David Daniel McNamara

University of Liverpool | UoL · Department of Earth, Ocean and Ecological Sciences

Fractures play an important role as fluid flow pathways in geothermal resources hosted in indurated greywacke basement of the Taupo Volcanic Zone, New Zealand, including the Kawerau Geothermal Field. Over time, the permeability of such geothermal reservoirs can be degraded by fracture sealing as minerals deposit out of transported geothermal fluids...

Geophysical observations show spatial and temporal variations in fault slip style on shallow subduction thrust faults, but geological signatures and underlying deformation processes remain poorly understood. International Ocean Discovery Program (IODP) Expeditions 372 and 375 investigated New Zealand's Hikurangi margin in a region that has experien...

Information on structure, stress, and their inter-relationship is essential for understanding structurally controlled geothermal permeability. Active fault mapping, borehole image analysis, and well testing in the Te Mihi geothermal area, New Zealand allows us to refine structural and fluid flow architecture of this resource. The Te Mihi area is st...

We constrain orientations of the horizontal stress field from borehole image data in a transect across the Hikurangi Subduction Margin. This region experiences NW‐SE convergence and is the site of recurrent slow slip events. The direction of the horizontal maximum stress is E‐W at an active splay thrust fault near the subduction margin trench. This...

Quantifying tectonic stress magnitudes is crucial in understanding crustal deformation processes, fault geomechanics, and variable plate interface slip behaviors in subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand, is characterized by along‐strike variation in interface slip behavior, which may be linked to tectonic stress varia...

Eclogites are important components of subduction-collision zones, with the mineral omphacite acting as the supporting framework mineral that accommodates the majority of any accumulated strain. As such it is important to determine which deformation mechanisms operate in omphacite during and after its formation to understand the rheology of deformin...

Quantifying tectonic stress magnitudes is crucial in understanding crustal deformation processes, fault geomechanics, and variable plate interface slip behaviors in subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand is characterized by along-strike variation in interface slip behavior, which may be linked to tectonic stress variat...

Considering the global drive towarrd net-zero carbon emissions in the near future, the need to find clean sources of energy has never been more important. It is estimated that globally there are tens of thousands of depleted and abandoned oil fields that may be adapted to produce green energy. These may be re-cycled with the help of air injection,...

Greywacke basement rocks in New Zealand host conventional geothermal reservoirs and may supply important hotter and deeper geothermal energy resources in the future. This work combines petrological analyses and physical property measurements of Waipapa greywacke, a basement unit hosting New Zealand geothermal reservoirs, in order to understand bett...

Knowledge of the contemporary in‐situ stress orientations in the Earth's crust can improve our understanding of active crustal deformation, geodynamic processes, and seismicity in tectonically active regions such as the Hikurangi Subduction Margin (HSM), New Zealand. The HSM subduction interface is characterized by varying slip behavior along strik...

Constraint on the rock strength parameters within the subsurface is a fundamental requirement for accurate geomechanical modelling of aspects of reservoir stability and regional scale basin interactions. Insufficient rock strength data for offshore lithologies within the Taranaki Basin leads to a dependence on uncalibrated, empirical relationships...

Greywacke basement rocks in New Zealand host conventional geothermal reservoirs and may supply important hotter and deeper geothermal energy resources in the future. This work combines petrological analyses and physical property measurements of Waipapa greywacke, a basement unit hosting New Zealand geothermal reservoirs, in order to understand bett...

Quantifying fault damage zones provides a window into stress distribution and rheology around faults. International Ocean Discovery Program (IODP) Expeditions 372/375 drilled an active thrust splay fault within the Hikurangi subduction margin. The fault, which is hosted in Pleistocene clastic sediments, is surrounded by brittle fractures and faults...

Geothermal reservoirs require high permeability to sustain fluid flow, which is often controlled by fracture networks. Mineral precipitation in veins within these fractures records interaction between fluids and deforming crust. Understanding vein formation processes in an exhumed geothermal system is fundamental to understanding fluid flow and eff...

Fluid flow in geothermal reservoirs with low primary permeability is largely controlled by faults and fracture networks. Under certain conditions, hydrothermal veins can precipitate within fractures to form barriers to fluid flow, decreasing permeability and the efficiency of a potential resource. The microstructure and geochemistry of veins can be...

The Pāpaku Fault Zone, drilled at International Ocean Discovery Program (IODP) Site U1518, is an active splay fault in the frontal accretionary wedge of the Hikurangi Margin. In logging‐while‐drilling data, the 33‐m‐thick fault zone exhibits mixed modes of deformation associated with a trend of downward decreasing density, P‐wave velocity, and resi...

Slow slip events (SSEs) accommodate a significant proportion of tectonic plate motion at subduction zones, yet little is known about the faults that actually host them. The shallow depth (<2 km) of well-documented SSEs at the Hikurangi subduction zone offshore New Zealand offers a unique opportunity to link geophysical imaging of the subduction zon...

Projecting into the Third Dimension: 3D Ore Mineralogy via Machine Learning of Automated Mineralogy and X-Ray Microscopy - Volume 25 Supplement - Matthew R. Ball, Joshua F. Einsle, Matthew Andrew, David D. McNamara, Richard J.M. Taylor, Richard J. Harrison

Determining the potential for faults to slip is widely employed for evaluating fault slip potential and associated earthquake hazards, and characterising hydrocarbon seal integrity and reservoir properties. Here we use borehole and 3D seismic reflection data to estimate stress orientations and magnitudes, fault geometries and slip tendency in the s...

The Hikurangi Subduction Margin (HSM) of New Zealand is well-known for its variable seismic behaviour along strike, and across the Pacific-Australian subduction interface. Plate motion appears to be accommodated by a combination of slow slip events and slip in earthquakes. The mechanics of slow slip earthquakes and their relationship to seismic...

Ultrasonic image logs acquired in the DFDP-2B borehole yield the first continuous, subsurface description of the transition from schist to mylonite in the hangingwall of the Alpine Fault, New Zealand, to a depth of 818 m below surface. Three feature sets are delineated. One set, comprising foliation and foliation-parallel veins and fractures, has a...

Introductory student poster presented at the European Geothermal PhD Day (EGPD) 2018 in ETH Zurich. A poster introducing my PhD project investigating fracture sealing mechanisms in geothermal reservoirs. Winner of "Best Poster Award"

Three datasets are used to quantify fracture density, orientation, and fill in the foliated hanging wall of the Alpine Fault: (1) X-ray computed tomography (CT) images of drill core collected within 25 m of its principal slip zones (PSZs) during the first phase of the Deep Fault Drilling Project that were reoriented with respect to borehole televie...

Discerning the contributions to fluid flow in a geothermal reservoir from intrinsic and structural permeability components is an important, yet difficult task. High-quality, resistivity borehole image log data (Formation MicroImager; FMI) collected from the Whakamaru Group ignimbrite in well WK271, Wairakei Geothermal Field, New Zealand, has been u...

International Ocean Discovery Program (IODP) Expedition 372 combined two research topics, slow slip events (SSEs) on subduction faults (IODP Proposal 781A-Full) and actively deforming gas hydrate-bearing landslides (IODP Proposal 841-APL). Our study area on the Hikurangi margin, east of the coast of New Zealand, provided unique locations for addres...

The location of permeable zones, and preliminary quantification of a geothermal well's production or injection capacity are routinely interpreted from well pressure, temperature, and flow measurements made at different injection rates and during heating after shut-in (also referred to as PTS or completion test data). The spatial resolution of feed...

The bulk permeability of upper crustal rocks in the Taupō Rift, central North Island, New Zealand is a function of the development and intersection of active and inherited faults, caldera collapse structures, and/or lithology. To date, major fault trends within the rift have been described as: 1) 030-045°, the dominant rift trend of north of Lake T...

The orientations and densities of fractures in the foliated hanging-wall of the Alpine Fault provide insights into the role of a mechanical anisotropy in upper crustal deformation, and the extent to which existing models of fault zone structure can be applied to active plate-boundary faults. Three datasets were used to quantify fracture damage at d...

Borehole imaging captures geological information on lithology, structure, and stress in the Earth’s subsurface. This paper synthesises currently analysed borehole imaging data acquired in geothermal fields in the Taupo Volcanic Zone. Structure and stress orientations agree with the tectonic trend, though display variation between and within geother...

Analysis of fracture orientation, spacing, and thickness from acoustic borehole televiewer (BHTV) logs and cores in the andesite-hosted Rotokawa geothermal reservoir (New Zealand) highlights potential controls on the geometry of the fracture system. Cluster analysis of fracture orientations indicates four fracture sets. Probability distributions of...

Acoustic borehole televiewer (BHTV) logs provide measurements of fracture attributes (orientations, thickness, and spacing) at depth. Orientation, censoring, and truncation sampling biases similar to those described for one-dimensional outcrop scanlines, and other logging or drilling artifacts specific to BHTV logs, can affect the interpretation of...

Faults comprise zones of crushed, sheared and fractured rock that have the potential to influence the migration of stored CO2. Fault-zone permeabilities of 10⁻⁹ to 10⁻¹⁹ m² are controlled by many interdependent factors including; fault-zone architecture and rock types, mechanical strength and permeability of host rock, orientation and magnitude of...

Permeability hosted in andesitic lava flows is dominantly controlled by fracture systems, with geometries that are often poorly constrained. This paper explores the fracture system geometry of an andesitic lava flow formed during its emplacement and cooling over gentle paleo-topography, on the active Ruapehu volcano, New Zealand. The fracture syste...

Many of New Zealand's geothermal reservoirs are hosted in rocks with low intrinsic permeability. As such, successful development of these resources relies on understanding the role subsurface structures, such as fractures and faults, play in reservoir permeability. Further complexity is added to this understanding due to the constantly evolving per...

This report discusses the topic of induced seismicity resulting from the operations of subsurface CO2 injection at Carbon Capture and Storage (CCS) sites. The potential for induced seismicity to occur in CCS projects is an important factor when considering the capability of a project site’s storage reservoir to retain injected CO2 for long periods...

X-ray computed tomography (CT) scans of drill-core, recovered from the first phase of the Deep Fault Drilling Project (DFDP-1) through New Zealand's Alpine Fault, provide an excellent opportunity to study the damage zone of a plate-bounding continental scale fault, late in its interseismic cycle. Documentation of the intermediate-macro scale damage...

Screening of New Zealand's sedimentary basins indicates several gigatonnes of carbon dioxide storage capacity might be available. However, carbon dioxide storage is currently untested in New Zealand, and it is likely that most theoretical storage capacity will be discounted once detailed assessments are made.

Structures such as fractures and faults have an important role as fluid flow pathways in geothermal fields, as the reservoir rocks hosting geothermal resources can often have little to no intrinsic permeability. As such, understanding and characterizing this structural network is vital to developing reservoir models and field operation and developm...

This report discusses the topic of induced seismicity resulting from the operations of subsurface CO2 injection at Carbon Capture and Storage (CCS) sites. The potential for induced seismicity to occur in CCS projects is an important factor when considering the capability of a project site’s storage reservoir to retain injected CO2 for long periods...

Geothermal resources are often hosted within volcanic, plutonic, and basement-type lithologies. As such their matrix permeability can be very low and the transport and circulation of geothermal fluids will be dominated by fractures. Understanding the flow of hydrothermal fluid through fractured rock is thus essential to the efficient utilisation of...

Screening of New Zealand's sedimentary basins indicates several gigatonnes of carbon dioxide storage capacity might be available. However, carbon dioxide storage is currently untested in New Zealand and it is likely that most theoretical storage capacity will be discounted once detailed assessments are made. New Zealand's position on an active Neog...

The Rotokawa Geothermal Field of New Zealand has seen significant development over the last 20 years and has been the study site for new and innovative geological and geothermal research. This includes the one of the first direct data acquisition and characterisation of subsurface structure and stress properties via borehole image logs, a robust st...

Active faults in rifts commonly provide high crustal permeability and control geothermal fluid pathways. However, active faults can also pose surface deformation hazards to geothermal power plants and associated infrastructure. The New Zealand Ministry for the Environment (MfE) guidelines recommend avoidance of active faults for construction of new...

The use of borehole televiewer logging is a recent addition to the well logging toolkit available to the geothermal industry in New Zealand. The information acquired from borehole televiewer (BHTV) equipment, such as the Acoustic Formation Imaging Technology (AFIT) tool provides valuable geological information about the geothermal reservoir. This p...

The successful targeting of permeable fractures in geothermal fields is aided by understanding the spatial and geometric characteristics of fracture populations. Studies of numerous outcrop, and a limited number of geothermal reservoirs using cores and borehole logs, indicate that fracture frequency and width most commonly follow power-law distribu...

Geometric characterisation of a geothermal reservoir's structures, and their relation to stress field orientation, is vital for resource development. Sub-surface structure and stress field orientations of the Rotokawa Geothermal Field, New Zealand have been studied, for the first time, using observations obtained from analysis of three acoustic bor...

Fracture networks within greywacke basement rocks often control fluid flow in geothermal reservoirs in New Zealand. Thermal, hydrological, chemical, and mechanical processes affect the evolution of these fracture networks. Damage mechanics offers a framework that can be used in the numerical modeling of failure and permeability evolution of geother...

Fluid flow in the high-temperature (300 • C), andesite-hosted Rotokawa geothermal reservoir (Taupo Volcanic Zone (TVZ), New Zealand) is largely controlled by fractures and faults but their geometries are still poorly understood. The aim of this study is to measure and derive geometric parameters characterising fractures in andesitic formations in o...

General Comments Robust geothermal activity in the Great Basin, USA, is a product of both anomalously high regional heat flow and active fault-controlle