Vaca Muerta: A Technical Approach to the Path of Sustainability in Water Reuse
Authors: Velo Rosario Daniela , Arias María Lila , Weimann Mauro Iván , Mottes Nicolás , Pérez Sebastián Miguel 
Published: January 2025

Water management is critical for developing unconventional reservoirs because of two principal factors: first of all, the amount of water required to perform hydraulic fracturing and secondly, but equally important, the amount of water that returns with the production of the hydrocarbons (flowback and produced water).

All of the water currently utilized in hydraulic fracturing within the Vaca Muerta (VM) formation (Neuquen Basin, Argentina) is sourced from surface water; and all of the water recovered from well production is then injected into disposal wells. This strategy presents challenges associated with disposal wells, regarding their limited capacity and exhaustive controls required by environmental authorities. Moreover, there is a possibility that producing wells may have to be shut down, due to unexpected increases in their water-cut if total water production exceeds the available injection capacity of the disposal wells. This will inevitably mean a delay in the production, resulting in an associated economic loss.

For this reason, YPF has planned and carried out a number of field and laboratory tests to evaluate the feasibility of reusing produced water for hydraulic fracturing. Although this is known to be the practice in other basins, the challenge for VM is to make it economically viable within the localized conditions, characteristics and constraints. This would also allow us to turn what is currently a waste stream into a resource, with the consequential positive environmental impact of reducing the freshwater consumption for hydraulic fracturing.

The purpose of this paper is to present the workflow that was implemented, to evaluate and mitigate the possible negative impacts associated with such water reuse in VM. The procedures used are briefly described below:

A matrix-based risk analysis was applied to assess the potential impact of changes in the mix-water characteristics on various aspects: field operations, well productivity, surface facility integrity and flow assurance. Based on this, a series of field and laboratory tests were then designed to quantify the identified risks and decide whether changes to the fracture fluid formulation were required to mitigate them.

Laboratory tests were carried out with two principal objectives. First, to understand the effect of the new water source on the rheological behaviour of the fracture polymer system (HVFR) currently used in the operations. Second, to study their compatibility with the reservoir fluid. Additionally, regained conductivity tests were also carried out to have a measure of any potential damage to the proppant pack, resulting from the change in water source.

Field tests were performed to calibrate the operational responses of the polymers used with freshwater, understanding their proppant transport capability, the impact on friction and the operating time. Customized polymers for higher salinity water conditions would be considered later, in order to adjust to the most appropriate pumping schedule for the new water condition.

Preliminary conclusions indicate that the feasibility of fracturing with blends of produced water within VM has been demonstrated; through simply increasing the polymer concentrations, that were originally used with the freshwater source alone, without potential impact on the productivity.