Directional hydraulic fracturing technology for prefabricated longitudinal guide seams in a coal mine tight sandstone roof

Abstract

Triaxial hydraulic fracturing experiments were used to study the initiation pressure variation and acoustic emission characteristics of different guide seams sizes during roof hydraulic fracturing. Numerical simulations were used to explore the feasibility of multiple boreholes with prefabricated guide seams. An experiment of hydraulic fracturing on a pillar-free working face was also carried out in a coal mine. The results show that the specimens with guide seams reduced the initiation pressure, with the number of acoustic emission events and initiation pressure being inversely proportional to the size of the guide seams. Specimens without guide seams were deflected by stress and produced multi-level cracks, while the specimens with guide seams did not produce large secondary cracks and deflection. When the stress difference was small, three holes penetrated but not under large stress differences. The hydraulic fracturing technology of prefabricated longitudinal guide seams was tested in the Ningtiaota Coal Mine, and the auxiliary transportation roadway of S1201 working face was successfully retained for reuse in adjacent working faces.

Numerical Simulation of Proppant Transportation and Placement Law In Fractured Coal Reservoirs

“…Based on the theory of fluid mechanics, the law of conservation of mass and energy must be obeyed during the movement of fluid [18][19][20].…”

Mechanisms of Hydraulic Fracture Propagation and Multi-well Effect during Multiple Vertical Well Fracturing in Layered Reservoirs with Low Permeability

“…At present, researchers have studied fracture propagation using various methods. − Among them, experimental research can directly observe and analyze the morphology of fracture propagation and its influencing factors, which has become the most commonly used method to study hydraulic fracture propagation in low-permeability reservoirs. However, most experimental specimens are limited to a small scale as a result of the limited experimental conditions. − Currently, hydraulic fracturing experiments use cubic specimens with a side length of 100–300 mm to explore the propagation morphology and law of fractures. − Some studies have attempted to extend the fracture propagation length by enlarging specimens to determine the laws of deflection and bifurcation of fractures during fracturing. , Recently, with the continuous innovation of large-scale fracturing experimental equipment, the side length of the specimen reaches 2060 mm, greatly improving the reliability of the research results . Experimental research has helped us to understand the mechanism of fracture propagation during hydraulic fracturing in low-permeability reservoirs to some extent.…”