CO₂ Acidizing Treatment of a Deepwater Subsea Well without Intervention

An openhole gravel-pack completion was performed in the vertical section of a high-permeability oil formation in a deepwater subsea well. The openhole section was drilled with a synthetic oil-based drill-in fluid and completed with a circulating gravel pack using weighted brine.

Initial production was satisfactory at over 10,000 BOPD. However, 11 months later, after a constant decline in production, the well was producing at an unacceptable rate of 3,000 BOPD. Analysis of the formation mineralogy from an offset well in the same formation indicated a strong tendency for fines migration. In addition, there was concern that filter cake from the synthetic drill-in fluid could still be in place and would provide some restriction to optimum production rate. A HF sandstone acidizing treatment incorporating a CO₂ preflush process for matrix oil well stimulation was recommended.

Since the well was a deepwater subsea completion, a rig intervention would have been extremely expensive. Therefore, the possibility of performing the matrix CO₂ treatment through the flow line from the TLP floating production facility was reviewed and determined to be feasible.

Procedures incorporating the use of the permanent downhole pressure gauges for rate and pressure control resulted in restoring a sustained production rate of 7,000 BOPD. The procedure and steps used for determining and executing the final treatment design will be presented.