Tailoring the Frac Fluid's Paradigm in Vaca Muerta. A Complete Review from Traditional Guar to New High Viscosity Friction Reducer Systems – Case History

Abstract

Developing unconventional reservoirs requires a continuous optimization process to increase well productivity while reducing costs. Over the last years, the oil & gas industry has adopted a new fracturing fluid system (High Viscosity Friction Reducer-HVFR) for regular hydraulic fracturing operations in shale reservoirs around the world. In 2017, Total Austral performed the first trials in Argentina with this type of fluids in 3 tight gas wells. With good results obtained in these tight wells, it was then decided to adopt this fluid as the new basis to complete and stimulate all Vaca Muerta shale wells. In an early stage, the classical guar-based fluid was replaced by a new emulsion base (liquid) HVFR system as part of a hybrid pumping schedule. To validate this new fluid introduction, several laboratory tests were carried out, including water analysis, hydration curves, dynamic rheology test and single particle fall test. Field trials were then conducted, showing consistently promising results in different oil and gas wells. Further in time, various improvements in the fluid formulation were introduced to comply with different applications and objectives, for example: use of medium salinity waters; implementation of surfactants booster to improve friction reduction/rheological aspects, and optimization of product dosification to minimize costs. Afterward a new stage was launched, replacing emulsion base HVFR additives by powder base HVFR systems and applying a similar workflow for validation (lab test, field trials, friction calibration, well trials and full implementation). By the end of 2019, the first stimulations with this new system were successfully completed in Argentina. Finally, a new set of laboratory tests was carried out; these tests used an advanced rheometer oscillatory-shear with parallel-plate and a friction loop to obtain a comprehensive rheological understanding of the fluid (viscosity, elasticity, and friction profiles). Viscosity behaviors were assessed on a wide range of shear rates and the influence of elasticity was examined over a range of frequencies. The achievements and results obtained in the last five years have positively impacted our unconventional developments from technical, logistic, economic, and environmental viewpoints. Among these, we can mention booster application allowing to reach a faster and higher fracture rate in longer slim wells; fluid system adaptability to several fresh water sources applied in different fields; the optimization process impacting on costs and material volumes without jeopardizing operations reliability even when using lower additives concentrations, and powder system showing lower treatment pressure even in longer wells with slim architecture. Another aspect worth highlighting is the reduction in enviromental impact brought about by this optimization process, moving from guar system, through HVFR emulsion to HVFR powder, by reducing location footprint, additives logistics and CO2 emissions and thus providing enhanced operational simplicity and reliability. This paper will cover the historical timeline and the work done to change, improve and optimize the frac fluid used for hybrid pumping design in Vaca Muerta. It will also show a predetermined set of laboratory tests, planed field trials, coordinated implementation, and progressive improvement obtained in field operations.