Borehole Geophysics And Hydraulic Testing Aids in Determining Geotechnical Parameters in a Nearshore Fractured Sedimentary Deposit
D. Gartner, B. Rigler, R. Gee, M. Donaldson, B. Birt and G. Mason
Event name: 81st EAGE Conference and Exhibition 2019
Session: Near-Surface Geoscience - Global Significance, Markets, Applications and Case Studies
Publication date: 03 June 2019
Info: Extended abstract, PDF ( 1.39Mb )
Price: € 20
Geotechnical work on nearshore tunnels requires a level of precision and accuracy in the determination of subsurface parameters that is more rigorous than most applications of geophysical logs. As such, these projects demand a wealth of measurements of the subsurface by geophysical means. As a case study, we present work done in the planning of a nearshore cable tunnel for the National Grid beneath the Menai Strait in North West Wales, United Kingdom. Advanced wireline logging was conducted in nine boreholes along the proposed project. The expansive suite of logs, including DMR, optical and acoustic televiewer, orientated four arm caliper, gamma-gamma density and full-waveform sonic led to an accurate understanding of the rock strength and geo-mechanical properties. DMR measurements provided continuous total porosity and pore-size distribution data. Permeability estimations were also performed using DMR Porosity and T2 distribution data. Packer test derived, in-situ permeability results were used to refine and support the DMR data to provide continuous data for the whole borehole length. This application of an expansive suite of methods among the high resolution and in situ nature justified the use of wireline geophysical logging and particularly the DMR method more broadly in the construction and engineering sectors.