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Characterization of the Lias of the Lusitanian Basin, Portugal, as an Unconventional Resource Play


Porto Energy recognized the potential of the Lias (Lower Jurassic) as an unconventional resource play while drilling Triassic pre-salt prospects in Portugal's Lusitanian basin. Through its subsidiary Mohave O&G, Porto then embarked on a program to acquire additional geological data to characterize that potential and to address questions raised by previous work about TOC, thermal maturity and environment of deposition. This program included drilling 23 shallow wells (160 m average depth up to 451 m) to collect cuttings and cores in the Lias section over a wide geographic area. Each well was logged and Geolog with a geochemical field unit, analyzed over 500 samples for TOC, Tmax and other geochemical parameters. Geolog also ran each sample through XRD and XRF and cuttings from 15 old oil and gas wells were included in the effort. Part of the challenge was addressing issues of TOC differences between outcrop, cuttings and cores; how to determine average TOC values; Tmax differences between sources of data; and bias in Ro data due to basinal location. Based on these analyses, additional work done in the program and past analyses, Porto ascertained the extent of the resource play in the basin, its environment of deposition (carbonate deposition in a sag basin versus an open marine carbonate ramp as previously thought), its resource play parameters and “sweet spot” areas to drill in the next phase of its exploration of the Lias. The Lias is characterized throughout the basin by a TOC average range of 2.3 to 5.9%, Ro values of 0.5 to 1.8 and quartz-carbonate content of 63.8 to 83.7%. Also, porosity (from shallow wells) ranges from 0.2 to 19.8% over a total thickness of up to 400 m (average 200 m). The Lias is dominantly kergoen type II in the prospective middle of the basin with drilling depths of 1000 to 3500 m. The identified sweet spots of the Lias play cover over 3000 sq km (over 800,000 acres). The Lusitanian basin's Lias shares many of the properties of other unconventional resource plays in North America (Eagle Ford, Niobrara and Utica) as well as other Lias plays in Europe.