Because most of our company's production is in open water of navigable channels, management has been vitally concerned about controlling offshore wells in the event of storm navigation or other catastrophic occurrence. A comprehensive study has been made of this potentially dangerous situation. We hope it proves beneficial not only to us, but also to the other operators who have cooperated with us and who are producing oil and gas in the open seas.
A subsurface safety valve is used to shut in a well automatically at some depth below the bottom of the sea, or below ground level, if the wellhead equipment or other surface production equipment fails. The majority of installations of subsurface safety valves is in offshore wells, although they also are being used in onshore areas where sabotage of the wellhead is even a remote possibility.
The object of this paper is to:
Give a brief history of the development of subsurface safety valves.
Review surface controlled subsurface safety valves.
Discuss troubles we experienced in Iran with our first installations.
Discuss work done to improve our valves and eliminate troubles.
Discuss performance of valves in Iran and Egypt.
Discuss development of a valve for use in gas wells, including test work in Oklahoma.
Show sketches of valves.
Provide schematic sketches of typical installations.
As long ago as 1936, accelerated drilling of high pressure oil and gas wells in inland waters near town sites and other dangerous or isolated places required a device to protect wells from uncontrolled flow caused by accident or other damage to surface equipment. To meet this need, many types of safety valves were built and tried, most of them being of the velocity-operated type. These valves were designed to operate by increased velocity, or by the pressure differential across the valve caused by the increased velocity of flow, or by a drop in pressure to a predetermined value, caused by the rupture of some part of the well equipment on the surface. The velocity operated valve is subjected to inherent variables of flowing wells which made it difficult for average operating people to calculate and set the closing rate accurately.
While the velocity-operated valve is suitable for flowing wells producing at reduced rates, it is less suitable in areas where large volumes of flow are permitted. In wells produced at rates at or close to their potential, it is hard to predetermine spring settings to guarantee closure in an emergency.
With the rapid extension of the offshore fields into the shipping lanes of such areas as Lake Maracaibo and the Gulf of Mexico, it became apparent that a safety device should be developed which would not have the disadvantages of the velocity-operated valve.
In Venezuela, work was started on a surface controlled subsurface safety valve which would not be dependent upon the velocity off low to close the valve. As a result of this effort} the ball valve came into being. It is used in many of the oil wells in Lake Maracaibo, Venezuela.
