The Nesjavellir geothermal field is located in the active volcanic zone in southwest Iceland The field is under development for district heating for Reykjavik During the last 25 years, eighteen exploration/production wells have been drilled into the field. The deepest well, NJ-11, was drilled in 1985 to a depth of 2265 m. The well intersected several aquifers C O M ~ to at least four aquifer systems drilling was completed an interaguifer cross flow was observed and possible blow-out conditions prevailed. Temperature surveys showed that a fluid with temperatures in excess of 380?C entered the well near the bottom and flowed up the well to the main feed zone at 1226111 depth. Return circulation with water could not reverse the flow indicating that the deep aquifer pressure was in excess of 220 bars. Considerable time was spent in order to quench the bottom aquifer but without success. Finally the well was filled with gravel at a depth between 1700-1900 m before it was completed with a slotted liner.

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