Evaluation of Driller s and Wait and Weight Methods in the Well Killing Operations

With today s search for more and remote black gold, drilling gets deeper along with more complex well paths which reduces the margins for errors. This increases focus and requirements to personnel s experience and knowledge, and are one of the most important factor in terms of reducing the risk and consequence if an incident should happen. After taking a kick a well control situation has occurred. In order to regain well control there are established several methods that can be used to regain well control. Driller s method is a two circulation method. After a kick is taken and the BOP is closed, the pressures in the annulus and drill pipe are read and written down. Based on these pressures new kill mud can be weighted up, the main purpose of the new mud is to balance the formation pressure after the kick has been circulated out of the well. In the first circulation stage inflow fluid is circulated out of the well. Since the BOP is closed the return flow has to go through the choke line, which is a line on the outside of the riser and up to surface. At the end of the choke line there is placed a choke valve. This can be regulated between open and closed position. The choke enables regulation which is used to hold and maintain a constant bottom hole pressure during the entire kill operation. The bottom hole pressure is kept equal to the pore pressure plus a safety margin to make sure the pressure is above the formation pressure. The second circulation stage is when the new kill mud is introduced to the well and circulated down the drill pipe and up annulus. After the second stage, the entire well is filled with new kill mud and it is now able to balance the formation pressure on its own and drilling can proceed as intended before the kick started. The Wait and Weight (W&W) method is also known as the one circulation method. When a kick is taken and BOP has been closed, pressures are noted, and new kill mud is pumped simultaneously as the kick is circulated out. This is different from Driller s method that uses two circulation stages, the first to get the kick out of the well using old mud and the second to replace old mud with new kill mud. The Driller s method and the W&W method uses the same choke line with the ability to regulate the choke. The goal is to maintain a constant bottom hole pressure between the formation and fracture pressure window. With this method it is more difficult to carry out the operation as the columns in both drill pipe and annulus will change as kill process is carried out. For the Driller s method (DM) and Weight and Wait (W&W) method, in many ways they use the same operational procedures when killing the well, but the thing that separates them from each other are when kill mud gets introduced into the system. Time consumption are also another aspect that separates them, where W&W uses less time compare to DM. W&W can also have an positive advantage, if the kill mud enters the annulus before the kick reaches the casing shoe, then it will be able to reduce the pressure from the kick acting on the casing shoe due to its heavier weight. If the casing shoe has a good quality then the Driller s method should be the chosen method. The shoe will in DM be exposed to large pressures for a longer time period compare to W&W. Also if it takes a long time to weight up kill mud the DM should be used. One intention with this paper is to shed light on different elements related to well control, in this way it is possible to increase the overall understanding a bit more. The second intention with the paper is to give a broader understanding of two well control methods used today.Hopefully the paper will contribute to a broader understanding of well control.

Keywords:

kick , Well Control , Driller s method , Wait and Weight method , Well Killing Operations