Causes and methods of freeing differential pipe stuck

Solution of the problem

First of all, it should be emphasized that before the differential sticking of the drill string, a number of warning signs appear. These are the following: the increasing overpull in long connections, the increasing overpull as well as torque when the drill string is motionless for a while and the decreasing overpull after reaming. As soon as warning signs appear, a variety of specific preventive and mitigating actions must be taken to avoid differential sticking. The immediate action is to reduce connection and survey time to commence pipe movement. Since drilling fluid parameters are the most easily adjustable factors for reducing differential sticking, the following drilling fluid properties need to be optimized.
 mud density,
 mud solids content (both high and low-gravity solids),
 generic mud type,
 specific mud additives (lubricants, bridging particles, etc.),
 filter cake quality, which includes cake thickness, cake lubricity and cake strength.
Of course, as the variables mentioned above depend on each other, they cannot be altered individually. Although reducing the mud density is an option for avoiding differential sticking, minimizing the contact area is more feasible and poses a considerably lower risk than reduction the mud density.
In addition to the optimize properties of the drilling fluid, the design of the drill string is also another important factor that can be easily changed. Therefore, the use of drill collars with a square form or drill collars with spiral grooves also with external-upset tool joints, HWDP and stabilizers can reduce the sticking cases by minimizing contact area between the wellbore walls and the drill string. When the likelihood of differential sticking is high, large diameter DCs can be completely replaced with HWDP to minimize the contact area and to provide WOB. The figure 3 illustrates the upset contact areas of typical joints 5-inch drill pipe versus 5-inch HWDP.



Figure 3: Comparison of upset contact areas in DP and HWDP.

When sticking is a real threat, it is also critical to avoid slick assemblies. The use of a stabilized bottom hole assembly also minimizes wall contact between the DCs and the formation. The drilling jar is an additional tool in BHA that poses the same risk as a DC. The body of the drilling jar is also slick, which is undesirable, so with standoff subs, the jar's contact area could be reduced.