H13M-03
A new approach to hydrologic testing during drilling of a deep borehole and its application to the Swedish scientific deep drilling COSC project
Monday, 14 December 2015: 14:10
3018 (Moscone West)
Chin Fu Tsang1, Jan-Erik Rosberg2, Christopher Juhlin3, Auli P Niemi3, Christine Doughty1, Patrick F Dobson1 and Jens T Birkholzer1, (1)Lawrence Berkeley National Laboratory, Berkeley, CA, United States, (2)Lund University, Lund, Sweden, (3)Uppsala University, Uppsala, Sweden
Abstract:
Drilling of a deep borehole does not normally allow for hydrogeologic testing during the drilling period. The only time hydraulic tests are performed is when drilling encounters a large-transmissivity zone as evidenced by a large loss (or high return) of drilling fluid. The present paper proposes a new approach, that of conducting Flowing Fluid Electric Conductivity (FFEC) logging during the drilling period, with negligible impact on drilling schedule, yet providing important and accurate information on depth locations of both high- and low-transmissivity zones and their in-situ hydraulic conductivities. The information can be used to guide downhole fluid sampling and post-drilling detailed testing of the borehole. The proposed method has been applied to the drilling of a 2500-m borehole at Åre, Northern Sweden, which was initiated on April 28 and completed on August 26, 2014, with 99% core recovery. This borehole, named COSC-1, was drilled as part of the Swedish Scientific Deep Drilling COSC project, where COSC stands for Collisional Orogeny in the Scandinavian Caledonides. The project is a multidisciplinary project with the aim of gaining a deeper understanding of mountain belt dynamics in the Scandinavian Caledonides. Scientific investigations which include a range of topics from studies of ancient orogeny to the present-day hydrological cycle are conducted under six working groups: (1) tectonics, (2) geophysics, (3) geothermics, (4) hydrology, (5) microbiology and (6) drilling management and technology. In this talk, the new approach to hydrologic testing during the drilling period will be described and its application to the drilling of COSC-1 borehole presented. Results show that from 300 m to the borehole bottom at 2500 m, there are eight hydraulically active zones or fractures in COSC-1, with very low transmissivity values ranging over one order of magnitude.
