RIASSUNTO
Abstract
Drilling deeper wells with high angles are becoming the norm in the Gulf of Mexico. As time passes these wells require some type of intervention. Coiled tubing intervention being an economic option creates new challenges by pushing existing coiled tubing technology to its limits. Deeper holes increases string weights requiring stronger coiled tubing pipe, injector heads and surface equipment. Friction must also be addressed with improved fluid designs for reducing circulating pressures without compromising good solids transport capabilities or temperature stability.
Success of these deep interventions greatly depends upon proper equipment; job design, planning and execution of the plan to improve the original objectives achieved.
Evaluation of the objectives, well details, location concerns, and logistics are keys to designing the right coiled tubing string, selecting proper (BHA) bottom hole assemblies, fluids and procedures in these deep wells.
This paper describes the design, planning and execution of a record-depth job with 11/2"" coiled tubing in a 25,200 ft deep high-pressure gas well in the Gulf of Mexico. The objective of the job was to clean sand from the well, retrieve down-hole pressure and temperature gauges, and prepare the well for the re-completion with the rig.
Several steps were taken to ensure a successful job: A 28,700 ft 110,000 psi minimum yield strength coiled tubing string was designed and manufactured. A special hydraulically optimized fluid with high solids carrying and suspension capacity and relative low circulating pressures was designed and tested. In depth pre job planning was conducted. All these factors played key roles in success of the job.
Introduction
New wells are being drilled and completed to greater depths, which requires more technologically advanced coiled tubing to complete well interventions. In areas like the Gulf of Mexico where wells have a high TVD to MD ratio the coiled tubing technology is pushed to its limits.
In the deep-water sector of the Gulf of Mexico one of these high TVD to MD ratio wells required coiled tubing intervention to clean out sand from the wellbore and retrieve a set of temperature and pressure gauges.
Based on a slickline run, sand was expected from 15,100 ft down to the gauges at 24,700 ft. Preparing the well for the workover after retrieving the gauges required cleaning sand from the well down to 25,200 ft. This would enable cutting of the tubing on e-line.
The sand cleanout and the fishing operation with coiled tubing posed following challenges.
Maximum shut in pressure of 8,400 psi
Yield stresses on the coiled tubing string were predicted outside the working envelope for conventional 1.5"" OD strings.
Annular velocities inside 41/2"" tubing section were too low to carry the sand to surface.
High pump pressures were necessary to establish cleanout rates and rates to activate the fishing tools.
The design of a fit for purpose 1.5"" OD coiled tubing string was required to withstand the stresses placed on the coiled tubing while pulling out of hole (POOH) with a maximum wellhead pressure of 8,400 psi. Accommodation of these stresses required the string from an 110,000 psi yield high-grade material.