Case History-Based Training for Control and Prevention of Underground Blowouts
Authors: Smith J.R. , Bourgoyne A.T. 
Published: December 2007

The control and prevention of underground blowouts requires training of both field and engineering support personnel. Analyzing the case history of an underground blowout can be an effective way to provide practical training for both groups. A design model for this kind of training and an example based on an actual underground flow are described. The results of training both industry personnel and university students are reviewed.

Introduction

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.

The typical response to an apparent underground blowout, in our experience, is a trial and error approach. Both diagnosis and solutions are frequently conducted in this manner. Control operations usually start by trying to cure what is perceived to be the most likely problem and only revert to attempting to define the real problem after the first trial solutions fail. Common control methods include:pumping LCM, gunk or cement to the loss zone in an attempt to regain conventional control,bullheading kill fluids into the loss and/or producing zones,a dynamic kill using frictional pressure loss and fluid density to increase wellbore pressure opposite the producing zone,a weighted slug below the loss zone to overbalance the producing zone,a "sandwich kill" that bullheads kill fluid from both above and below the loss zone,a barite pill or cement plug to bridge and isolate the producing zone from the loss zone, anda bridge plug set to isolate the producing zone from the loss zone, or more commonly just to provide a subsurface closure while surface equipment is changed or pipe is run in the well.

Successful application of any of these methods usually requires an implementation strategy that includes:knowledge of the location, pressure, and flow characteristics of the producing and loss zones and the flow path,definition of a kill approach and sequence that fits the diagnosed situation and the ultimate objective,design of fluid constituents, densities, volumes, placement, and rates to achieve the intended approach,acquisition of the necessary people, equipment, materials, fluids, and instrumentation to implement the design,a plan for conducting the operation with predicted outcomes, usually pressures, to allow monitoring whether it is succeeding,an agreed upon basis for stopping the planned operation, analyzing it, and defining an alternate approach if the plan is not progressing as predicted,

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