Boring or penetrating the earth – With means movable relative to tool or shaft to control... – Valve prevents upward flow
Reexamination Certificate
2000-04-03
2001-11-20
Shaver, Kevin (Department: 3754)
Boring or penetrating the earth
With means movable relative to tool or shaft to control...
Valve prevents upward flow
C166S066700, C175S317000, C251S001100
Reexamination Certificate
active
06318482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blowout preventer adapted to be included in a drill string wherein, upon the occurrence of an uncontrolled blowout of fluid (liquid and/or gas) in a subsea well, the blowout preventer is released in a manner to adopt an activated or set position stopping the blowout.
2. Description of the Related Art
Blowout preventers based on expandable packer elements are often used when drilling top hole sections, i.e. borehole sections near the seabed where high pressure shallow gas pockets may be encountered, to prevent uncontrolled blowout if the pressure downhole of the blowout preventer is higher that provided by the hydrostatic pressure caused by the drilling mud above the packer.
Packer elements of prior art blowout preventers of the above type, such as that disclosed in published PCT application WO 88/08917, are generally designed to be capable of completely isolating the borehole below the packer. In contrast to this, the present invention relates to a blowout preventer permitting a certain degree of controlled fluid leakage to the annulus above the packer, whereby drilling mud may be caused to fill up the entire borehole in an emergency situation associated with a dangerous blowout from the subsea well.
In order to detect any so-called “shallow gas” in top-hole sections in the upper seabed stratum, one or more “pilot holes” are often drilled. The pilot hole is drilled with a smaller diameter than fill bore diameter, in order to permit an increase of the downhole pressure by increasing the pumping rate of the drilling mud. Drilling pilot holes means added costs. Using a blowout preventer according to the invention eliminates the need of initially drilling a such pilot hole, while it also provides the necessary safety with regard to any high pressure zones that may be encountered. The blowout preventer according to the invention which is based on a packer means with a leak feature, is primarily intended for use in the above mentioned top-hole sections, where the borehole is not provided with casing.
When, during prior art drilling, the bit at the end of the drill string encounters a one of the formation having a higher pressure than that produced by the hydrostatic fluid column in the subsea well, any fluid (liquid and/or gas) present will be able to flow into the well and out of it, if no particular measure has been taken to prevent it.
Often, when drilling the upper section of a subsea well, no blowout preventer is used, and normally seawater is used as a drilling fluid when drilling the well. Therefore, when using this prior and conventional drilling technique, it is particularly important to ascertain that there are no high pressure zones to be encountered along the intended drilling path.
When drilling at greater sea depth, however, the formations in the upper strata of the subsea well are less consolidated than those at shallow waters.
The radial expansion capability of the type of packer that is used in prior blowout preventers is limited, and therefore such prior blowout preventers may not be capable of providing a satisfactory sealing around the wall of the wellbore annulus if the formation is unconsolidated or washed out to have a diameter larger than normal. Such insufficient sealing capacity of prior packer elements is uncontrollable and not to be compared with the intended and controllable leaking capability of the blowout preventer of the present invention, the latter permitting a fluid circulation that may be brought to cause the wellbore to be completely filled with drilling mud in an emergency situation such as a blowout.
Prior blowout preventers of the type having inflatable packer elements which are deflated when lowered into the well in their inactive ready position, require a higher internal pressure in their inflated, set position than the pressure prevailing below the packer element in the subsea well. This is due to the fact that the unset packer element itself resists being inflated.
As explained above such inflatable packing elements suffers from insufficient expandability upon inflation. On very deep waters formations might be encountered which are unconsolidated or weak, resulting in a non-uniform borehole wall having varying cross-section along a length thereof, which would necessitate an expansion of the inflatable packing element beyond that for which it is designed. Thus, prior packing elements are not capable of being sufficiently expanded.
SUMMARY OF THE INVENTION
The primary object of the present invention is to eliminate or substantially alleviate drawbacks, deficiencies and restrains on the range of applications of prior art or art technology associated with the drilling for oil and gas, and thus to provide a simple, effective and safe blowout preventer capable of protecting subsea wells against a blowout from an unexpected pressure zone in the formation that is drilled.
This is achieved through the invention, by a type of blowout preventer as introductorily described, incorporating the new and specific features recited below.
In order to be capable of preventing inflow into the subsea well caused by a blowout from an unexpected pressure zone, the pressure in the lowest part of the well has to be increased until it exceeds the pressure prevailing in the formation. According to the invention this is achieved by activating the blowout preventer packer means which comprises a plurality of individual packer elements which, in their activated set position, closes or isolates the annulus between the blowout preventer and borehole wall.
The blowout preventer comprises a tubular body including a packer means adapted to adopt a deactivated or unset and an activated or set position, a latching and releasing means for retaining and releasing the packer means, and an activating means for activating the latching and releasing means. The tubular body of the blowout preventer is provided with passageways through which the fluidflow is directed from downstream inlet ports to upstream outlet ports. The upstream end of each passageway can be provided with one or more nozzles while their opposite closed or downstream end communicates with the annulus through a port.
The radially outer end openings of the ports are normally covered by the individual elements of the packer means when these elements are in their nonactivated position. The packer elements are in the form of relatively wide, self-contained slats one end (the upstream end) of which is attached at the exterior of so the tubular body of the blowout preventer while the free ends of the slats engage the exterior of the tubular body in the inactive position of the packer means.
The packer slats are made from steel or another appropriate metal or metal alloy subjected to a heat treatment imparting a springy property to the slats that tends to urge them radially outwards. The free end portions of the packer slats are kept in their inactive retracted position with the slat bodies biased radially inwards by means of the movable latching and releasing means. Owing to their springy nature the slat elements tend to swing or spring radially outwards with their free outer end portions sealingly engaging the opposite borehole wall upon release of the latching and releasing means.
The blowout preventer also comprises an activator means for activating the packer slat latching and releasing means, the latter advantageously being in the form of an annular latching or retaining part carried by a sleeve-like part sliding on the packer tubular body between a latching and a releasing position. When the latching and releasing means slides along the tubular body to release the slat ends, the radially outer openings of the inlet ports that were covered by a portion of the slats are uncovered to permit fluidflow into the passageways in the tubular body of the blowout preventer, and out therefrom through the nozzles in the outer ends of the passageways.
By adjusting the pump flow rate the downhole pressure can be adjusted to a safe level avoi
Bastianelli John
Rogalandsforskning
Shaver Kevin
Wenderoth , Lind & Ponack, L.L.P.
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