Methods for borehole stress testing
Overcoring stress measurement
SMCOY has developed a new fully mechanical overcoring cell based on the same principle as the LVDT cell.
The DDP36 probe, aka “The Miniprobe“, has a robust device design to measure with precision the horizontal stress components in 36 mm vertical boreholes (overcoring >76 mm).
The Miniprobe is best used in pair with the wireline system, allowing a fast installation, measuring and recovering process that reduces disruptions on the diamond exploration drilling process.
The Miniprobe has been developed as an alternative to the traditional hydraulic fracturing test and is nowadays our to go method on borehole measurements.
Hydraulic fracturing stress measurement
SMCOY had used Mini Frac Hydraulic fracturing equipment (Mindata Ltd) for in situ stress measurements with hydraulic fracturing technique.
With the dvelopment of the DDP36 probe, SMCOY has stopped the Hydraulic Fracturing Service as the Miniprobe provides faster and more reliable results.
In the hydraulic fracturing (HF) stress measurement an inflatable double packer system is used to seal a test section in a borehole. The test section is preferably located in primary stress state, where no interference from tunnel are present. The test section is pressurized using water and the water pressure is increased until a new rock fracture is induced. Usually 2 MPa higher pressure is used in packers than the test section in order to seal the test section properly and to prevent leaking through the packers. Also in the classic HF measurement the test section must locate in intact rock.
A schematic illustration of the hydrofracturing tool is presented below.
