The production system begins at the wellhead, which should include at least one choke, unless the well is on artificial lift. Most of the pressure drop between the well flowing tubing pressure (FTP) and the initial separator operating pressure occurs across this choke. The size of the opening in the choke determines the flow rate, because the pressure upstream is determined primarily by the well FTP, and the pressure downstream is determined primarily by the pressure control valve on the first separator in the process. For high-pressure wells it is desirable to have a positive choke in series with an adjustable choke. The positive choke takes over and keeps the production rate within limits should the adjustable choke fail.
On offshore facilities and other high-risk situations, an automatic shutdown valve should be installed on the wellhead. (It is required by federal law in the United States.) In all cases, block valves are needed so that maintenance can be performed on the choke if there is a long flowline. Whenever flows from two or more wells are commingled in a central facility, it is necessary to install a manifold to allow flow from any one well to be produced into any of the bulk or test production systems.
