Reinjection into Low Temperature Loss Zones

Abstract

A study was undertaken to resolve the discrepancies between the estimated capacities of injection wells at Ohaaki and actual capacities in service with 150?C separated geothermal water. The prior testing had been conducted using cold water injection to calculate the injectivity. The wells which had reduced capacity in service were those wells having major loss zones initially containing fluid at temperatures below 150?C. Testing was conducted using pumps for injection of hot and cold water into two wells, BR39 and BR40 with low temperature loss zones. Injectivity and pressure transient test results showed clearly that the hot water injection caused thermally induced permeability reduction near the wellbore. This skin effect was reversed when cold water was injected. Long term injection of hot water into these two wells since 1990 has shown that the reduction in injectivity caused by hot water does not increase with time as the thermal front moves away from the wellbore and that silica deposition has not been a problem. Injection of hot geothermal water into cool wells located ìoutsideî the hot geothermal reservoir has been successfully used in the management of injected water at the Ohaaki Geothermal Field.