Jarring and Fish Removal Operations
Events requiring jarring or retrieval that occur during coiled-tubing (CT) operations frequently mirror similar situations encountered during conventional fishing operations in cased-hole applications.
Events requiring jarring or retrieval that occur during coiled-tubing (CT) operations frequently mirror similar situations encountered during conventional ﬁshing operations in cased-hole applications. The following three scenarios are common to CT downhole operations and generally require a jarring assembly and/or an engagement device or correct ﬁshing tool to successfully retrieve a bottomhole assembly (BHA) or ﬁsh from the wellbore. Typically, bi-directional or upward/downward activating jars and slingers are used.
Mechanical or “locked” situations are common when engaging and shearing preset lock pins, screws, or shear rings to retrieve various prongs and locks or packers and plugs.
Differential sticking is a condition that results from reservoir pressure variances exerted over a length of the work string, preventing it from moving along the axis of the wellbore.
Sand or Debris Sticking
Sand or debris sticking occurs when circulation is interrupted and ﬁnes, cuttings, or debris are allowed to drop and settle around the CT or BHA components and against the wellbore wall, creating a friction or wedging effect.
When a BHA becomes stuck in the wellbore, jars are often run in a motor/milling BHA to deliver a blow that assists in regaining positive string movement. Jars are sometimes used in conjunction with underreaming BHAs to assist in the mechanical closure of the blades when the underreamer re-enters the tail pipe.
Before jarring tools are run on CT, the following factors should be taken into consideration:
- The ID of the jarring assemblies must pass the drop ball for any ball-assisted BHA function below the jars.
- Jarring assemblies run with motor applications must be equipped with a heavy-duty disconnect designed to withstand direct jarring loads. The disconnect should be run below the jar, on top of the motor, allowing for recovery of the jars and the upper section of the BHA should the bit become stuck and pipe movement cannot be re-established.
- CT has helical and sinusoidal characteristics that can affect the set-down and tension loads transmitted to the jars. Knowing these loading limits before running in the hole is imperative.
- Depending on the application, depth, and capabilities of the CT being used, a slinger may or may not be required. The CT string above the jars can simulate the slinger effect to a certain extent and may be sufficient to achieve the required impact loads required in motor-assisted operations.
- Know the tensile strengths of the ﬁsh, the ﬁshing string, and the work string when setting up a specific jarring string and determining impact loads with a jar program.
- Lubricator height is a crucial factor when running and removing the jarring assembly and successfully retrieving the obstruction. The ability to lubricate or cover the entire length of the BHA and the retrieved assembly or ﬁsh is necessary to maintain proper pressure control.