Case History Nevada 1989

Nevada 1989	Problem: Well control was lost during a trip out of the hole to run casing on a geothermal development well. The reservoir was entered prematurely and the typical string of 9-5/8” casing had not been set just above the reservoir. In 1-1/2 hours a 100’ diameter crater swallowed the rig substructure, leaving the derrick exposed above the monkey board. The well was flowing 5000gpm of 350º water, which became steam and water upon exiting. The surface location of the blowout had not been properly referenced, there were no surveys and no drillstring was present in the hole, increasing the complexity of a successful intersection.
	Remedial Strategy: A relief well would be drilled and the blowout wellbore intersected within 10’ TVD of the top of the reservoir. The relief well surface location must be fairly close due to the geometry and no definitive target. The rig was positioned at 246’ from the approximate location of the blowout wellhead. A 30’ diameter uncertainty cone atop a 10’ TVD target was specified. It was believed that cold water injected near the top of the reservoir would stop the flow. High buildup rates would be required to achieve the displacement to the blowout well and to provide for an adequate proximity interval in the event that subsequent sidetrack(s) were necessary.
	Special Services: John Wright Company (JWCO) was contracted to supervise the special services.
	Challenges: The project was complicated by the following: A suitable surface location was severely limited by access, blowout effluent runoff and geometric constraints. No suitable electromagnetic ranging target was present after the drillstring was pulled from the hole and the exact location of the openhole target was unknown. A build and hole well design, with higher than normal build up rate was required. Minimizing the probability of a direct intersection and also reducing the TVD interval in which close proximity to the blowout would be maintained. No surveys existed for the target well. A 9-5/8" kill casing string must be set prior to entering the specified 30' diameter uncertainty target. An accurate relief well trajectory must be present at the casing point and an imminent intersection provided during the subsequent rotary drilling interval.
	Results: A 6-7º/100’ BUR with a bent sub/motor configuration and oriented with a steering tool were used to control the trajectory to the 9-5/8” casing point. Intersection of the blowout wellbore was made with a rotary BHA and loss of drilling fluids occurred at the predicted measured depth. An additional planned casing string was set to minimize the potential well control problems resulting from supercharging and/or unstable water flow(s). A 100bpm kill rate was expected, but a very low, 3-10bpm, rate was required. John Wright and Jim Woodruff supervised as Eastman Christensen’s RW Team.