Propagation of hydraulic fracture under the joint impact of bedding planes and natural fractures in shale reservoirs

Abstract

The generation of the complex fracture network through hydraulic fracturing is a prerequisite for economic exploitation of shale gas. Bedding planes and natural fractures in shale reservoirs exert a direct impact on the propagation of hydraulic fracture and the formation of the complex fracture network. Based on theoretical analysis and flow‐stress‐damage coupled approach, the propagation of hydraulic fracture under the joint impact of the bedding planes and the natural fractures is studied. The results show the main factors that influence the fracture propagation are the horizontal principal stress difference, the minimum horizontal principal stress, the approaching angle of bedding plane (AABP), the intersection angle of natural fracture (IANF), and the cohesion of the reservoir matrix and the bedding plane. The bigger the horizontal principal stress difference is and the smaller AABP and the cohesion are, the more likely hydraulic fracture will propagate toward the direction of the maximum horizontal principle stress; the smaller AABP and the cohesion are, the more easily it will propagate along the bedding planes; AABP and IANF are the key factors that affect the fracture network formation and both of them bear a negative correlation on the principal stress difference for the formation of the fracture network; the smaller the stress difference and the cohesion difference between the bedding plane and the reservoir matrix are, and AABP is close to IANF and they are in the middle of its value range, the more easily the fracture network forms. The research results are of great significance to reveal the propagation law of hydraulic fracture and the formation of the complex fracture network in shale reservoirs and the efficient exploitation of shale gas.

A Review of Hydraulic Fracturing Simulation

“…Depending on the stress conditions, the hydraulic fracture may reinitiate or terminate at the bedding plane. More recently, the influence of bedding planes with different mechanical properties and intersection angles with a hydraulic fracture is systematically investigated using numerical simulation [121,163]. The numerical results indicate that the bedding planes contribute to the complexity of stimulated fracture network [346].…”

Prediction criterion and numerical validation for the interaction between hydraulic fractures and bedding planes

“…HF is captured by the BP, and then the BP shear slips (slip); 3. HF passes through the BP (penetrate), as shown in Fig 1 . Through numerous theoretical analyses, physical experiments, and numerical simulations, several criteria have been proposed to predict the occurrence of these three interaction modes, such as the Blanton [26], Warpinski [27], Renshaw [28], Zhou [25], Gu [19], Cheng [29], Sarmadivaleh [30], and Gong [31] criteria. Some of these criteria depend on the output parameters in the construction process, some only consider whether HF penetrate the discontinuities, some are extremely complex to use directly, and most studies focus on the interaction between HF and NF.…”

Crack Evolution and Failure Modes of Shale Containing a Pre-Existing Fissure under Compression

“…Horizontal well fracturing technology is a common means to form industrial gas reservoirs and improve productivity. , Perforation orientation is important for the final fracturing effect. , Shale gas development in China is still in the initial stage from the perspective of development technology and production increase effect . As a typical anisotropic material, shale naturally contains bedding, and a large number of natural joints (fissures) have developed due to various tectonic actions. − Most studies on the shale reservoir focused on its mechanical properties and mechanism, − but few focused on the law of fracture initiation and propagation of fractured shale under load (such as fracturing). Generally speaking, the geometry of joints has an important influence on the strength and deformation characteristics of the jointed rock mass. − The primary joints serve as the reservoir space of shale gas, and the bedding serves as a methane seepage channel.…”