Improved stress determination procedures by hydraulic fracturing: rock fracture extension in hydraulic fracturing for conditions where the principal stresses are inclined to the axis at the pressurized borehole
Laboratory hydraulic fracturing tests using a straddle packer with inflatable rubber sealing elements were conducted to investigate the effects of varying borehole inclination with respect to the in-situ stress field and of varying pressurization flow rates.
Experiments were carried out on relatively large specimens of competent, brittle and impermeable rock containing vertical or inclined boreholes. These specimens were fractured hydraulically under biaxial loading, the fractures then being reopened by cycling the pressure at different flow rates.
Fracture orientation was determined by overcoring the borehole in the specimen. The pressure-time records obtained were of two types, dependent on fracture orientation to the borehole axis. In fracturing corresponding to a first type of pressure-time record, the direction of fracture initiation at the borehole is determined primarily by the borehole axis, the fracture orienting itself to the far field stress with propagation depending on breakdown pressure. Second type fractures can be initiated away from the borehole, propagating away from and back to the borehole and its direction is perpendicular to minimum principal stress. Numerical analyses were also carried out on experimental configurations to assist in the interpretation of pressure-time records produced experimentally.
Analytical and experimental studies indicate that: 1) it is possible to determine the normal stress component perpendicular to a fracture direction, from a first type of pressure-time record along with observation of the fracture on the borehole surface. If the fracture was produced by hydrostatic pressure, that normal stress component is the minimum stress component in the plane perpendicular to the borehole axis; 2) the minimum principal stress and its direction can be estimated from a second type of pressure-time record along with observation of the fracture at the borehole wall.
Additional publication details
|Publication Subtype||USGS Numbered Series|
|Title||Improved stress determination procedures by hydraulic fracturing: rock fracture extension in hydraulic fracturing for conditions where the principal stresses are inclined to the axis at the pressurized borehole|
|Series title||Open-File Report|
|Google Analytic Metrics||Metrics page|