The offshore drilling industry is faced with many different types of problems such as operation and logistics, weather, and actual drilling problems that hinder or halt all operations. One of the more costly drilling problems is differential pressure pipe sticking. A recent study on this problem showed that an average expenditure of more than $93,000 was required to resume drilling operations after the pipe had become stuck. If the severity of this problem can be reduced or eliminated altogether, then the total cost to the operator can be reduced and drilling can proceed more efficiently.
It was the general purpose of this work to study certain aspects of drilling fluids relative to pipe sticking and if possible, to define any parameters that could be used to avoid future incidences of stuck pipe. The approaches specifically used in this study were (1) an analysis of field cases of stuck pipe in an effort to define mud systems more conducive to pipe sticking, (2) an actual field case example of how the procedures presented within the paper were used to prevent pipe sticking on an offshore platform that had previously exhibited pipe sticking problems, and (3) laboratory results obtained in an effort to further determine the effects of mud types and mud additives on differential pressure pipe sticking.
Differential pressure pipe sticking is a drilling problem in which the drill string becomes embedded in a mud solids filter cake, usually across a permeable zone, and is held in place by an amount of differential pressure. Differential pressure is the difference between the drilling fluid hydrostatic pressure and the formation fluid pressure. This type of pipe sticking usually occurs after the pipe remains motionless in the wellbore for a period of time and is identified by no impedance of drilling fluid flow in the annular space and the inability to move the pipe in either vertical direction.
The principal methods used for releasing stuck pipe range from a chemical approach such as spotting fluids to mechanical methods including impact loading and hydrostatic reduction. Although each is theoretically sound, the manner of practical implementation often negates the methods effectiveness. Therefore, it would seem that preventive procedures are perhaps the best approach rather than being forced to resort to remedial pipe releasing techniques.
Helmick and Longley2 were the first to define the differential pressure pipe sticking mechanism. They conducted laboratory investigations with several pieces of test apparatus that were capable of obtaining differential pressures across a mud cake, total filtrate through a simulated permeable section, and the required pullout force on the pipe after it became stuck. They observed that regardless of set time, the pullout force of the rod stuck in the test apparatus could always be lowered by reduction of the differential pressure. However, even when no differential pressure was applied, a significant adhesive force was often required to move the rod. It was found that 45% of the force required to free the drill pipe was required to overcome the adhesion of the mud cake to the steel.