Inclination measurements of the SE-03 borehole on Surtsey

In 2021, Tobias Weisenberger and others made downhole measurements of the inclination of the SE-03 borehole, drilled in August-September 2017. The measurements reveal that the average angle from vertical is 33.4±0.2° rather than 35°. The discrepancies in the actual inclination give variations in vertical and horizontal positions, up to 4.7 m depth and 8 m east than the predicted borehole paths.

Figure 1. Diagrams showing the inclination of the SE-03 borehole measured in August 2021. (A) measured angles of the borehole from vertical for the HQ3 drill bit (63.5 mm core diameter) to a presumed measured depth of 214 m (175 m b.s.) and the NQ3 drill bit (43 mm core diameter) to a presumed measured depth of 354 m. (B) predicted borehole path at 35° from vertical (blue) relative to the measured borehole path (red) (after Weisenberger et al., 2022). The final vertical depth is 294.7±1.2 m b.s., about 4.7 m deeper than the presumed vertical depth, 289.0 m b.s., at the presumed measured length of 354.05 m.

The SE-03 borehole was drilled towards west with an azimuth of 264° and a designed plunge of 35° from vertical (Jackson et al. 2019, https://doi.org/10.5194/sd-25-35-2019). Downhole measurements in August 2021 revealed, however, that the average angle of the borehole from vertical is 33.4±0.2° (Figure 1). The bottom of the borehole at the presumed 354.05 m measured depth (289 m b.s.) based on rod lengths during drilling actually corresponds to a total vertical depth of 294.7±1.2 m. This is 4.7 m deeper than the planned borehole path. The horizontal length from the drill head to the point vertically above the bottom is 195.1±1.0 m, about 8 meters farther to the east, than the designed borehole path of 203.1 m. The principal discrepancy in the borehole inclination begins at the transition from the HQ3 to NQ3 drill bit at 214 m b.s. vertical depth. The borehole terminates in a basaltic intrusion encountered at 343-352 m measured depth.

Citation

Weisenberger, T.B., M. T. Gudmundsson, B. T., Gunnarson, S. L. Jørgensen, M. D. Jackson, 2022, Measurements of the inclination of the SE-03 Borehole on Surtsey Volcano: Surtsey Research, 15, 121–126, doi: 10.33112/surtsey.15.9 .

Figure 1. Diagrams showing the inclination of the SE-03 borehole measured in August 2021. (A) measured angles of the borehole from vertical for the HQ3 drill bit (63.5 mm core diameter) to a presumed measured depth of 214 m (175 m b.s.) and the NQ3 drill bit (43 mm core diameter) to a presumed measured depth of 354 m. (B) predicted borehole path at 35° from vertical (blue) relative to the measured borehole path (red) (after Weisenberger et al., 2022). The final vertical depth is 294.7±1.2 m b.s., about 4.7 m deeper than the presumed vertical depth, 289.0 m b.s., at the presumed measured length of 354.05 m.