Summary
The Vaca Muerta Formation, the largest proven source rock in the Neuquima Basin, Argentina, has become, in the last four years a shale unit that holds an enormous potential as an unconventional Shale Gas and Oil resource play. Together with the Quintuco Formation, form a system, showing a high geological complexity related, primarily, to its large size and extension. The aim of this work is to characterize and describe the geological features of the Vaca Muerta system, in one of the core and strategic area of exploration as an example of a shale play. In an unconventional reservoir, oil and gas accumulations are not established by the floatability of hydrocarbons related to the water table, neither Darcy´s law can be applied as it is usually applied on the conventional reservoirs. It is therefore necessary to find accumulations with large continuity, at a regional scale, fully independent of a classical concept of a "trap", either structural or stratigraphic. These plays involve, mainly, a fine grained matrix (micrite, organic matter and clays) and a clastic fraction of silt and very fine sand with authigenic minerals (i.e. carbonates, pyrite and quartz), an important thick rock fraction with an important TOC percentage, etc. They present very low permeability values and hence need massive hydraulic stimulation in order to maintain a reasonably and economically sustainable production.
As a product of an intensive exploration programme in the Neuquén Basin, some core areas were identified as priority for the drilling campaign. One of these areas is located in the east-southern part of the basin. Exploration includes the drilling of 9 wells, core and cutting studies, well logs and seismic attributes analysis, leading to the identification of several sequences within the source rock that helped the geoscientist team to best delineate the regions for future exploration, appraisal and development of the field.
Geological Settings
The Neuquén Basin, located between latitude of 36° and 40° S in the west-central part of Argentina, is predominantly a Jurassic- Cretaceous rifted and backarc depositional basin. It covers most of Neuquén province, western part of Rio Negro and La Pampa provinces and southwest portion of Mendoza province. It’s limited to the east by the Sierra Pintada range, to the south by the North Patagonian massif, and to the west by the Andean volcanic arc. Sediments thickness reaches up to about 5500 m, and contains stacking marine and non-marine clastics, with subordinates carbonates and evaporates, covering an area of more than 140.000 km2 (Figure 1).
