A Maximum Safety Platform Completion System (1972)

Abstract This paper reviews a new approach to platform well completion that is currently being implemented in a new field development in 210 feet of water in the Gulf of Mexico. Maximum safety for individual wells is accomplished by using three "fail-close" valves and two manual valves on each well. A retrievable hydraulically actuated "downhole" control valve is located in the tubing string below the mud line. A subsea production tree comprised of both manual and hydraulically actuated "fail-close" gate valves is located approximately 66 feet below the water line. A "swab" valve unit equipped with both a manual and pneumatically actuated "fail-close" gate valve is located on the platform. A platform control system assures automatic "shutdown" of effected equipment in the event of any emergency, and permits selective manual control of individual wells. Introduction After the unfortunate and costly offshore platform disasters of the past, it is now apparent that all offshore operators in the petroleum industry are faced with potential disasters. These disasters can result from many causes such as physical damage due to storms or floating objects, chemical and corrosion deterioration, human error and equipment failure. Any of these disasters may result in uncontrolled hydrocarbon flow, which in turn can result in a well blowout, platform fire, pollution, and even cause loss of human life. Current completion techniques do not always lend themselves to control of these disasters. Initially, the oil industry addressed itself to the problem of developing post disaster action such as new methods for killing blowout wells and minimizing pollution. Next the oil industry turned its attention to preventive methods such as new and improved completion techniques. Major consideration has been given hydraulically actuated downhole control valves, even though they created some problems such as dimensional limitations effecting the casing-tubing programs. Also, a restriction in the tubing makes the valve susceptible to the production problems experienced with velocity valves such as sand and paraffin. The operation of the downhole control valves requires that hydraulic fluid be delivered to the downhole control valve from the surface. The method of supplying this hydraulic fluid to the downhole valve, either through a separate hydraulic line or lines or through an annular passage, creates still another completion problem. In spite of these problems, use of downhole control valves is justified as a disaster valve in the event of failure of the primary safety equipment. Placid Oil Company was investigating improved methods of preventing offshore platform disasters, and contacted equipment manufacturers regarding a new concept. A drawing of the concept was submitted for Placid's consideration (Figure 1). This concept called for the placement of underwater trees at the ocean floor under the platform with a casing riser extending up to the production platform. The production tubing strings would also extend up to the platform inside the casing riser. After several months of evaluation of the completion system and the platform design, the original concept evolved into the system presented here.