Shear failure analysis of a shallow depth unsupported borehole drilled through poorly cemented granular rock
- Authors: Hashemi, Sam , Taheri, Abbas , Melkoumian, Noume
- Date: 2014
- Type: Text , Journal article
- Relation: Engineering Geology Vol. 183, no. (2014), p. 39-52
- Full Text: false
- Reviewed:
- Description: Adopting an appropriate failure criterion plays a key role in the borehole stability analysis. In this paper the induced stresses on a vertical borehole wall were calculated based on the elastic theory. Then, to predict the stability of a borehole drilled through a poorly cemented sand formation, failure envelopes in different failure criterion domains were derived using the results from a series of precise laboratory tests conducted on solid and hollow cylinder specimens. The mixture used in specimen preparation was designed to simulate the properties of the samples collected from depths up to 200m at a drilling site in South Australia. The hollow cylinder test apparatus was developed by modifying a Hoek triaxial cell. These modifications allowed observing the process of debonding of sand grains from the borehole wall during the test and consequently, acquiring a better understanding on the failure mechanisms of a borehole drilled through poorly cemented sand formations. Three well-known failure criterion domains; Coulomb, Drucker–Prager and Mogi, were considered versus the laboratory test data to investigate their capability to predict the shear failure of a borehole using the data from hollow cylinder tests. The obtained results showed the significance of selecting an appropriate failure domain for predicting the shear failure behavior of poorly cemented sands near the borehole wall. The results also showed that the Coulomb criterion is not well suited for predicting the borehole failure when there is no pressure acting inside the borehole. A failure envelope based on the Mogi domain was developed which can be used for the far-field stress states. The introduced failure envelope allows predicting the stability of a borehole drilled in poorly cemented sands.
The failure behaviour of poorly cemented sands at a borehole wall using laboratory tests
- Authors: Hashemi, Sam , Melkoumian, Nouné , Taheri, Abbas , Jaksa, Mark
- Date: 2015
- Type: Text , Journal article , Technical Note
- Relation: International Journal of Rock Mechanics and Mining Sciences Vol. 77, no. (2015/07/01/ 2015), p. 348-357
- Full Text: false
- Reviewed:
- Description: Borehole stability analysis is an important challenge for researchers in the field of geotechnical, mining and petroleum engineering. Several borehole instability problems during or after the completion of drilling, have been reported by a number of exploration companies in Australia. Many of these problems are reported in drilling projects in poorly cemented sand formations at depths of up to 200 m beneath the ground. The sand production problem, as it is known, has also been observed in weakly bonded sandstones where the debonding of sand grains can be triggered by fluid pressure and induced stresses leading to the failure of the sandstone at the borehole wall. The strength of a granular material formation is generated mainly by a natural cementing agent that bonds sand grains together.
- Description: Borehole stability analysis is an important challenge for researchers in the field of geotechnical, mining and petroleum engineering. Several borehole instability problems during or after the completion of drilling, have been reported by a number of exploration companies in Australia. Many of these problems are reported in drilling projects in poorly cemented sand formations at depths of up to 200 m beneath the ground. The sand production problem, as it is known, has also been observed in weakly bonded sandstones where the debonding of sand grains can be triggered by fluid pressure and induced stresses leading to the failure of the sandstone at the borehole wall [1], [2]. The strength of a granular material formation is generated mainly by a natural cementing agent that bonds sand grains together [3].