Results of a 13-Month Reinjection Test at Wairakei Geothermal Field, New Zealand

Abstract

Fluid (130°C) was reinjected, at a rate of about 570 t/h, at approximately 450 m depth, into the deep liquid zone near the center of the Eastern Borefield, using well Wk62. The fluid caused the deep liquid level, previously at about 330 m depth, to rise in a cone of impression which decayed when reinjection ceased. The shape and extend of the cone were determined from microgravity and pressure measurements, and suggest that fluid flowed westwards towards the Western Borefield and north eastwards towards an area of large ground subsidence. Good line source fits to pressure transients were obtained for pressure data in nearby wells. No pressure effects larger than 0.1 bar were measured in wells more than 500 m from Wk62. A tracer test gave large, rapid returns in nearby wells. Small (though barely significant) returns in two wells in the eastern part of the Western Borefield suggesting that small amounts of fluid may have reached there. Deep liquid temperatures in wells close to Wk62 decreased by about 40°C, and mass production from the Eastern Borefield fell by 45%. There was no induced seismicity.