New technology has been introduced to allow completion of the wireline logging program after the tool string has become lodged in the wellbore. Charges associated with extracting a stuck tool are substantial. These charges result from the nonproductive time during the fishing trip, an associated wiper trip, and re-logging the well. The ability to continue the logging program while retrieving the logging string from the wellbore is needed.
Logging While Fishing (LWF) is a hybrid of existing technologies combined with a new sub capable of severing a cable remotely. This new method is comprised of cut and thread fishing, drillpipe conveyed logging, and bridled tool techniques. Utilizing these techniques it is possible to complete wireline logging operations while removing a stuck tool from the wellbore.
Completing logging operations using this hybrid method will save operating companies time and money. Other benefits, depending on the situation, include reduced fishing time and an increased level of safety. This application has been demonstrated on jobs in the Gulf of Mexico, North Sea, Venezuela, and Southeast Asia.
During the course of wireline logging operations tools occasionally become stuck in the borehole and require fishing. It is conservatively estimated that wireline fishing operations in the Gulf of Mexico cost $5 million dollars in 1995. These costs result from the nonproductive time during the fishing trip, associated wiper trip, and re-logging the well. LWF is a method of retrieving a stuck fish and completing the logging run during the same pipe descent. Completing logging operations using LWF saves time and money. It also provides well information in some cases where data may not otherwise have been obtained. Other benefits of LWF include reduced fishing time and an increased level of safety.
The causes of stuck logging tools are similar to those of stuck drillpipe (differential sticking, keyseating, junk, etc.). For wireline fishing the first consideration is whether the tool or the cable is stuck. This determination is made using stretch determination charts (Schlumberger 1995). Then, depending on the situation there are three methods for retrieving a stuck wireline tool, standard, sidedoor sub, and cut and thread.
Standard fishing is commonly done by pulling the weak point out of the head of the tool. The tool is then recovered like any other fish. With the weak point and cable removed from the well it is simply a matter of tripping drillpipe down to the stuck tool. This method is appropriate only for cased hole or in small diameter open holes that preclude other techniques. Dangers of this technique in an open hole environment include the possibility of breaking the cable rather than the weak point and difficulties washing over the fish with the grapple if the tool is not centered in a small borehole.