In this study, a special focus was dedicated to the effect of elastic anisotropy of shales on the in-situ stress contrast between different layers and its implications on the vertical containment of hydraulic fractures (HF) and how they relate to the widely observed fracture driven interaction (FDI) phenomena and undesirable HF height growth. The reported elastic and mechanical properties of the main members of the Bakken petroleum system in the Williston Basin (i.e. Upper and Lower Bakken Shale, Middle Bakken, and Three Forks) were used to estimate the in-situ stresses based on anisotropic rock properties and use the minimum horizontal stress profile for HF modeling. The estimated stress profile appeared to be very different from the one calculated based on the isotropic formation assumption. The anisotropic stress model, as reported by other researchers, is more realistic in transversely isotropic rocks and rocks with a high volume of clay and TOC and generated more reliable results that conform better with other indicators and observations from other types of data associated with HF geometry.
Accurate estimation of the minimum principal in-situ stress is a milestone in the successful design of hydraulic fracturing (HF) jobs (Ganpule et al., 2015). The role of accurate stress variations with depth becomes more pronounced where HF is performed in different horizons to explore what is called stacked pay. Estimation of in-situ horizontal stresses is mainly attributed to the inherently simplistic assumptions of the commonly used stress models (Zoback, 2007). However, the revolution in the oil and gas industry due to production from Shale plays indicated the necessity of using anisotropic, or what is so-called as transverse isotropic (TI) assumption for the different geological layers for improved estimation of the horizontal stresses. In this study, we showcased the importance of laboratory characterization of the elastic and mechanical properties for accurate prediction of stress profiles and how they can change our designs and improve the profitability of our investments by generating more reliable stress models that are coherent with what is indicated by other types of data. This can serve as a strong base for improved planning. This is proved through our case study performed using data from the Bakken petroleum system in the Williston Basin. It was found that the HF geometries predicted from simulation using a well-calibrated anisotropic stress model strongly agreed with HF geometries observations from microseismic data reported in many other studies such as McKimmy et al. (2022) and Lorwongngam et al. (2018).
