Challenging environment requires innovative solution

A subhydrostatic deepwater reservoir had produced for years. Although production rates continued to be economical, reservoir pressures were depleted below the hydrostatic equivalent of seawater. An infill well had been completed with seawater, resulting in a 103,421-kPa [1,500-psi] overbalance. The operator needed to isolate the reservoir without evacuating the marine riser. Spotting fluid loss pills after the sand-control installation would have reduced the flow rate and ultimate recovery and would have severely complicated the well unload from this low-energy reservoir. Conventional fluid-loss devices could not be used because their success depended mainly on a minimal fluid-loss rate when the devices were set.

The operator had experienced failures when attempting to set mechanical fluid-loss devices (ceramic flappers and fluid-loss balls) in this high-fluid-loss-rate environment. Because a riser fill valve was in place to avoid evacuation, postponing setting the mechanical fluid-loss device until after the well reached equilibrium was not an option. The subsea blowout preventer system’s ability to impose reverse pressures on critical components was limited, and therefore other methods were not suitable. For example, it was not desirable to strip the drillpipe through the annular while concurrently allowing the wellbore fluid to come to equilibrium and then pulling the wash pipe out of the gravel-pack assembly.

The operator had Schlumberger install the FIV Formation Isolation Valve because of the valve’s track record of success and its ability to meet the operational parameters for the well conditions. The well experienced a steady fluid-loss rate of 6 bbl/min after the sand control installation. This fluid-loss rate was substantially higher than the recommended rate for setting the mechanical fluid-loss devices that the operator typically used in its deepwater subsea completions. Even so, the rate was below the 25 bbl/min maximum fluid-loss rate of the FIV valve. The wash pipe was pulled from the gravel-pack assembly, and the shifting tool (located at the end of the wash pipe) closed the FIV valve uneventfully, stopping all fluid loss.

FIV valve opens with high differential pressure

With the FIV closed, the upper completion was safely installed in the well without concern for fluid loss and reservoir damage. The next challenge was to open the FIV valve. The FIV valve’s Trip-Saver one-time opening mechanism was designed to operate with a maximum of 1,000 psi delta pressure across the ball. Unfortunately, well scheduling issues did not allow enough time to acquire the equipment needed to test whether the FIV valve could be opened at the higher pressure differential in this well. Therefore, because of the concerns about whether the valve would open with the high differential or close with the high fluid loss rate, several contingency plans were developed. If the valve failed to open, a tractor stroker would be used to mechanically shift it on electric line. If electric line was unable to open the FIV valve, the FIV ball would be milled. If the valve failed to close, the plan was to spot a fluid-loss pill inside the gravel-pack assembly, install the completion, and use coiled tubing to wash the pill out of the screen and acidize the well.

The valve successfully closed and sealed at a fluid loss rate in excess of the design parameters for the conventional fluid-loss device that the operator customarily used in its subsea wells, thus allowing the operator to run a riser fill valve to avoid evacuating the marine riser. The valve also was successfully opened hydraulically with the Trip Saver mechanism, avoiding additional runs to establish communication with the reservoir before the well was placed on production. The successful installation and use of the FIV valve ultimately saved the operator valuable time and operating costs.