Patent Application
20110308803
The field of the invention is jet fracturing in open hole and more particularly initiation of fractures with extending members while propagating the initiated fractures with pressurized fluid delivered into the open hole fractures through a jet tool or/and into the surrounding annulus.
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.
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. 12/463,944 filed May 11, 2009 and entitled Fracturing with Telescoping Members and Sealing the Annular Space and is also commonly assigned.
The present invention uses telescoping members and drives them out against the borehole wall with sufficient force to mechanically initiate the fracture. The telescoping members can be driven out by flowing through them or displacing them forcefully from within a bottom hole assembly using mechanical force such as a wedge device or a swage that also affords the option of expanding the diameter of the tubular housing in which the telescoping members are located. The telescoping members can have a constriction in them to function as the jet or simply a through passage that will act as a fluid jet when sufficient fluid volume with enough differential pressure is delivered through the jet nozzles. In another embodiment the positioning of the jets around a housing so that there is at least one nozzle within 22.5° in either of two opposed directions from the location of where the circumferential stresses are expected to the least compressive stress concentration which is the same as the most tensile stress concentration so that the fractures formed are less tortuous and subsequent production is enhanced. The jets can be disposed in a single or multiple rows depending on the telescoping member size and the borehole diameter. By getting at least one nozzle close to the more stressed location in the formation at the borehole the fracture initiated and propagated will be less tortuous. These and other benefits of the present invention will be more readily understood by those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is determined by the appended claims.
A series of jet nozzles have a telescoping structure designed to impact the borehole wall and initiate a fracture. The nozzles can be extended through fluid pumped through them or with some mechanical force from within the bottom hole assembly. The leading ends of the telescoping assembly can be sharp and hardened to facilitate the initiation of a formation fracture in an open hole. The telescoping structures can be disposed in a single or multiple rows with the circumferential spacing being such that each telescoping structure is designed to cover a target circumferential distance of 45 degrees or less so that jetted fluid from at least one jet will be within 22.5 degrees of a location of maximum formation stresses to reduce the tortuosity of the created fractures from jetting through the nozzles with possible enhancement of the fracturing from added annulus pressure.
In one embodiment a jet nozzle 10 that can be one of many is made of several telescoping components such as 12 and 14 that are nested. There can be more than two nested components depending on the degree of extension needed to engage the wellbore wall 16. The preferred application is in open hole. The innermost nested component that will extend the furthest and forcibly strike the wellbore wall 16 is designed to initiate fractures from impact. It can have one or more sharp points 17 at the leading end to break and penetrate into the formation. The leading end can also be hardened to prevent the sharp points on the leading end from breaking off when driven into the formation 18. The telescoping elements 12 and 14 define a passage that serves as the jet or alternatively there can be an orifice or other constriction to create not only a jet force to fracture the formation further but it can also initially accelerate members 12 and 14 toward the wellbore wall 16 to start the fractures. The telescoping members 12 and 14 can be ratcheted together to allow them to extend radially to hit the wellbore wall 16 and to hold them extended and prevent collapse back into the housing 20. The pressure drop through the jet nozzle assembly causes the telescoping parts such as 12 and 14 to move against the borehole wall 16 with great force to initiate a fracture. Alternatively the jets 10 can be initially obstructed so that pressure delivered behind them drives the telescoping members 12 and 14 out and the plugs can then be blown out or dissolved or removed by any other means. It should be noted that extension of the telescoping members is for the purpose of impact against the wellbore wall 16 and that sealing against the wellbore wall is not required. It is the wall impact that is intended to initiate the fracture using the sharp leading end at 17. Alternatively the leading end can be hardened but blunt and the wall impact used to initiate the fracture at the wellbore wall 16. Subsequently flow commences and enters the fracture initiated by the sharp points 17 so that the fracture opens further and propagates away from the borehole. Continued pressure application with some flow as the fractures enlarge coming through the telescoping components 12 and 14 has the effect of extending the fractures further away from the borehole and holding them open as an optional proppant is delivered to hold the fractures open even when the pressure through the jets is backed off. As another option the telescoping members can have screens in them and can be subsequently used to produce the formation 18.
The fractures 22 after being initiated with the telescoping components 12 and 14 can be extended by pressure delivered through the housing 20 or around the outside of it in an annulus 24 from the surface.
In another embodiment the location of the jets 10 on the body 20 enhances the quality of the fractures created by reducing tortuosity. The jets can be of the telescoping design as shown in
The features of the telescoping jets that initiate the fractures by penetrating the formation as described above can also be used in tandem with the spacing of the jets to obtain less tortuosity as also described above.
Those skilled in the art will appreciate that the present invention initiates fractures mechanically in a jet fracturing environment so that the initiated fractures are further propagated by fluid pressure delivered through the jets and/or the annulus surrounding the jet housing. Apart from the unique way of initiating the fractures the present invention associates jet placement with the zones of the least compressive stress concentration in the formation that are located a distance of at least a diameter of the wellbore into the formation. By disposing at least one jet no further than 22.5 degrees from the least compressive stress concentration, the resulting tortuosity is greatly reduced. Spacing the jets 10 in single or multiple rows in a nested arrangement where the circumferential distance between adjacent jets is about 45 degrees achieves this result. In more general terms the present invention recognizes the relation between the orientation of the jets toward a lower compressive stress concentration zone to reduce fracture tortuosity, depending on the deviation of the borehole for a given stress environment.
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.
