Vaca Muerta Formation: From World Class Source Rock to World Class Shale Play
Iván Lanusse Noguera
Head of Unconventional Plays Management, YPF
Over the last two years, the Vaca Muerta Formation, the main proven source rock in the Neuquén Basin, has been transformed into a reservoir that promises to be a colossal Non-Conventional Shale Gas and Oil Resource Play without precedent.
In 2007, YPF began the analysis of this major Argentine source rock as a prospective unconventional play. In order to get the big picture, geochemical and geological data gathering took place during 2007 and 2008, which resulted in a ranking that was topped by the Vaca Muerta Formation. The analyzed elements were, basically, the organic richness, thermal maturity, thickness, regional distribution and depth.
During 2009, once it was determined that Vaca Muerta had the most suitable conditions to become a shale gas play, an effort was made to determine the YPF operated blocks with the greatest potential according to the geology (Ro>1%) and surface facilities as well.
Consequently Loma La Lata’s block was chosen to start the exploration of the Vaca Muerta Shale Gas Play in the Neuquén Basin. The available data (wells and seismic), which is/are remarkable in quantity and quality, allowed YPF to get a preliminary understanding of Vaca Muerta’s geology (geochemistry, geophysics and petrophysics).
Several elements, such as TOC, Ro, thickness, overpressure and legacy wells test in Vaca Muerta, have defined the northwestern area of Loma La Lata’s block as the best prospect. On the other hand, the main identified risks were the presence of hydrocarbon liquids, proven in some legacy well tests in the central and eastern part of the block, and the unknown behavior of the Vaca Muerta marls under massive hydraulic stimulation treatments (i.e. whether or not it was brittle enough).
In 2010, after a first stage of regional characterization and Loma La Lata’s data evaluation, the first two wells were drilled and became gas and oil discoveries from the shale play.
Two years after the first shale gas discovery, more than 24 exploration wells (YPF operated blocks) have been completed with several hydraulic stimulation stages, and have proved hydrocarbon production (gas, condensates and oil) from the Vaca Muerta marls all over the basin (Neuquén and Mendoza provinces), verifying legacy well records in different thermal maturity conditions.
The analysis of recent and pre existing wells (logs, cutting, cores), the seismic interpretation, and the diverse well productivity show a high level of heterogeneity within the Vaca Muerta marls vertically and laterally (from nano to macroscale). The study of these “facies” changes is in progress with the aim of achieving a better reservoir understanding and with the ultimate target of predicting possible “sweet spots”.
One of the most important Vaca Muerta Challenges is the geological understanding, which is the key to better define the next steps for an unprecedented and massive development in Argentine basins.
AAPG Search and Discovery Article #90165©AAPG 2012 GEOSCIENCE TECHNOLOGY WORKSHOP, 2-4 December 2012, Buenos Aires, Argentina