Comparing Friction Reducers' Performance in Produced Water from Tight Gas Shales

Abstract

Technology Update Natural gas plays a key role in meeting the energy demands of the United States, and the production of natural gas from tight shale formations is expanding rapidly as the demand for clean and efficient energy rises. Slickwater fracturing, a hydraulic fracturing technique whereby a water-based fluid is injected into a well at intense pressures—causing the formation rock to crack, or fracture—is the most commonly used stimulation technique in tight gas reservoirs. Slickwater fracturing treatments involve combining a base fluid with a friction reducer, a polymer that enables faster pumping of the fluid into the formation, and a propping agent, or proppant—a granular substance, such as sand, that is carried into the formation by the fluid and holds the fractures open once the treatment is complete. Each stage of a slickwater-fracturing treatment requires tens of thousands of barrels of fracturing fluid. Furthermore, each slickwater treatment generates a great deal of wastewater, as most of the fracturing fluid will flow back out of the well, and production brines, or produced water, will flow back over the long term. Programs for managing produced water are on the rise, as technology for convenient and economical treatment of wastewater improves. However, often the most cost-effective and convenient use of produced water is to reuse it in subsequent fracturing treatments. Evaluation of friction-reducer performance in the reused water is crucial because produced water from most of the US tight shale formations contains elevated levels of dissolved solids, compared with fresh or tap water. Reusing waters with high levels of total dissolved solids (TDS) can lead to adverse interactions between the friction reducer and the base fluid. The adverse interactions result in elevated treating pressures, and this is often overcome by introducing more of the friction reducer into the mixture, which leads to higher chemical costs for the treatment.