Defining Boundaries and Structures of Broadlands Geothermal Field, New Zealand, by Geophysical Methods—Case History1
G. F. Risk, 1981. "Defining Boundaries and Structures of Broadlands Geothermal Field, New Zealand, by Geophysical Methods—Case History", Energy Resources of the Pacific Region, Michel T. Halbouty
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Resistivity measurements have clearly outlined the lateral limits of the Broadlands field to depths of about 1 km. Temperature profiles in 31 wells about 1 km deep show a pattern in good agreement with the reservoir boundary outlined by the resistivity measurements.
Locating zones of enhanced permeability is an important requirement but has proved a more difficult task. Measurements of the resistivity anisotropy at about 0.5 km depth show a reasonable correlation with flow rates in one area. Two areas where very high temperatures (>260°C) are measured at all depths are interpreted as being places where upwellings of hot source water may be rising through deep permeable channels.
Gravity anomalies indicate that the depth of the graywacke basement rocks ranges from 1 to 2 km across the field and that there are areas of enhanced near-surface density which coincide with long-term discharge paths.
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The energy and mineral resources of the vast Pacific basin and its neighboring land areas play a vital role in meeting the ever-growing needs of society worldwide. Building on the foundation of a highly successful conference held in 1978, this volume contains 51 of the 135 papers presented there. Subjects included are general and specific in nature--oil, gas, and coal resources; geothermal fields, uranium; tin; evaporites, trace elements; water resources; magma energy and fuels from magma. Geological and geophysical techniques, and also the new tool of remote sending for petroleum and minerals exploration are represented. Tectonics, structure fundamentals, subsurface hazards, international treaties and the law of the deep sea are discussed. Seventeen countries and regions are represented in these papers: Thailand, Nicaragua, the United States, Japan, Peru, Antarctica, El Salvador, Australia, Mexico, Taiwan, New Zealand, China, Chile, Indonesia, Canada, and the Pacific Ocean.