Proceedings of the 6th New Zealand Geothermal Workshop 1985. Recharge at Broadlands -Ohaaki- geothermal field 1967-1983 determined from repeat gravity measurements. New Zealand Geothermal Workshop [7-9 Nov. 1984, New Zealand].

Hunt, T.M.

[1984]

171
CIENA

0-86869-056-2

A revision of previous repeat gravity measurements, made in 1967 and 1974, shows that for the period 1967-1974 (during which time drawdown tests were made) negative gravity differences of about -0.8 to -1.2 µN/kg amplitude occurred over all of the field. Simple modelling suggests that these differences were the result of a net mass loss of about 24-35 x 10(9) kg and hence there was little or no mass recharge. Data from a recent survey made in 1983, show that for the period 1974-1983 (during which time there was a reduced amount of mass withdrawal) positive gravity differences of about 0.4 µN/kg amplitude occurred in most parts of the field. Modelling suggests these differences resulted from a net mass gain of about 11 x 10 (9) kg, and hence total natural recharge was about 25 x 10 (9) kg. During both periods there was mass loss from a large area west of the field, the cause of which is unknown. Elsewhere, outside the field, there have been no significant mass changes.

Presenta diagrs., gráfs., maps.

NUEVA ZELANDIA; ENERGIA GEOTERMICA; CAMPOS GEOTERMICOS; INGENIERIA DE RESERVORIO; GRAVIMETRIA;