Steven Sewell

Mighty River Power · Geoscience

In the last decade, in partnership with Mercury NZ Limited (formerly Mighty River Power), Victoria University of Wellington postgraduate students have used seismic data from New Zealand's geothermal fields to elucidate the structure and geomechanical properties of several geothermal systems in the Taupō Volcanic Zone. Recent projects have focussed...

Catalogs of microseismicity are routinely compiled at geothermal reservoirs and provide valuable insights into reservoir structure and fluid movement. Hypocentral locations are typically used to infer the orientations of structures and constrain the extent of the permeable reservoir. However, frequency-magnitude distributions may contain additional...

We investigate the relation between geothermal field production and fracture density and orientation in the Ngatamariki and Rotokawa geothermal fields, located in the Taupo Volcanic Zone, New Zealand using shear wave splitting (SWS). We determine the SWS parameters for 17 702 microseismic events across 38 stations spanning close to 4 yr from 2012 t...

Fluid injection into the Earth's crust can induce seismic events that cause damage to local infrastructure but also offer valuable insight into seismogenesis. The factors that influence the magnitude, location, and number of induced events remain poorly understood but include injection flow rate and pressure as well as reservoir temperature and per...

Imaging of seismic properties has the potential to provide important information on the physical and thermodynamic properties of rocks and their pore fluids within and adjacent to geothermal reservoirs. Obtaining accurate seismic velocity models is also important for reducing uncertainty in microseismic event locations, particularly for event depth...

Improving upon standard earthquake detection techniques, specifically in areas where events are likely induced by fluid injection, can be useful in characterizing and monitoring the state of a geothermal resource with time. Using an earthquake catalog of 637 events occurring between 1 January and 18 November 2015 as our initial dataset, we implemen...

In order to investigate the fracture orientation in the Ngatamariki and Rotokawa geothermal fields and compare them to the orientation of maximum horizontal stress, we determine the shear wave splitting for 1919 earthquakes across 22 stations during 2015. The seismic catalogue provides a large number of microearthquakes from both fields. Due to the...

This paper documents how Mercury NZ Limited used a model-based approach to refine the reservoir management strategy at the Rotokawa geothermal field. We describe the data analysis required to refine our conceptual understanding of the reservoir and how this conceptual model was implemented as a numerical model of a sector in the field known as the...

Improving upon standard earthquake detection techniques, specifically in areas where events are likely induced by fluid injection, can be useful in characterizing and monitoring the state of a geothermal resource with time. Using an earthquake catalog of 637 events occurring between 1 January and 18 November 2015 as our initial dataset, we implemen...

We have determined subsurface structure using the refraction microtremor (ReMi) method at the Ngatamariki geothermal field, Central North Island, New Zealand. The local geology is such that refraction and reflection studies are hindered by energy scattering and attenuation in the near-surface layers. The ReMi method uses surface waves from ambient...

Best practice field management requires identification of the key processes acting within the reservoir and understanding of the relationships between reservoir and process chemistry changes with the potential to impact resource and infrastructure sustainability. Following the initial development of the 34MWe Rotokawa Geothermal Power Station, the...

Located in the Taupo Volcanic Zone, production in the Rotokawa geothermal field began in 1997 with a 27 MWe flash-binary power station, expanded to 34 MWe in 2006. In 2010, the installed capacity increased to 172 MW with the commissioning of triple-flash condensing 138 MWe Nga Awa Purua. To date, there are thirteen production wells supplying steam...

This paper describes the development of the main conceptual model elements that have been used as a basis for numerical modelling and well targeting at the Rotokawa Geothermal Field. These elements are largely based on characterising the natural state of the reservoir, prior to production, but significant new knowledge has been gained from monitori...

Ngatamariki Geothermal Field is the most recently developed field (2013) in the Taupo Volcanic Zone (TVZ) New Zealand for electricity generation. This paper summarises the geological, geophysical and chemistry findings of the last 30 years, and states the current knowledge and understanding of the field. The field, located 17 km northeast Taupo, ex...

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...

At the Rotokawa Geothermal Field, the integrated interpretation of microseismic (MEQ) data with other geoscience and reservoir engineering data has helped identify and constrain important elements of the reservoir model, including a major structure that likely influences reservoir fluid flow. MEQ monitoring began when injection moved to deeper well...

New Zealand's geothermal systems are mostly located in high-temperature, volcano-tectonic settings, but background levels of local natural microseismicity (micro-earthquakes) are quite variable. Triggered or induced seismicity effects from geothermal operations have also been very mixed. Understanding the reasons for these differences leads to bett...

Rotokawa geothermal field, Taupo Volcanic Zone (TVZ), New Zealand, has experienced persistent microseismicity since deep injection of condensate and brine began in 2005. Microseismicity is thought to be induced mostly by contraction due to injected fluid, c. 200 °C colder than natural reservoir temperatures, causing a reduction in the normal stress...

Kawerau is a multi-tapper field with Mighty River Power (MRP) and Ngati Tuwharetoa Geothermal Assets (NTGA) both having to ensure they have sufficient injection to maintain operations at full capacity, as well as providing a balance between maintaining pressure support to the field and preventing thermal breakthrough to the production areas. The K...

The Okataina Volcanic Centre (OVC) is one of eight caldera systems, which form the central part of the Taupo Volcanic Zone, New Zealand. During its ~ 625 kyr volcanic history, which perhaps equates to ~ 750 kyr of magmatic history, the OVC has experienced two definite periods of caldera collapse (Matahina, ~ 322 ka, and Rotoiti, for which dates of...

Induced microearthquake (MEQ) activity has been observed at Rotokawa Geothermal Field since deep reinjection began in 2005. Following temporary observations in 2005 and 2006, continuous MEQ recording began in 2008 and continues. A dense network and careful site selection have provided data of sufficient quality to provide constraints for reservoir...

At the Rotokawa Geothermal Field, the integration of microearthquake (MEQ) data into a space and time visualization of geoscience data has helped identify and constrain important elements of the reservoir model, including a major structure that likely influences reservoir fluid flow. MEQ monitoring began when injection moved to deeper wells in 2006...