1.1.1 Gray Inside BOP
The Gray inside BOP is a heavy-duty drop check valve with a conical plug to reduce the cutting action of the mud on the valve seat, ensuring positive closure whenever required. Installed in the drill string, it protects the rotary swivel, rotary hose, standpipe, and mud pumps from drill pipe kicks. It may be used along with high-pressure pumps to maintain well control by preventing high-pressure backflow.
A special release tool allows the valve to be held open to permit stabbing into position against a backflow of fluid. This optional release tool can be installed on the float valve and the entire assembly kept ready on the rig floor for quick installation at the first signs of serious backflow when drill pipe is pulled from the well.
Standard inside BOP units are designed for service pressures up to 10,000 psi, but all sizes may be supplied on special order for higher service pressures. Size requirements are based on the box and pin thread, and size of casing or drill pipe.
O-rings normally supplied are limited to use at well temperatures below +250OF, but other compositions are available to use at extremely high or low temperatures. Special metallurgical requirements may be met for extremely low temperatures or corrosive environments.
1.1.2 Kelly Guard Valves
Hydril's Kelly guard is a manually operated ball valve used to close the bore of the drill string to flow. Kelly guards facilitate well control and prevent mud spillage. They are attached above and below the Kelly to close the bore to upward flow from the wellbore, or downward flow during a connection. Kelly guard has a one piece, compact body for easy handling and provides protection up to 15,000 psi. Hydril test all shells at 1 V2 times its rated working pressure. Kelly guard is a 'Kelly cock' valve as defined by API Specification 7 for Rotary Drilling Equipment.
1.1.3 Top Drive Drill/Drill Pipe Safety Valves
Top drives incorporate an upper and lower Kelly guard as pictured. Their design allows the upper splined valve to be manually opened and closed with an actuator in place as well as remote operation.
Check guard is a drop-in check valve for the drill string. The check valve remains at surface until needed and is retrievable by wire line. It provides the driller with a means to control the drill pipe pressure when required. The check valve prevents upward flow through the drill pipe, but also allows fluid to be pumped downward to circulate the well. Only the landing sub is installed as the drill string is run. When control is needed, the valve is pumped down the string where it latches automatically in the landing sub. The check valve sits in the landing sleeve, latching positively. The sleeve has recessed areas into which the check valve packer seals. The valve seals pressure up to 10,000 psi yet is lightweight and easily handled. The valve can be retrieved by tripping the pipe out of the hole or by wire line.
Landing Sub After the correct size check valve is determined, choose a matching landing sub.
Select a landing sub with threaded connections and outside diameter compatible with the mating tool joints of the drill string.
Use the largest size check valve that can pass through the drill string to the landing sub to provide the largest flow area for circulation.
Determine the smallest inside diameter through which the check valve must pass. Verify Kelly, lower Kelly valve, tool joints, and sometimes drill collars.
The check valve OD must be at least 1/16 inch smaller than this inside diameter. Once smallest bore is determined, read across table for correct valve size.
Figure 6 - Drop-Down Check-Guard Sub Valve and Retrieving Tool
Drill pipe float valves are normally installed directly above the drill bit. In the simplest terms they are NRVs (non-return valves). They enable circulation down the drill string only and provide instantaneous shut-off from the annulus whenever the pumps are turned off. While drilling their main function is to prevent backflow while making connections. They also provide fluid flow control at the bottom of the drill string during tripping or when shut-in. Two common types are the spring loaded float valves and the flapper type float valve.
The flapper type valve incorporates a built-in latch which allows tripping the drill string into the hole with the valve in the open position, thus eliminating the need to fill the pipe. This also has the effect of reducing surge pressure. The latch is automatically released by initial circulation of mud. As soon as circulation is stopped the valve closes. Some flapper valves are vented to permit the reading of pressures during shut in conditions.
The spring loaded Baker float valve has similar functions as mentioned above. Some variations are 'ported' with a 5 mm hole drilled through the centre of the valve, enabling drill pipe pressure to be recorded during shut-in conditions.
The main dis-advantages when running float valves are summarised by higher surge pressures, inability to read drill pipe pressure or reverse circulate, and having to stop to fill the pipe.
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