Abstract The Carrack Field, located in the Southern North Sea Blocks 49/14b and 49/15a, has of the order or 15 bcm (530 bcf) gas initially in place and is operated by Shell UK Ltd. The field consists of a pop-up structure in the south of the field and extends to the north with a gently-dipping monoclinal structure. The reservoir comprises sandstones of the Permian Silverpit and Leman Sandstone formations, which contain c. 85% of the in-place resources. The quality of the reservoir decreases rapidly to the north. Gas is also produced from Carboniferous sandstones of late Duckmantian (Westphalian B)–Bolsovian (Westphalian C) age. Initially, the field was in pressure communication both laterally and vertically with a single gas–water contact. During production time, however, the three main fault blocks behaved independently, and decimetre-thick shale intervals acted as vertical baffles between the sandstone units. The Carrack Field has been in production since 2003 and is developed by a single platform with seven mainly deviated wells. The current production rate is c. 0.7 MMm 3 /day (25 MMscfgd). Until the end of field life in the 2030s, the field is expected to produce gas of the order of a few bcm. The main remaining opportunity is the undeveloped Carrack West compartment.

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 northwestw ard. 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 m 3 /m 3 (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.