http://hdl.handle.net/10379/6701 Sun, 29 Oct 2017 23:52:00 GMT 2017-10-29T23:52:00Z http://hdl.handle.net/10379/6745 Feasibility of storing carbon dioxide on a tectonically active margin: New Zealand Field, B.D.; Lawrence, M.J.; Nicol, A.; McNamara, David D.; Arnot, M.J.; Coyle, F.; Higgs, K.E.; Mountain, B.; Gerstenberger, M.; Daniel, R.; Bunch, M.A.; Barton, B. New Zealand's sedimentary basins was found to have available several gigatonnes of CO2 storage capacity. However, CO2 storage is currently untested in New Zealand. The country's position on an active Neogene plate boundary raises additional key factors that will influence final site selection. Some risk factors will also influence the relationship between social acceptance and the design of regulations. Despite the risks, hydrocarbon producing fields in Taranaki indicate that viable reservoir-seal pairs are likely to be present. Sun, 13 Sep 2015 00:00:00 GMT http://hdl.handle.net/10379/6745 2015-09-13T00:00:00Z http://hdl.handle.net/10379/6719 Exploring structure and stress from depth to surface in the Wairakei Geothermal Field, New Zealand McNamara, David D.; Bannister, Stephen; Villamor, Pilar; Sepúlveda, Fabian; Milicich, Sarah D.; Alcaraz, Samantha; Massiot, Cécile 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 development plans that will maximize the potential of a geothermal resource. Presented here are the preliminary results of three recent studies, micro-earthquake analysis, borehole logging, and active fault mapping, carried out in the Wairakei Geothermal Field to determine the structural character of the system, if and how it contributes to fluid flow, and how the structural observations from these studies inform and relate to each other. Across all three techniques a dominant NE-SW structure strike orientation is observed with lesser population of N-S, E-W and NW-SE, consistent with the broad Taupo Volcanic Zone observed trend. Further analysis of the data is required to resolve important structural questions around the Wairakei Geothermal Field including: whether the data supports the model of the Wairakei Geothermal Field being an expression of enhanced permeability due to its location in an inferred rift accommodation zone, how the links between observed structures at the surface and subsurface can be resolved, and what role to these structures play in geothermal fluid flow from depth to surface? Mon, 22 Feb 2016 00:00:00 GMT http://hdl.handle.net/10379/6719 2016-02-22T00:00:00Z http://hdl.handle.net/10379/6718 Geothermal structural geology in New Zealand: Innovative characterisation and micro-analytical techniques McNamara, David D.; Massiot, Cécile 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 permeable nature of these geothermal reservoir structures. The same fractures and faults which operate as interconnected, open, fluid flow pathways, can also behave as fluid flow barriers due to geothermal mineral precipitation over time. Increased industry application of borehole logging technology, and the development of innovative geothermal data processing and interpretation, has allowed structural geologists to make advances in characterising the subsurface structure of the Taupo Volcanic Zone. These novel data reveal structural heterogeneity at a variety of scales, from changing dominant orientations across the Taupo Volcanic Zone, to decimetre changes in fracture orientation within a single well. Additionally, these techniques allow observation of the variability in in situ horizontal stress directions for the first time, revealing active subsurface structures. At a much smaller scale, the application of novel, advanced, microscopy techniques to analyse the micro-structure of geothermal vein minerals provides information on evolving geothermal reservoir fluid properties, and stress conditions. Crystallographic analysis of microstructures found in geothermal calcite veins can provide insight into the differential stress history of the reservoir, while the operation of temperature dependent, calcite crystal slip systems, may provide a tool to record evolving geothermal reservoir temperatures. Wed, 23 Nov 2016 00:00:00 GMT http://hdl.handle.net/10379/6718 2016-11-23T00:00:00Z http://hdl.handle.net/10379/6717 Fracture width and spacing distributions from borehole televiewer logs and cores in the Rotokawa Geothermal Field, New Zealand Massiot, Cécile; McNamara, David D.; Nicol, Andrew; Townend, John 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 distributions, with exponential, log-normal, gamma, and power-exponential distributions also reported. This paper presents the first statistical analysis of fracture width and spacing in the high-temperature Rotokawa Geothermal Field, Taupo Volcanic Zone, New Zealand. The fracture dataset comprises: (1) c. 3.6 km of acoustic borehole televiewer (BHTV) logs from three wells and, (2) c. 33 m of core. Statistical distributions have been fitted to the BHTV data using a maximum likelihood estimation method and statistical models selected using the Schwarz Bayesian Criterion. Fracture widths observed on BHTV logs range between c. 1 -105 mm. Image resolution and sampling bias reduce the useable range of fracture width to less than one order of magnitude (c. 8 -50 mm). Over this range, considering the sampling effects and core observations, the fracture width is best modelled by an exponential distribution with coefficients between 0.13±0.01 and 0.29±0.02, which should be treated as a lower bound. Analysis of fracture spacing of the four fracture sets identified on BHTV logs indicates that the dominant set (striking NE -SW) is best modelled by a log-normal distribution, while power-law, power-exponential and gamma are also possible for individual wells. These spacing distributions indicate the presence of a characteristic scale which has not been observed in other geothermal reservoirs hosted in crystalline formations. The characteristic scale may be associated with mechanical interfaces associated with stratigraphic layering, faults, or cooling joints and/or sub-horizontal flow-banding in andesitic formations. Stratigraphic layering can consist of a succession of lava flows with intercalated breccia layers in the andesites, welding variations in tuffs and sedimentary layering in the sedimentary formations sampled by the BHTV logs. The subordinate fracture set striking N -S is best modelled by a pareto (power-law) distribution which suggests that the spacing is more likely to be controlled by tectonic processes than by layering. This N -S fracture set is predominant in only one of the wells studied which may indicate a structural control on their occurrence in the vicinity of this well. Low fracture spacing ( Sun, 19 Apr 2015 00:00:00 GMT http://hdl.handle.net/10379/6717 2015-04-19T00:00:00Z