Patent Application
20120298781
The field of the invention is nozzles used in formation fracturing and more particularly nozzles used to enhance the initiation and propagation of formation fractures by adding a feature of continuing extension during fracturing and diverting fracture flow away from extended portions and into portions still capable of further extension.
Fracturing in open hole is a complex subject and has been studied and written about by various authors. Whether using explosives or fluid jets one of the problems with the initiated fractures is in the way they propagate. If the propagation pattern is more tortuous as the fractures emanate from the borehole an undesirable condition called screenout can occur that can dramatically decrease the well productivity after it is put on production.
Hydraulically fracturing from any borehole in any well orientation is complex because of the earth's ambient stress field operating in the area. This is complicated further because of the extreme stress concentrations that can occur along the borehole at various positions around the well. For instance, there are positions around the borehole that may be easier to create a tensile crack than other positions where extreme compressive pressures are preventing tensile failure. One way that has been suggested to minimize this condition is to use jets that create a series of fan shaped slots in the formation with the thinking that a series of coplanar cavities in the formation will result in decreased tortuosity. This concept is discussed in SPE 28761 Surjatmaadja, Abass and Brumley Elimination of Near-wellbore Tortuosities by Means of Hydrojetting (1994). Other references discus creating slots in the formation such as U.S. Pat. Nos. 7,017,665; 5,335,724; 5,494,103; 5,484,016 and US Publication 2009/0107680.
Other approaches oriented the jet nozzles at oblique angles to the wellbore to try to affect the way the fractures propagated. Some examples of such approaches are U.S. Pat. Nos. 7,159,660; 5,111,881; 6,938,690; 5,533,571; 5,499,678 and US Publications 2008/0083531 and 2009/0283260.
Other approaches involved some form of annulus pumping in conjunction with jet fracturing. Some examples of this technique are U.S. Pat. Nos. 7,278,486; 7,681,635; 7,343,974; 7,337,844; 7,237,612; 7,225,869; 6,779,607; 6,725,933; 6,719,054 and 6,662,874.
Pulsing techniques have been used in jet drilling or in conventional drilling to pulse the bit nozzle flow as described in U.S. Pat. Nos. 4,819,745 and 6,626,253. Also related to these applications is SPE paper 130829-MS entitled Hydraulic Pulsed Cavitating Jet Assisted Deep Drilling: An Approach to Improve Rate of Penetration.
Jets mounted to telescoping assemblies have been suggested with the idea being that if the jet is brought closer to the formation the fracturing performance will improve. This was discussed in U.S. application Ser. No. 12/618,032 filed Nov. 13, 2009 called Open Hole Stimulation with Jet Tool and is commonly assigned to Baker Hughes Inc. In another variation of telescoping members used for fracturing the idea was to extend the telescoping members to the borehole wall and to set spaced packers in the annulus so as to avoid the need to cement and to allow production from the telescoping members after using some of them to initially fracture the formation. This was discussed in U.S. application Ser. No. 12/463944 filed May 11, 2009 and entitled Fracturing with Telescoping Members and Sealing the Annular Space and is also commonly assigned.
The present invention seeks to improve the extent of the fracturing that is accomplished beyond the initial formation perforation that is initiated explosively or with a direct impingement nozzle. This is accomplished with a telescoping assembly that directs jet streams from each stage. As the largest stage extends fully the flow of fracturing fluid to it is cut off and redirected to the smaller stages that it surrounds. In turn as the perforation grows from jet impingement some portion of the assembly can continue to extend to keep the gap distance from the nozzle face to the depth of the perforation to a minimum so as to improve the starting and propagating of fractures.
A fracturing jet nozzle assembly has nested telescoping sections that each has nozzles in them. The outermost stage makes for a large perforation as it and the adjacent stages begin extension. As the stage adjacent the outermost stage continues to extend into the perforation and reaches maximum extension the nozzles in the outermost stage are cut off from fracturing fluid flow and that flow is in turn redirected to the remaining stages that have not yet fully extended. The innermost stage preferably does not get cut off from jet fluid flow even at its full extension.
The present invention deals with this issue in a way that allows the nozzle to telescope as the perforation gets larger during the fracturing process. Using nozzles in the adjacent outer stages to enlarge the perforation to make further stage extension possible the apparatus also cuts off jet fluid to fully advanced stages as the next stage inboard goes to full extension. In this manner the outermost stage with jet flow makes the perforation larger to enable the adjacent stages that are inboard to advance as the perforation grows. As the next stages advance they also direct a larger flow to the now enlarged perforation to further aid the stages that have not yet fully advanced to further do so. The innermost stage that is generally coincident with the axis of the assembly sees a continuous flow to full extension without flow cutoff. The detailed explanation for how the above is accomplished is illustrated in detail below with regard to
The inner stage 72 has a front face 88 and a rear segmented flange 90 that has alternating tabs 92 and gaps 94 as seen in
Variations on the preferred embodiment are also envisioned. While three stages are described, two or more stages can be used. The nozzle pattern on any specific stage can have unequal spacing on a common radius or use of a single or multiple rows of nozzles or a random placement of the nozzles on any particular stage. The stages can be built out of a hardened material or the nozzles themselves can be hardened inserts in a stage built out of a softer material where the inserts are supported in the outer wall of the stage or with a flange internally to the stage to hold the insert in position with flow running through the insert. While the use of tabs that advance to cover the nozzles in the surrounding stage are preferred other devices that shut off flow to an exterior stage when the next adjacent stage gets to maximum extension are also contemplated. While the interior stage 72 is illustrated with a single nozzle 74 with a common axis to the axis of the other stages, it can also have multiple nozzles in an ordered or random spacing. While the nozzles in the various stages have been shown on exes that are parallel to the axis of the overall assembly, the orientation of the nozzle axes can be askew in more than a single plane or one plane to the axis of the assembly so that the nozzle axis may not even intersect with the axis of the assembly so as to cause one or more of the stages to rotate as the jet stream exits so as to deliver a pulsating impact to a particular location in the perforation to enhance the initiation and propagation of fractures from the perforation. Ratchet devices can be used to prevent any retraction of stages after extension.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.
