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Volcanic reservoirs are becoming increasingly important in the targeting of petroleum, geothermal and water resources
globally. However, key areas of uncertainty in relation to volcanic reservoir properties during burial in
different settings remain. In this contribution, we present results from borehole logging and sampling operations
within two fully cored c. 1.5 km deep boreholes, PTA2 and KMA1, from the Humu[U+02BB]ula saddle region
on the Big Island of Hawai’i. The boreholes were drilled as part of the Humu’ula Groundwater Research Project
(HGRP) between 2013-2016 and provide unique insights into the evolution of pore structure with increasing burial
in a basaltic dominated lava sequence. The boreholes encounter mixed sequences of ‘a’¯a, p¯ahoehoe and transitional
lava flows along with subsidiary intrusions and sediments from the shield to post-shield phases of Mauna
Kea. Borehole wireline data including sonic, spectral gamma and Televiewer imagery were collected along with
density, porosity, permeability and ultrasonic velocity laboratory measurements from core samples. A range of
intra-facies were sampled for analysis from various depths within the two boreholes. By comparison with core
data, the potential for high resolution Televiewer imaging to reveal spectacular intra-facies features including individual
vesicles, vesicle segregations, ‘a’¯a rubble zones, intrusive contacts, and intricate p¯ahoehoe lava flow lobe
morphologies is demonstrated. High quality core data enables the calibration of Televiewer facies enabling improved
interpretation of volcanic reservoir features in the more common exploration scenario where core is absent.
Laboratory results record the ability of natural vesicular basalt samples to host very high porosity (>50%) and permeability
(>10 darcies) within lava flow top facies which we demonstrate are associated with vesicle coalescence
and not micro-fractures. These properties may be maintained to depths of c. 1.5 km in regions of limited alteration
and secondary mineralization and, therefore, additional to fractures, may comprise important fluid pathways at
depth. Alteration and porosity occlusion by secondary minerals is highly vertically compartmentalized and does
not increase systematically with depth, implying a strong but heterogeneous lateral component in the migration and
effects of hydrothermal fluids in these systems. The distribution and timing of dyke feeder zones coupled with the
scale and spatial distribution of lava flows making up the lava pile form first order influences on the preservation
potential of volcanic reservoir properties during burial. Our results demonstrate the complex relationship between
the primary hydrogeology of lava flow fields and the resulting effects of hydrothermal fluid circulation on reservoir
property evolution with burial.