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ABSTRACT:Creation of a fracture network in a hydraulic fracturing process is essential for subsurface energy extraction and CO2 sequestration. It is facilitated by reactivation of pre-existing intersecting weak layers and cemented cracks in the rock. In this study, a poromechanical model is developed for the hydraulic fracturing process in rocks containing such pre-existing weak layers. Based on the mixture theory, the crack band model is used to simulate the growth of a crack system. The governing equations with the parameters for hydromechanical coupling are derived, to describe the evolution of the opening and branching of cracks caused by water injection. Microplane model M7 is adopted to characterize the deformation and fracturing of the solid skeleton of the rock, and the Poiseuille law is used to characterize fluid flow through the hydraulic fractures. Numerical simulations are performed to reproduce and interpret recently published laboratory-scale hydraulic fracturing experiments conducted at Los Alamos National Laboratory (LANL). In these experiments, the rock was represented by confined plaster slabs containing orthogonal intersecting weak layers of higher porosity. Numerical simulations reveal how poromechanical characteristics such as the Biot coefficient and the fluid injection rate lead to various typical fracture modes observed in the experiments. These modes include formation of one dominant planar crack or various orthogonal fracture networks.
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Laboratory Experiments Contrasting Growth of Uniformly and Nonuniformly Spaced Hydraulic Fractures
Abstract Hydraulic fractures that grow in close proximity to one an other interact and compete for fluid that is injected to the wellbore, leading to dominance of some fractures and suppression of others. This phenomenon is ubiquitously encountered in stimulation of horizontal wells in the petroleum industry and it also bears possible relevance to emplacement of multiple laterally propagating swarms of magma‐driven dykes. Motivated by a need to validate mechanical models, this paper focuses on laboratory experiments and their comparison to simulation results for the behavior of multiple, simultaneously growing hydraulic fractures. The experiments entail the propagation of both uniformly and nonuniformly spaced hydraulic fractures by injection of glucose or glycerin‐based solutions into transparent (polymethyl methacrylate) blocks. Observed fracture growth is then compared to predictions of a fully coupled, parallel‐planar 3D hydraulic fracturing simulator. Results from experiments and simulations confirm the suppression of inner fractures when the spacing between the fractures is uniform. For certain non‐uniform spacing, both experiments and simulations show mitigated suppression of the central fractures. Specifically, the middle fracture in a 5‐fracture array grows nearly equally to the outer fractures from the beginning of injection. Furthermore, with some delay, the other two fractures that are suppressed with uniformly spaced configurations grow, and eventually achieve a velocity exceeding the other three fractures in the array. Hence, these experiments give the first laboratory evidence of a model‐predicted behavior wherein certain nonuniform fracture spacings result in drastic increases in the growth of all fractures within the array.
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- Award ID(s):
- 1645246
- PAR ID:
- 10450821
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 126
- Issue:
- 1
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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