Applying blowout prevention concepts that have been developed for drilling operations to a completion/workover situation is improper in many cases. In fact, application of all rules required by drilling well control courses and manuals will result in dangerous situations on many workovers. Furthermore, the majority of class time in a typical well control school is devoted to minimizing surface casing pressure during a kick, a principle that has almost no application in a completion/workover situation.
There are at least sixteen key differences between workover wells and drilling wells that demand a different set of requirements for safe well control. These important differences continue to be revealed in the form of surprises as warkover crews struggle to comply with a multitude of very strict rules, all of which have evolved from situations encountered while drilling. This paper will emphasize these key differences and will introduce an idea for replacing current Completion and Workover Blowout Prevention Specifications with just a few easily understood specifications based on the Barrier Concept.
Blowout prevention concepts have been developed for drilling operations over the course of many years. They have resulted in a proliferation of well control schools where these techniques are taught, and are being introduced to petroleum engineering students during their junior and/or senior years. However, many of these concepts are being incorrectly applied to completion/workover operations and may result in a dangerous situation. Therefore, the purpose of this paper is two-fold:
To emphasize key differences between completion/workover operations and drilling operations that demand different procedures for preventing blowouts.
To introduce an idea for replacing current completion/warkover blowout prevention specifications with a few easily understood specifications based on the Barrier Concept.
Figure 1 shows a comparison of the same well undergoing two different stages of completion. In condition A, the well is between rigs. The drilling rig has been moved out after setting and cementing the primary casing string. The casing is currently filled with 11.0 ppg [1318 kg/m3] mud. While waiting for a smaller rig to become available for completing the well as a gas producer, cased hole logs are being run with no rig and no blowout preventer stack on the wellhead. This type of situation is generally perceived as one that is hazardous and has the potential for an uncontrolled blowout. Condition B shows the same well during completion. Note that the well has been perforated and has been killed with 10.0 ppg [1198 kg/m3[ clean completion fluid. The lower-most BOP has been disassembled to change pipe rams to fit the final production tubing. This operation would be perceived as a normal procedure during final completion of the well. The real question, however, is which well configuration is most conducive to a kick and potential uncontrolled blowout?
This question can be answered by looking at the pressure overbalance at the reservoir and the degree of communication between the productive formation and the wellbore. In Condition A, the well is in little danger of taking a kick.