Journal issues: 2/2001
11 December, 2001
DRILLING THROUGH SHALLOW GAS ZONES IN HUNGARY
The prospecting activity for CH is more than 60 years old in Hungary. During this long time we had 73 documented blowouts and more undocumented kicks. Well control was difficult and expensive here because of the abnormally high temperatures and the extreme overpressures of the formations. Among the blowouts we had 12 oil and gas, 1 steam with 180 C° surface temperature, 4 CO2 blowouts with -30 C° surface temperature. 15 rigs were destroyed, 10 craters were formed by the blowouts and, unfortunately, a thrown DC killed one toolpusher. Shallow gas blowouts are perhaps the most difficult well control problem. A shallow gas blowout on a rig can cause large financial losses. For example, a blowout resulted in the total loss of a rig in Hungary. This event created a fishing lake near to Hajdъszoboszlу. Studying the previous blowouts is very important for the drillers, engineers and instructors so as to prevent any well control problems. The results, observations and conclusions help to change the practice and technology in order to avoid any risk situations during normal drilling operations. By the favorable results of the skilled, well-trained drillers, better and better tools and equipment, day by day practical experience, and the special Well Control Training School, we have had only one blowout in the last 10 years. This paper reviews shallow gas blowouts while drilling in Hungary and discusses current industry myths about shallow gas, typical results from a shallow gas blowout that affect the kill operation, kill options, selection criteria and well killing guidelines. The objectives of this case study are to describe procedures which will reduce the risk and cost of controlling the flow if a blowout occurs and build the experiences into our training programs to prevent this accident. Conclusion of this study include the recommended well control procedures and the required well control equipment for Hajduszoboszlo field.
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