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. To help understand volcanic facies in the subsurface, data setsthat enable detailed comparisons between down-hole geophysical data and coredvolcanic intervals are critical. However, in many cases, the collection ofextended core intervals within volcanic sequences is rare and oftenincomplete due to challenging coring conditions. In this contribution weoutline and provide initial results from borehole logging operations withintwo fully cored lava-dominated borehole sequences, PTA2 and KMA1, on the BigIsland of Hawai`i. Data for spectral gamma, magnetic susceptibility, dipmeterresistivity, sonic, total magnetic field, temperature and televiewer wirelinelogs 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 thecasing of both wells, extending the coverage for PTA2 to the surface andcovering the interval from ca. 300 to 1200 m for KMA1. High-quality corematerial was available for both boreholes with almost complete recovery whichenabled high-resolution core-to-log integration. Gamma data are generally lowcommonly in the range ca. 7–20 gAPI but are shown to increase up to API ofca. 60 with some intrusions and with increases in hawaiite compositions inthe upper part of PTA2. Velocity data are more variable due to alterationwithin porous volcanic facies than with burial depth, with a general degreasedown-hole. The high-resolution televiewer data have been compared directly tothe core, enabling a comprehensive analysis of the variations in theteleviewer responses. This has enabled the identification of key featuresincluding individual vesicles, vesicle segregations, strained vesicles,chilled margins, rubble zones, intrusive contacts and pāhoehoe lobemorphologies, which can be confidently matched between the televiewer dataand the full diameter core. The data set and results of this study includefindings which should enable improved borehole facies analysis throughvolcanic sequences in the future, especially where down-borehole data and imagesbut no core are available.

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Understanding volcanic facies in the subsurface: a combined core, wireline logging and image log data set from the PTA2 and KMA1 boreholes, Big Island, Hawai`i