A subsea test tree comprises a housing defining a flow path, a valve member mounted in the housing and an actuator coupled to the housing. A drive arrangement extends through a wall of the housing to operatively connect the actuator to the valve. The actuator is operable to operate the valve member to control fluid flow along the fluid pathway. Also disclosed are improvements to actuators.

A valve system for ensuring well closure upon exposure to a predetermined condition even where a well access line is disposed through the valve. This system may be configured with a supplemental power supply capable of effectuating a cutting closure of the valve. Thus, any obstructing well access line such as coiled tubing may be cut during closure to ensure sealing off of the well, even if the cutting mechanism is separated from its traditional power supply by shear or parting of a portion of the landing string. Once more, the supplemental power sufficient for a cutting closure is only provided in the event of a predetermined condition such as the emergence of a potentially hazardous tubular separation.

A pressure tolerant battery that may be utilized in a subsea riser includes one or more lithium polymer cells enclosed in a pressure compensated housing. The pressure tolerant battery can be mounted on a landing string a disposed in the riser annulus to provide electrical power to landing string and subsea well system devices.

A technique facilitates control over flow of hydraulic actuating fluid used to perform a plurality of actuating functions in a subsea well application. A control module is employed for controlling a plurality of hydraulically controlled components and is located along a subsea test tree at a position relatively close to the hydraulically controlled components. The control module, in turn, is controlled electronically via an electric line which provides electric control signals corresponding to desired control instructions regarding the hydraulically controlled components. By moving the control module closer to the hydraulically controlled components response time is greatly reduced.

A technique facilitates fluid flow control with respect to a fluid flowing through a component of a landing string by avoiding or protecting mechanisms otherwise susceptible to debris. A valve is provided in a well component of a landing string and comprises a flexible element. The flexible element is oriented for flexing in an inward direction with respect to an internal flow passage through the landing string. The flexible element enables selective closing off of the internal flow passage without exposing certain types of mechanical mechanisms to fluid flowing through the landing string.

A system and method to eliminate the need for a dummy run comprises a logging assembly to detect the position of one or more blow-out preventer (BOP) rams and a hang off location. During a logging operation, the logging assembly logs the positions of the BOP rams and wear bushing. The logged positions are then used to determine the correct placement of the subsea test tree (SSTT) in relation to its hanger. Thus, the need to perform a dummy run is eliminated because correct placement of the SSTT can be determined during routine logging operations.

A circulation mechanism in a subsea assembly is selectively actuated to allow fluid communication between the riser annulus and tubing string to immediately kill the well using heavy-weight fluid in the riser annulus; perform well control operations by adjusting the weight or other properties of fluid in the tubing string or riser annulus; and/or to circulate the riser of a deep-water well undergoing well testing or intervention.

A system to be used within carbon capture and sequestration (CCS) and its associated method herein includes at least one mounting structure that may be associated with at least one Christmas tree which is adapted for injection of media which is associated with the CCS into at least one subsea reservoir, where a branch media pipeline may provide the media from the at least one mounting structure to the at least one Christmas tree, and where at least one choke may be in the at least one mounting structure to control a pressure of the media to provide a predetermined and chemical-free response to hydrates formation in a steady state flow of the media prior to the injection of the media into the Christmas tree.

A subsea actuation system with a, at least partly, retrievable position indicator is disclosed. The subsea actuation system being connectable to a subsea structure with a valve with a rising valve stem, the rising valve stem comprising a rotation-to-linear mechanism for operating the valve, the subsea actuation system comprising an interface for receiving rotational input from a separate retrievable actuator. The interface comprises a cylindrical bucket comprising an opening in an axial direction of the cylindrical bucket, and a shaft for receiving the rotational input from the retrievable actuator, the shaft being connected to the rotation-to-linear mechanism. The position indicator is configured for indicating an amount of rotational movement of the shaft and hence a position of the valve, and at least a part of the position indicator is configured to be positionable at, and retrievable from, the interface.