Expansion law and influence factors of hydraulic fracture under the influence of coal pillar

• Published in: Arabian journal of geosciences 2021-06, Vol.14 (11), Article 961
• Main Authors: Xia, Binwei, Ou, Changnan, Zhang, Xuan, Fu, Yuanhao
• Format: Article
• Language: English
• Subjects: Coal; Coal mines; Coal mining; Crack propagation; Crack tips; Deflection; Design optimization; Direction; Earth and Environmental Science; Earth science; Earth Sciences; Elasticity; Fracture mechanics; Horizontal orientation; Hydraulic fracturing; Hydraulic mining; Mechanics; Mining; Morphology; Original Paper; Reservoirs; Steering; Stress distribution; Stress propagation
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-021-07240-x

In the process of coal mining, the remaining coal pillars in the overlying strata have a greater impact on the lower mining pressure. Hydraulic fracture can provide a strong control effect, but the crack extension law is still unclear. In order to study the morphology of hydraulic fracture under the influence of coal pillar concentrated stress, based on the elasticity and fracture mechanics, the hydraulic fracturing extension model is established. The expansion law of hydraulic fracture and its influencing factors were studied to propose the steps of predicting its expansion and clarify the influence degree of each factor and the optimal steering scheme. The results show that there are uneven stress fields in the floor rock under the coal pillar, which will lead to the deflected propagation of hydraulic fracture. The steering angle of hydraulic fracture is affected by the pressure in the crack, the uniform load of the coal pillar, the vertical and horizontal distance of the crack tip, the width of the coal pillar, and the influence degree decreases successively. The concentrated stress has a directional influence on the propagation of hydraulic fracture, and the influence degree is deeper in the horizontal direction. The influence range is wider in the vertical direction. There is an area where the deflection angle of hydraulic fracture is relatively larger. The results of the study can provide the theoretical basis for the design and optimization of hydraulic fracturing parameters of hard roof under the influence of coal pillars.