The in-situ stress condition of an unconventional play has a fundamental influence on well productivity because stress controls how the rock responds to hydraulic fracturing, affects proppant-fracture conductivity and alters reservoir properties such as permeability and porosity. In this study, pore pressure and minimum horizontal stress are assessed in the Utica and Point-Pleasant play using easy-to-acquire data and traditional poro-elastic concepts.
The result exposes the existence of significant in-situ stress variations in the play and suggests that changes in kerogen maturity, tectonic stress and lithology cause these variations. Integration of completion and production data confirms that stress variability has strong implications on well performance. Transformation of the kerogen in oil and then gas generates overpressure in the reservoir that decreases the net-confining stress and leads to high well productivity in the dry gas area. Horizontal stress increases significantly in structured areas due to tectonic footprint, leading to higher breakdown pressure during stimulation and lower well productivity. Stress contrast between the carbonate rich Point-Pleasant and clay-rich Utica formations allows increasing pumped fluid volume without excessive fracture upward growth. This study, while being applied to the Utica play, provides methodologies easily applicable to other unconventional plays.
The in-situ stress condition of an unconventional reservoir has a fundamental impact on its productivity because stress affects both the reservoir properties and the fracture initiation and propagation. Variation in net effective stress modifies fracture conductivity, reservoir permeability and porosity (Barree, Gilbert, & Conway, 2009; Heller, Vermylen, & Zoback, 2014). Hydraulic fractures initiation requires that the induced downhole pressure exceed the minimum horizontal stress. Fractures will always propagate along the path of least resistance and create width in a direction that requires the least force meaning that fracture will propagate parallel to the greatest principal stress and perpendicular to the plane of the least principle stress, the minimum horizontal stress orientation (Zoback, 2010). Fractures vertical growth may also easily be limited by high stress layers. (Warpinskhy, Schmidt, & Northrop, 1982).
