The present application relates to a method of producing a side pocket mandrel body for use in a side pocket mandrel assembly of a hydrocarbon well, which side pocket mandrel body comprises:a first end displaying a first connection arrangement for connecting the side pocket mandrel body to an up-hole section of a production tubing of the hydrocarbon well, and a second end displaying a second connection arrangement for connecting the side pocket mandrel body to a down-hole section of the production tubing,a longitudinal, through-going main conduit for communicating with a central passageway of the production tubing, anda side pocket section comprising at least one side pocket for retrievably housing an injection fluid flow control device.

A hydrocarbon well generally comprises a production tubing which extends down hole into a wellbore of the well for the purpose of communicating well fluid from one or more subterranean formations through a central passageway of the production tubing to the well's surface.

Hydrocarbon wells are frequently equipped with side pocket mandrel assemblies comprising a side pocket mandrel body and one or a plurality of injection fluid flow control devices, e.g. valve members, e.g. gas lift or injection valves, which are mounted in the side pocket mandrel body in order to allow fluid, e.g. injection fluid, to flow from an annulus outside of the mandrel body and into the central passageway, e.g. to stimulate the production flow rate of the hydrocarbon well.

One type of injection valve which may be mounted in a side pocket is disclosed in WO2007/091898A1, which is herein incorporated by reference in its entirety.

Typically, the injection fluid flow control devices are retrievably mounted in the mandrel body such that they can be retrieved and replaced via the central passageway of the production tubing, e.g. by means of slickline or wireline operations.

A side pocket mandrel body is typically elongated and comprises a first end displaying a first connection arrangement for connecting the mandrel body to an up-hole section of the production tubing, and a second end displaying a second connection arrangement for connecting the mandrel body to a down-hole section of the production tubing. The first and second connection arrangements may typically comprise inner or outer threads for forming threaded connections with the up-hole and down-hole production tubing sections.

The mandrel body comprises a main or central, longitudinally extending through-going channel or conduit, which is arranged to communicate with the central passageway of the production tubing when the mandrel body is connected to the up-hole and down-hole production tubing sections. The main conduit typically has a diameter which generally corresponds to the diameter of the central passageway, and when the mandrel body is mounted in the hydrocarbon well, the main conduit is typically aligned with the central passageway of the up-hole and down-hole production tubing sections.

The mandrel body also comprises a side pocket section comprising at least one side pocket providing receptacles for the above-discussed injection fluid flow control device or devices. The side pocket or pockets, which are typically elongated, are generally arranged laterally offset the main conduit, i.e. generally parallel to the main conduit.

The mandrel body further comprises at least one first opening or passage providing a fluid conduit from the outside of the mandrel body to the side pocket section, and at least one second opening or passage providing a fluid conduit from the side pocket section to the main conduit of the mandrel body, which first and second passages provide a passageway for an injection fluid from the outside of the mandrel body to the main conduit via the side pocket section, thus allowing the injection fluid flow control device or devices of the side pocket section to regulate the flow of injection fluid from the outside of the mandrel body and into the main conduit. Typically, the flow control device or devices are capable of preventing fluid flow in the other direction, i.e. from the main conduit and to the outside of the mandrel body.

If the side pocket section comprises a plurality of side pockets, the mandrel body may comprise additional passages providing fluid conduits between the side pockets allowing the injection fluid flow control devices in the side pockets to be connected in series. For example, if the side pocket section comprises a first side pocket for receiving a first flow control device and a second side pocket for receiving a second flow control device, which first and second fluid control devices are arranged to be operate in series, e.g. one after the other in the flow direction of the injection fluid, it may be advantageous to arrange said at least one first opening such that it provides a fluid conduit from the outside of the mandrel body to an inlet port of the first side pocket, to arrange said at least one second opening such that it provides a fluid conduit from an outlet port of the second side pocket to the main conduit, and to arrange at least one third opening or passage such that it provides a fluid conduit from an outlet port of the first side pocket to an inlet port of the second side pocket, e.g. as is disclosed in EP2536917B1, which is herein incorporated by reference in its entirety.

Due to the complex internal geometry of a side pocket mandrel body, the mandrel body is produced by welding a plurality of body sections together to form the completed mandrel body. This allows easy machining of the internal structures of the mandrel body since these internal structures, prior to the joining of the body sections, can be easily accessed. However, joining body section in this manner requires extensive quality checks of the welded seams at the time of production and also throughout the operable life-time of the mandrel body. Such quality checks may comprise non-destructive testing (NDT), e.g. computed tomography (CT) scanning using x-rays. However, such testing is time consuming and expensive. This is in particularly true for down-hole equipment, such as a down-hole mounted side pocket mandrel body.

Consequently, there is a need for a method of producing a side pocket mandrel body which at least partly reduces the need for non-destructive testing. The present invention relates to such a method.

The method according to the present invention comprises that steps of:providing a continuous, solid piece of material with the through-going main conduit,in the solid piece of material, forming said at least one side pocket by machining a bore into the solid piece of material such that an internal wall section of the solid piece of material is brought to separate the main conduit from the machined bore,plugging an entrance opening of the machined bore with a fluid-tight plug,providing at least one opening from an outside of the mandrel body into the at least one side pocket, thereby forming an injection fluid inlet,providing at least one opening in the wall section, thereby forming an injection fluid outlet, andproviding the solid piece of material with the first and the second connection arrangements, thereby rendering the side pocket mandrel body connectable to the up-hole and down-hole sections of the production tubing.

The step of forming the at least one side pocket by machining a bore and subsequently plugging the entrance opening of the bore makes it possible to produce the mandrel body from a continuous, solid piece of material. This, in turn, makes it possible to produce the mandrel body without resorting to welding mandrel sub-parts together, which makes away with the extensive quality checks of the welded seams.

The step of forming said at least one side pocket may advantageously comprise the sub-step of machining structures for interacting with latches and seals of the injection fluid flow control device in an internal surface of the machined bore. Alternatively, the step of forming said at least one side pocket may advantageously comprise the sub-step of inserting a hollow cylinder into the machined bore prior to the step of plugging the entrance opening, which cylinder, on the inside surface thereof, comprises structures for interacting with latches and seals of the injection fluid flow control device.

The step of plugging the entrance opening of the machined bore with a fluid-tight plug may advantageously comprise the sub-steps of providing the plug with external threads, providing the entrance opening with internal threads, and screwing the plug into the entrance opening.

During the step of forming said at least one side pocket by machining a bore into the solid piece of material such that an internal wall section of the solid piece of material is brought to separate the main conduit from the machined bore, it may be advantageous to machine the bore through the solid piece of material such that the bore, after machining, displays an entrance opening and an exit opening. In such a case, the method according the invention need to comprise the step of plugging the exit opening as well as the entrance opening.

