High-TDS Produced Water-Based, Low-Damaging Fracturing Fluids for Applications at 300°F or Higher

Abstract

Water usage in hydraulic fracturing jobs has been increasing continuously, mostly due to multistage hydraulic fracturing of horizontal wells in unconventional reservoirs. Meanwhile, nearly 100 billion barrels of produced water, often with total dissolved solids (TDS) higher than seawater, is being generated every year from oilfield operations. Operating cost could be lowered if produced water is used in place of fresh water in fracturing activities, due to the reduced fresh water consumption and produced water disposal cost. Formulating slickwater or linear fracturing fluids with high-TDS produced water is a common practice. Crosslinked fluids have also been prepared with salt and hard produced water for medium and low temperature applications. At elevated temperatures above 250°F, it becomes much more challenging to make stable crosslinked fluids with untreated produced water due to the damage caused by the high water salinity and hardness. Without resorting to scale inhibitors and/or high fluid pH, fracturing fluids prepared with untreated high-TDS produced water have so far shown stability at around 275°F. With careful selections of the fluid additives, a new high-temperature fracturing fluid system was recently formulated with untreated produced water having TDS at or above 295,000 mg/L. Made up of metal-crosslinked polysaccharides, the fluids were stable at high temperatures of 300°F or more. In representative tests, the fluid viscosity stayed above 100 cP (at 100 s−1 shear rate) for 2 hours at 300°F. To reduce the scaling tendency and enhance the gel cleanup, the fluid pH was suppressed to 7.2 or below as measured at surface temperature, resulting in a regained permeability of 77% in the conductivity test. Overall, the new produced water-based fluid system showed satisfactory performances at 300°F in fluid viscosity and stability, regained conductivity, and scaling tendency. The key roles played by the additives to render the fluid stability at 300°F will be discussed for the high-temperature fracturing fluids prepared with high-TDS produced water, and the laboratory test results will be presented in detail.

Electro-Responsive Green Gels for Lower Environmental Impact Shale Gas Extraction

“…The industry is focused on the development of alternative polymers that can replace guar gum (GG), due to occasional high prices and short supply, as well as public concerns about fresh water supplies . At the same time, several efforts have been made to develop environmental- and equipment-friendly additives that can be applied at high temperatures and extremely low or high pH conditions. , Other research directions include the development of slickwater systems that can use less or no water, the formulation of hydraulic fracturing fluids by recycling the produced water with a high salinity content, the improvement of viscoelastic surfactant (VES)-based fluids to be compatible with high salinity-produced water, divalent ions in formations as well as high-temperature environments, and the development of “energized fluids” based on CO 2 and nitrogen with enhanced proppant transport capability. ,− A very promising approach for the formulation of a new generation of frac fluids is the design of stimuli-responsive systems, whose rheological and mechanical properties can undergo controlled and reversible modifications in response to an external stimulus. , The stimulus or external field applied include thermal, electric, magnetic, pH, ultraviolet/visible light, ionic or metallic interactions, or combinations thereof. , For gas and oil applications, the most investigated systems are thermo- and salt-responsive materials because their rheological behavior can be effectively modulated using the intrinsic variations of temperature and salt composition inside the formations . The need for a clear-cut control on the fluid modifications leads to the development of more efficient systems, which respond to different chemical stimuli.…”