Restart flow in long, horizontal well damaged by mudcake buildup

In long horizontal wells, flowing back and cleaning up a well that has been completed with sand screen ICDs can be a challenge. Drilling mud, drawdown, flowback method, and screen size are all important in selecting the most appropriate method. Conventional methods include conditioning the mud to pass through the screens before the completion has been run, using chemicals to dissolve the mudcake, and flowing back the well by injecting nitrogen through the coiled tubing.

In cases of severe damage, however, a formation may be at risk of collapse because of an extreme underbalance during flowback or other drilling-mud-related issues. For wells already completed with ICDs, any flowback and cleanup treatments should be done only through the ICD nozzles, a process that complicates the flowback.

An operator in the Middle East asked Schlumberger to restart flow in a long horizontal well severely damaged by mudcake buildup. The damage had been created by injections of nitrogen into the formation at the toe of the horizontal section during coiled tubing flowback operations. The well had been completed with ResFlow ICDs to equalize the flow along the length of the wellbore and thus required that the flow pass through the ICD nozzles.

Dissolve mudcake and stimulate flow by pumping MUDSOLV service through ICD nozzles

Schlumberger had to first determine the required injection pressures and volumes to pump the MUDSOLV filtercake removal service. Because the degree of damage was unknown and the fluid would have to pass through ICD nozzles, several simulations were run. Reservoir simulation software was used to run different cases with different annular permeabilities (1 to 1,000 mD) to estimate the injection pressure required and volumes for each compartment. Since the pressure drop across the nozzles of each ICD is known as a fixed rate, a crossplot was developed to estimate the expected injection pressures during treatment.

The simulation results indicated that pumping should begin at 1.6 bbl/min at 700 psi and that the flow rate and pressure should be increased if the formation took on more fluid.

The MUDSOLV service was pumped throughout the ICD horizontal section to treat the stages. A drillstem test string was then run, and nitrogen was injected through the coiled tubing to initiate flow. The well was flowed and tested for fluid phase concentration.

The stage stimulation results showed that from stages 1 to 13, losses occurred with high injection pressures of up to 1,300 psi. These losses indicated that the formation was using the MUDSOLV service to begin dissolving the compacted mudcake. After stage 13, the well remained stable and the injection rates and pressures were as expected. The results of the injection pressures indicated that in the stages with injection pressure above the expected model pressure, the formation was tight. The required volumes were pumped through each stage.

Restarted flow at full potential

After 112 hours of selective stage stimulation treatment with the MUDSOLV service, the damage was removed and the well flowed back with its full potential at 93% oil. An integrated effort between job design and execution showed that stage stimulation can be an effective means of treating wells installed with ICDs when and where damage has occurred.