When the drill string becomes stuck downhole, the oil and gas sector uses a specific wireline technique called pipe recovery. The drill rig cannot continue its operations due to stuck pipe. Since this causes expensive downtime, ranging from $10,000 to $1,000,000 per day, it is crucial to find a solution as soon as possible. Pipe recovery refers to the procedure by which the stuck pipe's location is determined and the free pipe is cut or backoffed from the jammed pipe. This makes it possible to run fishing equipment down the hole later to grab onto and unstick the jammed pipe.
Causes of Stuck Pipe
Differentially Stuck Pipe
The geological formation downhole occasionally has a significantly lower pressure than the drilling fluid being used. When the pipe string comes into contact with the exposed formation the difference in pressure will cause the pipe to be sucked against the formation. If the rig is able to circulate drilling fluid back to the surface that is often a good indication of differentially stuck pipe. One technique for freeing the stuck pipe, or avoiding the issue to begin with, is to rotate the pipe string while pulling out of the hole.
Key Seated Stuck Pipe
Key seating occurs when the drill string becomes off-centered in the wellbore, and the pipe collars become caught on a deviation in the wellbore. If the rig is able to move the drill string freely downhole, but every time the drill string is pulled upward it becomes stuck at the same point, then it is likely that the pipe is caught in a key seat.
Cave-in Stuck Pipe
An unstable formation can result in a cave in. The collapse of the formation can pin the pipe inside the wellbore preventing its movement.
Mechanically Stuck Pipe
This can be the result of objects, i.e. slips or pipe wrenches, being dropped down the hole lodging against the BHA.
Communication between Wells
In areas with a high concentration of oil wells, it is not unusual for wells to communicate through the formation for distances of up to mile. During a fracking operation thousands of gallons of fluid and sand are pumped down one well to open up the formation surrounding that wellbore. Often large amounts of that proppant and fluid will travel through the formation and into a nearby well. This sand can lodge on top of a packer or coil tubing in the well sticking the pipe.
Tubing Stuck in Production Wells
Tubing in production wells is often exposed to a number of highly corrosive chemicals, such as H2S. This corrosion can deteriorate the tubing to the point that it separates from the wellhead causing the tubing to fall downhole. The impact of several thousands of pounds of tubing on the bottom of the hole can severely damage the tubing, causing kinks or a corkscrew effect in the tubing, making it difficult to retrieve out of the hole. Sand coming in through holes in the casing or a malfunctioning production packer can also cause tubing to become stuck in production wells.