Unconventional Variables that Impact on the Fracture Height Growth on Vaca Muerta Formation and its Implications for Fracture Simulation and Well Productivity

Abstract

The Vaca Muerta (VM) formation is the primary target for unconventional field development in the Neuquén Basin (Argentina), with hundreds of wells drilled in recent years and numerous studies conducted to understand its production potential. The processes that influence the hydraulic fracture geometries in the Vaca Muerta formation are constantly being evaluated, particularly due to the complexity coming from the dispersion of the formation properties and from the lateral and vertical variability (Sagasti et al., 2014). Fracture height is a relevant parameter for several decisions, including landing point selection for exploration or appraisal areas, an input to production models, and a parameter for calibrating the hydraulic fracture simulations. In this paper, we describe and discuss several variables that influence the fracture height growth in anisotropic laminated unconventional reservoirs beyond the commonly accepted ones, with particular emphasis on Vaca Muerta. We also identify the general implications of these concepts for fracture simulation and well productivity. We focus on the following variables: principal stress state, degree of resolution of the 1D geomechanical models, laminations, and lithological contrasts. The main results of this work are: Most Vaca Muerta formation is under a strike-slip stress regime (Garcia et al., 2013). In this situation and based on the results of 1D anisotropic geomechanical models (Espindola et al., 2021), the anisotropy given by the ratio between the overburden and the minimum horizontal stress (Sv/Shmin) has a relevant influence on the fracture height and, consequently, on the well production performance. This affirmation is based on microseismic evidence.As was observed in previous work (Hryb et al., 2020), the computation of 1D geomechanical models with low- and highresolution inputs (logs vs. core data) impact the fracture height simulation. In this paper, we use an example to highlight these differences and the consequences of the averaging process used during the zoning step of the fracture simulation, which affect the obtained fracture height growth.The importance of reservoir laminations on fracture height has been addressed in many publications (Ng et al., 2019; Li et al., 2017; Kresse et al., 2019; Li et al., 2022; Mehrabi et al., 2021). The challenges lie in their detection, characterization and accurate modelling of the interaction between the hydraulic fracture and the lamination. This paper describes a practical workflow, developed in-house, to characterize laminations and use them as input for fracture simulation. In this workflow, lithological contacts are extrapolated from logs using a fit-to-purpose core-log calibration.Laboratory tests (Athavale A.S. et al., 2008) and observations in Vaca Muerta outcrops suggest that the lithological contrasts may play a relevant role in fracture height growth. The different geomechanical behaviors between adjacent lithological layers are potentially strong barriers to fracture propagation. We also discuss recent field data acquisitions that contribute to the understanding and calibration of fracture height: child-child FDI (Weimann et al., 2023) and production allocation by geochemistry (Fasola et al., 2022). Finally, we provide a summary of the above effects, their influence on fracture height, and their implications for fracture simulation and well productivity.