Abstract

The objective of this chapter is to introduce the case of the first large-scale oil shale development in Argentina. The work is focused on the reservoir characterization of the liquid-rich shale of the Vaca Muerta Formation in the Loma Campana block that was carried out to optimize the drilling campaigns executed since the oil discovery in 2010 and was supported by a comprehensive data acquisition program accomplished between 2010 and 2012. Data gathered involved three-dimensional (3-D) prestack depth migration (PSDM) seismic reprocessing, core and cutting analyses, mudlogging and e-logs, geomechanical, petrophysical, and geochemical studies, diagnostic fracture injection test (DFIT), microseismic monitoring in vertical and horizontal wells, wellhead pressures and temperatures, downhole pressures captured via retrievable gauges, time-lapsed production logging surveys, tracer tests, pressure–volume–temperature (PVT) analyses, and production records.

According to the regional stratigraphic framework, the Vaca Muerta Formation in Loma Campana begins with two aggradational transgressive–regressive (T–R) sequences that represent the target of the current development.

The analysis and interpretation of the data showed that the Vaca Muerta Formation in Loma Campana is 80–300 m (262–984 ft) thick, gradually thickening northwestward. The most common lithofacies include organic-rich fossiliferous calcareous mudstones, silty mudstones, heterolithic marlstones, wackestones, and ash beds. The total organic carbon (TOC) varies between 2.3% and 7.6% (average values from static model) decreasing upward, and the mineralogic composition consists of 33% siliciclastic material (quartz and plagioclase), 46% carbonates (calcite and dolomite), 18% clays (illite and interbedded illite/smectite), and 3% pyrite (average values, dry weight w/w).

The local structural framework is characterized by a north–northeastern gently dipping monocline (depths ranging from 2800 to 3100 m—total vertical depth or TVD [9186–10,171 ft]). In a mainly strike-slip regime, the maximum horizontal stress (SH_max) is in the range of N90° and N110°, and Vaca Muerta’s pore pressure gradient is around 0.87 psi/ft. Oil density ranges from 38° to 60° API and gas–oil ratio (GOR) from 90 to >3500 m³/m³ (500–20,000 scf/bbl) with increasing maturity westward.

Well productivity has improved year after year because of operational experience and subsurface knowledge. Standard lateral length has evolved from 1000 m (3300 ft) in 2012 to 2500 m (8200 ft) in 2019. The main drivers to continue improving well estimated ultimate recovery (EUR) are: increasing precision in well placement and continuous optimization of stimulation design. By the end of 2019, the production from the Vaca Muerta play reached 56,000 BOE/d with 548 active producing wells (93% of the production from 184 horizontals), becoming the second largest oil field in Argentina.

The development of the Loma Campana block is a milestone for the oil and gas industry in Argentina; the results obtained in terms of production, cost reduction and scale economy led to break the industry’s inertia, to develop new infrastructure, to position the Vaca Muerta Formation on the world map of unconventional plays, and to attract new investments and partners.