In the Vaca Muerta shale of the Neuquén basin, Argentina, the most prolific intervals tend to be the most difficult to hydraulically fracture because of the abnormally high fracture gradients present in some parts of the basin. Thus, it becomes very important to have a good understanding of the anisotropic geomechanical properties of this heterogeneous formation prior to developing the completion strategy.

A calibrated, anisotropic 1D mechanical earth model (1D MEM) was developed and used to optimize the completion strategy for a vertical well in the Vaca Muerta shale. The output from the 1D MEM, including the principal stresses, anisotropic elastic properties, pore pressure, and rock strength, were used to define the reservoir intervals with the best characteristics for initiation, propagation, and maintenance of a conductive complex fracture network. Next, the reservoir intervals with the highest hydrocarbon generation tendency were determined from petrophysical and image logs acquired in the well. This formed the basis for selecting the optimum number of stages and perforation strategy for the well.

Sensitivity analysis revealed the impact of the hydraulic fracture properties on the production performance. The analysis showed that higher fracture conductivity greatly improves the well performance in the deeper Vaca Muerta intervals, whereas larger fracture surface area is more beneficial across the shallower intervals. Thus, a unique completion strategy was developed for each interval to optimize the well performance. Three hydraulic fracture stages were planned initially, but because of casing limitation, only the first stage was executed. A time-lapse acoustic measurement acquired from the well corroborated the propped fracture height predicted during the completion design phase.

The study showed that proper characterization of the anisotropic geomechanical behavior of the Vaca Muerta formation improves the development of a completion strategy, which ultimately optimizes economic performance of the well.

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