The Vaca Muerta Formation (Neuquén Basin) is a world class Shale reservoir that covers oil, condensate and gas windows, with more than 300 horizontal wells drilled in the whole basin. This case study is located in the Shale Oil window that includes 30 horizontal wells on production, in a zone characterized by a huge areal and lithological variability due to the nature of the mix carbonate-siliciclastic depositional system. The main objective of this work is to characterize petrophysical and sedimentological properties of Vaca Muerta Fm. at log resolution to visualize and adjust the landing zones, relate to well productivity and extrapolate this information to a static model.
Logs and core integration workflows allowed to obtain 11 electrofacies honoring the composition and texture of the formation. The electrofacies composition is calculated from the basic electrical logs (Gamma Ray, Density, Photoelectric Factor and Compression Sonic) and interpreted kerogen volume, while the textural component was imposed by working the supervised electrofacies models with the sedimentological description of the rock. Subsequently, each electrofacies was assigned petrophysical properties such as porosity and water saturation from well logs calibrated with laboratory data.
The Vaca Muerta Formation consists primarily of a mixed carbonate-siliciclastic basinal facies in the largely progradational Quintuco-Vaca Muerta system. There are between 150-450 meters of organic-rich strata, all of which have the potential to produce, but there is also significant vertical and lateral heterogeneity related to the intercalation of different lithologies, the clinoform geometry and areal position. A better understanding of the reservoir characteristics of each of these facies, their distribution and their link to petrophysical properties is a key variable to select the best landing zones to develop the area.
The main findings of this study are: i) electrofacies model shows that organic content (electrofacies E7-E11) and porosity increases north and northwestwards for all LZ, ii) the mineral proportion for each electrofacies varies within the depositional system position (e.g. carbonate content increases southeastward, iii) in general, best productive wells are related to better electrofacies, iv) Electrofacies E1 & E2 (low TOC) show higher Sw and low TOC, while E7-E11 exhibits lower Sw, v) the model highlights new upside opportunities with additional hydrocarbon potential, vi) the geological and electrofacies model allowed to improve the understanding on the depositional system that will help to build robust paleoenvironmental maps.