Well Orientation and Fracture Turning

ABSTRACT: Horizontal wells and hydraulic fractures are key enablers for developing unconventional fields. Horizonal wells are normally drilled in the direction of minimum horizontal stress to develop transverse fractures perpendicular to wellbores. However, wells are sometimes drilled at angles off in-situ stress to accommodate lease boundaries, operational limitations, and geological uncertainties. Following a comprehensive study of US unconventional field data, a series of Finite Element and Discrete Element (FEDEM) simulations have been developed to capture and confirm fracture turning for a cased-and-perforated horizontal well, with various alignment angles between wellbores and in-situ stress. Fracture geometries, fracture apertures, breakdown pressures, and net pressures are calculated and compared to quantify the impacts of turning. In addition, different stress anisotropies are applied to clarify their roles in initiating, turning, and propagating fractures. These findings clarify the significance and control of fracture turning when wells are not aligned with in-situ stress to optimize well and fracture designs and improve stimulation efficiency in unconventional fields. These insights and workflows can also be applied to other hydraulic fracturing applications such as enhanced geothermal systems (EGS) and mining. 1. INTRODUCTION: FIELD AND LABORATORY OBSERVATIONS When developing unconventional fields, horizontal wells are normally drilled in the direction of minimum horizontal stress so that hydraulic fractures can be initiated transversely and perpendicular to the wellbore. This design maximizes the reach of hydraulic fractures and stimulated rock volume. However, sometimes wells are drilled at angles off the direction of in-situ stress to accommodate lease boundaries, operational limitations, and geological uncertainties. The misalignment of well trajectory and in-situ stress can significantly affect stimulation efficiency and well productivity. Based on the data from more than 71,000 wells in multiple US unconventional plays, a recent study determined that majority of fields showed strong and sinusoidal correlation of production with well-stress alignment (Gabry et al., 2024). For example, the production from Eagle Ford wells declined more than 30% when they were oriented 20 degrees away the minimum horizontal stress (Shmin) direction (Fig. 1). Similar trends were observed in other unconventional plays such as the Utica, Bakken, Marcellus, and Granite Wash. Meanwhile no significant production effect was observed in the Barnett, Haynesville, and Wattenberg/Niobrara, where reservoir properties and completion qualities are more dominant.