--> --> Abstract: Gas Resource Potential from Maastrichtian–Eocene Reservoir in Magallanes Basin, Chile, by Zurita, Enrique; Carpinelli, Aldo; Trejo, Sebastian; and Saa, Ariel; #90166 (2013)

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Gas Resource Potential from Maastrichtian–Eocene Reservoir in Magallanes Basin, Chile

Zurita, Enrique1; Carpinelli, Aldo; Trejo, Sebastian; and Saa, Ariel
1[email protected]

During the late Maastrichtian towards the early Selandian a succession of glauconitic sandstones and siltstones was widely deposited in the Magallanes Basin as result of the onset of the foreland basin stage. The convention of "Zona Glauconitica" has been used since 1947 to refer this unit comprising from basin floor to fluvio-deltaic geological successions.

Frequent gas shows, including; trip gas, gas cut fluids, gas blow-outs, overpressure and U.V. fluorescence of the organic solution extracted from cuttings, are ordinarily reported during drilling of production and exploration wells aimed at deep targets. Formation tests performed on that specific stratigraphic zone from at least 10 wells showed: poor gas production, abrupt decline within 24 hours, lack of water production and absence of quality reservoir. These evidences were interpreted as the expression of molecular-scale dissolved hydrocarbon phase in the poral space and very low permeability reservoirs.

In 2010-2011, experimental hydraulic fracture operations were performed on Zona Glauconitica for two exploration wells previously drilled by ENAP during the 1970s’: Cabana-1 and Cabana-2, both located in the northwestern portion of Tierra del Fuego in an area prone to gas shows from that particular stratigraphic interval.

Resulting well test from pre-fractured completion reported 106 and 177 Mscf/d of gas, respectively. After conventional fracturing gas rates increased to 2,119 and 3,000 Mscf/d respectively for these wells. Pressure measurements obtained from Cabana-1 exhibited 570 psi of overpressure; i.e. 16% above normal hydrostatic pressure (0.43 psi/ft). Weekly monitoring showed that production gas rates stabilized at 1,767 Mscf/d, however, reliable long term production profile is still missing since gas production facilities are not yet in place.

Available data suggests that Cabana reservoir is constituted by siltstone or/and clay-rich sandstone. As these both reservoir candidates exhibit very low permeability (<0.1mD), a possibly Tight-Gas reservoir scheme has been proposed for the area. Nevertheless, possible involvement of higher-permeability thin beds or/and natural small scale fractures should be considered as they may be, at least partly, responsible for the gas production observed.

Main efforts are now directed to acquire additional information and testing different hypotheses regarding hydrocarbon origin, reservoir characterization as well as production performance.

 

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013