Fluids Migration Behind Casings: An Offshore Well Integrity Issue Restoration Experience of AGM043 in Gabon, West-Africa

Abstract

Minimizing risks in offshore oil and gas production facilities is of upmost importance for oil producers to reduce possibilities of liability claims, hydrocarbons production rate loss, and most importantly environmental impacts. In this regard, well integrity parameters such as MAASP and MAWOP become key tools to carefully follow and watch production tubings and annulus pressures behaviors at the surface. AGM043 is an oil producing well which presented a high downgraded situation mainly with abnormal pressure in the annuli A and B and the christmas tree not holding the pressure. The pressure rate observed in the annulus B (104 bars) was considered higher than the limit set as per the MAASP (72 bars) presenting a risk of fracture at the 13-3/8″ casing shoe. To regain full integrity of the well, since purging the annuli did not contribute to pressure stabilization and due to the presence of gas (mainly methane), actions were taken to conduct a well killing job split in four phases: Phase 1: Purging, investigate communication point between tubing and annuli, echometer for fluid level determination. Phase 2: Well killing by bull heading in the tubing and lubricate and bleed in the annuli. Phase 3: Establishment of a double barriers Phase 4: Valves changes and test of Christmas tree integrity. This manuscript discusses the rise of an abnormal pressure behavior in the annular, its management, and the lessons learnt at the end of the integrity regain after the killing job offshore Gabon. The experience gained can be applied to other wells with similar problems.