Annular Barrier Re-Establishment Using a Long-Life, High-Strength Polymer Gel System

Abstract

Abstract Well A-01A in the Valhall field has been on production since late 1993, but its performance has been unstable with proppant and chalk flowback. Mechanical impairments have been repaired, the subsurface safety valve (SSSV) was locked open, and an insert SSSV was installed in May 2001. Although the control line was repeatedly treated with a pressure-activated sealant, leakage has been a recurring problem. Recently, a production tubing annulus communication was detected in Well A-01A. The leak point was believed to be at the seal assembly at the bottom of the production tubing string. The operator and service company engineers evaluated the mechanism of the leak and its severity. In January 2003, 30 bbl of a long-life, high-strength polymer system (HSPS) were placed in the annular space between the 5 ½-in. production tubing and 9 5/8-in. casing. Applying this polymer system as an annular barrier was a new technique. A temporary gel plug (TGP) consisting of a hydroxy propyl guar polymer and a crosslinker was pumped both ahead and behind the HSPS for placement accuracy and to prevent contamination. Because the well was at low pressure, base oil was used as a displacement fluid. The base oil helped reduce hydrostatic head under placement. The well was kept producing at normal rates during the operation, and pumping was completed within 4 hr with no production loss and no downtime. Annulus pressure was dramatically reduced from 1,300 psi to less than 250 psi. Some pressure increase was observed following well intervention work, but later pressure stabilized at 600 to 700 psi. When the well was shut in, there was no pressure increase observed in the annulus, while the tubing pressure increased from approximately 800 to 2,000 psi. Currently, the well is producing oil at 2,200 BOPD. Stable annulus pressure and normal production performance indicate that the annular gel plug is effectively blocking the communication. The use of this long-life polymer gel plug as an annular barrier is intended to keep the well producing until a tubing workover is possible and a permanent barrier is established. Payback time for the total cost of this operation is approximately four days. This paper describes the polymer gel systems, placement technique, operational aspects, and benefits of the method used.