Hydraulic fracturing near interfaces

Conference · Sat Sep 01 04:00:00 EDT 1979

OSTI ID:5560888

Shaffer, R J; Hanson, M E; Anderson, G D

Theoretical and experimental studies are being conducted of pressure driven fractures near interfaces that separate differing materials. When a crack propagates in material A toward a well bonded interface at half the dilatational wave speed, there is an amplification in the likelihood of crack penetration into material B. This amplification increases as material A becomes stiffer relative to B. The stress intensity factor of the leading crack tip decreases as the crack approaches a stiffer material and increases as the crack approaches a more flexible material. Additionally, when existing cracks are present near the interface, the effects of the change in material properties are reduced. In equilibrium analyses with unbonded interfaces, where shear stresses are transmitted via friction, a decrease in the coefficient of friction reduces the likelihood of crack penetration into the adjacent material when both materials are identical; however, decreasing friction tends to draw the crack toward the interface. Friction coefficients and hydrofracture penetration characteristics were measured in Indiana limestone and Nugget sandstone. There is a least stress required across the interface for a hydrofracture to cross the interface; this stress depends on rock type, interface surface finish, and water content.

• Research Organization: California Univ., Livermore (USA). Lawrence Livermore Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5560888
• Report Number(s): UCRL-83419; CONF-800204-4
• Country of Publication: United States
• Language: English

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