Abstract
To capture the hydraulic fractures in heterogeneous and layered rocks, a numerical code that can consider the coupled effects of fluid flow, damage, and stress field in rocks is presented. Based on the characteristics of a typical thin and inter-bedded sedimentary reservoir, China, a series of simulations on the hydraulic fracturing are performed. In the simulations, three points, i.e., (1) confining stresses, representing the effect of in situ stresses, (2) strength of the interfaces, and (3) material properties of the layers on either side of the interface, are crucial in fracturing across interfaces between two adjacent rock layers. Numerical results show that the hydrofracture propagation within a layered sequence of sedimentary rocks is controlled by changing in situ stresses, interface properties, and lithologies. The path of the hydraulic fracture is characterized by numerous deflections, branchings, and terminations. Four types of potential interaction, i.e., penetration, arrest, T-shaped branching, and offset, between a hydrofracture and an interface within the layered rocks are formed. Discontinuous composite fracture segments resulting from out-of-plane growth of fractures provide a less permeable path for fluids, gas, and oil than a continuous planar composite fracture, which are one of the sources of the high treating pressures and reduced fracture volume.
Highlights
Hydraulic fracturing is widely used in the petroleum engineering, mining, and geotechnical industries
Besides in-situ stresses, fracture propagation across interface depends on many other factors, in which the interface properties play a key role in the interaction of the hydraulic fracture with the interface
We investigated the potential for fracture propagation across, termination at, or step-over at a bedding interface by examining the fracturing process and associated stress evolution as the fracture approaches the interface
Summary
Hydraulic fracturing is widely used in the petroleum engineering, mining, and geotechnical industries. (a) the sedimentary characteristics of bar sand subfacies and beach sand subfacies in one of beach-bar sandstone reservoirs in Shengli Oilfield of China [3]; (b) outcrop of a shale formation, where the horizontal beddings are cut by the vertical fractures (denoted by red dashed line) to form fracture networks, Well A and B are the conceptual vertical and horizontal wells [8]; and (c) a hydraulic fracture that grew vertically in a coal seam and horizontally along the interface between the coal and the roof rock (the hydro-fracture is shown in yellow and the black arrows represent the fracturing direction) [9]. Is employed to investigate the potential mechanisms of hydraulic fracture initiation and subsequent propagation near and/or on the interfaces in a series of numerical models.
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