Surface flow head surface test tree
The surface flow head is the primary closing and safety assembly located on the surface. The surface flow head is attached to the top of the test string, sufficiently high above rotary table to accommodate rig heave. It should have a pressure rating equal to or greater than the maximum expected surface pressure, and have sufficient tensile strength to pick up the weight of the test string to unseat the packer. The assembly consists of various components and the components selected for each test depend on the downhole tools, drilling rig and the test objective. The following components may appear on a surface flow head:
- A lift nipple which provides a means of latching the elevators onto the test string above the surface control head.
- An adaptor sub which can be used in place of the lift nipple so that a joint of drillpipe or 'pup joint' can be installed on top of the control head.
- A bar drop sub can be used to hold and release the bar that shears the pin if an impact reversing sub is run.
- A flo-tee contains side ports that allow flow to exit from the drillpipe to the flow line or kill line. In a 3"<i inch 10 000 p.s.i. WP flow head, the three valves (swab, flow and kill wing) are in a solid block system.
- A swivel is included in the surface test string when downhole tools are operated by the rotation of the test string. The swivel permits the test string to be rotated. The control umbilical for the SSTT is wrapped around the test string to accommodate rotation.
- The master valve is the in-line shut-off valve located below the Flo-Tee. It should be full bore valve and should allow rapid closing.
- A swab valve is installed to provide vertical access to the test string.
- An access valve can be run above the master valve(s). The access valve provides an injection port to permit injection of alcohol or chemicals into the flow stream. This is particularly important with gas wells and with wells in cold climates. It also provides a pressure gauge port on the test string.
- A kill wing valve is a manual valve which is hooked up to the cement unit with an in-line check valve. The kill wing valve should remain open during testing operations to allow immediate (bullhead) killing of the well, if required.
- A flow wing valve is the hydraulically actuated fail-safe valve that permits immediate shutting-off of the flow at surface. It can be operated from the rig floor, or from locations remote from the rig floor.
- Wireline lubricators, when used, should be of sufficient length to handle the longest tool to be run. The lubricator should be pressure rated to withstand the maximum expected surface pressure. The lubricator is rigged up on top of the flowhead (the lift nipple removed).
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