-scale property of the Acrylic acid-allylpolyethoxy carboxylate copolymer (AA-APELn or ALn) towards CaCO3 and iron(III) in the artificial cooling water was studied through static scale inhibition tests. The observation shows that both calcium carbonate and iron(III) inhibition increase with increasing the degree of polymerization of ALn from 5 to 15, and the dosage of ALn plays an important role on calcium carbonate and iron(III)-inhibition. The effect on formation of CaCO3 was investigated with a combination of scanning electronic microscopy (SEM), Transmission electron microscopy (TEM), X-ray powder diffraction (XRD) analysis and Fourier transform infrared spectrometer, respectively. The results showed that the ALn copolymer not only influences calcium carbonate crystal morphology and crystal size but also the crystallinity. The crystallization of CaCO3 in the absence of inhibitor was rhombohedral calcite crystal, whereas a mixture of calcite with vaterite crystals was found in the presence of the ALn copolymer. Inhibition mechanism is proposed that the interactions between calcium or iron ions and polyethylene glycol (PEG) are the fundamental impetus to restrain the formation of the scale in cooling water systems.