Forming perturbed in-line perforation pairs

Abstract

A bottom hole assembly includes a downhole conveyance that is extendable from a terranean surface, through a wellbore, and to a subterranean formation; and a perforating tool configured to couple to the downhole conveyance and create at least one pair of perforations. The at least one pair of perforations is arranged along a longitudinal direction of the wellbore such that a first perforation in the at least one pair of perforations is oriented at an azimuthal offset angle relative to a second perforation in the at least one pair of perforations.

Description

FORMING PERTURBED IN-LINE PERFORATION PAIRSCLAIM OF PRIORITY

[0001] This application claims priority7to U.S. Patent Application No. 18 / 642,400 filed onApril 22, 2024. the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] The present disclosure relates to forming perforations in oil and gas wells, and geothermal and CO2 injection (CCS) wells.BACKGROUND

[0003] In the oil and gas industry7, perforation jobs are performed across the pay zone to create a flow path from the formation into the wellbore. Perforation jobs can be performed using downhole perforating tools that include a perforation gun, an abrasive jet perforating tool, or similar type of tool. A perforating gun generally holds several explosive-shaped charges. The shaped charges can be configured to focus the explosive energy in a specific direction and create perforations through the casing and cement, penetrating into the surrounding formation. An abrasive jet perforating tool deploys high-pressure abrasive fluid jets to cut through the casing, cement and into the surrounding formations. In some cases, one- third of perforation clusters do not yield oil or gas. Knowing where to appropriately place perforations, determining the hydraulic fracturing stages and achieving desired perforation geometry still remains a challenge for the oil and gas industry.SUMMARY

[0004] The present disclosure describes methods, devices, systems and techniques for forming perturbed in-line perforation pairs.

[0005] In an example implementation, a bottom hole assembly includes a downhole conveyance that is extendable from a terranean surface, through a wellbore, and to a subterranean formation; and a perforating tool configured to couple to the downhole conveyance and create at least one pair of perforations. The at least one pair of perforations is arranged along a longitudinal direction of the wellbore such that a first perforation in the at least one pair of perforations is oriented at an azimuthal offset angle relative to a second perforation in the at least one pair of perforations.

[0006] In an aspect combinable with the example implementation, the azimuthal offset angle ranges between about 0 degree and about 60 degrees.

[0007] In an aspect combinable with the one. some, or all of the previous aspects, the azimuthal offset angle ranges between about 0 degree and about 20 degrees.

[0008] In an aspect combinable with the one, some, or all of the previous aspects, the azimuthal offset angle ranges between about 0 degree and about 180 degrees.

[0009] In another aspect combinable with one, some, or all of the previous aspects, a separation distance between the first and second perforations along the longitudinal direction of the wellbore is equal to or less than about 1 / 6 foot.

[0010] In another aspect combinable with one, some, or all of the previous aspects, the perforating tool includes a plurality7of shaped charges, and detonating directions of the shaped charges are phased at azimuthal angles smaller than about 60 degrees.

[0011] In another aspect combinable with one, some, or all of the previous aspects, the perforating tool includes a plurality of shaped charges, and detonating directions of the shaped charges are phased at azimuthal angles smaller than about 20 degrees.

[0012] In another aspect combinable with one, some, or all of the previous aspects, the at least one pair of perforations includes a first pair of perforations, the azimuthal offset angle is a first azimuthal offset angle of the first pair of perforations.

[0013] In another aspect combinable with one, some, or all of the previous aspects, the at least one pair of perforations includes a second pair of perforations, and the second pair of perforations is arranged along the longitudinal direction of the wellbore such that a first perforation in the second pair of perforations is oriented at a second azimuthal offset angle relative to a second perforation in the second pair of perforations.

[0014] In another aspect combinable with one. some, or all of the previous aspects, a spacing distance between the first pair of perforations and the second pair of perforations is equal to or larger than about 1 / 6 foot.

[0015] In another aspect combinable with one, some, or all of the previous aspects, the first azimuthal offset angle of the first pair of perforations is equal in magnitude to the second azimuthal offset angle of the second pair of perforations.

[0016] In another example implementation, a bottom hole assembly includes a downhole conveyance that is extendable from a terranean surface, through a wellbore, and to a subterranean formation; and a perforating tool configured to couple to the downhole conveyance and create a plurality of pairs of perforations. Each pair of perforations is arranged along a corresponding longitudinal direction of the wellbore such that a first perforation in each pair of perforations is oriented at a corresponding azimuthal offset angle relative to a second perforation in each pair of perforations. The corresponding azimuthal offset angle ranges between about 0 degree and about 60 degrees.

[0017] In an aspect combinable with the example implementation, the plurality of pairs of perforations has a same azimuthal offset angle.

[0018] In another aspect combinable with one, some, or all of the previous aspects, at least two of the pairs of perforations have different azimuthal offset angles.

[0019] In an aspect combinable with one, some, or all of the previous aspects, the azimuthal offset angle ranges between about 0 degree and about 20 degrees.

[0020] In another aspect combinable with one, some, or all of the previous aspects, at least two of the pairs of perforations are arranged along different azimuthal planes of the wellbore.

[0021] In another aspect combinable with one, some, or all of the previous aspects, the corresponding longitudinal direction of the wellbore include a direction parallel to a surface of the Earth.

[0022] In another aspect combinable with one, some, or all of the previous aspects, the plurality of pairs of perforations is spaced apart from one another at an unequal distance.

[0023] In another aspect combinable with one, some, or all of the previous aspects, a spacing distance between adjacent pairs of perforations is equal to or larger than about 1 / 6 foot.

[0024] In another example implementation, a method to form perforations includes positioning a perforating tool adjacent a subterranean formation within a wellbore: and operating the perforating tool to form a plurality of perforation clusters in the subterranean formation. At least one of the perforation clusters includes a pair of perforations arranged along a longitudinal direction of the wellbore. A first perforation in the pair of perforations isoriented at a corresponding azimuthal offset angle relative to a second perforation in each pair of perforations. A spacing distance between adjacent perforation clusters is larger than 1 / 6 foot.

[0025] In an aspect combinable with the example implementation, the corresponding azimuthal offset angle ranges between 0 degree and 60 degrees.

[0026] In an aspect combinable with one, some, or all of the previous aspects, the azimuthal offset angle ranges between about 0 degree and about 20 degrees.

[0027] In another aspect combinable with one, some, or all of the previous aspects the perforating tool includes a high-pressure coiled tubing jetting tool, a laser tool, or an abrasive jet perforating tool.

[0028] In another aspect combinable with one, some, or all of the previous aspects, the perforating tool includes a plurality of shaped charges.

[0029] In another aspect combinable with one, some, or all of the previous aspects, the perforating tool includes a high-pressure coiled tubing jetting tool, a laser tool, or an abrasive jet perforating tool.

[0030] In another aspect combinable with one. some, or all of the previous aspects, operating the perforating tool includes orienting detonating directions of the shaped charges at an azimuthal phase angle equal in magnitude to the azimuthal offset angle of the pair of perforations of a corresponding one of the perforation clusters.

[0031] In another aspect combinable with one, some, or all of the previous aspects, the azimuthal phase angle is smaller than 60 degrees.

[0032] In another aspect combinable with one, some, or all of the previous aspects, the azimuthal phase angle is smaller than 20 degrees.

[0033] In another aspect combinable with one, some, or all of the previous aspects, a separation distance between the first and second perforations of the pair of perforations along the longitudinal direction of the wellbore is equal to or less than 1 / 6 foot.

[0034] The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 is a schematic diagram of a hydraulically fractured wellbore with a bottom hole assembly.

[0036] FIGS. 2A through 2C illustrate schematic views of an example perturbed in-line perforation cluster.

[0037] FIGS. 2D and 2E illustrate schematic views of another example perturbed in-line perforation cluster with varying azimuthal offset angles.

[0038] FIGS. 3 A through 3C illustrate schematic views of an example pair of perturbed inline perforations in a perforation cluster.

[0039] FIG. 3D illustrates schematic views of two example pairs of perturbed in-line perforations in two perforation clusters.

[0040] FIG. 4A illustrates an example of transverse fractures orientations initiated from perturbed in-line perforation cluster as predicted by a numerical simulation.

[0041] FIG. 4B illustrates simulation results of fracture initiation pressures with the example perturbed in-line perforation and other configurations of perforation clusters.

[0042] FIG. 4C illustrates a lab example experimental result of a hydraulic fracture initiation in a block test with a helical perforation cluster.

[0043] FIG. 4D illustrates a lab example experimental result of a hydraulic fracture initiation in a perturbed in-line perforation cluster.

[0044] FIG. 4E illustrates a top view of the hydraulic fracture from the lab example experimental result of FIG. 4D.

[0045] FIG. 4F illustrates a plot of borehole pressures acquired during fracturing phases in the experiments described in FIGS. 4C and 4D.

[0046] FIG. 4G illustrates a schematic view of an example horizontal wells with an initiation of fractures near a water zone.

[0047] FIG. 5 illustrates a flow chart of an example process for creating one or more pair of perturbed in-line perforations.

[0048] It is to be understood that the various exemplary implementations shown in the figures are merely illustrative representations and are not necessarily drawn to scale.DETAILED DESCRIPTION

[0049] Perforating tools, e.g., perforating guns or abrasive jet perforating tools, are used in the oil and gas industry for creating perforation cluster in well casings and surrounding formations. Abrasive jet perforating tool includes nozzles that direct a mixture of high-pressure fluid and abrasive particles toward the target area. In operation, the nozzles are often placed in a location in the wellbore facing the target at a fixed standoff distance. Perforating guns can include shaped charges and a perforating gun body. Shaped charges are positioned at specific angles within the gun body and configured to direct high-pressure and high-velocity' jets of metal particles toward the well casing and the surrounding rock formation. Abrasive jet perforating tools, with their high fluid flux combined with abrasive particles, offer the advantage of generating perforations of large diameters and free of compaction zones, compared to perforating guns. On the other hand, the perforating guns can create deeper perforations.

[0050] The geometry of perforation cluster plays a key role in initiating fractures in the formations at reasonably practical pressures. The geometry of the perforation cluster includes diameter, depth, spacing, azimuth with respect to the borehole / in-situ stresses and / or configuration of perforations. The perforation cluster can have in-plane perforation configuration which includes several perforations in the same plane transverse to the wellbore. The perforation cluster can also have an in-line configuration where all perforations are arranged in the same longitudinal plane but spaced along a straight line on the wellbore surface and oriented towards the same azimuthal direction. Additional configuration of perforation cluster includes a helical configuration, where perforations are phased azimuthally in an increment of 60 degree and arranged in different transverse planes.

[0051] This disclosure describes at least one pair of perturbed in-line perforations formed by a bottom hole assembly. In some aspects, the bottom hole assembly includes a downhole conveyance that is extendable from a terranean surface, through a wellbore, and to a subterranean formation. A perforating tool is configured to couple to the dow nhole conveyance and create at least one pair of perforations. The at least one pair of perforations is arranged along a longitudinal direction of the wellbore such that a first perforation in the at least one pair of perforations is oriented at an azimuthal offset angle relative to a second perforation in the at least one pair of perforations.

[0052] Implementations of the present disclosure can provide one or more of the following technical advantages. For example, the techniques described herein can create perforationclusters where each cluster is comprised of a pair of perturbed in-line perforations (two perforations offset by a small azimuthal angle and separated by a small distance along wellbore axis). In example implementations, the perforations in a cluster are spaced along the wellbore axis, e.g., the longitudinal direction of the wellbore, and extend radially into the formation at varied azimuthal directions w ithin a small range of angles with respect to the certain principal azimuthal orientation. This perturbed in-line pair configuration enables the initiation of transverse hydraulic fractures at a lower fracture initiating pressure (FIP) and facilitates further fracture growth under reduced hydraulic pressure. The transverse hydraulic fracture is a preferred orientation in multiple stage fracturing (MSF) stimulation of horizontal well, as the transverse hydraulic fracture can be close to the preferred fracture plane and, when repeated at multitude of wellbore depths, yield larger reservoir contact area. Moreover, utilizing perturbed in-line pair configurations allow s for fracture initiation along the direction of the perforation or in a direction closely aligned with it, thereby offering control over fracture direction by manipulating the perforation orientations. This perturbed in-line pair configuration can be implemented using various commercially available downhole tools, e.g., perforation guns or abrasive jet perforating tools. In contrast to helical configuration where perforation orientations span a complete circle of 360 degrees, perforations in a perturbed in-line pair cluster are directed within a narrow azimuthal range with respect to the principal orientation, thus allowing realization of equal standoff distances between individual charges and casing. Equal standoff distances can provide desired consistent perforation diameters, enhancing operational efficiency and wellbore performance.

[0053] FIG. 1 is a schematic diagram of a wellbore system 110 that includes a hydraulically fractured wellbore 120 with a bottom hole assembly. Generally, FIG. 1 illustrates a portion of one implementation of the wellbore system 110 in which wellbore 120 is formed into a naturally fractured subterranean formation (or reservoir) 140 for the production of one or more hydrocarbon fluids to a terranean surface 112 (through the wellbore 120 and, if used, one or more wellbore tubular strings). Fractured subterranean formation 140 that holds the hydrocarbon fluid(s) can be present beneath several other formation rock layers. The formation 140 can include a primary porous medium of the formation rock. An irregular system of microscopic fractures and small cavities can be typically present in the primary porous rock medium. Natural fractures 175 in the formation 140 can also be present across a wide range of scale, ranging from microfractures to extensive fractures or faults of thousands of meters.

[0054] As shown, the wellbore system 110 accesses a subterranean formation 140 that provides access to hydrocarbons located in such subterranean formation 140. A drillingassembly (not shown) may be used to form the wellbore 120 extending from the terranean surface 112 and through one or more geological formations in the Earth. One or more subterranean formations, such as subterranean formation 140, are located under the terranean surface 112. As will be explained in more detail below, one or more wellbore casings, such as an intermediate casing 130 and production casing 135, may be installed in at least a portion of the wellbore 120. In example implementations, a drilling assembly used to form the wellbore 120 may be deployed on a body of water rather than the terranean surface 112. For instance, in example implementations, the terranean surface 112 may be an ocean, gulf, sea, or any other body of water under which hydrocarbon-bearing formations may be found. In short, reference to the terranean surface 112 includes both land and water surfaces and contemplates forming and developing one or more wellbore systems 110 from either or both locations.

[0055] In example implementations of the wellbore system 110, the wellbore 120 may be cased with one or more casings. As illustrated, the wellbore 120 includes a conductor casing 125, which extends from the terranean surface 112 shortly into the Earth. A portion of the wellbore 120 enclosed by the conductor casing 125 may be a large diameter borehole. Additionally, in example implementations, the wellbore 120 may be offset from vertical (for example, an inclined wellbore). Even further, in example implementations, the wellbore 120 may be a stepped wellbore, such that a portion is drilled vertically downward and then curved to a substantially horizontal wellbore portion. Additional substantially vertical and horizontal wellbore portions may be added according to. for example, the ty pe of terranean surface 112, the depth of one or more target subterranean formations, the depth of one or more productive subterranean formations, or other criteria.

[0056] Downhole of the conductor casing 125 can be the intermediate casing 130. The intermediate casing 130 may enclose a slightly smaller borehole and protect the wellbore 120 from intrusion of, for example, freshwater aquifers located near the terranean surface 112. The wellbore 120 may than extend vertically downw ard. This portion of the wellbore 120 may be enclosed by the production casing 135. Other casings, not specifically shown in this figure, can be included within the wellbore system 110 without departing from the scope of this disclosure.

[0057] As shown in FIG. 1, a cement layer 155 (or cement 155) is installed in an annulus between each illustrated casing (conductor casing 125, intermediate casing 130, and production casing 135) and the adjacent geologic formation (such as subterranean formation 140). Cement 155 can be circulated downward, during the construction of the wellbore system 110, through one or more casings and back upward into the annulus between the particular casing and theadjacent geologic formation in order to, for example, bond the casing to the formation. Once solidified in the annulus, the cement 155 can provide a barrier to fluid entry into the wellbore 120 as well as maintain the casings in place.

[0058] In the schematic of FIG. 1, the wellbore 120 has been hydraulically (or otherwise) perforated to create perforations 160, each of w hich, for example, extending through the casing 135. Multiple perforation clusters 160a, 160b and 160c can be formed simultaneously or sequentially. Such perforations in the formation 140 can be accomplished by any known technique (or any technique developed therefore). Although shown as a cased wellbore, the wellbore 120 (for example, at a depth at which the perforation clusters 160a, 160b and 160c are formed) can be an open hole completion (thereby eliminating, in some aspects, the need for perforating through the casing 135). The perforation cluster 160 can have a common schematic of perforations, as illustrated in FIG. 1. In example implementations, the perforation cluster 160 can have a perturbed in-line perforation configurations as described with further details in FIGS. 2A-5.

[0059] A downhole conveyance 150 is deployed to convey tools and instruments downhole. The downhole conveyance 150 is extendable from a terranean surface 112, through a w ellbore 120, and to a subterranean formation 140. The downhole conveyance 150 can be a wireline, e.g., a single or multi-strand wire cable. Wireline cables can incorporate conductors for electrical power and data transmission. The downhole conveyance 150 can be a coiled tubing, e.g., a continuous length of steel or composite tubing wound on a reel which can convey fluids, tools, and equipment into the wellbore 120 while providing pressure control and flexibility. The downhole conveyance 150 can also be a slickline, e.g., a single-strand wire or cable used for light-duty operations such as setting or retrieving downhole equipment, taking fluid samples, or conducting basic well interventions. The downhole conveyance 150 can also be a drilling pipe. Drilling pipes can be used in the drilling process to convey drilling fluids, transmit torque, and carry out other functions necessary for drilling operations.

[0060] The uphole end of the downhole conveyance 150 can be coupled to a top subassembly (not shown). The top subassembly can include various tools and equipment crucial for downhole operations. For example, the top subassembly can include a top drive or a blowout preventer (BOP). The top drive can be a motorized drilling system installed on the drilling rig’s mast or derrick. It rotates the drill string, providing the necessary torque and rotational power to drill the well. BOP can be configured to prevent uncontrolled releases of formation fluids (blowouts) during drilling, completion, or production operations. It can include a seriesof valves and hydraulic mechanisms that can seal off the wellbore, effectively isolating pressure zones and mitigating blowout risks.

[0061] In the schematic of FIG. 1 , a bottom hole assembly 100 is shown run into the wellbore 120 on the downhole conveyance 150 (e.g., a wireline, slickline, coiled tubing, or other conveyance). In example implementations, the bottom hole assembly 100 includes an abrasive jet perforating tool. The abrasive jet perforating tool utilizes high-pressure abrasive jets to cut through the well and penetrate into the formation. Abrasive jets can be streams of water or another suitable liquid mixed with abrasive materials (e.g., sand or ceramic particles) propelled at high velocity. This method can create larger perforation diameters compared to perforating guns. The abrasive jet perforating tool can have nozzles to direct the abrasive particles toward the target formation. As the abrasive particles propel at high velocities, they effectively cut slots in the well and penetrate the rock, forming perforations.

[0062] In example implementations, the bottom hole assembly 100 includes a perforating gun. Perforating guns deploy shaped charges that generate high-velocity, concentrated jets of explosive charges. The shaped charges are strategically positioned within the perforating gun, and upon initiation, they create perforations by penetrating the well casings and surrounding rock formations. Perforating guns can achieve greater penetration depths than the abrasive jet perforating tool. They can be valuable in hard or consolidated formations where the focused energy from the shaped charges allows for efficient perforation. The choice between an abrasive jet perforating tool and a perforating gun depends on several factors, including formation characteristics, wellbore conditions, and geometry required for perforations.

[0063] The geometry of perforations can play an important role in well productivity, reservoir management, and overall operational success. For example, the size and diameter of perforations directly impact the flow of fluids between the reservoir and the wellbore, and pressure distribution during hydraulic fracturing. Larger perforations allow for increased flow rates and faster hydraulic fracture initiation and propagation. The spacing between adjacent perforations determines the density of the induced fractures. In addition, perforations serve as the initial points of contact between the w ellbore and the formation during hydraulic fracturing. The depth of the perforations influences the direction and extent of fracture propagation. Further, the orientation of perforations relative to natural fracture networks or bedding planes can influence w ell performance. In some cases, aligning perforations perpendicular to natural fractures or bedding planes can enhance reservoir connectivity and productivity. In general, consistent perforation geometry, e g., diameter, depth, and / or space, helps prevent flow imbalances and production inefficiencies.

[0064] As shown in FIG. 1, a control system 999 can be communicably coupled (wired or wirelessly) to the bottom hole assembly 100 to operate the bottom hole assembly 100. The control system 999 can include a computer-readable medium (e.g., a non-transitory computer- readable medium) storing computer instructions executable by one or more processors. The one or more processors can execute the stored computer instructions to perform operations described in this disclosure. The control system 999 can be configured to control the fluid pressure. This includes monitoring, adjusting, and maintaining the pressure of the fluid circulating during well operations. Additionally, the control system 999 can be configured to respond to various inputs or triggers, automatically adjusting the fluid pressure as necessary to accommodate changes in operating conditions or demands. Furthermore, the control system 999 can control operations of the bottom hole assembly 100. For example, the control system 999 can control the timing of the perforating shots, adjust the position (e.g., target depth) and orientation of the perforating tool, and / or initiate explosive charges.

[0065] Although not shown in FIG.l, it is understood that the wellbore 120 can include a horizontal portion, e g., a horizontal well parallel to the terranean surface 112. In general, a horizontal well is drilled horizontally through a reservoir formation. The horizontal well can intersect more reservoir rock compared to a vertical well. This allows for increased contact with the hydrocarbon-bearing formation, which can enhance production rates of oil or gas.

[0066] FIGS. 2 A though 2C illustrate schematic views of example perturbed in-line perforations to induce transverse fractures. More specifically, FIGS. 2A through 2B illustrate three-dimensional (3D) views of the example perforations, and FIG. 2C illustrates a view? of the example perforations as they are projected in a traverse plane. As shown, the perforations are arranged along a direction, e.g., Z direction in FIG. 2B. In example implementations, the perforations include one or more first perforations 601. one or more second perforations 602 and one or more third perforations 603. The perforations 601, 602, 603 can be implemented as perforations 160 in FIG. 1.

[0067] As shown in FIG. 2C, the first perforation 601 extends along a first direction 611. The first direction 611 can be a radial direction of the wellbore 120, orthogonal to the w ellbore wall. Second perforations 602 extend along a second direction 612. which is at a first offset angle 621 with respective to the first direction 611. The second perforations 602 can be one or more even-numbered perforations. For example, when labeling perforations sequentially along the Z-axis (see FIG. 2B), starting with the first perforation as #1, the perforation cluster shown in FIGS. 2A through 2C includes six perforations labeled from #1 to #6. Specifically, the even- numbered perforations can include perforation #2 602(a), perforation #4 602(b), andperforation #6 602(c). Third perforations 603 extend along a third direction 613, which is at a second offset angle 622 with respective to the first direction 611. The third perforations 603 can include one or more odd-numbered perforations. For example, odd-numbered perforations can include perforation #3 603(a) and perforation #5 603(b). The one or more second perforations 602 and the one or more third perforations 603 are alternating with each other along the longitudinal direction of the wellbore, e.g., the Z direction. Effectively, the perforations are arranged in a perturbed in-line configuration, where the first perforation 601 extends orthogonal to a wellbore axis with azimuths of successive perforations 602, 603 being perturbed by a small angle, e.g., 10 degrees, in either direction away from the azimuth of the first perforation 601. As noted above, when projected onto transverse plane, the even- numbered perforations 602 can be oriented on one side of the first perforation 601, while odd- numbered perforations 603 can be oriented on the opposite side of the first perforation 601. Although not shown, it is understood that the perforations 601, 602, 603, can be narrower at the deeper sections of the perforations, e.g., near the tip of the perforations, as illustrated in FIG. 1.

[0068] In example implementations, the magnitudes of first offset angle 621 and the second offset angle 622 range between 0 degree and 25 degrees. In another example implementation, the magnitudes of first offset angle 621 and the second offset angle 622 range between 0 degree and 180 degrees. At least one of the second direction 612 or the third direction 613 is different than the first direction 611. In other words, at least one perforation extends along a direction different from other perforations. In example implementations, the first offset angle 621 is equal in magnitude and opposite in sign to the second offset angle 622. For example, the first offset angle 621 can be about -10 degree, and the second offset angle 622 can be about +10 degree. That is, second perforations 602, e.g.. the even-numbered perforations, are oriented at +10 degree from the direction of the first perforation 601. Third perforations 603, e.g., the odd-numbered perforations, are oriented at -10 degree from the direction of the first perforation 601. In another example, the first offset angle 621 is about -20 degree, and the second offset angle 622 is about +20 degree.

[0069] In example implementations, the first offset angle 621 is unequal in magnitude and opposite in sign to the second offset angle 622. For instance, the first offset angle 621 is about -10 degree, and the second offset angle 622 is about +25 degree. In another example, the first offset angle 621 is about +10 degree, and the second offset angle 622 is about -20 degree. Unequal offset angles can be advantageous in some cases to create asymmetric stress gradients around the perforations. This asymmetry can effectively induce transverse fractures (avoidingformation of longitudinal fractures that ty pically occur w ith symmetrical in-line configuration) and induce preferential fracture growth in specific directions.

[0070] In example implementations, the first perforation 601, e.g., perforation #1, extend along the same direction as the second perforations 602 or the third perforations 603. In other words, either the first offset angle 621 or the second offset angle 622 is zero degree. For example, the first offset angle 621 is about -20 degree, and the second offset angle 622 is about 0 degree. In this configuration, the first perforation 601 has the same direction as the third perforations 603, e.g., odd-numbered perforations. In another example, the first offset angle 621 is about 0 degree, the second offset angle 622 is about +20 degree. In this configuration, the first perforation has the same direction as the second perforations 602, e.g., even-numbered perforations. In example implementations, the perforations are equally spaced along the longitudinal direction of the wellbore, e.g., the Z direction in FIG. 2B.

[0071] Although not shown, it is understood that second perforations 602 or the third perforations 603 can include any combinations of perforations in the perforation cluster. For example, the second perforations 602 can include perforation #2, #3 and #6, while the third perforations 603 can include perforation #4 and #5. It is further understood that the first perforation 601 can include one or more perforations.

[0072] In example implementations, the perforation cluster includes six perforations per foot. It is further understood that the perforation cluster can include any quantity' of perforations shot at any density.

[0073] In example implementations, second perforations 602 or third perforations 603 are titled in the same general directions away from the first perforation, but at vary ing offset angles. In some cases, this unequal offset angles can further reduce the FIP compared to equal offset angles. This reduction in FIP can be attributed to the asymmetric stress distribution induced by the varying offset angles.

[0074] FIGS. 2D and 2E illustrate schematic views of an example perturbed in-line perforations with vary ing angles. The perforation cluster 700 includes perforations arranged in-line along a longitudinal direction of the wellbore 120, e.g., Z direction in FIG. 2D. In other words, multiple perforations are spaced linearly along the Z direction. The perforations include one or more first perforations 601, second perforations 602 and third perforations 603. The first perforation 601 extends along a first direction. The first direction can be a radial direction of the wellbore 120 (see FIG. 2C). Second perforations 602 extend along second directions at first offset angles 621 with respective to the first direction. Second perforations 602 can be even-numbered perforations. In example implementations, at least two of the second directionsare different from each other. For example, perforation 602(a), 602(b) and 602(c) extend in the same general direction, e.g., the negative X direction, away from the first perforation 601 but with slightly different offset angles. For example, the offset angles for perforation 602(a), 602(b) and 602(c) can be -10 degree, -15 degree, and -5 degree respectively.

[0075] Third perforations 603 extend along third directions at second offset angles 622 with respective to the first direction. The third perforations 603 can be odd-numbered perforations. The second offset angles 622 are opposite to the first offset angles 621. As shown, third perforations 603 are consistently deviated from the first perforation 601 along the positive X direction with azimuthal opposite to that of the second perforations 602. In example implementations, the third perforations 603 have unequal offset angles. For example, the offset angles for perforation 603(a) and 603(b) can be +15 degree, and +10 degree respectively.

[0076] In example implementations, the first offset angles 621 and the second offset angles 622 are between 0 degree and 25 degrees. In example implementations, the first offset angles 621 and the second offset angles 622 are between 0 degree and 180 degrees. At least one offset angle is non-zero. In other words, at least one perforation extends toward a direction distinct from the other perforations.

[0077] In example implementations, the second perforations 602 and the third perforations 603 are alternative with each other along the longitudinal direction of the w ellbore, e.g., the Z direction. For example, the second perforations 602 are even -numbered perforations, while the third perforations 603 are odd-numbered perforations. Alternatively, the second perforations 602 can be odd-numbered perforations, while the third perforations 603 can be even-numbered perforations.

[0078] In example implementations, each of the perforations extends along a unique direction. For example, as shown in FIGS. 2D and 2E, the offset angles for perforation #l-#6 are 0, -10 degree, +15 degree, -15 degree, +10 degree, and -5 degree respectively. In example implementations, the last perforation (e.g., perforation #6 602(c)) has the same orientation as the first perforation (e.g., perforation #1 601), while the middle perforations have opposite perturbed azimuth relative to the first perforation.

[0079] In example implementations, the perforating tool includes shaped charges, and the directions of the shaped charges are phased at an azimuth smaller than 60 degrees. For example, the creation of perturbed in-line perforation cluster can be achieved by setting the phasing of shaped charges in a perforation gun at 0, + / - 10 degrees to create an azimuthal perturbation of + / - 10 degree relative to the first perforation. In example implementations, the phasing of shaped charges can be adjusted within a range of 0 to 60 degrees to accommodatevarious geometrical requirements for the perforations. In an example, each shaped charge is capsuled in a capsule module capable of swiveling around a gun axis, enabling the adjustment of the orientation of the charges. The orientation of the charges can be controlled by the control system 999, as described in FIG. 1 , or pre-determined during the preparation of the perforation gun at the surface. In example implementations, the perforating tool includes shaped charges, and the directions of the shaped charges are phased at an azimuth smaller than 180 degrees. It is understood that the perturbed in-line perforations can be created using any other suitable tools, including without limitation high-pressure coiled tubing jetting tools, laser tools, or abrasive jet perforating tools.

[0080] FIGS. 3 A through 3C illustrate schematic views of an example pair of perturbed inline perforations in a perforation cluster. As shown, a perforation cluster includes a pair of perforations 800. The pair of perforations 800 includes a first perforation 852 and a second perforation 854. The first perforation 852 and the second perforation 854 of the pair of perforations 800 are arranged along a longitudinal direction of the wellbore, e.g., Z direction in FIG. 3C. The first perforation 852 is oriented at an azimuthal offset angle 858 relative to the second perforation 854. In example implementations, the perforation cluster includes only the pair of perforations 800. In example implementations, the azimuthal offset angle 858 ranges between 0 degree and 180 degrees. In example implementations, the azimuthal offset angle 858 is equal to 20 degrees. In example implementations, the azimuth of offset angle ranges between 0 and 20 degrees.

[0081] The first perforation 852 is spaced apart from the second perforation 854 along the longitudinal direction of the wellbore, e.g., the Z direction, as illustrated in FIG. 3C. In example implementations, a separation distance 856 between the first perforation 852 and the second perforation 854 along the longitudinal direction of the wellbore is equal to or less than 1 / 6 foot. In some cases, a smaller separation distance between the first perforation 852 and the second perforation 854 facilitates formation of a single preferred fracture plane (PFP), instead of two separate fracture planes. With a smaller separation distance, the formation can break along a single path rather than along multiple paths corresponding to each perforation. In example implementations, the separation distance 856 along the longitudinal direction of the wellbore is equal or less than 0.5 foot. In example implementations, the separation distance 856 along the longitudinal direction of the wellbore is equal or less than one foot. In example implementations, the separation distance 856 along the longitudinal direction of the wellbore is equal or less than two feet.

[0082] In example implementations, the perforating tool includes a plurality of shaped charges, and detonating directions of the shaped charges are phased at azimuthal angles smaller than 60 degrees. The detonating directions of the shaped charges can be phased at an angle equal to the azimuthal offset angle of the pair of perforations 800. In example implementations, the detonating directions of two shaped charges can be phased at an angle of 20 degrees to create the pair of perforations 800 with an azimuthal offset angle of 20 degrees.

[0083] FIG. 3D illustrates schematic views of two example pairs of perturbed in-line perforations in two perforation clusters. As shown, the first perforation cluster includes the first pair of perforation 950. The second perforation cluster includes the second pair of perforation 960. The two perforation clusters 900 can be formed in the subterranean formation. Any pair of perforations 950, 960 can be implemented as the pair of perforation 800 as described in FIGS. 3A-3C. The two pairs of perforations 950, 960 are arranged linearly along the longitudinal direction of the w ellbore, e.g., Z direction in FIG. 3D.

[0084] In example implementations, the first pair of perforations 950 includes a first perforation 952 and a second perforation 954. The second pair of perforations 960 includes a first perforation 962 and a second perforation 964. The two perforations in the same pair can be oriented along different directions with an azimuthal offset angle. An azimuthal offset angle can an offset angle in a transverse plane, as illustrated above in FIG. 2C. In example implementations, the first perforation 952 of the first pair of perforations 950 has a first azimuthal offset angle 956 relative to the second perforation 954 of the first pair of perforations 950. Likewise, the first perforation 962 of the second pair of perforations 960 has a second azimuthal offset angle 966 relative to the second perforation 964 of the second pair of perforations 960. The first azimuthal offset angle 956 can be equal to or different from the second azimuthal offset angle 966. In example implementations, both the first azimuthal offset angle 956 and the second azimuthal offset angle 966 are equal to 20 degrees. In example implementations, the first azimuthal offset angle 956 is 15 degrees, while the second azimuthal offset angle 966 is 20 degrees.

[0085] In example implementations, the first perforations 952, 962 in each pair of perforations 950. 960 are oriented along the same azimuthal direction. Likewise, the second perforations 954, 964 of each pair of perforations 950, 960 are oriented along the same azimuthal direction.

[0086] In example implementations, the first azimuthal offset angle 956 is equal to the second azimuthal offset angle 966. while each perforation in both pairs of perforations is oriented along unique direction. In example implementations, the first perforation 952 of thefirst pair of perforations 950 extends along a first direction. The second perforation 954 of the first pair of perforations 950 extends along a second direction with an azimuthal offset angle, e.g., +20 degrees, relative to the first direction. The first perforation 962 of the second pair of perforations 960 extends along a third direction with an azimuthal offset angle, e.g., -5 degrees, relative to the first direction. The second perforation 964 of the second pair of perforations 960 extends along a fourth direction with an azimuthal offset angle, e.g., +15 degrees, relative to the first direction.

[0087] The first pair of perforations 950 is spaced apart from the second pair of perforations 960 by a spacing distance 970 along the longitudinal direction of the wellbore, e.g., Z direction. In example implementations, the spacing distance 970 is the closest distance between any two perforations from adjacent pairs of perforations. In example implementations, the spacing distance 970 is the distance between the second perforation 954 of the first pair of perforations 950 and the first perforation 962 of the second pair of perforations 960, as illustrated in FIG. 3D.

[0088] In example implementations, the spacing distance 970 between the first pair of perforations 950 and the second pair of perforations 960 is equal to or larger than 1 / 6 foot. In example implementations, the spacing distance 970 is larger than 2 feet. In some cases, a longer separation distance can reduce the interference between stress fields generated by neighboring pairs of perforations. This interference arises due to the overlapping influence zones of neighboring pairs of perforations. A longer spacing distance 970 between neighboring pairs of perforations reduces the spatial overlap between these zones, thus reducing the likelihood of conflicting stress fields. In addition, the techniques described herein can reduce the number of perforations required to generate a fracture. With the pair of perforations, a ratio of 1 fracture per 2 perforations can be achieved.

[0089] Although not shown, it is understood that three or more perforation clusters can be created in the formation 140 with each perforation cluster including only one pair of perforations. In example implementations, the spacing distance 970 between adjacent perforation clusters is equal to or larger than 1 / 6 foot. In example implementations, each pair of perforations is arranged along a corresponding longitudinal direction of the wellbore 120. A wellbore can have a vertical segment (e g., as shown in FIG. 1) and / or a horizontal segment (e.g., as showTi in FIG. 4G). The longitudinal direction of the vertical segment of the wellbore 120 can be a vertical direction perpendicular to a surface 112 of the Earth. The longitudinal direction of the horizontal segment of the wellbore 120 can be a horizontal direction parallel to the surface 112 of the Earth. The longitudinal direction of the horizontal segment of thewellbore 120 can also be a vertical direction perpendicular to the surface 112 of the Earth. The longitudinal direction of the horizontal segment of the wellbore 120 can also be an oblique direction at a given azimuthal angle (neither vertical direction perpendicular to the surface 112 of the Earth, nor horizontal direction parallel to the surface 112 of the Earth).

[0090] The one or more pairs of perforations that are formed adjacent the vertical segment of the wellbore can be arranged or spaced along the vertical direction. In contrast, the one or more pairs of perforations that are formed adjacent the horizontal segment of the wellbore can be arranged or spaced along the horizontal direction. The one or more pairs of perforations that are formed adjacent the horizontal segment of the wellbore can also be arranged or spaced along the vertical direction. In example implementations, at least two pairs of perforations are arranged along different azimuthal planes of the wellbore. For example, a pair of perforations, which is adjacent the vertical segment of the wellbore, can be arranged along the vertical direction. Another pair of perforations, which is adjacent the horizontal segment of the wellbore, can be arranged along the horizontal direction.

[0091] In example implementations, a first perforation in each pair of perforations is oriented at a corresponding azimuthal offset angle relative to a second perforation in the same pair. Each pair of perforations can have the same azimuthal offset angle between the two perforations. In example implementations, the azimuthal offset angles range between 0 degree and 180 degrees. In example implementations, the azimuthal offset angles range between 0 degree and 20 degrees. In example implementations, the azimuthal offset angles range between 0 degree and 60 degrees.

[0092] In example implementations, at least two pairs of perforations have different azimuthal offset angles. In example implementations, three pairs of perforations are formed. Two pairs of perforations have the same azimuthal offset angle, e.g., 20 degrees, which is different from the azimuthal offset angle, e.g., 15 degrees, of the third pair of perforations.

[0093] In example implementations, multiple pairs of perforations are spaced apart from one another at an unequal distance. In example implementations, a first pair, a second pair, and a third pair of perforations are formed consecutively in the wellbore, which are unequally spaced apart. In other words, the separation distance between the first pair of perforations and the second pair of perforation can be different from the separation distance between the second pair of perforations and the third pair of perforations. In some cases, varying separation distances between adjacent pairs of perforations can be configured for creating stress fields tailored to different types of formations. For example, formations that are more heterogeneous or prone to uneven distribution of fluids or stresses may benefit from denser perforations orshorter separation distances between adjacent pairs of perforations. In contrast, formations that are more homogeneous with higher permeability may require less dense perforations.

[0094] FIG. 4A illustrates an example of directions of hydraulic fractures initiated at individual perforations in perturbed in-line perforation cluster, as predicted by numerical simulation of cased and cemented horizontal wellbore drilled parallel to a minimal reservoir stress. In FIG. 4A, contours 829 represent circles projected onto the cylindrical wellbore wall, with diameters about five times larger than those of the perforations. Contours 829 illustrate vicinities of individual perforation tunnels, with their intersections indicating areas where mechanical stresses are influenced by the presence of two neighboring perforations. Thus, in an example implementation of ±10 degrees azimuthal perturbation, neighboring perforation tunnels are closely positioned enough to influence the induced mechanical stresses of each other in such way that maximum tension in the rock or formation can develop along the directions 828 as illustrated in FIG. 4A. In this way, a nearly transverse fracture can initiate at the wellbore following the directions 828 and be guided by the neighboring perforations. As it grows away from the zone dominated by the hoop stress (e.g., circumferential stress) of the main wellbore, initiated fracture can gradually become transverse and perpendicular to the minimal reservoir stress. In contrast, with greater perforations azimuthal differences (e.g., 60 degrees) around the circumference of the wellbore in a traditional helical perforation cluster, and with other factors (e.g., perforation spacing) being equal, the mechanical stress interaction between perforations can become significantly weaker. This raises the likelihood of fractures initiating longitudinally along the hoop stress of the main w ellbore.

[0095] FIG. 4B illustrates simulation results of fracture initiation pressures (FIP) wtith example perturbed in-line perforation and other configurations of perforation clusters. More specifically, the fracture initiation pressures are compared among different configurations of perforation clusters, e.g., helical clusters, perfectly in-line clusters, and perturbed in-line perforation clusters. A theoretical model of fracture initiation from wellbores weakened with perforations is utilized in this simulation. This model incorporates the effect of cemented steel casing by including corresponding model subdomains with elastic properties different from rock / formation. The model is based on 3D linear elastic analysis of rock stress in the vicinity of the perforation cluster loaded internally by the pressure of fracturing fluid and predicts initiation of fracture using a non-local fracturing criterion based on the stress-averaging principle (SAMTS), assuming perfect bonding between casing, cement, and rock. The simulations were conducted under the following conditions, resembling the field case of horizontal wellbore drilled parallel to the minimal horizontal stress in a reservoir subjected tostrike-slip regime of in-si tu stresses. Exactly same conditions were also reproduced in the below reported hydraulic fracturing block tests conducted in parallel in the lab: wellbore diameter (Dw) = 1.25 inch (approx. 32 mm); Wellbore radius (Rw) = 0.5*Dw= 0.625 inch (approx. 16 mm); Maximum horizontal stress (SHmax) = 2,625 psi (1.81e+7 Pascal); Vertical stress (SV) = 2,250 psi (1.55e+7 Pascal); Minimum horizontal stress (SHmin) = 1,688 psi (1. 16e+7 Pascal); Perforation length (Lp) = 2.0*R„; Perforation diameter (Dp) = 0.333*Rw.

[0096] The simulation results were presented in FIG. 4B, with arrows. 406. 407. 408, showing the predicted directions of fractures initiated at perforations. The graphs illustrate distributions of predicted FIP values along individual perforation tunnels with respective to distance from the w ellbore wall measured in wellbore radius Rw. To facilitate the comparisons between different configurations. FIP values are normalized by the average value FIP0 obtained for the helical cluster. The FIP values of longitudinally initiated fractures are show n with triangles (see diagram (a) of FIG. 4B). The FIP values of transversely initiated fractures are shown with dots and squares (see diagrams (b) and (c) of FIG. 4B). Diagram (a) of FIG. 4B illustrates the simulation result for a perfectly in-line perforation cluster. Diagram (b) of FIG. 4B illustrates the simulation result for a helical cluster. Diagram (c) of FIG. 4B illustrates the simulation result for the example perturbed in-line perforation cluster. In this example simulation, the perturbed in-line perforation cluster 400 has 6 perforations with offset azimuthal angles at 0, +10 degree, -10 degree, +10 degree, -10 degree, +10 degree, respectively.

[0097] As illustrated in the diagram (a) of FIG. 4B. although the perfectly in-line cluster exhibited a low er fracture initiation pressure (FIP) value, it initiated a longitudinal fracture 406, which is expected to require significantly higher pressure to propagate further until it reorients to a transverse fracture. In contrast, as illustrated in the diagram (c) of FIG. 4B, the perturbed in-line perforation cluster 400 initiated a transverse fracture between neighboring perforations, which are developed along the directions 408. Additionally, comparing the diagram (b) of FIG. 4B and the diagram (c) of FIG. 4B, the FIP with the perturbed in-line perforation cluster 400 is about 20% low er than that with the transverse fracture FIP of helical cluster. This shows a clear advantage of the perturbed in-line cluster compared to the other two cluster configurations.

[0098] The theoretical advantage of the perturbed in-line cluster, as described in FIG. 4B, was also validated through large-scale hydraulic fracturing block experiments conducted in the laboratory' using a true-triaxial load frame. These experiments were carried out on 24x18x18 inch (height x width x length) blocks of tight and competent sandstone, where a miniature 1.25 inch in diameter borehole was placed throughout and along the top-bottom centerline of theblock, followed by installation of steel casing tubing using high-strength epoxy as a cement. Depending on particular tested cluster configurations, six (6) helical or perturbed in-line perforations were placed through the casing in the center. The rest of remaining testing parameter were kept the same and followed the same test conditions utilized in the simulations described earlier in FIG. 4B.

[0099] FIG. 4C illustrates a lab example experimental result of a hydraulic fracture initiation in a block test with a helical cluster for reference. FIG. 4D illustrates a lab example experimental result of a hydraulic fracture initiation in a block test with a perturbed in-line perforation cluster. FIG. 4E illustrates a top view of the hydraulic fracture from the lab example experimental result of FIG. 4D. In this particular experiment, the perturbed in-line perforation cluster had a configuration as shown in FIG. 2A, with offsets angles 0, +10 degree, -10 degree, +10 degree, -10 degree, +10 degree, respectively. FIG. 4F illustrates a plot of borehole pressures acquired during the fracturing phases in each experiment described in FIGS. 4C-4D. To facilitate the comparison, borehole pressure curves for both perturbed in-line and helical configurations are overlapped. This reveals an excellent and expected match in linear portions of the curves, as borehole pressure was ramped up following initial pump stabilization at low pressures and almost till the moment of fracture breakdown.

[0100] Following the accepted practice in interpreting the hydraulic fracturing test results, an absolute maximum of borehole pressure (e.g., fracture breakdown pressure (FBP) or breakdown pressure (BDP)) and FIP (e.g., a borehole pressure at the very moment of rock failure at the critically stressed region near borehole or perforation) are differentiated. FBP value can be higher than FIP, depending on fluid injection rate and viscosity . The FIP value correlates with the predictions of the rock strength-based model presented above. It can be determined when the borehole pressure curve begins to deviate from the linear loading trend shortly before breakdown. As summarized in the table of FIG. 4F, the experiments showed that the perturbed in-line cluster resulted in a reduction of FIP by approximately 34% compared to the helical cluster, which is higher than 20% predicted by the model in FIG. 4B. Perturbed in-line cluster is shown similar reduction of 32% for FBP compared to helical cluster.

[0101] To study orientation of initiated fractures, 4-inches-diameter core plugs were drilled out from the tested blocks. Diameter of the cores allowed to extract portions of the rock containing borehole and perforation cluster. FIG. 4C shows the core 836 including the borehole and helical perforations. The helical perforation cluster has 6 perforations, 1201, 1202, 1203, 1204, 1205, and 1206. It was observed that the helical cluster initiated longitudinal fractures 410 (see top-view schematic in FIG. 4C), started at perforation #3 1203 andperforation #6 1206 and propagated against the intermediate stress SV, although the model favored initiation transverse fractures against minimal stress SHmin. In contrast, as illustrated in FIGS. 4D and 4E, two 4-inches-dimaeter core plugs, e.g., the first core 830 and the second core 832, extracted from the block with perturbed in-line cluster confirmed initiation of transverse fracture 812 at neighboring perforations 5 and 6 facing east (E) face of the block, consistent with the theoretical simulations as described in FIG. 4B. The transverse fracture 812 is grown in the extending direction of perforations till it broke out at the east (E) face as a perfectly transverse fracture. As for the opposite direction, e.g., west (W) direction, fracture turned longitudinally along the wellbore and ceased very soon as that required opening against the higher intermediate stress, SV (see FIGS. 4D and 4E).

[0102] As shown in FIG. 4D by photographs of cores, e.g.. a first core 830 and a second core 832, extracted from the near-wellbore region, the perturbed in-line configuration initiated transverse fracture 812 at neighboring perforations #5 and #6, which propagates away from the wellbore in a direction close to the direction of the perforations. This indicates that the perturbed in-line configuration can control the direction of fracture initiation and propagation based on the directions of the perforations. In example implementations, the perturbed in-line configuration in this lab experiment can reduce the fracture pressure by about 34% compared to a result of experiment with helical cluster with the same perforation density. The perturbed in-line configuration initiates transverse fracture in this example experiment, while the helical cluster initiated longitudinal fracture against intermediate stress. Such perturbed in-line configurations could prove valuable when fractures are created in proximity to sensitive areas, such as water zones or reservoir boundaries, to prevent fractures from extending into unwanted areas.

[0103] As illustrated in FIG. 4D, a single transverse fracture 812 can be originated from two perforations, e.g., the perforation #5 and #6. Without limiting to any particular theory, fracture did not originate from those in the middle (e.g., perforations #3 and #4) likely because they were surrounded by perforations above (e.g., perforations #1 and #2) and below (e.g., perforations #5 and #6). Therefore, only two perforations, e.g., a pair of perforations, can produce a similar fracture pattern. The pair of perforations can have the configuration as illustrated above in FIGS. 3A-3C. In example implementations, two or more pairs of perforations are utilized, as illustrated above in FIG. 3D.

[0104] FIG. 4G illustrates a schematic view of an example horizontal wells 820 with an initiation of fractures near a water zone. When fractures are initiated near certain geological features, such as water zones 802, it is important to prevent the fractures from propagating intothose areas. Initiating fractures strategically is an important aspect to ensure that fractures remain within the target zone and do not extend into areas where they could cause unintended consequences, such as water contamination or breakthrough to the wellbore. This can be achieved by managing the location of the perforation clusters and the geometry of individual perforations, e.g., direction, diameter, spacing, and / or depth of each perforation. As shown, to prevent the fractures from propagating into undesirable areas, e.g., the water zone 802, the perforation cluster 160(a) and 160(b) can be configured to initiate fractures in a direction away from the water zone 802. This can be achieved by utilizing the perturbed in-line arrangement (in pairs) of perforations. As noted above, the perturbed in-line perforations have advantages of creating transverse fractures 806 along a direction that aligns closely with the direction of perforations. By orienting the perforations away from the water zone 802, fractures are consequently induced in a direction away from the water zone 802.

[0105] It is understood that wellbores can extend along varying directions relative to the terranean surface 112, e.g., vertical wellbore, horizontal wellbore, or an inclined wellbore with an arbitrary angle. Depending on the orientation of wellbores and in-situ stress regime, the perforations with perturbed in-line pair configuration can extend vertically or horizontally in a horizontal wellbore, or horizontally in a vertical wellbore. For a horizontal wellbore 820, the perturbed in-line pair perforations can be vertical (top side 402 or bottom side 404 of horizontal wellbore 820), horizontal (left or right side of horizontal wellbore 820), or azimuthally -oblique at any given angle with respect to the wellbore axis (e.g. oriented in-line at an azimuth of 60 degrees). Perturbed in-line perforation pairs (vertical, horizontal, or oblique) with individual perforations within a perforation cluster can have any random or systematic combination of azimuths to achieve any desired benefit / objective. For a vertical wellbore, the perturbed inline perforation pairs can be oriented in any direction relative to the wellbore axis. Alternatively, the perforation pairs can extend along directions at a tilted angle with respective to the terranean surface 112 in an inclined wellbore. In example implementations, perturbed in-line perforation pairs (vertical, horizontal, or oblique) have ahigh cluster density7, e.g., more than 60 clusters (60 perforation pairs) per 300 feet of wellbore length. In another example implementation, perturbed in-line perforation pairs (vertical, horizontal, or oblique) have a lower cluster density7, e g., less than 60 clusters (60 perforation pairs) per 300 feet of wellbore length.

[0106] FIG. 5 is a flow chart of an example process for creating one or more pair of perturbed in-line perforations. At step 1102, a perforating tool is positioned adjacent a subterranean formation 140 within a wellbore 120, as illustrated in FIG. 1.

[0107] At step 1104, a plurality of perforation cluster is formed in the subterranean formation. At least one of the perforation clusters includes a pair of perforations which is arranged along a longitudinal direction of the wellbore. A first perforation in each pair of perforations is oriented at a corresponding azimuthal offset angle relative to a second perforation in each pair of perforations. The pair of perforations can be, e.g., the pair of perforations 800 of FIGS. 3 A through 3C, or the pairs of perforations 950, 960 of FIG. 3D. In example implementation, a perforation cluster includes only one pair of perforations. The perforating tool can form the plurality of perforation clusters by moving from one perforation cluster location to another. The perforating tool can be configured to form only two perforations (e.g., a pair of perforations) during each operation at each perforation cluster location. The perforating tool can be configured to form multiple pairs of perforations simultaneously during each operation at multiple perforation cluster locations.

[0108] In example implementations, the perforating tool includes multiple shaped charges. In example implementations, operating the perforating tool includes orienting detonating directions of the shaped charges at an azimuthal phase angle equal to the azimuthal offset angle of a corresponding pair of perforations. In example implementations, detonating directions of the shaped charges are oriented at an azimuthal phase angle of 20 degrees. This can be utilized to create a pair of perforations with an azimuthal offset angle of 20 degrees.

[0109] Thus, particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous. Moreover, aspects described with reference to any figure or any implementation can be combined with aspects described with any other figure or any other implementation.

[0110] It is understood that the articles “a,” “an,” and “the” in this disclosure are intended to mean that there are one or more of the elements in the preceding descriptions. The terms “including.” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one example” or “an example” of the present disclosure are not intended to be interpreted as excluding the existence of additional examples that also incorporate the recited features. For example, any element described in relation to an example herein may be combinable with any element of any other example described herein. Numbers, percentages.ratios, or other values stated herein are intended to include that value, and also other values that are “about” or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by examples of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%. within 1%. within 0.1%, or within 0.01% of a stated value.[OHl] A person having ordinary' skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may’ be made to examples disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the examples that falls within the meaning and scope of the claims is to be embraced by the claims.

[0112] The terms “approximately.” “about,” and “substantially” as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of a stated amount. Further, it should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “up” and "down" or “above” or “below” are merely descriptive of the relative position or movement of the related elements.

Claims

WHAT IS CLAIMED IS:

1. A bottom hole assembly, comprising: a downhole conveyance that is extendable from a terranean surface, through a wellbore, and to a subterranean formation; and a perforating tool configured to couple to the downhole conveyance and create at least one pair of perforations, the at least one pair of perforations arranged along a longitudinal direction of the wellbore such that a first perforation in the at least one pair of perforations is oriented at an azimuthal offset angle relative to a second perforation in the at least one pair of perforations.

2. The bottom hole assembly of claim 1, wherein the azimuthal offset angle ranges between about 0 degree and about 60 degrees.

3. The bottom hole assembly of claim 1, wherein the azimuthal offset angle ranges between about 0 degree and about 20 degrees.

4. The bottom hole assembly of claim 1, wherein the azimuthal offset angle ranges between about 0 degree and about 180 degrees.

5. The bottom hole assembly of claim 1, wherein a separation distance between the first and second perforations along the longitudinal direction of the wellbore is equal to or less than about 1 / 6 foot.

6. The bottom hole assembly of claim 1, wherein the perforating tool comprises a plurality of shaped charges, and detonating directions of the shaped charges are phased at azimuthal angles smaller than about 60 degrees.

7. The bottom hole assembly of claim 1, wherein the at least one pair of perforations comprises a first pair of perforations, the azimuthal offset angle is a first azimuthal offset angle of the first pair of perforations, and the at least one pair of perforations comprises a second pair of perforations, the second pair of perforations arranged along the longitudinal direction of the wellbore such that a first perforation in the second pair of perforations is oriented at a second azimuthal offset angle relative to a second perforation in the second pair of perforations.

8. The botom hole assembly of claim 7, wherein a spacing distance between the first pair of perforations and the second pair of perforations is equal to or larger than about 1 / 6 foot.

9. The botom hole assembly of claim 7, wherein the first azimuthal offset angle of the first pair of perforations is equal in magnitude to the second azimuthal offset angle of the second pair of perforations.

10. The botom hole assembly of claim 1, wherein the perforating tool comprises a high-pressure coiled tubing jeting tool, a laser tool, or an abrasive jet perforating tool.

11. A bottom hole assembly, comprising: a downhole conveyance that is extendable from a terranean surface, through a wellbore, and to a subterranean formation; and a perforating tool configured to couple to the downhole conveyance and create a plurality of pairs of perforations, each pair of perforations arranged along a corresponding longitudinal direction of the wellbore such that a first perforation in each pair of perforations is oriented at a corresponding azimuthal offset angle relative to a second perforation in each pair of perforations, the corresponding azimuthal offset angle ranging between about 0 degree and about 60 degrees.

12. The botom hole assembly of claim 11. wherein the plurality of pairs of perforations has a same azimuthal offset angle.

13. The botom hole assembly of claim 11, wherein the azimuthal offset angle ranges between about 0 degree and about 20 degrees.

14. The botom hole assembly of claim 11 , wherein at least two of the pairs of perforations have different azimuthal offset angles.

15. The botom hole assembly of claim 11, wherein at least two of the pairs of perforations are arranged along different azimuthal planes of the wellbore.

16. The bottom hole assembly of claim 15. wherein the corresponding longitudinal direction of the wellbore comprise a direction parallel to a surface of the Earth.

17. The botom hole assembly of claim 11. wherein the plurality of pairs of perforations is spaced apart from one another at an unequal distance.

18. The botom hole assembly of claim 11 , wherein a spacing distance between adjacent pairs of perforations is equal to or larger than about 1 / 6 foot.

19. The botom hole assembly of claim 11 , wherein the perforating tool comprises a high-pressure coiled tubing jeting tool, a laser tool, or an abrasive jet perforating tool.

20. A method to form perforations, comprising: positioning a perforating tool adjacent a subterranean formation within a wellbore; and operating the perforating tool to form a plurality of perforation clusters in the subterranean formation, at least one of the perforation clusters comprising a pair of perforations arranged along a longitudinal direction of the wellbore, a first perforation in the pair of perforations being oriented at a corresponding azimuthal offset angle relative to a second perforation in each pair of perforations, a spacing distance between adjacent perforation clusters being larger than 1 / 6 foot.

21. The method of claim 20, wherein the corresponding azimuthal offset angle ranges between 0 degree and 60 degrees.

22. The method of claim 20, wherein the corresponding azimuthal offset angle ranges between 0 degree and 20 degrees.

23. The method of claim 20, wherein the perforating tool comprises a high- pressure coiled tubing jeting tool, a laser tool, or an abrasive jet perforating tool.

24. The method of claim 20, wherein the perforating tool comprises a plurality of shaped charges.

25. The method of claim 24, wherein operating the perforating tool comprises: orienting detonating directions of the shaped charges at an azimuthal phase angle equal in magnitude to the azimuthal offset angle of the pair of perforations of a corresponding one of the perforation clusters.

26. The method of claim 25, wherein the azimuthal phase angle is smaller than 60 degrees.

27. The method of claim 20, wherein a separation distance between the first and second perforations of the pair of perforations along the longitudinal direction of the wellbore is equal to or less than 1 / 6 foot.

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