An underground blowout occurs when formation fluids flow from one subsurface zone to another in an uncontrolled manner. The results range from being indiscernible to catastrophic. An underground blowout can result in minor transfers of fluids that may never be identified or in flow which reaches the sea floor or ground surface. If the flow reaches the surface, a crater, loss of equipment, and sometimes loss of life may result. A major complication in handling underground blowouts is the difficulty in diagnosing what is actually happening in the subsurface. Once an underground blowout is identified, the risk of surface cratering must be considered. Another major difficulty is the lack of a systematic approach to analyzing and controlling the flow. These are aggravated by the relative lack of coverage of underground blowouts in conventional industry well control training. This difficult and complex subject usually accounts for less than 5% of the time or material covered. Overall, it is our opinion that shortcomings exist in all areas relating to underground blowouts: training, prevention, identification, diagnosis, control, and verification of control. An Iranian offshore oil field is located 75 km west of kharg island containing three main production platform AA, AB and AC, with the total capacity of 220000 BPD, each about 80000 BPD. 67 wells out of 107 wells drilled in this oil field, are oil producer now. There are 20 wells on A-11 which produce oil from Ghar and Damam formation. Costly underground blowouts result in mud losses, wasted rig time, often ineffective remediation materials and techniques, and sometimes lost holes, sidetracks, abandoned wells, relief wells, and lost petroleum reserves. The underground blowout can be the most difficult, dangerous, and destructive situation in well control. If the blowout is shallow, cratering can result and endanger the lives of all involved. The underground blowout is often denied since the usual manifestations of a blowout are hidden from view. It is imperative that the blowout be recognized and diagnosed as soon as possible in the early of recent year, while drilling17 1/2" hole of well no. A-11-20, at depth 383m, huge flow of gas was observed and after closing the well, as the formation below shoe was fractured, due to increase pressure to above MASP, gas flowed from seabed, in addition, gas and water flowed from 30" conductor pipe of A-11-17 to lower deck up to 8 meters height. Underground blowout was controlled by engineering planning with no fire after 60 days. It was designed base on three main concepts: Surface blowout control to allow continues work safely on the platform Identify source of gas flow Underground blow out control. In this paper underground blowout control in Abozar oil field will be discussed in detail procedure.

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