PETRONAS has undertaken a large EOR project offshore Malaysia involving the use of Immiscible Water-Alternating-Gas (iWAG) wells for fluid injection. These iWAG injection wells will allow the alternate injection of both treated seawater and hydrocarbon gas. A significant concern for these wells is tubing corrosion resistance and integrity for over a 25-year injection life.
The initial conceptual design for the iWAG injection tubing utilized Glass Reinforced Epoxy (GRE) & 25Cr tubing material due to the presence of dissolved oxygen in the injected water. The use of these materials present challenges due to limitations in downhole flow device installation with the GRE tubing and high cost of 25Cr tubing. The project team searched for alternative, fit for purpose materials to meet the project's requirements. Based on the recent PETRONAS success case of 17Cr utilization, the team examined the possibility of using 17Cr or lower grade CRA material for injection purposes.
By pioneering the first application of 15Cr OCTG as an iWAG injection tubing material in the world, several risks had to be considered. Additionally, all risks had to be mitigated via various approaches ranging from detailed engineering planning to field execution and operation. The process of selecting this metallurgy involved criteria such as cost, performance, manufacturability and operational execution. The selection methodology included a comprehensive evaluation and recommendation process that consisted of:
Evaluation of currently used metallurgical properties and limitations Identification of alternatives based on operating conditions, cost and manufacturing constraints Metallurgy qualification through comprehensive laboratory testing. Conducting tubing installation risk analysis Reviewing tubing operational, intervention and abandonment scenarios throughout the well life cycle
The successful selection and installation of 15Cr was attributed to:
The metallurgy selection, tubing procurement and installation process involving multidisciplinary and multifunctional groups both internal and external to PETRONAS. Rigorous testing at two separate laboratory facilities yielding test results which met and exceeded the required performance criteria. A 15Cr tubing make up efficiency of 100%. Impressive performance during operations resulting in a gross running speed of 371 ft/hr versus an average pipe running speed of 810 ft/hr. Use of low penetration dies to prevent slippage during tubing connection make up. This was critical since CRA material is very sensitive to scratching during contact with metal equipment. This potential metal scratching can lead to corrosion. On time delivery of 15Cr tubing from the OCTG provider ensuring sufficient time for preparation of completion accessories prior to offshore load out.
Utilization of 15Cr as an alternative to Duplex and Glass Reinforced Epoxy (GRE) materials has also contributed a direct cost saving of 27% to the project.
