sources of energy for geothermal direct heat use - GNS Science

Figure 11 Location of onshore abandoned oil and gas wells. .........................................................16Figure 12Figure 13Potential uses of heat from abandoned hydrocarbon wells.............................................17Location of flooded abandoned underground coal and mineral mines, used incalculating the available low-grade heat from flood waters in mine caverns. .................18Figure 14 Map of New Zealand showing the conductive heat flow contours (Allis et al, 1998)),hot spring systems and their discharge temperatures in the TVZ, Ngawha and areasoutside these two, abandoned hydrocarbon wells and the location of someunderground coal and gold or copper mines...................................................................22Figure 15Potential energy from conventional and unconventional sources of heat in NewZealand. *Does not include the edges of geothermal systems in the TVZ. ....................23TABLESTable 1Table 2Table 3Table 4Table 5Table 6Table 7Conservative projected energy use, in megawatts thermal (MWt) and petajoules (PJ),of parallel direct heat usage in power-producing geothermal systems. ............................7Specific heat capacity and bulk density values of andesite, greywacke and water.Greywacke density data is from Malengreau et al (2000), upper value for andesitefrom Johnson and Olhoeft (1984). The heat capacity of greywacke is that ofsandstone (www.edumine.com) and the heat capacity of granite(www.EngineeringToolbox.com) at 27 o C and 100 kPa is used as a proxy for andesite.Water constants are from Weast et al (1989)....................................................................9Areas with thermal gradients of 21-33 o C and >33 o C outside environmentally- andsocio-politically- sensitive regions administered by the Department of Conservation,shown in Figure 8. The total area of New Zealand is 264,787 km 2 . Percentages arewith respect to total land area..........................................................................................12Estimate of heat reserves from 250m for ground source heat pump use. In thecalculation, porosity is arbitrarily set at 0.01, the thermal gradient used for lowthermal gradient regions is 28 o C/km, 50 o C/km for the TVZ, 40 o C/km for Coromandeland Ngawha Northland and 33 o C/km for the rest of the North Island and parts of theSouth Island. C= heat capacity, ρ= density; initial temperature = 15 o C; recoveryfactor = 1%.......................................................................................................................14Estimate of heat reserves from depths where temperatures are about 120 o C. In thecalculation, porosity is 0.01, the thermal gradients used for the different regions arethe same as in Table 4. ...................................................................................................15Extractable heat energy from warm waters in abandoned underground mines..............19Present and potential extractable energy from geothermal systems in New Zealandfor direct heat use. See calculations in appendices. GSHP= ground source heatpump................................................................................................................................21APPENDICESAppendix 1Appendix 2Waste water and steam from power generating geothermal systems in the TVZ(cascade and parallel uses) .........................................................................................27Warm grounds and waters at edges of high-temperature geothermal systems in theTVZ...............................................................................................................................29Appendix 3 Abandoned Hydrocarbon wells ....................................................................................30GNS Science Report 2007/16ii