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True triax

True triax

Senior Research Scientist

The new True Triaxial system from MTS is being installed summer of 2017. This unique system designed by SINTEF will expand our existing large hollow cylinder test capabilities by allowing for larger size of rock specimens, true triaxial conditions with added radial flow capability.

Specifications

  • 100 MPa confining stress
  • 50 MPa vertical deviatoric stress
  • 50 MPa horizontal deviatoric stress
  • Truncated samples, 200 mm diameter (and 400 mm diameter in biaxial mode)
  • Hollow-cylinder tests
  • Radial flow
Geometry of sample preparation, with opposing surfaces truncated from initially cylindrical specimen, where pistons apply additional stress above the confining stress. This unique geometry has been shown to reduce unwanted stress concentration present in the corners of traditional prism-shaped specimens, while allowing for minimally perturbed radial flow with good hydraulic sealing of the specimen.
View inside the triaxial cell from above, showing the lateral pistons applying additional radial stress directly on the rock specimen. The rest of the specimen's surface is exposed to the (lower) radial stress generated by pressurizing oil in the cell. Feed-through tubing distributes pore fluid directly on the outer surface of the hollow cylinder specimen or/and in the borehole, with high-rate pumps enabling radial flow, either inwards or outwards.
Side view of the triaxial cell, revealing placement of the specimen and feed-through flow lines. The lateral pistons are shown, as well as the top piston generating the third stress component (axial stress).

Specimens

Different geometry and sizes

Truncated samples (true triaxal-mode)

  • 200 mm specimens
  • 100 mm specimens
  • 50 mm specimens

Round specimens (biaxial-mode)

  • 400 mm specimens

Typical length to diameter ratio: 1:1

Photograph of the inside assembly with a rock specimen mounted in the middle. Strain gauges are placed around the specimen to monitor deformation during testing.

Areas of use

Sand production
the True Triaxial system will help refine sand prediction models to take into account field-relevant stress anisotropy around a well. This will improve the predictive accuracy of volumetric sand production models, helping operators optimize well productivity throughout its lifetime.

Borehole stability
The new system will allow for more realistic testing of overburden shale samples, especially targeting difficult deviated trajectories, where stress anisotropy has a large destabilizing effect. The interaction between stress anisotropy and fabric anisotropy will be studied in more detail.

Gas and oil shales
Testing will improve models of fracture productivity as a function of well orientation and stress.

Hydraulic fracturing (for larger samples, up to 400 mm)
The rig will permit more accurate hydraulic fracturing tests, used in biaxial mode on the largest samples to allow for longer fractures. Additionally, the effect of stress anisotropy on fracture topology can be studied on smaller samples.

Any other area where non-isotropic stress distribution is essential (i.e. most areas).

Photograph showing the true triaxial cell inserted in the load frame, providing the axial stress component.

Pictures

Installation of the new system in SINTEF's Formation Physics laboratory in Trondheim.

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Contact information

Postal address:
P.O. Box 4763 Torgarden, NO-7465 Trondheim
Visiting address:
S.P. Andersens vei 15 B, NO-7031 Trondheim
Phone: +47 464 17 000