Case History: Lessons Learned From Retrieval of Coiled Tubing Stuck by Massive Hydrate Plug When Well Testing in an Ultradeepwater Gas Well in Mexico

Summary A well-testing operation was performed to confirm productivity potential in an ultradeepwater area where a 5,660-ft exploratory well had been drilled. This was a gas well drilled from a semisubmersible drilling rig. Because well testing from semisubmersible rigs is a critical and sensitive operation, all planning had been carefully reviewed by the operator to ensure a safe, environmentally friendly operation. The formation of hydrate plugs during ultradeepwater well testing is a critical concern because water can be trapped and form a solid crystalline structure around gas when there are low temperatures near the mudline. This hydrate formation is a common occurrence in deepwater drilling operations, particularly while using water-based mud. Thermodynamic inhibition may not be effective in these cases because several limitations in achieving the required injection rate exist. Oilwell testing operations in deep and ultradeep water have become common practice around the world, and vast experience with these types of operations has been acquired; experience with gas wells, however, has not been as comprehensive, and only a few gas wells have been tested under the conditions presented in this type of scenario. Because of the low number of gas wells tested in these deepwater conditions, best-practice information is limited. The intention of this paper is to present a case history and the lessons learned during a well-testing operation in which water production in the gas well was greater than anticipated during the cleanup period. A massive hydrate plug was formed while coiled tubing was being pulled out of hole, and the coiled tubing became stuck. The steps taken to free the coiled tubing will be discussed, and the discussion will include the following: Conditions that must be present to form hydratesHow the problem in this case was resolvedHow to help prevent hydrate formationBest practices for well testing in deepwater gas wells to maintain safety and economic viability This case history discusses a gas well being drilled with a semisubmersible drilling rig in ultradeep water, offshore Mexico.