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

Abstract

Abstract. 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.

Marine electrical imaging reveals novel freshwater transport mechanism in Hawai‘i

“…In the east of Hawai'i island, resistivity surveys identified shallow resistive anomalies that represent high-elevation groundwater on the east flank of Mauna Kea (34). In addition, resistivity log from the PTA2 borehole (situated west of Mauna Kea) exhibits a notable increase in resistivity at a depth of 1130 m, most likely associated with freshwater-saturated basaltic rocks (47). Drilling resistivity logs from borehole KP-1 located on the eastern flank of Hawai'i detected a shallow freshwater basal lens underlain by saltwater-saturated rocks (37,46).…”

Stress Field Interactions Between Overlapping Shield Volcanoes: Borehole Breakout Evidence From the Island of Hawai'i, USA

“…), the plot below shows the borehole breakout azimuth distribution versus borehole breakout frequency ( n : number of breakouts); (f) borehole breakout opening (2θ) versus cumulative borehole breakout length (above) and versus borehole breakout frequency (below). Legend of the main volcanic facies (modified after Jerram et al, 2019): a: pāhoehoe; b: ‘a’ā; c: transitional; d: intrusions; e: conglomerate/breccia.…”

“…The PTA2 borehole sampled the shield stage strata (from approximately 300 m to the bottom) and the post‐shield sequence, including Hamakua and Laupāhoehoe lavas (0 to approximately 300 m; Figure 3a). The stratigraphic section is dominated by basaltic lava deposits (including ‘a’ā, transitional, and pāhoehoe facies; HGRP website; Jerram et al, 2019) with subsidiary occurrences of ash, breccia, and volcanoclastic layers, as well as thick cinder deposites and some identified intrusive layers (Figure 3b).…”

“…The Humu'ula Groundwater Research Project (HGRP) drilled two boreholes in order to obtain a complete data set of fully cored volcanic rocks with associated borehole measurements and to characterize the groundwater resources in the saddle region (Jerram et al, 2019). The PTA2 borehole was drilled in the saddle region between Mauna Kea and Mauna Loa and offers a unique opportunity to study the previously untested subsurface of central Hawai'i.…”

The 3D facies architecture and petrophysical properties of hyaloclastite delta deposits: An integrated photogrammetry and petrophysical study from southern Iceland

“…Clearly chemical alteration may have an important influence on permeability evolution beyond simple mechanical compaction (e.g. Jerram et al, ), however, it is an important point that different volcanic facies in close proximity to each other may have significantly different mechanical strengths which contribute to highly variable fluid flow evolution and preservation potential during early burial.…”