This invention relates, in general, to equipment and techniques utilized in conjunction with operations performed in relation to subterranean wells and, in particular, to a method for generating discrete fracture initiation sites and propagating dominant planar fractures therefrom.
Without limiting the scope of the present invention, its background will be described in relation to reservoir stimulation operations performed from a wellbore that traverses a hydrocarbon bearing subterranean formation, as an example.
It is well known in the well drilling and completion art that hydraulic fracturing of a hydrocarbon bearing subterranean formation is sometimes desirable to increase the permeability of the reservoir formation in the production interval or intervals adjacent to the wellbore by performing a stimulation operation. According to conventional practice, a fracture fluid such as water, oil, oil/water emulsion, gelled water, gelled oil, carbon dioxide and nitrogen foams, water/alcohol mixtures or the like is pumped down the work string with sufficient volume and pressure to open the desired fractures in the reservoir formation. In addition, during certain stages of the fracturing operation, the fracture fluid may carry a suitable propping agent, such as sand, gravel or engineered proppants, which are deposited into the fractures and serve the purpose of holding the fractures open following the fracturing operation.
During the fracturing operation, the fracture fluid must be pumped into the formation at a flow rate that is sufficiently high enough to generate the required pressure to fracture the reservoir formation and allow the entrained proppants to enter the fractures and prop the formation structures apart. As such, the proppants in the fractures create highly conductive paths from the reservoir formation to the wellbore. Importantly, the success of the fracturing operation is dependent upon the ability to inject large volumes of hydraulic fracture fluid into desired locations within the reservoir formation at a high pressure and high flow rate.
It has been found, however, that it is difficult to achieve the desired stimulation in certain completions, such as long horizontal completions, due to uncertainty regarding fracture initiation and fracture propagation in the reservoir formation after performing conventional perforating operations. Accordingly, a need has arisen for an improved perforating and fracturing method that is operable to create communication tunnels through the casing and into the reservoir formation for fluid production. A need has also arisen for such an improved perforating and fracturing method that is operable to reduce the uncertainty regarding fracture initiation and fracture propagation in the reservoir formation.
The present invention disclosed herein is directed to an improved perforating and fracturing method that is operable to create communication tunnels through the casing and into the reservoir formation for fluid production. In addition, the improved perforating and fracturing method of the present invention is operable to reduce the uncertainty regarding fracture initiation and fracture propagation in the reservoir formation.
In one aspect, the present invention is directed to a method for performing a downhole perforating and fracturing operation from a wellbore positioned within a subterranean formation. The method includes locating a perforating gun string within the wellbore, detonating a first perforating gun to create a first discrete fracture initiation site in the formation, repositioning the perforating gun string within the wellbore, detonating a second perforating gun to create a second discrete fracture initiation site in the formation, pumping a fracture fluid into the wellbore and propagating a single dominant planar fracture from each of the discrete fracture initiation sites.
The method may also include setting a plug in the wellbore between a first stage and a second stage of the operation prior to detonating the first perforating gun, locating a plurality of perforating guns within the wellbore and for each undetonated perforating gun in the perforating gun string, repositioning the perforating gun string within the wellbore and detonating one of the undetonated perforating guns to create a sequence of discrete fracture initiation sites in the formation. In addition, the method may include detonating a focused explosive element, detonating a collection of shaped charges, detonating at least two shaped charges focused at one of the discrete fracture initiation sites, detonating at least three shaped charges focused at one of the discrete fracture initiation sites, detonating a circumferentially extending linear shaped charge or detonating a pair of oppositely disposed circumferentially extending linear shaped charges.
In another aspect, the present invention is directed to a method for performing a downhole perforating and fracturing operation from a wellbore positioned within a subterranean formation. The method includes locating a perforating gun string having a plurality of perforating guns within the wellbore, detonating a first perforating gun to create a first discrete fracture initiation site in the formation, for each undetonated perforating gun in the perforating gun string, repositioning the perforating gun string within the wellbore and detonating one of the undetonated perforating guns to create a sequence of discrete fracture initiation sites in the formation, pumping a fracture fluid into the wellbore and propagating a single dominant planar fracture from each of the discrete fracture initiation sites.
In a further aspect, the present invention is directed to a method for performing a downhole perforating and fracturing operation from a wellbore positioned within a subterranean formation. The method includes locating a perforating gun string having a plurality of perforating guns within the wellbore, setting a plug in the wellbore between a first stage and a second stage of the operation, for each perforating gun in the perforating gun string, repositioning the perforating gun string within the wellbore and detonating one of the perforating guns to create a sequence of discrete fracture initiation sites in the formation, pumping a fracture fluid into the wellbore and propagating a single dominant planar fracture from each of the discrete fracture initiation sites.
For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:
While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention.
Referring initially to
In the illustrated embodiment, a workstring 24 has been deployed within wellbore 12 via a wireline. Even though
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It should be noted by those skilled in the art that the use of directional terms such as above, below, upper, lower, upward, downward, left, right, uphole, downhole and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure, the uphole direction being toward the surface of the well and the downhole direction being toward the toe of the well.
Referring now to
The creation of discrete fracture initiation sites 42, 44, 46, 48, 50, 52 provide a high level of certainty regarding the location of the fractures created during a subsequent hydraulic fracturing operation. This is achieved through the use of the perforating guns and perforating method of the present invention. For example, compared to conventional spiral pattern perforating guns, wherein the typical perforating interval may be between one and six feet, the perforating guns of the present invention form a much shorter perforating interval on the order of a few inches. In addition, instead of having a several foot long pattern of perforations at, for example, 60 degrees spiral increments, the perforating guns of the present invention form only a few or even a single perforation in each perforating interval.
This improved perforating technique of the present invention eliminates the creation of competing fractures that are typically present when conventional spiral pattern perforating guns are used. These competing fractures can divert fluid away from a dominant fracture and reduce stimulation effectiveness. In addition, this improved perforating technique of the present invention reduces the near wellbore tortuosity that is created when fluid attempts to exit a wellbore through a several foot long spiral pattern of small perforations. Further, this improved perforating technique of the present invention reduces the required treating pressure during the fracturing operation. Since all the perforations shot from conventional spiral pattern perforating guns commonly do not allow flow, the treating pressure is typically higher than predicted because the flow area is reduced by one or more perforations being closed or blocked, thereby increasing perforation friction pressure and reducing the capability to place proppant. As such, by injecting all the fluid entering each fracture through a single entry point instead of multiple, tortured paths, a single dominant planar fracture can be created from each discrete fracture initiation site. The single dominant planar fractures created from discrete fracture initiation sites can be modeled more accurately than conventional fractures, which leads to better estimates of production from the treated reservoir and a better overall understanding of the fracturing process and fractured formation.
Following the perforating operation, workstring 24 may be retrieved to the surface. A fracture fluid 54 may now be pumped downhole into wellbore 12. Fracture fluid 54 may be of any suitable type such as water, oil, oil/water emulsion, gelled water, gelled oil, carbon dioxide and nitrogen foams, water/alcohol mixtures or the like. The fracture operation preferably begins with the pumping of a pad fluid followed by a fluid carrying a propping agent, such as sand, gravel or engineered proppant. The fracture fluid is pumped downhole with sufficient flowrate and pressure to open the desired fractures in formation 18. Importantly, as discussed above, due to the creation of discrete fracture initiation sites 42, 44, 46, 48, 50, 52 within formation 18, entry of fracture fluid 54 into formation 18 and propagation of fracture fluid 54 through formation 18 is controlled and predictable. Specifically, as illustrated, discrete fracture initiation sites 42, 44, 46, 48, 50, 52 enable the creation and propagation a single dominant planer fracture 56, 58, 60, 62, 64, 66 from each discrete fracture initiation site 42, 44, 46, 48, 50, 52, as best seen in
In the illustrated embodiment, perforating guns 28, 30, 32, 34, 36, 38 are depicted as triple jet perforating guns having focused shaped charges that form three openings through casing 20. The three jets then converge in formation 18 to create a discrete fracture initiation site 42, 44, 46, 48, 50, 52 within formation 18. Forming discrete fracture initiation sites as described in the present invention reduces the uncertainty associated with fracture initiation and fracture propagation in formation 18 as compared with conventional perforating techniques. For example, cluster type perforating guns are typically used to perforate the casing in order to form the required communication tunnels through the casing and into the formation for fluid production. These perforating guns commonly have a plurality of shaped charge positioned in a spiral pattern or inline pattern with a desired number of shots per foot to enable a suitable production rate.
When detonated, these perforating guns form a plurality of individual perforations that extend through the casing into the formation. Unfortunately, due to the number and location of these perforations, when fracture fluid is later pumped into the wellbore, a cluster of fracture initiation points are present in the formation. This cluster of fracture initiation points hinders the creation and propagation of a dominant planer fracture. As such, an unacceptable level of uncertainty is associated with fracture initiation and fracture propagation when conventional perforating techniques are employed. Unlike conventional perforating guns, the perforating guns of the present invention create discrete fracture initiation sites within the formation. As illustrated in the present embodiment, convergence of the multiple perforating jets in the formation creates the desired discrete fracture initiation sites.
Referring now to
Preferably, housing 112 contains a detonator (not pictured) that is coupled to an electrical energy source. The detonator may be any type of detonator that is suitable for initiating a detonation in a detonating cord 114. Detonating cord 114 is operably coupled to the initiation ends of shaped charges 102, 104, 106 allowing detonating cord 114 to initiate the high explosive within shaped charges 102, 104, 106. The three shaped charges 102, 104, 106 may be referred to as a focused explosive element and will generally be referred to as a collection of shaped charges. In the illustrated embodiment, shaped charges 102, 104, 106 are positioned axially relative to one another such their discharge ends generally point in the same circumferential direction of housing 112. Accordingly, as used herein the term axially oriented will be used to describe the relationship of shaped charges within a collection of shaped charges wherein adjacent shaped charges are generally axially displaced from one another and generally point in the same circumferential direction.
In the illustrated embodiment, shaped charges 102, 104, 106 are oriented to converge toward one another. For example, center shaped charge 104 is oriented substantially perpendicular to the axis of housing 112 while outer shaped charges 102, 106 are oriented to converge toward center shaped charge 104. In one preferred orientation, the angle of convergence between adjacent shaped charges 102, 104, 106 is between about 10 degrees and about 20 degrees. Other preferred orientations include angles of convergence between about 5 degree and about 40 degrees. It should be noted that the desired angle of convergence for a particular perforating gun assembly being used to perforate a particular wellbore will be dependent on a variety of factors including the size of the shaped charges, the diameter of the perforating gun assembly and wellbore casing, the desired depth of penetration into the formation and the like. Optional attenuating barrier such as attenuating barrier 116 between shaped charges 102, 104 and attenuating barrier 118 between shaped charges 104, 106 may be used to prevent fragments of the outer two shaped charges from interfering with the jet development of the center shaped charge.
Even though
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Even though the shaped charges depicted in
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While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.
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Number | Date | Country | |
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20130032347 A1 | Feb 2013 | US |