In 1985 and 1986 at least one joint industry project studied the concept of using a flexible riser to service a subsea well. As one step to help prove the concept viable, wireline tools were successfully installed downhole in a test well through a section of flexible pipe. Thesimulated riser, (flexible pipe) was offset 26? from the wellbore center, while maintaining aradius curvature of 30? into the well tubing.
The results of this test could help establish a call out wireline service using afloating service vessel (Figure 1). The results also demonstrated the system would be applicable to floating production systems using flexible risers.
Wireline tools used for production well maintenance are rigid over their length, and, except fOr extreme "dog legs", not required to negotiate short bends when installing thesetools in a wellbore. Installing conventional wireline tools through a flexible pipe requires consideration of several factors, i.e., tool length, tool OD, tubing size, riser size and curvature of the riser, as well as the dynamics involved.
A test well installation was made selecting a tubing size of 3 1/2" 00 coupled to a 4" IO flexible pipe to simulate the riser. By using knuckle joints in the wireline service string and maintaining a 30? radius in the flexible pipe, quite a few conventional wireline tools were successfully installed, retrieved and/or operated in the test well.
These same wireline tools were again installed in the test well using a conventional lubricator mounted directly on the well. Datawas collected and compared with the flexible pipe run data. Results indicated that wirelineoperations can be conducted through a flexible pipe.
A separate test conducted at the same time, measured possible wiretracking effects inside the flexible pipe.
The following objectives were established for the test:
Can wireline operations be successfully performed through a flexible pipe used as a riser? If so, identify the components of a wireline tool string.
Can jarring operations be conducted at an acceptable level to set and retrieve wireline tools?
Identify 3" nominal wireline tools (chokes) that pass through a 4" ID flexible pipe while maintaining a 30? minimum radius.
Identify production logging tool packages for passage through this same flexible pipe.
Verify tool passage/riser ID/radius calculations for wireline (slick) and production logging tools.
Use of tool passage/curvature calculations for sizing tool packages.
Assessment of wireline tracking inside the flexible pipe that resulted from the tests.
The Test Well [total depth - 6500?) was completed with 3-1/2" OD (3" nominal) EU tubing with the equipment installed in the tubing string as shown in Figure 2.
In order to simulate a flexible riser above the wellhead, a crane was used to support the wireline lubricator and flexible pipe, as illustrated in Figures 3 and 4.
A fixture referred to as a "spine" was fabricated from 3-1/2" pipe. This spine was mechanically bent to form a 30? radius.
