Inside Bops

Drill Pipe Float Valves

The drill pipe float valve and the flapper type of back pressure valve, serve essentially the same purpose, but differ in design.

These valves provide instantaneous shut-off against high or low back pressure and allow full fluid flow through the drill string. Another advantage is that it prevents cuttings from entering the drill string, thus reducing the likelihood of pulling a wet string. Abnormal pressures and anticipated subnormal pressure zones should be the deciding factor regarding what type of valve to run or the possibility of not running any valve at all. Expectations of abnormal pressures have shown the vented type of flapper valve to be the most popular because of the ease involved in recording shut-in drill pipe pressures. The disadvantages are that the pipe must be filled while tripping in, and reverse circulation is not possible.

Figure 6.6.1

Figure 6.6.1

Gray Valve Well Control

SECTION 6 : WELL CONTROL EQUIPMENT

Figure 6.6.2 - Kelly Cock

Figure 6.6.3 - Gray Valve

Figure 6.6.2 - Kelly Cock

Gray Valve Drilling String

Figure 6.6.3 - Gray Valve

Drill Stem Open Hole Test Tool

Installing a Checkguard improves well control significantly. It serves as a check valve to prevent upward flow through the drill string while permitting downward mud pumping or flow from injectors.

While stripping drill pipe into the hole, Checkguard control upward pressure in the annulus and in the drill pipe. Latching the check valve into the landing sub contains the pressure in the drill pipe.

Prior to shearing drill pipe, install the check valve to protect against the release of well pressures. Installation of the check valve simplifies well control, since formation pressures cannot communicate up the drill string.

While tripping, Checkguard contains upward well bore pressure in the drill pipe, allowing the top connection to be open.

Figure 6.6.4

Figure 6.6.4

Drill Pipe Float Valve Ball Type

SECTION 6 : WELL CONTROL EQUIPMENT

Checkguard uses a spring and ball design. Fluid can be pumped through the valve from the top. But when fluid tries to flow from the bottom to the top, it is sealed by the spring-loaded ball against the seat.

A large rubber packer provides sealing when fluid attempts to flow around the valve. The packer is engaged by the tapered body. The body is driven upward by pressure from below. The more pressure from below, the tighter the seal is.

Installation and Retrieval

Install the landing sub in the drill string while tripping into the hole. Position the landing sub in the lower end of the drill string.

Install the check valve by dropping it into an open tool joint. Connect the kelly and pump the check valve into the landing sub. Use the drill pipe safety kelly guard and lower the kelly guard if excessive back flow exists.

Retrieve the check valve by installing a sinker bar above the retrieving tool and using a wire line. Use normal wire line procedure. Another way is to trip the drill string and remove the check valve from the landing sub with the retrieval tool.

Operating tips include ensuring the packer rubber is clean and pliable. Check for foreign substances such as paint, grease and dirt on the packer surface. Check for cracking and embrittlement of packer. Never oil rubber packer. Replace packer if condition requires.

The check valve should be disassembled, cleaned and lubricated (not packer) once it is retrieved from the landing sub after downhole use.

The valve should be stored in a protected area, away from sun and rain while not in use. This protects the working parts and packer.

SECTION 7 :

INSPECTION, TESTING AND SEALING COMPONENTS

7A 7B 7C 7

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