Development and Use of High-TDS Recycled Produced Water for Crosslinked-Gel-Based Hydraulic Fracturing

Large quantities of high-total dissolved solids (TDS) produced water are generated during oil and gas production in Eddy County, New Mexico (more than 164 million bbl in 2011). Most of the high-saline produced water is reinjected into disposal wells at an average cost of USD 0.75 to USD 1.00 per bbl. Caused in part by the persistent drought conditions in New Mexico, beneficial use of produced water is receiving attention in the oil and gas industry. One alternative being considered is the use of produced water for hydraulic fracturing operations. Typically, wells in the Delaware basin require 40,000 to 60,000 bbl of fresh water each for hydraulic fracturing job during well development. As such, reclaiming produced water as the base fluid for fracturing not only helps alleviate the industry’s dependence on fresh water but can also lower the overall cost of the well stimulation treatment. Using produced water exceeding TDS values of 270,000 ppm is key to reclamation and reuse programs in the Delaware basin. This paper discusses a project to (1) identify the critical parameters and the corresponding optimal ranges in the laboratory, that will allow use of treated produced water as a base fluid for crosslinked-gel-based hydraulic fracturing, and (2) evaluate the validity of the laboratory findings under actual field conditions. High-TDS produced water from a Brushy Canyon producing well near Carlsbad, New Mexico was used as the base fluid for the bench-scale experiments. Crosslinked gels were formulated with carboxymethyl hydroxypropyl guar gum (CMHPG), a zirconium-based crosslinker, sodium chlorite breakers, and other ingredients. The apparent viscosity of the gels was measured using Chandler Model 5550 high-pressure/high-temperature (HP/HT) viscometers. The bottomhole temperature simulated in the experiments was approximately 140°F. The rheological effects of several parameters, including pH, salinity, and scaling tendencies, were evaluated. Other factors, including organics and suspended solids, are included in the discussion. In addition, a field test performed following the bench-scale experiments to validate the laboratory findings under the actual stimulation conditions is discussed. Results indicate that the fracturing treatment using high-TDS produced water successfully created a fracture network and transported sand into that fracture network. Introduction Produced water usually comprises both the formation water and injected fluids from previous treatments. It can contain hydrocarbons, high levels of TDS, suspended solids, and residual production chemicals. When stored on the surface for extended periods of time, produced water is subject to evaporation, which can further increase the salt concentration in the water. Traditionally, flowback and produced water generated during completion and production operations is typically disposed of down saltwater injection wells, which are typically regulated by state oil and gas agencies under the Underground Injection Control program of the Safe Drinking Water Act. Using produced water for hydraulic fracturing has many benefits, such as reducing disposal of produced water, reducing fresh water consumption during completion and production operations, and economic benefits realized by the operator. If produced water is gathered at or near the site of production and a minimal treatment is applied for use in hydraulic fracturing fluids, recycling and reuse programs may become economical and environmentally beneficial. As hydraulic fracturing in shale plays continues to require large amounts of fresh water for oilfield operations (i.e., 4 to 6 million gal/well in some cases), reusing produced water reduces the consumption of fresh water. Fresh water is becoming more difficult to obtain from traditional sources because of increased restrictions on water availability from subsurface or surface sources (Gleick 1994). The Delaware basin has undergone extensive development during the past few years. This has resulted in the discovery of many, mostly oil-producing, fields. A large percentage of the productive wells have produced water along with the oil. A