Chet Hopp edited Geologic_and_geophysical_setting_Both__.md  almost 8 years ago

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#Geologic and geophysical setting  Both the Ngatamariki and Rotokawa geothermal fields are located in the southern Taupo Volcanic Zone (TVZ) on the North Island of New Zealand; approximately 15 and 17 km north of the town of Taupo, respectively. Rotokawa is a high temperature (>300°C at 1-2.5 km below sea level) reservoir with a circular footprint measuring roughly 6 km across \cite{Sherburn_2015}. Ngatamariki, also a high temperature system at >280°C and similar in depth to Rotokawa, measures roughly 7 km2 \cite{Chambefort_2016}. Sequences of andesites, rhyolites and volcaniclastic sediments overlie greywacke basement at roughly 3 km below sea level at both fields, although lateral heterogeneity of these units is considerable as is the depth to basement \cite{McNamara_2016} \cite{Chambefort_2014}. The geological structure at Rotokawa is dominated by three faults cutting through the field which have been modeled based on offsets in well cuttings of the basement greywacke as well as of Rotokawa Andesite /cite{wallis2013structural} \cite{wallis2013structural}  \cite{McNamara_2016}. These faults, from West to East are the Production Field Fault (PFF), Central Field Fault (CFF) and Injection Field Fault. At Ngatamariki, two important features dominate the local geological structure. The first is the Aratiatia Fault Zone in the southern end of the field and the other is a shallow (<2 km) intrusive body, the presence of which was confirmed by drill cutings from wells NM4, NM8 and NM9 \cite{Chambefort_2014}. Given the low-permeability nature of much of the host rock, reservoir permeability at both fields is thought to be dominated by fractures and faults within the reservoirs along the prevailing NE-SW structural trend \cite{McNamara_2016}. However, the structure surrounding the shallow intrusives present in the northern half of Ngatamariki likely complicates the structural grain.