Rock strength and the presence of fractures can have a big impact on the location and design of new structures and their foundations. Wireline logging can provide readings for both and is especially important in locations where collecting core samples is difficult, such from poorly consolidated facies (especially for offshore boreholes) and when Cone Penetration Tests are unreliable.
Rock strength can be estimated using measurements derived from sonic and density logs. One common technique uses the seismic compressional (P) velocity to estimate Unconfined Compressive Strength (UCS). The P-wave velocity can also be combined with the flexural (S) wave velocity and density to give stress/strain properties including Poisson’s ratio, bulk modulus and Young’s modulus. The RG PS-suspension logger includes a dipole source for measurement of P and S velocities in soft formations.
Fractures, Faults & Voids
Optical and acoustic televiewers and micro-resistivity imaging tools characterise features that intersect the borehole wall. These include bedding, drilling-induced/natural fractures and faults. Integrated orientation measurements allow the inclination and direction of features to be measured relative to true north, magnetic north or the borehole dip direction.
Sonar surveys (available from our surface division) are used to map underground voids and disused mine workings to aid risk assessment and remediation planning.