Exploration history of the igneous reservoirs of the Rio Grande Valley (Mendoza), Neuquén Basin (Argentina)

Oil seeps related to igneous rocks in the Neuquén Basin have been known since pre-Hispanic times (16th century) and have been explored in the southern Mendoza province since the late 19th century. In the 1980s YPF began the exploration of igneous rocks as hydrocarbon reservoirs in the Río Grande Valley area. The possible productivity of these ‘unconventional’ reservoirs was recognized by studying outcrops and well data of sills and dikes emplaced in different formations of the fold and thrust belt of the northern Neuquén Basin. Mudlogging control, as well as the evaluations with drill stem tests (DST), were decisive to define these reservoirs as prospective. From petrographic reports on samples from outcrops and cores, six lithological types could be distinguished in the igneous units for this region. Recent works confirm that this volcanism belongs to two predominant cycles from the late Oligocene to the Miocene (“Molle”) and middle to upper Miocene (“Huincán”). Although in igneous reservoirs it is difficult to forecast the estimated ultimate recovery (EUR), sills that crosscut the source rocks of the Vaca Muerta and Agrio formations demonstrate surprisingly high production rates, although the number of wells for the complete development is always difficult to establish.