Pipe recovery is a specific wireline operation used in the oil and gas industry, when the drill string becomes stuck downhole and prevents the drill rig from operating. Pipe recovery is the process by which the location of the stuck pipe is identified, and the free pipe is separated from the stuck pipe either by a backoff or a chemical cut. There are various causes of stuck pipes. Free point tools, backing off, and pipe cutting are used in pipe recovery.
Background Stuck pipe prevents the drill rig from continuing operations. This results in costly downtime, ranging anywhere from $10,000–$1,000,000 per day of downtime, therefore it is critical to resolve the problem as quickly as possible.
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.
Free point The term free point is used to describe the delineating point between the stuck pipe and the free pipe in a pipe string. Every joint of pipe above the free point is free, meaning it can rotate freely and be moved in and out of the hole, provided it was not attached to the remaining joints of stuck pipe below the free point. An example is a piece of string suspended by one of its ends, with the rest of it hanging down. If a portion of the hanging string is held, then the part of the string above the held span would be considered free, since it can be moved in any direction by the end from which the string hangs. The section of hanging string being held and the string hanging below it is stuck, as actions performed on the free string will not affect the string being held or the remaining string below it.
Pipe stretch free point estimate The pipe stretch free point estimate is a good starting point for identifying the free point.
Pull the drillstring to the pipe's neutral weight, which is the combined weight of blocks and the weight of the drill string and make a mark(X1)(in) at the top of the rotary table. Identify the recommended overpull by multiplying 2208.5 by pipe weight/ft. Pull the calculated overpull(F) (Not to exceed the yield strength of the pipe) causing the free portion of the pipe to stretch to a new position (X2)(in). Use the following equation to calculate the free point from the rig floor: Lsp = 735,294(X2 − X1)Wdp ÷ F where Lsp = depth of stuck point (ft), (X2-X1)= The stretch of the pipe from the reference point (in.), Wdp = weight of drill pipe (lbs/ft), and F = the additional pull required (lbs.) The stretch test does not take into account drill collars, heavyweight drill pipe, and/or wellbore deviation.
Tools The following tools are operated using a wireline truck.
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