Float Valve Sub

I. Core Functions and Roles of Float Valve Sub

a) Prevent backflow inside the drill string to ensure the safety of personnel and equipment.

This is its most primary security function. When a single drill string is connected, the drill is lifted or a wellspring occurs, if there is no obstruction inside the drill string, high-pressure formation fluids (oil, gas, water) will be ejected upward along the interior of the drill string, causing wellhead contamination, personnel injury and fire risk. The check valve inside the float valve sub can effectively seal the interior of the pipe string and prevent this kind of backflow.

b) Provide a "hydraulic hammer" basis for the action of the drilling jar.

The existence of the float valve sub prevents the drilling fluid in the drill string from being rapidly replenished downward when it is rapidly lifted, thus creating a brief "vacuum" or low-pressure area in the local drill string below the impactor. This low-pressure area significantly reduces the damping effect of the drilling fluid on the upward movement of the drill string, enabling the driller to stretch the hammer shaft with a smaller tension and a faster speed, thereby ensuring that the hammer can efficiently and reliably release a powerful impact force.

c) Reduce the "blowout" phenomenon when lifting the drill.

During the lifting process, the drill string is lifted from the wellbore, and its volume will create space, causing the drilling fluid level inside the wellbore to drop. Without a float valve, the drilling fluid in the drill string would flow back to the wellbore and "spurt" out from the wellhead, dirtiness the drilling platform and equipment. The float valve sub "locks" the drilling fluid inside the drill string, making the drilling operation cleaner and safer.

d) Auxiliary well control.

When signs of welling are detected and well closure operations are carried out, the float valve sub can serve as an additional internal barrier, working in conjunction with the blowout preventer group to jointly control the wellhead pressure.

II. Structure and Types of Float Valve Sub

The float valve sub itself is a thick-walled joint that has undergone special processing, and its core lies in the check valve inside. Common types of valves include:

• Flap valve: Like a door, it can only open in one direction.

• Float valve: A cavity with a ball placed inside. When pumping drilling fluid, the ball is washed away. When the pump stops or backflows, the ball falls back onto the valve seat under the action of pressure and gravity, achieving a seal.

• Disc valve: Similar to a flap valve, but the sealing surface is disc-shaped.

• Advanced float valve subs are usually also equipped with bypass holes or ball-type activation mechanisms.

III. Precautions for Use of Float Valve Sub

1. Monitor pump pressure: The float valve sub will increase the pressure loss of the entire circulation system. It is necessary to calculate and monitor the pump pressure in advance to avoid overpressure.

2. Prevention of clogging risk: If the drilling fluid contains large amounts of cuttings or debris, it may jam the valve ball or valve plate, preventing them from closing or opening normally. Therefore, there are requirements for the cleanliness of drilling fluid.

3. Regular inspection and maintenance: After each drill lift, the sealing performance of the float valve sub and the flexibility of the moving parts should be inspected. Worn valve seats or balls need to be replaced in time; otherwise, they will lose their sealing ability.