Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
2000-04-21
2001-06-12
Tsay, Frank (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S117500
Reexamination Certificate
active
06244339
ABSTRACT:
FIELD OF INVENTION
The invention relates to apparatus for and a method of drilling and production of a lateral well, and more particularly but not exclusively to the drilling and production of multi-lateral wells from a single mother well.
BACKGROUND OF THE INVENTION
The demand for multi-lateral drilling is increasing as more horizontal wells are being used on development wells to improve reservoir drainage and productivity. Drilling multi-lateral wells provides the advantage that the productivity or recovery of hydrocarbons from a formation can be improved by drilling a number of branch wells, all of which feed a mother well. Drilling multi-lateral wells can also reduce the platform cost by reducing the number of slots required to exploit a given hydrocarbon formation.
In order to drill a multi-lateral well, it is known to mill a window in the casing of the mother well, and deflect a drilling tool through the window to drill the lateral well by using a deflection tool which is commonly known as a “whipstock”.
By using this conventional technique, lateral wells can be completed “barefoot” (that is no loner pipe is used to case off the lateral well). Barefoot completions are only satisfactory where the formations drilled are suitable for such a completion (such as a limestone formation).
However, where sands are encountered in the pay zone of the formation, which is very common, the well must be cased and perforated to allow production of the hydrocarbons to take place without the lateral well “sanding off” or collapsing. In addition, many wells are geo-pressured which requires that the well is cased off and a pressure seal is effected at the junction of the lateral well liner and the mother well casing. Conventionally, cement is used to effect the pressure seal at the junction. However, cement seals may be relatively unreliable or create a relatively low pressure resistant seal.
In order to insert casing into the lateral well, several techniques are known. For instance, it is known to have a casing with a section of side wall which incorporates an outlet tube and which is pivotably coupled to the casing by a hinge mechanism. The pivotable section is moveable from a first position in which the outer surface of the casing is cylindrical and the inner bore of the casing is substantially narrowed by the outlet tube; and a second position in which the inner bore of the casing is cylindrical and the outlet tube protrudes from the casing.
However, this type of arrangement has the disadvantage that the diameter of the lateral well is limited with respect to the diameter of the mother well due to the pivotable outlet tube arrangement, as it must be contained within the main casing during installation.
A further disadvantage in the drilling of lateral wells from a mother well is that the maximum bend for conventional drilling assemblies is about 15 degrees per hundred feet. Thus, the initial (maximum) deviation angle of a lateral well from the mother well is limited to approximately 4° to 5°. This angle limitation therefore requires a large window in the side of the casing through which the drilling assembly will exit the casing, and this window may typically be 12 feet long.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided apparatus for drilling a second borehole from a first borehole comprising a first casing section and a second casing section, the first and second casing sections being rotatably coupled to each other by a rotatable joint, such that the first and second casing sections may be rotated about the joint from a first position, in which the longitudinal axes of the first and second casing sections are substantially coincident, to a second position in which the longitudinal axis of the first and second casing sections are at a mutually oblique angle, and such that the longitudinal axis of one of the casing sections extends through an aperture in the other casing section when the casing sections are in the second position.
Preferably, the plane of the rotatable joint is at an oblique angle to the longitudinal axis of the casing string adjacent the joint.
In accordance with a second aspect of the present invention, a method of drilling a second borehole from a first borehole comprises inserting a casing string comprising a first casing section and a second casing section into the first borehole with the longitudinal axes of the first and second casing sections substantially coincident, rotating the first and second casing sections relative to each other to move the second casing section to a position in which the longitudinal axis of the second casing section is at an oblique angle to the longitudinal axis of the first casing section; inserting a drilling device into the first casing section and causing it to pass into the second casing section, and drilling the second borehole from the second casing section.
A liner can be subsequently inserted into the second borehole and coupled to the second casing section.
Preferably, the apparatus further comprises a third casing section adapted to be inserted through the said one casing section into the other casing section and exit the other casing section through the aperture in the other casing section when the casing sections are in the second position. Preferably, the third casing section is inserted before the second borehole has been drilled typically after the installations of the first and second casing sections.
Typically the aperture in the second casing section and/or the aperture in the third casing section (if present) may be provided with sealing means. The sealing means may be provided by an elastomeric seal, a metal to metal seal or a seal which is energised when the liner is inserted into the second borehole.
Preferably, the method further includes the initial step of under-reaming a section of the first borehole at which the apparatus is to be located prior to inserting the apparatus into the first borehole.
Preferably, the drilling device is diverted into the second casing section by a diversion device, such as a whipstock, located in the third casing section. Typically, the diversion device is removable from the third casing section after the second borehole has been drilled.
REFERENCES:
patent: 5398754 (1995-03-01), Dinhoble
patent: 5411082 (1995-05-01), Kennedy
patent: 5427177 (1995-06-01), Jordan, Jr. et al.
patent: 5458209 (1995-10-01), Hayes et al.
patent: 5579829 (1996-12-01), Comeau et al.
patent: 6138761 (2000-10-01), Freeman et al.
patent: WO 96 23953 (1996-08-01), None
Howrey Simon Arnold & White , LLP
Tsay Frank
Weatherford / Lamb, Inc.
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