Driller’s Method vs Wait and Weight Method : One offers distinct well control advantages
By Rana S Roy, Conroy James Nini, Paul Sonnemann, Berton Thomas Gillis, Chevron
Drill Pipe Pressure Schedules
THE TWO WIDELY used constant
bottomhole circulating methods are the Driller’s Method and the Wait and Weight (W&W) Method. Well control experts are oftenstrongly opinionated on selecting the better method to circulate an influx out of the wellbore. The purpose of this article is to highlight the major advantages and disadvantages of the two methods. The basic principle of both methods is to keep bottomhole pressure (BHP) constant at or, preferably, slightly above the formation pressure. The Driller’s Method requires two circulations. During the firstcirculation, the influx is circulated out with the original mud weight. Constant BHP is maintained by holding circulating drill pipe pressure constant through the first circulation. If the original mud weight is insufficient to balance the formation pressure, the well is killed by circulating a heavier mud (kill mud) in a second circulation. To hold constant BHP during the second circulation, one oftwo procedures is employed. Casing pressure is held constant while pumping kill mud from surface to bit, and drill pipe pressure is held constant thereafter until kill mud is observed returning to the surface. Alternately, during second circulation, a drill pipe pressure schedule can be calculated and followed while pumping kill mud from surface to bit, and drill pipe pressure is held constantthereafter. The W&W Method involves only one circulation. The influx is circulated out, and the kill mud is pumped in one circulation. While pumping kill mud from surface to bit, a drill pipe pressure schedule has to be calculated and followed. The drill pipe pressure is held constant thereafter until kill mud is observed returning to the surface. The W&W Method is sometimes called the Engineer’sMethod because it involves more calculations compared with the Driller’s Method. There is a widespread misconception that the Driller’s Method is preferred only because it is simple. We will discuss vari-
Schedule not compensated for hole angle
KOP 888 Strokes Schedule compensated for hole angle
200-psioverbalance TD 2,221 Strokes EOB 1,688 Strokes
Figure 1: In a deviated hole/tapered drill string scenario, the drill pipe pressure schedule under the Wait and Weight Method becomes harder to calculate than in a vertical wellbore. In this case, if rig personnel do not correctly compensate for hole deviation, there will be a 200-psi overbalance thatcould be detrimental to weak formations.
ous reasons why the Driller’s Method could be better for circulating an influx in many or even most wells drilled. Any drilling organization or company can adopt a policy of recommending just one well control method so that everybody in the organization can be competent in at least one method. This may help in avoiding confusion in the field and promoteunderstanding of how to efficiently circulate a kick out of the wellbore without creating major well control problems. There is a shortage of experienced personnel in the drilling industry, and ensuring competency in one method could lead to fewer disasters. We have to keep in mind, however, that even experienced personnel do not routinely kill wells. They may kill only a few wells in their entirecareer. We can achieve operational excellence by ensuring their competence in one method. It may be better to use a good method expertly than a slightly better method inexpertly. cations are various types of wells and their geometry. Deviated hole / tapered drill string: The drill pipe pressure schedule for the W&W Method is fairly simple to calculate if the wellbore is vertical and there is one...