Abstract
In a deep water well completed with coil tubing gas lift (CTGL), significant threat on flow assurance issues has been identified due to the Joule-Thompson effect generated from the high differential pressure of the supplied gas at 3400psi with the required pressure in the well which is below 1500psi. Several wells which have low liquid rate flowing colder with the CTGL due to the Joule Thompson-effect elevated the risk of hydrate formation. Monitoring of Wellhead Temperature (WHT) alone can be a challenge since WHT is below ambient and indication of WHT increase can be interpreted as either as an increase in liquid rate or well quit flowing. The paper describes operator experience in developing an effective flow assurance scheme for prevention and treatment should the well experience hydrate related plugging and devises a strategy for contingencies and remedial actions to reactivate wells effectively without significant production deferment.
A holistic approach to manage flow assurance issues in below ambient WHT deep-water dry tree wells completed with CTGL was designed, undertaken, and proven effective. Thorough investigation to analyze the root cause of the blockages along the production tubing was conducted. Several intervention options were considered with very limited clearance for the type of intervention can be conducted in the wells of concern. Decision was made to proceed with the bull-heading method via the CTGL as it was found to be the most cost efficient and quick solution. Preventive measures were then taken to avoid similar future events from happening.
Three deep-water dry tree wells which was completed with CTGL were experiencing blockages in the production tubing during an unplanned shutdown. The total potential of these wells amounts to 2600bopd and warranted the team to investigate a quick solution before attempting a workover which is costly and requires longer duration for planning before execution. Two out of the three wells treated with exothermic chemical injection were successful and restored 2000bopd production. Pre-qualification testing demonstrated similar trends of pressure communication between CTGL and tubing head pressure (THP) on the successful well treatment. Chemical solution which produced heat by exothermic reaction was bullheaded into the well with immediate communication established after injection. A standard operating procedure was then developed to manage the wells under this category and prevent future blockage.
Culmination of the unique approach for wells with slim tubing (CTGL) to resolve a problem should be looked at from various angles. Investigation must be conducted until the flow restriction root-cause has been identified. Preventive measures then can be taken to avoid similar occurrence which will minimize value leakages and economic impact to the field. De-risking via conducting pre-qualification and Design of Experiment based on scenarios prior to arriving at solution helps to increase chances of successful treatment.
