Summary
Located in the Argentinean Neuquén Basin, the Vaca Muerta formation is a thick succession of Late Jurassic-Early Cretaceous organic rich siliceous marlstones and mudstones with clay content below 30%. It is the main source rock of the reservoirs in the basin that have been producing since 1918. The El Trapial area is situated in the North West part of the basin. The Vaca Muerta formation is encountered at burial depth ranging from 2000–4200 m, and it extends over various thermal maturity windows in the study area from early oil to wet gas maturity windows. The organic-rich interval has a thickness of around 350 meters, with total organic carbon ("TOC") ranging between 2 to 8% and average total porosity of 10%. Following the local maturity trends, hydrocarbon type has been found to vary laterally and presumably vertically. The maturity variations in the El Trapial area poses the challenge of understanding productivity drivers in the peak oil, late oil and gas condensate windows, with each maturity type potentially responding to different factors.
A field study was initiated in 2011, analyzing resources with the available information (five wells with vintage logging suites and 80 percent of 3D seismic coverage), and then continued with a drilling campaign of four vertical exploratory wells with an aggressive data acquisition program. Full wireline log suites were run in the exploratory wells and more than 400 m of core was acquired. Laboratory studies were performed on conventional core, sidewall cores and cuttings samples to characterize the reservoir properties and to calibrate petrophysical and geomechanical models.
Among the various petrophysical challenges offered by Vaca Muerta, the characterization of the porosity system is critical to understand the reservoir quality. Only considering the organic and inorganic pore systems brings into play many more questions regarding their respective contributions to oil production, in the early and late stages, and their relationship with potential formation water production. The NMR T2 distribution combined with laboratory data is the key to assess a better understanding of the pore system.
The present work defines a new effective pore model for the El Trapial area to interpret the NMR T2D. The study relies on an extensive core measurement database and enables a improve prediction of the better productive zones in Vaca Muerta.
