Limited freshwater resources, strict water disposal legislation and costly recycling regulations lead to the ever increasing use of produced and flowback water for hydraulic fracturing processes. Despite the economic and environmental benefits of using produced or flowback water for fracturing, high concentrations of total dissolved solids (TDS) and multivalent cationic and anionic species present significant challenges to current friction reduction technologies.
The industry demands new chemistries to address the challenges of maximizing and sustaining the performance of friction reducers up to 300,000 mg/L TDS brine. Attempts to tailor molecular properties of friction reducer formulations include incorporating salttolerant polymers and improving the surfactant package’s rapid and complete polymer release while maximizing product stability and shelf life. These reformulations exhibit potential in the field; however, they incur additional performance challenges and production, application and cost concerns.
Conventional friction reduction polymeric products (friction reducers) are water-in-oil emulsion formulations (inverse emulsions), wherein long-chain polyacrylamide co-polymers are stored inside water droplets and dispersed in a continuous oil phase. The hydraulic fracturing process involves pumping a friction reducer into a large volume of hydraulic fracturing brine water (fracturing fluid) at a high flow rate, thus releasing friction- reducing polymer into the fracturing fluid.
The hydrated and disentangled polymers alter generalized flow from turbulent to laminar, resulting in increased pumping efficiency. These polymers are less effective, remaining in a compressed state and are unable to expand and effectively reduce friction when introduced into produced waters containing positively charged ions such as calcium and magnesium. Produced waters containing positively charged iron may crosslink, flocculate or lyse the polymer potentially causing formation damage.
Inverse emulsion polymerization is a widely used technique to obtain high molecular weight polymers; however, it may exacerbate environmental concerns and requires extensive research to develop an environmentally friendly formulation. This, in turn, could increase cost and add to the environmental footprint during field operations. It is ideal to have a friction reducer that is free of hydrocarbon solvents and surfactants, which releases the polymer instantaneously, especially in high TDS produced water in the presence of iron. Utilizing a new dispersion polymerization technique, Solvay’s new friction reducer significantly improves the efficiency of operations with instant hydration and improved friction reduction properties in produced waters. It functions due to absence of complexities from an inverse emulsion approach such as those related to oil migration and stripping/capture of oil and additional surfactants, which can alter formation wetting profiles and produced oil/water emulsification, to invert the emulsion. This approach delivers an environmentally friendly and cost-effective friction reducer by reducing the freshwater volume demand and the cost of water disposal operations.
Dispersion polymerization utilizes water-soluble monomers and aqueous salt solution instead of oil, water and surfactants as reaction media. A specially engineered polymeric stabilizer enables the monomers to grow and build micron-size polymer particles. In the conventional application of dispersion polymerization, polymer particles are stabilized by the physical adsorption of a polymeric stabilizer to prevent the formation of aggregates and coagulates during polymerization progression.
Solvay has recently developed a dispersion polymerization technique that significantly improves the phase separation that results from the physical adsorption of the stabilizer. This new technology is centered on Solvay patented technology and involves a telomeric hydrophilic stabilizer, which promotes polymerization on the stabilizer leading to the formation of stable polyacrylamide particles via chemical adsorption in aqueous media. The molecular weight, architecture and particle size of the polymeric stabilizer from this new polymerization can be controlled, creating a unique and stable dispersion in salt media eliminating the current challenges observed with the conventional dispersion polymers.
Green friction reducer
Friction reduction efficiency of the novel Solvay dispersion PAM co-polymer is investigated via friction loop tests in freshwater and high TDS synthetic produced waters up to 300,000 mg/L. The equipment is designed to measure the pressure drop during the recirculation process, which helps simulate the friction reduction performance under practical treating pressures in a laboratory setup.
Friction reduction performance can be evaluated by two main factors: hydration speed and performance at an extended period of time. Hydration speed indicates how fast the polymer is released to the base fluid during a stimulation treatment. Friction reduction performance at an extended period shows how resistant the friction reducer is to mechanical shear over time.
The friction reduction performance for a spectrum between freshwater up to 300,000 mg/L TDS synthetic produced water (for 5 gal/min flow rate within 0.1875-in inside diameter tube) is shown in Figure 1. With only 0.5 gallon per thousand (gpt) loading in freshwater and 1 gpt in high TDS waters, the dispersion polymer begins to reduce friction rapidly after injection into the flowloop tank. This new polymer hydrates within a few seconds even in the high TDS waters and can withstand the mechanical shear over 5 minutes. The absence of an oil phase in this dispersion polymer enables instant hydration and shows performance insensitivity to high TDS conditions.
The friction reduction performance of Solvay’s new friction reducer in the presence of iron also is tested at 200,000 mg/L TDS brine for a spectrum between 0 to 50 ppm iron (iii) as seen in Figure 2. With only 0.5 gpt loading, the new friction reducer formulation is tolerant to iron, and the friction reduction performance is not affected by its presence in the synthetic produced water. Being resistant to iron would prevent the flocculation of the polymer during hydraulic fracturing operations and eliminate potential formation damage when compared to conventional friction reducers.
In addition, Solvay’s friction reducer performance is robust when used with common stimulation additives. It is compatible with many common nonemulsifiers, flowback surfactants, scale inhibitors, biocides and breakers in freshwater and produced waters.
Solvay’s water-based friction reducer is an environmentally friendly alternative to the conventional inverse emulsion polymers with significantly improved hydration and long-term performance in freshwater to high TDS produced waters, even in the presence of iron. In addition to the environmental benefits, it provides the potential for cost savings through reduced water disposal cost and freshwater demands.
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