To ensure safety during drilling operations, the rig floor must be equipped with various safety valves, including:
– FOSV (Float Operated Safety Valve), with the appropriate threads or crossovers for all drill string connections.
– Inside Blowout Preventer (IBOP).
– Upper and lower Kelly valves. On rigs with a Top Drive System (TDS), one of the Kelly valves should be remotely operable from the driller’s position.
– Dart Landing Sub: If a dart landing sub is installed, ensure that the darts are of the appropriate size for that specific sub.
The FOSV (DPSV) is a ball valve, typically controlled by a crank, designed to prevent backflow in the drill string during tripping operations. When a kick is detected while tripping, an API Spec 8C compliant FOSV should be installed. Since the valve cannot be remotely operated, the operating wrench must be readily available to the rig floor personnel. The FOSV should always be stored in the open position, kept in a warm place, and easily accessible in case of an emergency. The valve should also be able to withstand both collapse and burst pressures in the well.
Pressure Test Requirements for a FOSV, Kelly Cock, and IBOP: Initially, pressure tests should be performed with water, simulating the flow direction from the formation to the rated working pressure of the components. Subsequent tests must meet at minimum the Maximum Anticipated Surface Pressure (MASP) for the hole section.
IBOP (Inside Blowout Preventer)
An IBOP is a back-pressure valve designed to allow the driller to pump down the drill pipe while preventing backflow during a kick. The valve is held in the open position with a release tool, enabling it to be installed against backflow. The IBOP is typically installed above the FOSV to allow for the stripping of the drill string into the well against wellbore pressure. Importantly, the driller cannot reverse circulate or run wireline past an installed IBOP.
Dart and Dart Landing Sub
A dart is a check valve, often used in well control operations to prevent fluid flow up the drill string. Once the dart is in position, reverse circulation is impossible, and the well is sealed. Darts can, however, be retrieved using a wireline overshot or some other retrieval tools.
Before deploying a dart, the dart landing sub (catcher sub) needs to be pre-installed while the string is being made up. Key considerations before dropping the dart include:
* Ensure the landing sub (catcher sub) has been installed.
* Confirm that the dart is the correct size for the landing sub.
* Ensure the dart is smaller than the smallest ID between the surface and landing sub. ie. There is no obstruction in the string above the landing sub
Potential Issues with Darts:
* High-viscosity or heavy mud may require the dart to be pumped down.
* The landing ring should be installed properly in the landing sub to ensure the dart can latch in place.
* A washout in the sealing areas during drilling could lead to backflow during kicks.
* Darts may become stuck in drill string restrictions above the landing sub.
* The driller will need to use a wireline overshot tool to retrieve a dart before attempting to run wireline operations.
Kelly Cock Valves
Kelly cocks are valves designed to protect the swivel, standpipe, mud pumps, and rotary hoses from pressure surges.
Two types of Kelly cock valves are available: single and dual ball valve models.
The lower Kelly cock can prevent drilling fluid loss when disconnecting the Kelly. It uses right-hand threads and is common on conventional “Kelly rigs,” while the upper Kelly cock features left-hand threads to prevent unscrewing during drilling operations.
Kelly cocks are manually operated with a hand crank wrench. Caution should be exercised, as some models may have an insufficient external pressure rating for stripping operations, and certain lower Kelly cocks may have an OD too large for stripping into slim holes.
Upper Kelly Cock: This valve is pressure-tested initially to the rated working pressure of the equipment, typically 10,000 psi, and subsequent tests should meet or exceed the MASP.
Usage of Upper Kelly Cock: The upper Kelly cock should be closed when drill pipe pressure is about to exceed the rated working pressure of the swivel, rotary hose, standpipe, or pump.
Top Drive Valves
Top drives come equipped with two ball valves. The upper valve is air or hydraulically operated and controlled from the driller’s console.
Once the manual top drive valve is closed and disconnected, a crossover may be needed to install a FOSV. If the manual valve has been disconnected from the top drive, another valve or spacer should be installed to replace it.
Crossover Subs (X-over Sub)
The rig floor must be equipped with all necessary crossover subs to install both a FOSV and IBOP, ensuring compatibility with all thread types in the drill string, including the Kelly and drill collars.
Drill String Float Valve
A drill string float valve is a check valve that is sometimes installed above the bit to provide additional blowout protection, keep cuttings out of the drill string, and prevent the bit from plugging while making connections. There are two types: the spring/plunger type and the flapper type. Baffle plates may be placed above the float to prevent damage from dropped wireline tools.
Advantages of Installing a Bit Float:
* Prevents flow up the string while tripping, during a Kelly hose burst, or after a pop valve on the mud pump blows.
* Reduces the chance of plugging the bit and mud motor during trips.
* Prevents backflow during a kick.
* Allows for the safe installation of a FOSV without backflow during a kick.
Disadvantages of Installing a Bit Float:
* The SIDPP (Shut-in Drilling Pump Pressure) cannot be directly read without starting the pumps.
* Reverse circulation is not possible.
* The drill pipe must be filled at intervals during trips to avoid collapse.
* Increased surge pressure during trips and connections, requiring slower tripping speeds.
* Flapper-type floats may “hang open” in horizontal wells.
* Spring-loaded ball floats are not full-bore and may obstruct the passage of balls or go-devils.
* Bit floats without ports cannot bleed off trapped pressure below a bridge.
For more information on these and other Well Control subjects, read my Well Control Manual, which may be purchased in the Catalogue section of this website at: Well Control Manual V2.6 by Edwin Ritchie
Drill String Safety Valves
To ensure safety during drilling operations, the rig floor must be equipped with various safety valves, including:
– FOSV (Float Operated Safety Valve), with the appropriate threads or crossovers for all drill string connections.
– Inside Blowout Preventer (IBOP).
– Upper and lower Kelly valves. On rigs with a Top Drive System (TDS), one of the Kelly valves should be remotely operable from the driller’s position.
– Dart Landing Sub: If a dart landing sub is installed, ensure that the darts are of the appropriate size for that specific sub.
FOSV (Fully Opening Safety Valve) or DPSV (Drill Pipe Safety Valve)
The FOSV (DPSV) is a ball valve, typically controlled by a crank, designed to prevent backflow in the drill string during tripping operations. When a kick is detected while tripping, an API Spec 8C compliant FOSV should be installed. Since the valve cannot be remotely operated, the operating wrench must be readily available to the rig floor personnel. The FOSV should always be stored in the open position, kept in a warm place, and easily accessible in case of an emergency. The valve should also be able to withstand both collapse and burst pressures in the well.
Pressure Test Requirements for a FOSV, Kelly Cock, and IBOP: Initially, pressure tests should be performed with water, simulating the flow direction from the formation to the rated working pressure of the components. Subsequent tests must meet at minimum the Maximum Anticipated Surface Pressure (MASP) for the hole section.
IBOP (Inside Blowout Preventer)
An IBOP is a back-pressure valve designed to allow the driller to pump down the drill pipe while preventing backflow during a kick. The valve is held in the open position with a release tool, enabling it to be installed against backflow. The IBOP is typically installed above the FOSV to allow for the stripping of the drill string into the well against wellbore pressure. Importantly, the driller cannot reverse circulate or run wireline past an installed IBOP.
Dart and Dart Landing Sub
A dart is a check valve, often used in well control operations to prevent fluid flow up the drill string. Once the dart is in position, reverse circulation is impossible, and the well is sealed. Darts can, however, be retrieved using a wireline overshot or some other retrieval tools.
Before deploying a dart, the dart landing sub (catcher sub) needs to be pre-installed while the string is being made up. Key considerations before dropping the dart include:
* Ensure the landing sub (catcher sub) has been installed.
* Confirm that the dart is the correct size for the landing sub.
* Ensure the dart is smaller than the smallest ID between the surface and landing sub. ie. There is no obstruction in the string above the landing sub
Potential Issues with Darts:
* High-viscosity or heavy mud may require the dart to be pumped down.
* The landing ring should be installed properly in the landing sub to ensure the dart can latch in place.
* A washout in the sealing areas during drilling could lead to backflow during kicks.
* Darts may become stuck in drill string restrictions above the landing sub.
* The driller will need to use a wireline overshot tool to retrieve a dart before attempting to run wireline operations.
Kelly Cock Valves
Kelly cocks are valves designed to protect the swivel, standpipe, mud pumps, and rotary hoses from pressure surges.
Two types of Kelly cock valves are available: single and dual ball valve models.
The lower Kelly cock can prevent drilling fluid loss when disconnecting the Kelly. It uses right-hand threads and is common on conventional “Kelly rigs,” while the upper Kelly cock features left-hand threads to prevent unscrewing during drilling operations.
Kelly cocks are manually operated with a hand crank wrench. Caution should be exercised, as some models may have an insufficient external pressure rating for stripping operations, and certain lower Kelly cocks may have an OD too large for stripping into slim holes.
Upper Kelly Cock: This valve is pressure-tested initially to the rated working pressure of the equipment, typically 10,000 psi, and subsequent tests should meet or exceed the MASP.
Usage of Upper Kelly Cock: The upper Kelly cock should be closed when drill pipe pressure is about to exceed the rated working pressure of the swivel, rotary hose, standpipe, or pump.
Top Drive Valves
Top drives come equipped with two ball valves. The upper valve is air or hydraulically operated and controlled from the driller’s console.
Once the manual top drive valve is closed and disconnected, a crossover may be needed to install a FOSV. If the manual valve has been disconnected from the top drive, another valve or spacer should be installed to replace it.
Crossover Subs (X-over Sub)
The rig floor must be equipped with all necessary crossover subs to install both a FOSV and IBOP, ensuring compatibility with all thread types in the drill string, including the Kelly and drill collars.
Drill String Float Valve
A drill string float valve is a check valve that is sometimes installed above the bit to provide additional blowout protection, keep cuttings out of the drill string, and prevent the bit from plugging while making connections. There are two types: the spring/plunger type and the flapper type. Baffle plates may be placed above the float to prevent damage from dropped wireline tools.
Advantages of Installing a Bit Float:
* Prevents flow up the string while tripping, during a Kelly hose burst, or after a pop valve on the mud pump blows.
* Reduces the chance of plugging the bit and mud motor during trips.
* Prevents backflow during a kick.
* Allows for the safe installation of a FOSV without backflow during a kick.
Disadvantages of Installing a Bit Float:
* The SIDPP (Shut-in Drilling Pump Pressure) cannot be directly read without starting the pumps.
* Reverse circulation is not possible.
* The drill pipe must be filled at intervals during trips to avoid collapse.
* Increased surge pressure during trips and connections, requiring slower tripping speeds.
* Flapper-type floats may “hang open” in horizontal wells.
* Spring-loaded ball floats are not full-bore and may obstruct the passage of balls or go-devils.
* Bit floats without ports cannot bleed off trapped pressure below a bridge.
For more information on these and other Well Control subjects, read my Well Control Manual, which may be purchased in the Catalogue section of this website at: Well Control Manual V2.6 by Edwin Ritchie