Feasibility of Using Produced Water for Crosslinked Gel-Based Hydraulic Fracturing

Abstract

A vast quantity of produced water (3.8 million barrels in 2002) is generated during gas production in the San Juan Basin, New Mexico.Most of the saline produced water is re-injected into disposal wells at an average cost of $1-$4 per barrel.Due to the persistent drought condition in New Mexico, beneficial use of the produced water is receiving increasingly more attention in the gas production industry.Based upon the Resource Management Plan (2003) proposed by the Bureau of Land Management, about 10,000 new wells will be approved on federal land in the San Juan Basin for the next 20 years.Given the volume of fresh water required for hydraulic fracturing during well development, reclaiming produced water as the base fluid for fracturing not only may alleviate the impact of fresh water shortage, it also may lower the cost of well stimulation treatment. This project aims at 1) identifying the critical parameters and the corresponding optimal ranges in the laboratory, which will render produced water applicable as the base fluid for crosslinked gel-based hydraulic fracturing and 2) evaluating the validity of the laboratory findings under actual stimulation conditions in the field. Produced water from a gas-producing well near Aztec, 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, persulfate breakers, and other ingredients.The apparent viscosity of the gels under different shear rates was measured using Fann Model 35A viscometers and the bottom-hole temperature simulated in the experiments was about 128 ºF.The rheological effects of several parameters, including pH, hydration time, ionic strength, and presence of sulfate, were evaluated.The experimental results demonstrated the feasibility of using untreated produced water from Aztec, NM as a base fluid for crosslinked gel-based hydraulic fracturing.Hydration time and pH were shown to influence the maximum apparent viscosity significantly in the absence of breakers.A positive correlation was observed between the maximum viscosity and the hydration time.For the solution pH, gellation at pH 5.5 exhibited the best rheological performance.By adjusting the hydration time, the gel loading, and the amount of breakers applied, it is conceivable that crosslinked gels with optimal rheological characteristics can be formulated with untreated produced water as the base fluid for well stimulations. A field test was performed following the bench-scale experiments to validate the laboratory findings under the actual stimulation conditions.A well located in San Juan County, New Mexico was restimulated using 70Q CO2 foamed 30-lb crosslinked gel.Untreated produced water was used as the base fluid for the crosslinked CMHPG gel.Natural gas production averaged 50 thousand standard cubic feet per day (MCFPD) prior to the stimulation and was increased to an average of 100 MCFPD after treatment indicating that the fracturing treatment using untreated produced water was successful in increasing the formation productivity.

An Independent Scientific Assessment of Well Stimulation in California Volume II: Potential Environmental Impacts of Hydraulic Fracturing and Acid Stimulations

“…Well completion reports filed through mid-December, 2014, indicate that there were only 43 documented instances of oil and gas operators using produced water for well stimulation in California, accounting for about 13% of the water used for well stimulation in 2014. Produced water reuse for well stimulation has been shown to be feasible (e. g. Huang et al, 2005) and is becoming more common across the United States. For example, recycling of wastewater for well stimulation has increased in the Marcellus Shale region: prior to 2011, 13% of wastewater was recycled, and by 2011, 56% of wastewater was recycled (Lutz et al, 2013).…”

The New Reality of Hydraulic Fracturing: Treating Produced Water is Cheaper than Using Fresh

“…Although formulations exist for compatible gel crosslinking at low to neutral pH (Huang, et al 2005;Legemah, et al 2015), a common and cheap alternative uses borate and requires high pH. Boric acid-B(OH) 3 -is a Lewis acid with water and forms B(OH) 4 with increasing pH (pK a ϭ 9.0 -9.2).…”

A Novel Approach to Crosslink Delay of Low-pH Fracturing Fluid

“…One possible explanation for this is that protonation of the ligands complexed with zirconium in the crosslinker ensure faster release of zirconium cation for crosslinking with carboxyl groups in the polymer. In addition, aquous based zirconium crosslinkers are known to undergo reduced hydrolysis and polymerization at lower pH in the presence of weakened or protonated ligand (Huang et al, 2005). Thus, the vortex closure of a crosslinked fluid can be tuned by varying the loading of fumaric acid present in the crosslinked fluid.…”