The choke manifold is a system composed of valves, fittings, lines, and chokes that provide multiple flow paths to regulate the flow of mud, gas, and oil from the annulus during a kick. This section will cover the choke manifold’s parts and functions and IADC recommendations for its use in drilling operations.
When a kick occurs, well control is maintained by shutting in the well (secondary well control). It is crucial to regain primary reasonable control as soon as possible. A blowout may occur if the shut-in pressure becomes too high before this can be achieved. Chokes bleed off drilling fluid to keep the pressure below the Maximum Allowable Annular Surface Pressure (MAASP). At the same time, heavier mud is pumped into the well to replace lighter mud and reestablish primary reasonable control.
It’s essential to manage the amount of drilling fluid carefully bled off to avoid further imbalance in hydrostatic pressure caused by lighter fluids mixed with gas.
A high-pressure choke line leads to the choke manifold, which typically includes:
– Adjustable chokes
– An accurate, quick-response pressure gauge
– Control valves
Note: Chokes regulate fluid release at a controlled rate to limit casing pressure and allow for the replacement of mud in the well with heavier mud.
Choke Manifold Function
Typical Choke Manifold for 5,000 psi Working Pressure Service-Surface Installation
If the drilling fluid’s hydrostatic pressure is insufficient to control subsurface pressure, formation fluids will enter the well. Back pressure is applied to maintain control by routing the flow through adjustable chokes until the healthy flow condition stabilises. The chokes are connected to the blowout preventer stack via valves, fittings, and lines that provide alternate flow paths or can completely halt the flow. This assembly is known as the choke manifold.
Choke Manifold Components
A typical choke manifold, designed for 5,000 psi working pressure, includes the following:
1. Choke: A device with an orifice that restricts fluid flow. It controls the drilling mud flow rate out of the well when closed in with the blowout preventer during a kick.
2. Choke Line: A pipe attached to the blowout preventer stack, through which kick fluids and mud are pumped to the choke manifold when the blowout preventer is activated.
3. HCR (Hydraulic Control Remote) Valve: This is a pressure-operated gate valve used in the flow line. It is designed for high-pressure applications, with sizes ranging from 4-inch to 6-inch and working pressures from 3,000 to 5,000 psi.
4. Chokes Types :
Manual Adjustable Choke: A needle valve-type choke with a tungsten carbide seat for wear resistance, used for initial flow restriction.
Hydraulic Choke: A choke with a replaceable seat of different sizes used for maintaining constant flow rates over extended periods, such as during production tests.
Remote-Controlled Choke: Operated from a control panel, usually located on the rig floor, and includes pressure gauges, a pump stroke counter, and control switches.
5. Choke and Kill Line Outlet Valves: These must meet specific requirements to ensure operational flexibility and safety, including minimum inner diameters and configurations that prevent excessive erosion or fluid friction.
IADC Recommendations for Choke Manifold Planning & Installation
Pressure Rating: All components upstream of and including the chokes should have a working pressure equal to the blowout preventer stack’s rated pressure.
Components: Should comply with specifications for anticipated pressure, temperature, and fluid corrosivity.
Connections: For working pressures of 3M and above, use flanged, welded, or clamped connections.
Placement: The choke manifold should be easily accessible and ideally located outside the rig substructure.
Testing: The choke manifold should be tested to full working pressure during initial installation, after maintenance or repair, and regularly as part of the BOP stack inspection schedule.
2000 & 3000 PSI Manifold
5000 psi Manifold
10000 & 15000 psi Manifold
Following these guidelines, the choke manifold can effectively maintain well control and manage pressure during drilling operations.