Hydraulic Fracture Crossing Natural Fracture at Non-orthogonal Angles, A Criterion, Its Validation and Applications

Abstract

Hydraulic fracturing treatments have become an indispensable part of well completion in shale gas field development. Shale formations often contain natural fractures and complex hydraulic fracture networks may form during a treatment. The complex fracture network is strongly influenced by the interaction between the hydraulic fracture and the pre-existing natural fractures. A criterion has been developed to determine whether a fracture crosses a frictional interface (pre-existing fracture) at non-orthogonal angles. This criterion is an extension of the one for orthogonal crossing originally developed by Renshaw and Pollard (1995). The dependence of crossing on the intersection angle is shown quantitatively using the extended criterion. The fracture is more likely to turn and propagate along the interface than to cross it when the angle is less than 90°. The validation of the criterion using laboratory experiments for various angles is described and discussed. When applied to laboratory experiments, good agreement between the criterion and experiments is observed for a wide range of angles. The criterion can be used to determine whether hydraulic fractures cross natural fractures under particular field conditions, and it has been incorporated in a hydraulic fracture model that simulates hydraulic fracture propagation in a natural fractured formation.

Examining the Effect of Cemented Natural Fractures on Hydraulic Fracture Propagation in Hydrostone Block Experiments

“…Blanton (1982) studied hydraulic fracture crossing and arrest in frictional interfaces within Devonian shale and hydrostone showing that stress state and approach angle between the hydraulic and natural fracture were key parameters. Renshaw and Pollard (1995) and Gu et al (2011) expanded on this approach developing crossing criterions based on analytical equations for frictional interfaces. Beugelsdijk et al (2000) and Zhou and Xue (2011) thermally induced pre-existing fractures in cement blocks to generate a fracture network for the hydraulic fracture to encounter, examining the impact of pre-existing fracture conductivity, stress state and injection rate on fracture path complexity.…”

Experimental studies

“…To validate the extended criterion for nonorthogonal crossing presented in Chapter Seven, laboratory tests were conducted in a polyaxial test cell [23]. A Colton sandstone block of 11 ¢¢ Â 11 ¢¢ Â 15 ¢¢ with a tensile failure strength of 588 psi was used in testing.…”

Fracture propagation in a naturally fractured formation

“…The condition given in Eq. (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26) ensures that Eq. (7-60) has a solution for 0 < f L0 < 1.…”

“…A branch-off may occur at an intersection with another fracture, or The HF-NF crossing behavior depends on the in situ stresses, rock and NF properties, frac-fluid property and its injection rate. During the last decades, extensive theoretical and experimental studies [17][18][19][20][21][22][23][24][25][26] have been carried out for developing a rule governing the HF-NF interaction.…”