SUBSEA WELLS

Solving specialized well intervention problems

Dynamic FEA models for snubbing buckling and riserless subsea wireline intervention can help design tubing requirements for many different well conditions.

Kenneth R. Newman, NOV CTES, Charles Overstreet, Cudd Energy Services and Pierre Beynet, BP

A dynamic Finite Element Analysis (FEA) calculation engine has been developed and is being used to solve specialized well intervention problems. This paper summarizes the theory used and documents two applications: 1) the buckling behavior of pipe (or bottomhole assembly) being snubbed through a packer, and 2) wireline being run from a boat to a subsea well to perform an intervention.

When a pipe, or BHA, is being snubbed into a well, large compressive forces are applied to push it through the packer into the well. These forces often cause the pipe to buckle in the surface equipment. Anti-buckling guides are often used to prevent excessive bending. Failures have occurred, especially when snubbing packers into a well. A modeling tool was developed, which calculates the maximum bending and stress in each pipe or BHA component.

Intervening in subsea wells from a boat is much less expensive than using a rig to perform the intervention. There are many questions about how the wireline will behave with the ocean currents, especially when performing an operation, which requires precise force/displacement control, such as operating jars. Currents in the water cause a significant lateral displacement of the wireline. If there is a sudden change in wireline tension at the surface, will the tension be translated through the wireline to the well? Will the wireline motion and its shape in the water absorb the change in tension? Will the operator on the boat be able to determine from his surface tension indicator when jars have fired, or when a plug has released? How should the depth measurement be corrected for the wireline’s lateral displacement? If the boat is moving vertically, how much will the wireline tools move up and down in the well?