A drill pipe float valve, also recognized as a non-return valve, is a specialized valve installed in the bottom hole assembly (BHA) and its primary function is to serve as a check valve, permitting the downward flow of drilling mud through the drill string but preventing any unwanted fluid from flowing back up into the drill string.
Key advantages of float valves
- Provide immediate shut-off against high or low back pressure and prevent fluid flow through the drill string.
- Prevent cuttings from entering the drill string, thus reducing the likelihood of pulling a wet string.
Disadvantages of float valves
- Require filling up pipe while tripping in hole
- Unable to perform reverse circulation
Types of Drill Pipe Float Valves:
- Plunger Type: The most prevalent type, featuring a plunger that seals against a seat to prevent reverse flow.
- Flapper Type: Utilizes a flapper resting on a seat to obstruct reverse flow.
Ported or Non-Ported Float Valve
A ported float valve features a small hole in its center, offering two significant advantages. Firstly, it enables the monitoring of drill pipe pressure post-well shut-in. Secondly, it helps minimize the risk of downhole fracture during well pack-off, as excess pressure can be released through the ported float. However, a drawback is that some influx may enter the drill string.
In contrast, a non-ported float valve completely seals the interior of the drill string, preventing communication unless the float is disturbed. The primary advantage is the prevention of influx into the string. Nevertheless, it comes with two drawbacks: 1) the need to pump the float to observe shut-in drill pipe pressure, and 2) the absence of a method to release downhole pressure in the event of wellbore pack-off. This limitation arises because, when surface pressure is reduced to zero and the float valve is closed, pressure becomes trapped between the pack-off and the string without a means of release.
References
Cormack, D. (2007). An introduction to well control calculations for drilling operations. 1st ed. Texas: Springer.
Crumpton, H. (2010). Well Control for Completions and Interventions. 1st ed. Texas: Gulf Publishing.
Grace, R. (2003). Blowout and well control handbook [recurso electrónico]. 1st ed. Paises Bajos: Gulf Professional Pub.
Grace, R. and Cudd, B. (1994). Advanced blowout & well control. 1st ed. Houston: Gulf Publishing Company.
Watson, D., Brittenham, T. and Moore, P. (2003). Advanced well control. 1st ed. Richardson, Tex.: Society of Petroleum Engineers.
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