This case history paper presents the details of the role played by coiled tubing in returning a high-profile, Gulf of Mexico oil/gas well to production after the well had to be shut in due to excessive sand production. The paper presents the following events/conditions:
The well could not be injected into in several attempts up to 9,300 psi. Since the well had produced sand, operators suspected that a sand plug existed.
The well was completed with 4 1/2", 15.1# production tubing.
Coiled tubing performed offline while the rig was performing completion operations. A hydraulic workover unit would have required the rig to be moved to aid in snubbing operations.
The well was 18,750 ft deep, with a wellhead pressure of 7,000 psi. The well was producing from two comingled gravel packs with a ceramic flapper installed in the upper gravel pack packer for fluid loss. The state of the flapper was unknown.
A coiled tubing string of 1.25" OD and 19860 ft long was designed for the job. Wall thickness tapered from 0.156 in. at the top to 0.134 in. at the bottom to support the tensile load of the string and provide maximum cycling capabilities at the location of the ceramic flapper.
The initial goal was to use coiled tubing to wash to the bottom of the lowest gravel pack and break through the ceramic flapper with an impact tool. Due to low annular velocities inside the production tubing a special xantham based polymer/CaCl2 mixture was required to wash sand to the surface. The use of coiled tubing to wash through the production tubing in this extreme pressure/depth application allowed the well to eventually be killed by bullheading kill fluid.
The paper also presents useful information on the following coiled tubing-related issues:
Tubing fatigue monitored by software that tracked tubing life and helped ensure that the tubing was not used beyond stress ratings.
Coiled tubing technology has extended the working envelope for high pressure applications.
