Wells – Processes – Placing or shifting well part
Reexamination Certificate
2002-07-01
2004-08-03
Bagnell, David (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S095100, C166S332300
Reexamination Certificate
active
06769490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a downhole surge pressure reduction method and apparatus for use in the oil well industry. More particularly, the method and apparatus of the present invention provides surge pressure reduction functionality while running a drilling/production liner or sub-sea casing down a borehole.
2. Description of the Prior Art
U.S. Pat. No. 5,960,881 (“the '881 patent”), which is incorporated herein by reference and which should be referred to with respect to the advantages provided by that invention, describes the principle of operation of a downhole surge pressure reduction system. The invention of the '881 patent has provided the oil well industry with the capability of running in a drilling/production liner faster and more reliably with a minimum of lost drilling fluid. Particularly, the surge pressure reduction system of the '881 patent includes a diverter device connected between a drill pipe and a drilling/production liner. The diverter device has a housing assembly with a set of flow holes and an axial bore formed therein. A sliding sleeve resides within the axial bore of the housing assembly. When the sliding sleeve is positioned above the set of housing flow holes such that the sleeve does not block the set of flow holes, communication is established between the axial bore of the housing assembly and the annular space between the housing assembly and the borehole. This is called the “open port position” and is established to facilitate surge pressure reduction when running a drilling/production liner through drilling fluid down a borehole. When the sliding sleeve is displaced axially downward such that the set of flow holes of the housing assembly is blocked by the sleeve, communication is interrupted between the axial bore of the housing assembly and the annular space between the housing assembly and the borehole. This is called the “closed port position” and is established to provide circulation of drilling fluid downward through the diverter device and to the bottom of the drilling/production liner without short-circuiting the flow of drilling fluid through the set of flow holes of the housing assembly. The closed port position is also established to facilitate cementing operations when the drilling/production liner reaches total depth of the borehole.
The diverter device disclosed in the '881 patent includes an indexing mechanism to facilitate shifting the sliding sleeve axially downward from the open port position to the closed port position. The indexing mechanism of the '881 patent includes: (1) a yieldable ball seat attached to the sliding sleeve to receive a drop ball, (2) a set of latching fingers formed on the sliding sleeve, (3) an upper groove formed on the inner wall of the housing assembly to receive the latching fingers of the sliding sleeve in the open port position, and (4) a lower groove formed on the inner wall of the housing assembly to receive the latching fingers of the sliding sleeve in the closed port position.
In operation, a drilling/production liner is run down a borehole using a drill pipe and a surge pressure reduction tool attached between the drill pipe and the drilling/production liner. Initially, the tool is set in the open port position to provide surge pressure reduction functionality while the tool is being lowered through drilling fluid down the borehole. In the open port position, the latching fingers of the sliding sleeve engage the upper groove in the housing such that the sliding sleeve does not inhibit communication via the set of flow holes of the housing.
As the drilling/production liner is lowered in the open port position, the drilling fluid flows upward through the drilling/production liner, into the tool, and outward into the annular space between the tool and the borehole via the set of flow holes. Once total depth is achieved, the surge pressure reduction tool must be in the closed port position to facilitate hanging and cementing operations. Therefore, a drop ball is released into the drill pipe to land in the yieldable ball seat thereby effectively sealing the sliding sleeve. Drilling fluid pressure is then increased above the drop ball to disengage the latching fingers from the upper groove of the housing assembly and shift the sliding sleeve axially downward into the closed port position where the latching fingers engage the lower groove of the housing assembly. Drilling pressure is once again increased above the drop ball to push the ball through the yieldable ball seat and out of the bottom of the drilling/production liner.
U.S. application Ser. No. 10/051,270 (“the '270 application”), which is incorporated herein by reference and which should be referred to with respect to the advantages provided by that invention, also discloses a diverter device with an indexing mechanism employing latching fingers. However, the '270 application also describes the principle of operation of a surge pressure reduction apparatus having a volume compensation device.
The volume compensation device of the '270 application provides a solution to problems observed during the running downhole of a drilling/production liner where the liner becomes plugged with drill cuttings and debris. Oftentimes, these drill cuttings and debris are created and left in the borehole during drilling operations. If the drilling/production liner becomes plugged while being run downhole, it may not be possible to shift the sliding sleeve downward into the closed port position. Therefore, with the sliding sleeve unable to shift out of the open port position, cementing operations cannot be performed at total depth and circulation operations cannot be performed if the drilling/production liner encounters a tight hole condition. This is due to a pressure build-up in the drilling fluid trapped between the yieldable ball seat sealed by the drop ball and the debris blocking the drilling/production liner. This pressure build-up causes a hydraulic lock condition in which the trapped drilling fluid resists the force exerted above the drop ball to shift the sliding sleeve axially downward. Therefore, the tool cannot be shifted out of the open port position and communication between the surface and the drilling/production liner via the drill pipe is short-circuited by the open set of flow ports of the tool.
A volume compensation device in accordance with the '270 application may be used to permit the surge pressure reduction tool to be shifted to the closed port position thus facilitating cementing operations and circulation of drilling fluid even in the event that the drilling/production liner becomes plugged with drill cuttings or downhole debris. The volume compensation device is connected between the drilling/production liner and the diverter device; and, when activated, the volume compensation device accumulates a volume of drilling fluid which is equal to or greater than the volume of drilling fluid displaced when the sliding sleeve moves from the open port position to the closed position.
While the inventions of the '881 patent and '270 application provide for more efficient running of drilling/production liners downhole, it has been observed that under certain conditions the indexing mechanism of these prior diverter tools may not function properly to shift the sliding sleeve into the closed port position. There are several reasons for this shifting problem. First, the latching fingers of the indexing mechanism were designed to release and shift the sleeve at low pressures (e.g., 200-300 psi), thus reducing the flexibility of the tool. Also, if the latching fingers of the indexing mechanism were installed in a position high in the housing, then atmospheric pressure is trapped between the lowest two sets of seals. Thus, when the tool is run downhole with the latching fingers in this position, the differential pressure between hydrostatic pressure and the atmospheric pressure creates a “hydraulic lock” condition thus preventing the
Allamon Jerry P.
MacFarlane Andrew M.
Miller Jack E.
Allamon Interests
Bagnell David
McConnell R. Perry
O'Neil & McConnell, PLLC
Stephenson Daniel P
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