Apparatus and method for forming a window or an outline thereof in the casing of a cased wellbore

Abstract: Apparatus for forming a window or the outline of a window in the casing of a cased wellbore comprises thermal means for forming a window or an outline of a window in said casing and locating means for positioning the thermal means in the casing. The thermal means comprises an oxidation chamber (561) having at least one outlet (562), arranged so that reaction materials (565) in the oxidation chamber react to produce sufficient heat to cause a heat jet to exit through the at least one outlet.

Description: This invention relates to an apparatus and a method for forming a window or the outline of a window in the casing of a cased wellbore. The practice of producing oil from multiple radially dispersed reservoirs, through a single primary wellbore has increased dramatically in recent years. To facilitate this, "kick-off" technology has been developed. This technology allows an operator to drill a generally vertical well and then drill one or more angled or horizontal holes off of that well at chosen depth(s). Because the initial vertical wellbore is often cased with a string of tubular casing, a "window" must be cut in the casing before drilling the "kickoff". In certain prior art methods windows are cut using various types of milling devices in combination with a whipstock. In these methods one or more "trips" of the drill string are needed. Rig time is very expensive and multiple trips take time and add to the risk that problems will occur. Considerable effort has been expended in trying to reduce the overall time taken in forming a window in the casing and the present invention addresses this problem. US-A-2758543 describes a cutting apparatus for forming the outline of a window in casing. The apparatus comprises an elongated explosive charge forming the outline of the desired window. The charge is placed in a groove in a carrier cylinder. The charge itself includes an elongate cavity used to direct the force of the explosion. According to one aspect of the present invention there is provided an apparatus for forming a window or the outline of a window in the casing of a cased wellbore, said apparatus comprising thermal means for forming a window or an outline of a window in said casing and locating means for positioning said explosive means in said casing, the thermal means comprising an oxidation chamber, characterised in that the oxidation chamber is provided with at least one outlet, arranged so that reaction materials in the oxidation chamber react to produce sufficient heat to cause a heat jet to exit through the at least one outlet, the outlet directing said heat jet. Whilst the present invention is primarily concerned with the formation of a window for sidetracking operations the window could be formed for other purposes. It should be noted that the present invention is concerned with the formation of a window in a casing and this should be constructed against the prior art process of perforating a casing in which a multiplicity of random small holes are formed in a pipe by detecting an explosive charge therein. Typically, a window will have a cross-sectional area of at least 75cm 2 , preferably at least 320cm 2 , and generally at least 635cm 2 . In accordance with a second aspect of the present invention there is provided a method of forming a window or the outline of a window in the casing of a cased wellbore, comprising: introducing an oxidation chamber having at least one outlet into the interior of the casing; causing reaction materials to react in the oxidation chamber so that they undergo a severe oxidation reaction producing sufficient heat to cause a heat jet to exit the oxidation chamber through the outlet; and directing the heat jet through the outlet towards the casing. Further features of the invention are set out in the dependent claims. For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a side view of a wellbore window creation system according to the present invention. Fig. 1 shows an apparatus 500 with a hollow container 561 in which occurs a relatively severe oxidation reaction of materials 565 which produces sufficient heat so that a heat jet 564 exits from within the container 561 to openings or nozzles 562 and then to an outlet (or outlets) 563 from which the heat jet 564 is directed at a tubular member in which an opening is to be formed. The nozzles are optional and are used to increase exiting reaction product flow velocity. The oxidation reaction, in certain embodiments, may be any known thermitic or pyranol reaction; also suitable propellants, e.g. solid rocket propellants, may be used. The device may be used to create an initial opening, initial ledge or initial window in the tubular, or may be used to create a completed window through a tubular. The device may be used on, releasably connected to, or secured beneath a mill or mills to create the opening. The device may also be used on, used with, releasably connected to, or secured to or above, a whipstock, diverter, or weight member. The system of Fig. 1 may be reciprocated up or down and/or rotated or swivelled from side to side to form an opening of a desired longitudinal extent, desired lateral extent, and desired shape.

Claims: Apparatus (560) for forming a window or the outline of a window in the casing of a cased wellbore, said apparatus comprising: thermal means for forming a window or an outline of a window in said casing, the thermal means comprising an oxidation chamber (561) and locating means for positioning said thermal means in said casing, characterised in that the oxidation chamber (561) is provided with at least one outlet (563), arranged so that reaction materials in the oxidation chamber react to produce sufficient heat to cause a heat jet (564) to exit through the at least one outlet, the outlet directing said heat jet. Apparatus as claimed in claim 1, wherein the or each outlet (563) comprises a nozzle (562) for directing the heat jet towards the casing. Apparatus as claimed in claim 1 or 2, wherein the reaction materials are chosen so that the reaction is a thermitic or pyranol reaction. Apparatus as claimed in claim 1 or 2, wherein at least one of the reaction materials is a solid rocket propellant. A method of forming a window or the outline of a window in the casing of a cased wellbore, comprising: introducing an oxidation chamber (561) having at least one outlet (563) into the interior of the casing; causing reaction materials to react in the oxidation chamber so that they undergo a severe oxidation reaction producing sufficient heat to cause a heat jet (564) to exit the oxidation chamber through the outlet; and directing the heat jet through the outlet towards the casing. A method as claimed in claim 5, wherein the severe oxidation reaction is a thermitic or pyranol reaction. A method as claimed in claim 5, wherein the reaction materials are solid rocket propellants. A method as claimed in claim 5, 6 or 7, wherein the heat jet is directed towards the casing through a plurality of nozzles.

Inventors: HAUGEN DAVID MICHAEL, MCCLUNG GUY LAMONTE, HAUGEN, DAVID MICHAEL, MCCLUNG, GUY, LAMONTE
Applicants: WEATHERFORD LAMB, WEATHERFORD/LAMB, INC.
Application year: 1996
Main classification: E21B29
IPC codes: E21B29, E21B43