Abstract

Following an enthusiastic period when organic-rich mudstones were stimulated irrespectively of their intrinsic properties, it is now recognized that each self-sourced unconventional play presents its own challenges and requires specific evaluation and stimulation techniques to reach commercial efficiency. The Vaca Muerta Formation is no exception. This world-class unconventional play has a continuous organic-rich section of significant thickness, reaching 500 m (1640 ft) in some places, which enables numerous possible stacked landing zones. Nevertheless, the stratigraphic column exhibits variations in the reservoir properties, including mineralogy, pore system, and organic content, coupled with variations in thermal maturity. Additionally, the formation has a highly layered nature with occurrences of ash beds, bed-parallel veins of fibrous calcite (aka beefs), and alternations of thin carbonate beds and thicker mudstone beds.

In the Vaca Muerta Formation, the pore system is complex and includes pores hosted within the inorganic matrix and different types of pores generated within the organic matter. This complexity has a fundamental impact on the characterization of the play. Presence, amount, connectivity, size, and shape of these pores vary with compaction, thermal maturation, mineralogy, and diagenesis. The estimation and characterization of the water volume in Vaca Muerta Formation is also a challenge. The presence of variable volume of movable water is suspected.