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.

The world consumption of hydrocarbons is projected to increase by some fifty percent in the next twenty years. Yet, many of the countries supplying the world's insatiable demand will, themselves, become net oil and gas importers in the very near future. It becomes ever more important, therefore, to maximize the productivity of each and every well. While many new wells benefit from improved drilling and completion practices, there are a significant number of mature wells that are still capable of producing at economic rates, if properly stimulated. One of the simplest and most cost effective methods to do this is by matrix acidising. Acidising has established itself as an indispensable technique for enhancing production from hydrocarbon reservoirs worldwide. Over the years, research scientists and engineers have developed and improved many chemicals and additives to enhance the efficiency of these acid systems, as well as reduce the health, safety and environmental impact they have on operations. Despite huge improvements in the last decade, many issues and concerns still exist today. Handling, mixing, storage, pumping and disposal of acid and acid additives remain critical concerns in the industry. In response to these concerns, new operational methods using specialized equipment, improved mixing techniques and new acid systems have been developed. This paper discusses the current practice, reviews its shortcomings and introduces these improved methods for enhancing HSE practices and optimizing operational efficiency in offshore operations. Finally, actual implementation of the technique in various offshore scenarios is discussed, describing the HSE and logistical advantages of the process, as well as the resulting synergies. Introduction The petroleum industry continuously seeks to improve, optimize and streamline its offshore operations. Logistics, HSE and Total Quality Management are all critical areas in achieving this objective. In response to this challenge, a novel approach to offshore acidising was implemented. The resulting efforts have led to enhanced and improved acid systems, processes and equipment. The new technique involves the application of continuous mix/process control technology to offshore matrix acidising operations. "Continuous mix" refers to the preparation of treating fluids, from concentrates plus water, on an "as needed" basis, without the intermediate steps of large-scale batch mixing and storage in surface tanks. Process control is a method by which the input flow of chemicals is automatically controlled and regulated by various output sensor measurements. This ensures defined parameters are maintained within specified boundaries andminimises variations within the process. Continuous blending of acid, chemical additives and water into a finished, fit-for-purpose, acid formulation, whether fully automated or not, makes good sense in matrix acidising operations. Regardless of operational and profitability targets, the health, and safety of personnel and protection of the environment are paramount.When materials being used are toxic and corrosive, potentially dangerous operating conditions exist. Continuous mix/process controlled acidising is inherently safer and addresses many of these concerns, as discussed in more detail below. Current Practice The use of matrix acidising to improve well productivity in both sandstone and carbonate reservoirs has been in practice for the best part of a century. Acid systems ranging from inorganic acid, organic acid and HCl:HF mixtures (Mud Acid) were first used. Over the years, there has been significant investment in research and development of acidising additives and fluid systems. These efforts have resulted in enormous improvements in the systems used for acid stimulation.Amongst these are novel high pH formulations, gelled acids, self-diverting acids and viscoelastic surfactant systems, to name but a few.