ARMA 21-1928: Stress-Measurement Campaign in Scientific Deep Boreholes: from Planning to Interpretation

This paper was prepared for presentation at the 55th US Rock Mechanics/Geomechanics Symposium held in Houston, Texas, USA, 20-23 June 2021. This paper was selected for presentation at the symposium by an ARMA Technical Program Committee based on a technical and critical review of the paper by a minimum of two technical reviewers. The material, as presented, does not necessarily reflect any position of ARMA, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of ARMA is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 200 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgement of where and by whom the paper was presented.

ABSTRACT

Three candidate sites for a deep geological repository are currently being explored in Northern Switzerland. The

exploration program involves drilling of at least two deep boreholes per site. A very dense stress test campaign (circa 20 stress tests per borehole) is being undertaken with a wireline formation testing tool. A detailed planning process has been developed to maximize

the success rate and the coverage of stress test stations, integrating all available information as it becomes available. A dedicated

stress testing protocol was also developed to ensure the most robust estimate of the stress. Improvements in the toolstring were introduced step by step to enable 100% coverage of the desired lithological column. For example, this is the first time that a single

toolstring with three packers has been run to perform the complete combination of sleeve fracturing, hydraulic fracturing and sleeve reopening tests. Preliminary comparison between the stress estimates for the first two boreholes are presented.