Geomechanics: Pressure, Stress Field, and Hydraulic Fractures

Abstract

Abstract This chapter summarizes and integrates some of the most relevant published results related to the geomechanics of the Vaca Muerta Formation and its relationship with structural geology, stratigraphy, and petrophysics. The Vaca Muerta unconventional play is overpressured in most parts of the Neuquen Basin. Direct measurements are not feasible because of the low permeability of these rocks. Indirect measurements used to assess the range of pore pressure derive from diagnostic fracture injection tests (DFIT) taken over several days, and the initial reservoir pressure estimated from production models of horizontal wells. The Neuquen Basin underwent several compressional tectonic episodes. The main direction of the maximum horizontal stress changed from northwest–southeast in the Middle Jurassic, to approximately east–west of present day, associated to the Andean tectonics. Maximum and minimum horizontal stress directions, a critical parameter to design horizontal wells, has been regionally characterized using abundant high-confidence indicators, such as wellbore breakouts, wellbore-induced fractures, and microseismic analysis. The chapter presents and discusses the estimation techniques of overpressure and minimum horizontal stress, the overpressure source mechanism, the overburden variations at the base of Vaca Muerta, a regional characterization of rock strength and elastic properties, and the current understanding of the stress regime and the hydraulic fracture behavior. Significant progress has been made during the past five years in the geomechanical characterization of the Vaca Muerta Formation. As drilling, coring, testing, and production data become available, more comprehensive databases are built and uncertainty is reduced. Whereas a few years ago analogs from other basins were the only available information, today, local databases of triaxial and other rock mechanic laboratory tests, together with well logs, are successfully used to elaborate local correlations.