Abstract
Unconventional hydrocarbon reservoirs in layered formations, such as tight sandstones and shales, are continually being developed. Hydraulic fracturing is a critical technology for the high-efficiency development of hydrocarbon reservoirs. Understanding the stress field and stability of the formation interface is vital to understanding stress propagation, preferably before the growing hydraulic fracture contacts the formation interface. In this study, models are developed for computing the stress field of hydraulic fracture propagation near the formation interface, and the stress fields within and at the two sides of the formation interface are analyzed. Four failure modes of the interface under the impact of hydraulic fracture propagation in its vicinity are identified, and the corresponding failure criteria are proposed. By simulating the magnitude and direction of peak stress at different parameters, the failure mode and stability of the formation interface are analyzed. Results reveal that when the interface strength is weak, the formation interface fails before the growing hydraulic fracture contacts it, and its stability is significantly related to a variety of factors, including the type of formation interface, rock mechanical properties, far-field stress, structural parameters, distance between the hydraulic fracture and formation interface, and fracturing execution parameters.
Highlights
Hydraulic fracturing is a critical technology for the highefficiency development of unconventional hydrocarbon reservoirs, such as tight sandstones and shale gas
It is necessary to analyze the stability of the formation interface under the impact of hydraulic fracture propagation in the vicinity of the formation interface
Criteria were proposed for determining the following four failure modes under the impact of hydraulic fracture propagation near the formation interface using the maximum normal stress intensity theory and the Mohr–Coulomb theory: tensile failure of rocks at either or both sides of the formation interface; shear failure at the formation interface; tensile failure at the formation interface; and complex failure
Summary
Hydraulic fracturing is a critical technology for the highefficiency development of unconventional hydrocarbon reservoirs, such as tight sandstones and shale gas. A formation interface complicates the mechanism of hydraulic fracture propagation, owing to the difference in pressure, rock material properties, interfacial strength, interfacial morphology, and rock failure behavior between the two sides of the formation interface (Guo et al 2017; Li et al 2018; Lu et al 2015; Tang et al 2019). When propagating from a lower-stress stratum to a higher-stress stratum, a fracture changes its direction in most cases It usually breaks through the formation interface and terminates after propagating for a small distance (Warpinski and Teufel 1987; Zhao et al 2009). A model, considering the differences in rock mechanical properties on both sides of the formation interface and the influence of formation dip, was developed for computing the stress field of hydraulic fracture propagation near the formation interface. The uniaxial tension problem show that the model is correct and reliable
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