Lava flow hosted reservoirs: a review

Abstract

Lava flows form important fluid reservoirs and have been extensively exploited for water aquifers, geothermal energy, hydrocarbon production, and more recently for carbon storage. Effusive subaerial mafic to intermediate lava flows account for vast rock volumes globally, and form reservoirs with properties dictated by well-known lava flow facies ranging from pāhoehoe through several transitional forms to ‘a’ā lava. These variations in flow type lead to critical differences in the pore structure, distribution, connectivity, strength, and fracturing of individual lava flows, which, alongside lava flow package architectures, determine primary reservoir potential. Lava flow margins with vesicular, fracture, and often autobreccia hosted pore structures can have porosities commonly exceeding 40% and matrix permeabilities over 1 E-11 m ² (> 10 darcy) separated by much lower porosity and permeability flow interiors. Secondary post-emplacement physicochemical changes related to fracturing, meteoric, diagenetic, and hydrothermal alteration can significantly modify reservoir potential through a complex interplay of mineral transformation, pore clogging secondary minerals, and dissolution which must be carefully characterized and assessed during exploration and appraisal. Within this contribution, a review of selected global lava flow hosted reservoir occurrences is presented followed by a discussion on the factors that influence lava flow reservoir potential.