The Effect of Chelating Agents on the Use of Produced Water in Crosslinked-Gel-Based Hydraulic Fracturing

Abstract

Hydraulic fracturing operations require large amount of water which, in some cases, could reach six million gallons per treatment. Fresh water, from surface and subsurface sources, is usually used to formulate the fracturing fluid. The use of produced water in hydraulic fracturing has gained increased attention in the last few years, as it would solve fresh water acquisition challenges and reduces its disposal costs. However, produced water usually contains high amounts of total dissolved solids (TDS) that prevents its compatibility with fracturing fluid additives and negatively affects the fracturing fluid rheology. This paper investigates the effect of different chelating agents on the use of high-TDS produced water in high pH borate-crosslinked gels used in hydraulic fracturing fluids. Samples of field-produced water were analyzed for different ion concentrations. Synthetic water was prepared with different amounts of Na, K, Ca, and Mg salts. The fracturing fluid was formulated using natural guar polymer, borate-based crosslinker, biocide, surfactant, clay controller, scale inhibitor, and pH buffer. Five chelating agents tested in this study included HEDTA, GLDA, di-sodium EDTA, di-ammonium EDTA, and sodium gluconate. Compatibility tests of the fluid system at 180ºF were conducted at different ion concentrations. Apparent viscosity of the fracturing fluid was measured using a high-pressure high-temperature rotational rheometer. All rheology tests were conducted at a temperature of 180ºF and were conducted according to API 13m procedure with a three-hour test duration. Results indicated the potentiality of high-TDS water to cause precipitate and, hence, formation damage. However, the use of chelating agents has reduced the precipitation of divalent cations and enabled the formulation of fracturing fluid at higher Ca and Mg concentrations. The use of 2.5 wt% of HEDTA has enabled the formulation of the fracturing fluid using synthetic produced water that contains TDS of 101,000 ppm with Ca and Mg concentrations of 2,500 and 200 ppm, respectively. The fracturing fluid showed an average viscosity of 150 cp at 100 s-1 despite the high-TDS and high-hardness environment. The use of GLDA reduced the Ca and Mg ion precipitation; however, its chelation effect was found to be limited to certain concentrations. Some chelating agents showed the ability to chelate the boron ion and/or reduce the system's pH value. Consequently, viscosity measurements indicated the breaking of the fluid viscosity after the addition of the chelating agent. This paper presents the use of chelating agents to maximize the effectiveness of produced water for hydraulic fracturing operations. Successful use of chelating agents would reduce produced water disposal costs and improve the environment by reducing the consumption of fresh water.

Quantity of flowback and produced waters from unconventional oil and gas exploration

“…However, saline formation waters that compose 92-96% of FP water are characterized by higher salts, metals, and NORM, which require much more intensive treatment or dilution to become useable for beneficial reuse. Alternatively, recent studies have suggested that new HF technologies can utilize hypersaline brines with TDS up to 90,000 mg/L, depending on the scale potential and ions present such as calcium, sulfate, and magnesium, allowing for minimal pretreatment before it is reused for HF (Elsarawy et al, 2016;Hayes, 2009) Based on the large variations in the salinity of formation water in the U.S. (Fig. 4), we can distinguish between formations associated with high (TDS> 200,000 mg/L; such as the Marcellus and Bakken formation), medium (50,000 to 100,000; Haynesville, Barnett), and lower (<50,000 mg/L; Niobrara, California, Eagle Ford) salinity brines.…”

Reusing Flowback and Produced Water with Different Salinity to Prepare Guar Fracturing Fluid

“…The presence of high valence cations, such as Ca 2+ and Mg 2+ , in flowback water has a significant impact on the performance of fracturing fluids, which can be effectively addressed by adding chelating agents [20]. In this study, the chelating ability of three different chelating agents were quantitatively evaluated by complexation titration experiments.…”

“…Chelating agents are compounds capable of forming water-soluble metal complexes with divalent and trivalent cations [20]. Because the chelating agents contain coordination atoms with greater negative charge, it can form cyclic compounds through strong coordination interaction with metal ions, thereby masking these metal ions.…”

“…Liu et al [22] developed a hydroxy acid chelating agent, AO-1, for fracturing, and used base fluids with Ca 2+ and Mg 2+ concentrations of 150.67 mg/L and 264.28 mg/L to prepare fracturing fluids. Elsarawy et al [20] selected and evaluated five different chelating agents and finally concluded that N-(2hydroxyethyl) ethylenediamine-N, N , N -triacetic acid (HEDTA) and glutamic acid N, N-diacetic acid (GLDA) enabled the increase in the resistance of fracturing fluid systems to Ca 2+ and Mg 2+ , having a better complexing and masking capacity. Muhammad et al [8] introduced a new smart fracturing fluid system that consists of GLDA and which can replace biocide, clay stabilizer, crosslinker, and breaker from fracturing fluid formulation.…”

Applications of Chelating Agents in the Upstream Oil and Gas Industry: A Review

“…Elsarawy et al 158 investigated the feasibility of five chelating agents (HEDTA, GLDA, diammonium EDTA, disodium EDTA, and sodium gluconate) as produced water fracturing additives. These chelating agents were mixed with different additives, among which were natural guar gum and borate cross-linker.…”