To help understand volcanic facies in the subsurface, data sets that enable detailed comparisons between down-hole geophysical data and cored volcanic intervals are critical. However, in many cases, the collection of extended core intervals within volcanic sequences is rare and often incomplete due to challenging coring conditions. In this contribution we outline and provide initial results from borehole logging operations within two fully cored lava-dominated borehole sequences, PTA2 and KMA1, on the Big Island of Hawai`i. Data for spectral gamma, magnetic susceptibility, dipmeter resistivity, sonic, total magnetic field, temperature and televiewer wireline logs were successfully acquired for the open hole interval ca. 889 m to 1567 m within the PTA2 borehole. Spectral gamma was also collected from inside the casing of both wells, extending the coverage for PTA2 to the surface and covering the interval from ca. 300 to 1200 m for KMA1. High-quality core material was available for both boreholes with almost complete recovery which enabled high-resolution core-to-log integration. Gamma data are generally low commonly in the range ca. 7–20 gAPI but are shown to increase up to API of ca. 60 with some intrusions and with increases in hawaiite compositions in the upper part of PTA2. Velocity data are more variable due to alteration within porous volcanic facies than with burial depth, with a general degrease down-hole. The high-resolution televiewer data have been compared directly to the core, enabling a comprehensive analysis of the variations in the televiewer responses. This has enabled the identification of key features including individual vesicles, vesicle segregations, strained vesicles, chilled margins, rubble zones, intrusive contacts and pāhoehoe lobe morphologies, which can be confidently matched between the televiewer data and the full diameter core. The data set and results of this study include findings which should enable improved borehole facies analysis through volcanic sequences in the future, especially where down-borehole data and images but no core are available.
Bibliographical noteData availability. A digital archive of core photos and detailed core run depth log information is available at https://www.higp.hawaii.edu/hggrc/projects/humuula-groundwater-research-project/(HGGRS, 2019). The down-hole data are published with a digital object identifier via GFZ Data Services (Kück, 2019).
Acknowledgements. This project was made possible by the collaborative outlook of the main partners (VBPR and DougalEARTH, GFZ, and the University of Hawai‘i) and the extensive background work undertaken by the researchers at the Hawai‘i Groundwater and Geothermal Resources Center (University of Hawai‘i) and
from the HGRP project. Jehanne Paris is thanked for helping organize the logging operations and helping in the field. Martin Töpfer and Marco Groh (Operational Support Group, OSG, of ICDP, GFZ) are thanked for ensuring the smooth running of the logging operations. Dougal Jerram and Sverre Planke are also supported by the Research Council of Norway, through its Centres of Excellence funding scheme, project 223272 at CEED, University of Oslo. We would like to thank Breno Waichel and John Shervais for constructive reviews and the editorial team
at Scientific Drilling for their prompt handling and meticulous guidance through the various stages from submission to publication.