Hydrocarbon production terminal

Abstract

An offshore oil production terminal system is described, of the type which includes a tall transfer structure that has a nonrotatable tower anchored to the sea floor and a rotatable portion that rotates with respect to the nonrotatable tower and is connected to a dedicated storage vessel. A fluid conduit of the system has a nonrotatable portion extending from the sea bed up alongside and through the tower to a fluid swivel at the top of the tower, the conduit also having a rotatable portion extending from the fluid swivel to the vessel. A choke located in the nonrotatable tower along the fluid conduit, decreases the high pressure of oil from the sea bed (e.g. 2,000 psi) to a moderate pressure (e.g. 200 psi) for passage through the fluid swivel, so that a moderate pressure fluid swivel can be utilized. In a system wherein the rotatable transfer structure portion is fixed to the vessel, the tower has a control deck at substantially the same level as the vessel deck and with a circular periphery. This facilitates entry of personnel onto the control system deck of the tower, and permits operation of a multitude of controls that are directly connected to various stationary valves and the like on the production trees at the sea bed without requiring rotational joints between the controls and the devices they operate. Power to produce pressured hydraulic fluid for controlling valves and the like, can be obtained by the passage of a powering fluid such as moderate pressure air (e.g. 200 psi) through a fluid swivel on top of the tower to an air-motor-hydraulic pump combination in the fixed tower, to produce high pressure hydraulic fluid (e.g. 3,000 psi) for control system operation.