Patent Publication Number: US-7711487-B2

Title: Methods for maximizing second fracture length

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation in part of U.S. patent application Ser. No. 11/545,749 filed on Oct. 10, 2006 which is hereby incorporated by reference as if fully reproduced herein. 

   BACKGROUND 
   The present invention relates generally to methods for inducing fractures in a subterranean formation and more particularly to methods to place a first fracture with a first orientation in a formation followed by a second fracture with a second angular orientation in the formation according to a time determination. 
   Oil and gas wells often produce hydrocarbons from subterranean formations. Occasionally, it is desired to add additional fractures to an already-fractured subterranean formation. For example, additional fracturing may be desired for a previously producing well that has been damaged due to factors such as fine migration. Although the existing fracture may still exist, it is no longer effective, or less effective. In such a situation, stress caused by the first fracture continues to exist, but it would not significantly contribute to production. In another example, multiple fractures may be desired to increase reservoir production. This scenario may also be used to improve sweep efficiency for enhanced recovery wells such as water flooding steam injection, etc. In yet another example, additional fractures may be created to inject with drill cuttings. 
   Conventional methods for initiating additional fractures typically induce the additional fractures with near-identical angular orientation to previous fractures. While such methods increase the number of locations for drainage into the wellbore, they may not introduce new directions for hydrocarbons to flow into the wellbore. Conventional method may also not account for, or even more so, utilize, stress alterations around existing fractures when inducing new fractures. 
   Thus, a need exists for an improved method for initiating multiple fractures in a wellbore, where the method accounts for tangential forces around a wellbore and the timing of inducing a subsequent fracture. 
   SUMMARY 
   The present invention relates generally to methods, systems and apparatus for inducing fractures in a subterranean formation and more particularly to methods to place a first fracture with a first orientation in a formation followed by a second fracture with a second angular orientation in the formation at a specified time determination. 
   An example method of the present invention is for fracturing a subterranean formation. The subterranean formation includes a wellbore having an axis. A first fracture is induced in the subterranean formation. The first fracture is initiated at about a fracturing location. The initiation of the first fracture is characterized by a first orientation line. The first fracture temporarily alters a stress field in the subterranean formation. A second fracture is induced, after a time delay, in the subterranean formation. The second fracture is initiated at about the fracturing location. The initiation of the second fracture is characterized by a second orientation line. The first orientation line and the second orientation line have an angular disposition to each other. 
   An example fracturing tool according to present invention includes a tool body to receive a fluid, the tool body comprising a plurality of fracturing sections, wherein each fracturing section includes at least one opening to deliver the fluid into the subterranean formation at an angular orientation; and a sleeve disposed in the tool body to divert the fluid to at least one of the fracturing sections while blocking the fluid from exiting another at least one of the fracturing sections. Another example of a fracturing tool according to the present invention includes a tool body to receive a fluid, the tool body comprising one fracturing section, which includes at least one opening to deliver the fluid into the subterranean formation at an angular orientation, wherein the direction change is provided by rotating or moving the tool. 
   An example system for fracturing a subterranean formation according to the present invention includes a downhole conveyance selected from a group consisting of a drill string and coiled tubing, wherein the downhole conveyance is at least partially disposed in the wellbore; a drive mechanism configured to move the downhole conveyance in the wellbore; a pump coupled to the downhole conveyance to flow a fluid though the downhole conveyance; and a computer configured to control the operation of the drive mechanism and the pump. The computer comprises one or more processors and a memory. The memory comprises executable instructions that, when executed, cause the one or more processors to determine the time delay between inducing the first fracture and inducing a second fracture, wherein the time delay is determined based, at least in part, on one or more stress fields of one or more affected layers during opening or closing of the fracture. 
   The fracturing tool includes tool body to receive the fluid, the tool body comprising a plurality of fracturing sections, wherein each fracturing section includes at least one opening to deliver the fluid into the subterranean formation at an angular orientation and a sleeve disposed in the tool body to divert the fluid to at least one of the fracturing sections while blocking the fluid from exiting another at least one of the fracturing sections. 
   The features and advantages of the present invention will be apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These drawings illustrate certain aspects of some of the embodiments of the present invention, and should not be used to limit or define the invention. 
       FIG. 1  is a schematic block diagram of a wellbore and a system for fracturing. 
       FIG. 2A  is a graphical representation of a wellbore in a subterranean formation and the principal stresses on the formation. 
       FIG. 2B  is a graphical representation of a wellbore in a subterranean formation that has been fractured and the principal stresses on the formation. 
       FIG. 3  is a flow chart illustrating an example method for fracturing a formation according to the present invention. 
       FIG. 4  is a graphical representation of a wellbore and multiple fractures at different angles and fracturing locations in the wellbore. 
       FIG. 5  is a graphical representation of a formation with a high-permeability region with two fractures. 
       FIG. 6  is a graphical representation of drainage into a horizontal wellbore fractured at different angular orientations. 
       FIGS. 7A ,  7 B, and  7 C illustrate a cross-sectional view of a fracturing tool showing certain optional features in accordance with one example implementation. 
       FIG. 8  is a graphical representation of the drainage of a vertical wellbore fractured at different angular orientations. 
       FIG. 9  is a graphical representation of a fracturing tool rotating in a horizontal wellbore and fractures induced by the fracturing tool. 
       FIG. 10   a  is a graphical representation of fracture generation. 
       FIG. 10   b  is a graph depicting the compression creep process. 
       FIG. 11  is a graphical representation of stress redirection by a fracture. 
       FIG. 12  is a graph depicting fracture gradient change for hard rock. 
       FIG. 13  is a graph depicting corrected stress change. 
       FIG. 14  is a graphical representation of creep effects in fracture development. 
       FIG. 15  is a graphical representation of maximizing the second fracture length based on the first fracture gradient change. 
       FIG. 16  is a graphical representation depicting typical shear stress and viscosity of a rock formation as a function of shear rate. 
   

   DETAILED DESCRIPTION 
   The present invention relates generally to methods, systems, and apparatus for inducing fractures in a subterranean formation and more particularly to methods and apparatus to place a first fracture with a first orientation in a formation followed by a second fracture with a second angular orientation in the formation. Furthermore, the present invention may be used on cased well bores or open holes. 
   The methods and apparatus of the present invention may allow for increased well productivity by the introduction of multiple fractures at different angles relative to one another in a wellbore. 
     FIG. 1  depicts a schematic representation of a subterranean well bore  100  through which a fluid may be injected into a region of the subterranean formation surrounding well bore  100 . The fluid may be of any composition suitable for the particular injection operation to be performed. For example, where the methods of the present invention are used in accordance with a fracture stimulation treatment, a fracturing fluid may be injected into a subterranean formation such that a fracture is created or extended in a region of the formation surrounding well bore  100  and generates pressure signals. The fluid may be injected by injection device  105  (e.g., a pump). At wellhead  115 , a downhole conveyance device  120  is used to deliver and position a fracturing tool  125  to a location in the wellbore  100 . In some example implementations, the downhole conveyance device  120  may include coiled tubing. In other example implementations, downhole conveyance device  120  may include a drill string that is capable of both moving the fracturing tool  125  along the wellbore  100  and rotating the fracturing tool  125 . The downhole conveyance device  120  may be driven by a drive mechanism  130 . One or more sensors may be affixed to the downhole conveyance device  120  and configured to send signals to a control unit  135 . 
   The control unit  135  is coupled to drive unit  130  to control the operation of the drive unit. The control unit  135  is coupled to the injection device  105  to control the injection of fluid into the wellbore  100 . The control unit  135  includes one or more processors and associated data storage. In one example embodiment, control unit  135  may be a computer comprising one or more processors and a memory. The memory includes executable instructions that, when executed, cause the one or more processors to determine the time delay between inducing the first fracture and inducing the second fracture. In certain example implementations, the time delay between the inducement of the first fracture and the inducement of the second fracture is based, at least in part, on physical measurements. In certain example implementations, the time delay between the inducement of the first fracture and the inducement of the second fracture is based, at least in part, on simulation data. In one embodiment, the control unit  135  determines the time delay based, at least in part, on one or more stress fields of one or more affected layers of the formation that are altered during the opening and closing of the first fracture. 
   Stress fields in one or more layers of the formation that are altered by the first fracture may be measured using one or more devices. In certain embodiments, one or more tilt meters  140  are placed at the surface and are configured to generate one or more outputs. The outputs of the tilt meters are indicative of the magnitudes and orientations of the stress fields. In other example implementations, the one or more tilt meters  140  are disposed in the subterranean formation. For example, the tilt meters  140  may be displaced in the formation at a location near the fracturing level. The outputs from the tilt meters  140  during the opening or closing of the first fracture are relayed to the control unit  135 . As mentioned above, the control unit  135  may determine the time delay based, at least in part, on one or more of these tilt meter outputs. 
   In other example systems, a plurality of microseismic receivers  145  are placed in an observation well. These microseismic receivers  145  are configured to generate one or more outputs based on measured stress fields of one or more affected layers. In one example implementation, the microseismic receivers  145  are placed in the observation well at a depth that is close enough to the level of fracturing to produce meaningful output. Microseismic receivers  145  may also be placed at about the surface. Outputs of the microseismic receivers  145  are received by the control unit  135 . The outputs of the microseismic receivers  145  include outputs generated during one or more of the opening and closing of the first fracture. In general, the microseismic receivers  145  listen to signals that may be characterized as “microseisms” or “snaps” when microcracks are occurring. The received signals of these “snaps” are received at multiple microseismic receivers. The system then triangulates the received “snaps” to determine a location from which the signals originated. In certain example implementations, the time delay is determined based, at least in part, on the one or more outputs of the microseismic receivers  145 . In certain example implementations, outputs from tilt meters, discussed above, are used in combination with the outputs from the microseismic receivers  145  to determine the time delay. 
   In some example implementations, the measured stress fields are used to determine one or more of stick-slip velocity, Maxwell creep, and pseudo-Maxwell creep. In some example implementations, the one or more of stick-slip velocity, Maxwell creep, and pseudo-Maxwell creep are, in turn, used to determine the time delay between the inducement of the first fracture and the inducement of the second fracture. 
   In some implementations, other formation characteristics of the formation that are measured during fracturing are used to determine the time delay. In certain example implementations, the control unit  135  determines the length of fracture of the first fracture in one or more of an inward and outward direction, based, at least in part, on the stress fields. In certain example implementations, the control unit  135  determines the stress change of a wavefront of the first fracture based, at least in part, on the stress fields. In some example implementations, the time delay is based on one or more of these other formation characteristics. 
   In certain example implementations, the one or more processors of control unit  135  are configured to monitor one or more of the extension of the first fracture and the expansion effect velocity of the first fracture. In certain example implementations, the one or more processors determine the time delay based, at least in part, on one or more of the monitored extension of the first fracture and the expansion effect velocity of the first fracture. 
   In other embodiments, the control unit  135  controls the pumping of the treatment fluid, which, in turn, controls a fracture extension velocity of one or more of the first and second fractures. In some example implementations, the pumping of the treatment fluid is controlled to prevent a fracture tip of the second fracture from advancing beyond one or more of a stick-slip front of the first fracture and a Maxwell creep front of the first fracture. In this instance, the fracture tip velocity of the second fracture may be simulated by the one or more processors. In other example implementations, the fracture tip velocity of the second fracture may be determined based, at least in part, on historical data from other fracturing operations. 
     FIG. 2  is an illustration of a wellbore  205  passing though a formation  210  and the stresses on the formation. In general, formation rock is subjected by the weight of anything above it, i.e. σ z  overburden stresses. By Poisson&#39;s rule, these stresses and formation pressure effects translate into horizontal stresses σ x  and σ y . In general, however, Poisson&#39;s ratio is not consistent due to the randomness of the rock. Also, geological features, such as formation dipping may cause other stresses. Therefore, in most cases, σ x  and σ y  are different. 
     FIG. 2B  is an illustration the wellbore  205  passing though the formation  210  after a fracture  215  is induced in the formation  210 . Assuming for this example that σ x  is smaller than σ y , the fracture  215  will extend into the y direction, following the minimum stress plane. The orientation of the minimum stress vector direction is, however, in the x direction. As used herein, the orientation of a fracture is defined to be a vector perpendicular to the fracture plane. 
   As fracture  215  opens, fracture faces are pushed in the x direction. Because formation boundaries cannot move, the rock becomes more compressed, increasing σ x . Over time, effects of compression are felt further from the fracture face location. The increased stress in the x direction, σ x , quickly becomes higher than σ y  causing a change in the local stress direction. When the stimulation process of the first fracture is stopped, the fracture will tend to close as the rock moves back to its original shape, especially due to the increased σ x . Even after the fracture is closed, the presence of propping agents that are placed in the first fracture to keep the fracture at least partially open causes stresses in the x direction. These stresses in the formation cause a subsequent fracture (e.g., the second fracture) to propagate in a new direction shown by projected fracture  220 . These stresses will be kept even at a higher level due to the latency of stresses due to the Maxwell creep or pseudo-Maxwell creep. The present disclosure is directed to initiating fractures, such as projected fracture  220 , while the stress field in the formation  210  is temporarily altered by an earlier fracture, such as fracture  215 . 
     FIG. 3  is a flow chart illustration of an example implementation of one method of the present invention, shown generally at  300 . The method includes determining one or more geomechanical stresses at a fracturing location in step  305 . In some implementations, step  305  may be omitted. In some implementations, this step includes determining a current minimum stress direction at the fracturing location. In one example implementation, information from tilt meters or micro-seismic tests performed on neighboring wells is used to determine geomechanical stresses at the fracturing location. In some implementations, geomechanical stresses at a plurality of possible fracturing locations are determined to find one or more locations for fracturing. Step  305  may be performed by the control unit  135  by computer with one or more processors and associated data storage. 
   The method  300  further includes initiating a first fracture at about the fracturing location in step  310 . The first fracture&#39;s initiation is characterized by a first orientation line. In general, the orientation of a fracture is defined to be a vector normal to the fracture plane. In this case, the characteristic first orientation line is defined by the fracture&#39;s initiation rather than its propagation. In certain example implementations, the first fracture is substantially perpendicular to a direction of minimum stress at the fracturing location in the wellbore. 
   The initiation of the first fracture temporarily alters the stress field in the subterranean formation, as discussed above with respect to  FIGS. 2A and 2B . The duration of the alteration of the stress field may be based on factors such as the size of the first fracture, rock mechanics of the formation, the fracturing fluid seeping into the formation, and subsequently injected proppants, if any. There is some permanency to the effects caused from injected proppants. Unfortunately, as the fracture closes the final residual effect attributed to the proppant bed is just a couple of millimeters frac face movement and may be less. Due to the temporary nature of the alteration of the stress field in the formation, there is a limited amount of time for the system to initiate a second fracture at about the fracturing location before the temporary stresses alteration has dissipated below a level that will result in a subsequent fracture at the fracturing being usefully reoriented. 
   A time delay between the induction of the first fracture and the second fracture may be necessary to increase the fracture length of the second fracture. After initiating a first fracture at a fracturing location in step  310 , the method includes determining a time delay between inducing a first fracture and inducing a second fracture (block  312 ). In certain example implementations, during the fracturing process, one or more effects and characteristics of the fracturing process are measured. These measured effects and characteristics for a particular fracturing process may differ according to the type of affected layer of the formation. These measurements may be used to determine the time delay in step  312 . In certain implementations, shear effects between affected layers are used to determine the time delay in step  312 . The time delay is determined from the creep velocity in a material exposed to stress. In hard rock, the Maxwell type creep phenomenon is very slow or even essentially non-existent in certain stimulations. The Maxwell phenomenon assumes that all material has an ability to deform over time. This movement, or deformation, is characterized by a conventional well-known relationship of viscosity—assuming that rock, for instance, is a viscous Newtonian fluid with viscosities with an order of magnitude of millions Poise. In comparison, water has a viscosity of 1 centi-Poise. The relationship is generally defined as Shear rate=du/dy=Shear Stress/viscosity. With a viscosity of millions, the shear rate is infinitesimally small. 
   Using the shearing phenomenon between layers, a pseudo-Maxwell creep phenomenon can be observed. When the shear stress is sufficiently large, then a “Mode II Sliding Fault” occurs. During this time, a small portion of the fault faces “sticks” to each other; while another portion “slips”—a main basis of the “stick-slip” theory. The sticking process is based on a dry friction model, and is therefore much larger than the slip process. This means that the stick-slip scenario can be approximated as “thixotrophic fluid,” with certain “out-of-limit” n′ K′ values. The Herschel-Bulkley relationship may therefore be used in the assumptions to compute the shear stresses as a function of different shear rates between the slip faces. The following relationship may be used: Shear Stress−Initial Shear Rate+K′*(Shear Rate)^n′. As an example,  FIG. 16  depicts Shear Stress versus Shear Rate for a slip plane located at a depth of 5000 ft., and selecting K′=0.8*depth, and n′=0.2, and initial shear equals 500 psi. The apparent viscosity  1600  at every shear rate may be computed using this “Newtonian” relationship. Shear stress  1605  is also plotted. The initial viscosity of the rock is approximately equal to 100 million Poise. This initial viscosity drops rapidly with velocity to about 5 million Poise. 
   The Maxwell creep relationship is more adaptable to soft rocks as such material is essentially liquefied. Even in such a situation, however, the particle size is generally large. During the movement process, some amount of stick-slip occurs. The stick-slip process in this example may be envisioned as balls (the large particle) jumping over other balls. The use of the Herschel-Bulkley approach would therefore be applicable directly since this process can be approximated to be a thixotropic behavior. As before, the “out of limit” n′ K′ values may be defined and the Herschel Bulkley relation may be used to compute the shear stress as a function of shear rate. 
   The time delay computations may largely depend upon the integration of the shear rates over the complete height of the fracture with respect to the displacement of the fracture face and the time during which fracture is being extended and fracture faces being pushed away from each other. This computation will result in the location of the maximum stress at the maximum extension point, as show in  FIG. 15 , at the time pumping of the first fracture is stopped. 
   In another embodiment, determination of a time delay between a first fracture and a second fracture is based, at least on in part, on evaluating the effects of closure of the first fracture after the first fracture stimulation has ceased. The effects of closure of the first fracture include, for example, one or more of stick-slip between the affected layers, Maxwell creep effects of the affected layers, pseudo-Maxwell creep effects of the affected layers, lapse of time between initiating the first fracture and closure of the first fracture, the maximum stress location at the maximum extension point caused by the first fracture during the outward direction of the fracture effects, and length duration of time as the stresses drop inwardly and outwardly. Maxwell creep is a plastic function that assumes that a formation is a liquid characterized by a viscosity. Maxwell creep may also be modeled in a pseudo-Maxwell domain, which assumes that a formation has a pseudo-plasticity. The concept of pseudo-plasticity considers letting a formation crack and then modeling the crack as a viscous element, with layers of the formation moving against each other. In a pseudo-Maxwell modeling domain the formation layers moving against each other react as a plastic element. One skilled in the art may also use ductility/pseudo ductile and malleability/malleable/pseudo-malleable characteristics of the formation in the same manner as pseudo-Maxwell creep for determination of the time delay. 
   In another implementation, the time delay determination may be based at least in part on determining when stress direction modification at the wellbore drops below a stress differential between minimum stress and maximum stress, to provide a maximum time delay for inducing the second fracture. At the maximum time delay, a second fracture may be initiated as shown in  FIG. 15 . 
   Yet another example time delay determination is based, at least in part, on when stress direction modification drops below the stress differential between minimum and maximum levels in the area of the tip. During this time, fracture tip velocity is simulated. To optimize the length of the second fracturing, the second fracture tip should not advance beyond the outward stick-slip or creep front created by the first fracture. Based on the fracture tip velocity, the pumping of treatment fluid may be controlled to prevent the fracture tip of the second fracture from advancing beyond a stick-slip front of the first fracture or a Maxwell creep front of the first fracture. 
   In another example implementation, the time delay is determined, at least in part, on one or more fracture opening effects of the affected layers. The fracture opening effects may be based upon localized fracture gradient changes of the first fracture or dilatancy of the affected layers. 
   In one example implementation, movement of the wavefront caused by the first fracture is monitored. In certain example implementations, the time delay is determined based, at least in part, on the velocity and intensity of the wavefront data of the first fracture. In some example implementations, one or more tilt meters or microseismic receivers are used to obtain one or more of the velocity and intensity of the first fracture wavefront. The data received from the one or more tilt meters and microseismic receivers may be transmitted in real-time by use of telemetry or SatCom approaches. 
   In certain example implementations, the time delay is determined based, at least in part, by monitoring closure of the first fracture. Closure at the mouth of the first fracture is especially useful in determining the total time delay that needs to be considered. In some implementations, the closure time, which could be very long or reasonably short, is added to the total delay time. Again, one or more tilt meters or microseismic receivers may be used independently or in combination to obtain closure of the first fracture data. 
   In yet another example implementation, extension and expansion velocity of the first fracture are monitored. The time delay may then be determined based, at least in part, on the expansion velocity and extension of the first fracture. 
   Therefore, in step  315  a second fracture is initiated at about the fracturing location before the temporary stresses from the first fracture have dissipated. In some implementations, the first and second fractures are initiated within 24 hours of each other. In other example implementations, the first and second fractures are initiated within four hours of each other. In still other implementations, the first and second fractures are initiated within an hour of each other. 
   The initiation of the second fracture is characterized by a second orientation line. The first orientation line and second orientation lines have an angular disposition to each other. The plane that the angular disposition is measured in may vary based on the fracturing tool and techniques. In some example implementations, the angular disposition is measured on a plane substantially normal to the wellbore axis at the fracturing location. In some example implementations, the angular disposition is measured on a plane substantially parallel to the wellbore axis at the fracturing location. 
   In some example implementations, step  315  is performed using a fracturing tool  125  that is capable of fracturing at different orientations without being turned by the drive unit  130 . Such a tool may be used when the downhole conveyance  120  is coiled tubing. In other implementations, the angular disposition between the fracture initiations is cause by the drive unit  130  turning a drillstring or otherwise reorienting the fracturing tool  125 . In general there may be an arbitrary angular disposition between the orientation lines. In some example implementations, the angular orientation is between 45° and 135°. More specifically, in some example implementations, the angular orientation is about 90°. In still other implementations, the angular orientation is oblique. 
   In step  320 , the method includes initiating one or more additional fractures at about the fracturing location. Each of the additional fracture initiations are characterized by an orientation line that has an angular disposition to each of the existing orientation lines of fractures induced at about the fracturing location. In some example implementations, step  320  is omitted. Step  320  may be particularly useful when fracturing coal seams or diatomite formations. 
   The fracturing tool may be repositioned in the wellbore to initiate one or more other fractures at one or more other fracturing locations in step  325 . For example, steps  310 ,  315 , and optionally  320  may be performed for one or more additional fracturing locations in the wellbore. An example implementation is shown in  FIG. 4 . Fractures  410  and  415  are initiated at about a first fracturing location in the wellbore  405 . Fractures  420  and  425  are initiated at about a second fracturing location in the wellbore  405 . In some implementations, such as that shown in  FIG. 4 , the fractures at two or more fracturing locations, such as fractures  410 - 425 , and each have initiation orientations that angularly differ from each other. In other implementations, fractures at two or more fracturing locations have initiation orientations that are substantially angularly equal. In certain implementations, the angular orientation may be determined based on geomechanical stresses about the fracturing location. 
     FIG. 5  is an illustration of a formation  505  that includes a region  510  with increased porosity or permeability, relative to the other portions of formation  505  shown in the figure. In this method it is assumed that more porous rock formations are more permeable. However, it is noted that in actual formations, that is not always the case. When fracturing to increase the production of hydrocarbons, it is generally desirable to fracture into a region of higher permeability, such as region  510 . The region of high permeability  510 , however, reduces stress in the direction toward the region  510  so that a fracture will tend to extend in parallel to the region  510 . In the fracturing implementation shown in  FIG. 5 , a first fracture  515  is induced substantially perpendicular to the direction of minimum stress. The first fracture  515  alters the stress field in the formation  505  so that a second fracture  520  can be initiated in the direction of the region  510 . Once the fracture  520  reaches the region  510  it may tend to follow the region  510  due to the stress field inside the region  510 . In this implementation, the first fracture  515  may be referred to as a sacrificial fracture because its main purpose was simply to temporarily alter the stress field in the formation  505 , allowing the second fracture  520  to propagate into the region  510 . Even though first fracture  515  is referred to as a sacrificial fracture, in present day technology prior to using this technique, first fracture  515  is the result of a conventionally placed fracture; thus offering conventional level of benefits. 
     FIG. 6  illustrates fluid drainage from a formation into a horizontal wellbore  605  that has been fractured according to method  100 . In this situation, the effective surface area for drainage into the wellbore  605  is increased substantially by fracture  615 . However, production flow through this fracture has to travel radially to the wellbore, thus creating a massive constriction at the wellbore. In the example shown in  FIG. 6 , a second, smaller fracture is created allowing fluid flow along plane  610  and fracture  615  are able to enter the wellbore  605 . In addition, flow in fracture  615  does not have to enter the wellbore radially.  FIG. 6  also shows flow entering the fracture  615  in a parallel manner; which then flows through the fracture  615  in a parallel fashion into fracture  610 . This scenario causes very effective flow channeling into the wellbore. 
   In general, additional fractures, regardless of their orientation, provide more drainage into a wellbore. Each fracture will drain a portion of the formation. Multiple fractures having different angular orientations, however, provide more coverage volume of the formation, as shown by the example drainage areas  801  and  802  illustrated in  FIG. 8 . The increased volume of the formation drained by the multiple fractures with different orientations may cause the well to produce more fluid per unit of time. 
   A cut-away view of an example fracturing tool  125 , shown generally at  700 , that may be used with method  300  is shown in  FIGS. 7A-7C . The fracturing tool  700  includes at least two fracturing sections, such as fracturing sections  705  and  710 . Each of sections  705  and  710  are configured to fracture at an angular orientation, based on the design of the section. In one example implementation, fluid flowing from section  710  may be oriented obliquely, such as between 45° to 90°, with respect to fluid flowing from section  705 . In another implementation fluid flow from sections  705  and  710  are substantially perpendicular. 
   The fracturing tool includes a selection member  715 , such as sleeve, to activate or arrest fluid flow from one or more of sections  705  and  710 . In the illustrated implementation selection member  715  is a sliding sleeve, which is held in place by, for example, a detent. While the selection member  715  is in the position shown in  FIG. 7A , fluid entering the tool body  700  exits though section  705 . 
   A valve, such as ball valve  725  is at least partially disposed in the tool body  700 . The ball valve  725  includes an actuating arm allowing the ball valve  725  to slide along the interior of tool body  700 , but not exit the tool body  700 . In this way, the ball valve  725  prevents the fluid from exiting from the end of the fracturing tool  125 . The end of the ball value  725  with actuating arm may be prevented from exiting the tool body  700  by, for example, a ball seat (not shown). 
   The fracturing tool further comprises a releasable member, such as dart  720 , secured behind the sliding sleeve. In one example implementation, the dart is secured in place using, for example, a J-slot. 
   In one example implementation, once the fracture is induced by sections  705 , the dart  720  is released. In one example implementations, the dart is released by quickly and briefly flowing the well to release a j-hook attached to the dart  725  from a slot. In other example implementations, the release of the dart  720  may be controlled by the control unit  135  activating an actuator to release the dart  720 . As shown in  FIG. 7B , the dart  720  causes the selection member  715  to move forward causing fluid to exit though section  710 . 
   As shown in  FIG. 7C , the ball value  725  with actuating arm may reset the tool by forcing the dart  720  back into a locked state in the tool body  700 . The ball value  725  also may force the selection member  715  back to its original position, before fracturing was initiated. The ball value  725  may be forced back into the tool body  700  by, for example, flowing the well. 
   Another example fracturing tool  125  is shown in  FIG. 9 . Tool body  910  receives fracturing fluid though a drill string  905 . The tool body has an interior and an exterior. Fracturing passages pass from the interior to the exterior at an angle, causing fluid to exit from the tool body  910  at an angle, relative to the axis of the wellbore. Because of the angular orientation of the fracturing passages, multiple fractures with different angular orientations may be induced in the formation by reorienting the tool body  910 . In one example implementation, the tool body is rotated to reorient the tool body  910  to fracture at different orientations and create fractures  915  and  920 . For example, the tool body may be rotate about 180°. In the example implementation shown in  FIG. 9  where the fractures  915  and  920  are induced in a horizontal or deviated portion of a wellbore, the drill string  805  may be rotate more than the desired rotation of the tool body  910  to account for friction. 
   Conventional fracturing does not generally consider the time factor between each subsequent fracture. In fact subsequent fractures are sometimes initiated many hours or even days apart. The plasticity of the formation has also not been considered conventionally as a major factor in the behavior of fracture development in the formation. When plasticity or creep is factored into evaluation of stimulating a well bore, time becomes a major factor as to where a fracture will initiate and extend.  FIG. 10   a  illustrates a more realistic “plastic” behavior for fracture generation given formation  1000  with wellbore  1020 . As a layer or group of layers in the formation  1000  is being fracture stimulated, the fracture faces will part from each other as shown. As the fracture faces move δX  1010  from each other; the boundary of the layer separates for a distance of X  1025  from the fracture  1015 . The rock beyond X  1025  is held by friction on the upper slip plane  1030  and lower slip plane  1035  as shown. At point X  1025 , the rock has not moved and hence, compression forces cause the rock to expand upwards; lifting the massive mass above it. After some time, due to plastic creep, the front X  1025  will slowly move to the right; opening the fracture  1015  somewhat while relaxing the overburden stress increase. 
     FIG. 10   b  is a graph depicting the compression creep process. A small section of the formation  1000  is divided into three sections,  1040 ,  1045 , and  1050 . As the fracture  1015  opens, compression only affects the first section  1040 . Front “X” is held in position at that instant. After a first period of time, the second section  1045  begins to compress plastically and quickly followed by shearing of the bond to the bordering formations. The shearing stops just before reaching section  1050 . Section  1045  quickly compresses elastically while section  1040  expands accordingly. Similarly, after a second period of time, longer than the first period of time, section  1050  begins to compress plastically. This process repeats itself until no further expansion occurs. 
   In general,  FIG. 11  depicts stress redirection by a fracture.  FIG. 11  shows two phenomena in the process depicted in  FIG. 10   a  and  FIG. 10   b . As a fracture (not shown) opens up, the formation  1100  is being compressed directly into the direction of arrow  1105 . A smaller amount of compression (as determined by the Poisson&#39;s ratio) is directed into the direction of the fracture itself as indicated by arrows  1110  and  1115 . The modification of stresses into directions  1110  and  1115  depends upon the compressibility of the formation  1100  itself and is not dependent upon the location of the fracture. Frac gradients are depth dependent. Therefore, modification of frac gradients are inversely dependent to the depth of the fracture.  FIG. 12  shows the fracture gradient change for hard rock (with compressibilities of 1.8E-7/psi) for two depths and the direct inverse dependency of the frac gradient effects. For the plots of  FIG. 12 , the fracture half-length was assumed to be 200 ft. and the fracture width during the stimulation job was 0.75″ (prior to closure). 
   The second phenomenon that can be described in  FIG. 11  is when a second fracture is created perpendicular to the first fracture. As the second fracture opens and extends, as per  FIG. 12 , the fracture stress gradient differential continues to drop with distance. For example, if the minimum and maximum stress gradients differ by 0.2 and the depth of the fracture is 10,000 ft, at approximately 90 ft the fracture will start to turn into the original fracture direction (parallel to the first fracture). However, based upon  FIG. 11 , the opening of the second fracture also pushes sideways as indicated by arrow  1105 . Again, a smaller amount of creep movement pushes into the direction of the fracture extension as indicated by arrows  1110  and  1115 . This latter “minor” push adds the maximum straight fracture extension to a few feet longer than 90 ft., as shown in  FIG. 13 . For sandstone formations, since it is a dilatant material and it has a volumetric creep less than zero, the “minor” push above extends the fracture even further than the previously discussed rock formations.  FIG. 13  shows the added “push” that maintains the fracture to extend somewhat longer into the unnatural minimum stress direction. It should be noted, that stress modification in softer rock is much less than in harder rock. However, stress differentials in softer rocks are also much less than in harder rock. Thus, the effectiveness of this process is equally acceptable in both soft and hard rock applications. 
   Plasticity relates to time. Placement of a 200 ft. fracture takes some time to perform and to allow for some occurrence of plastic creep motion. Even though the true plastic creep takes a much longer time, stick-slip motion can be characterized as behaving like plastic motion. The primary mechanics behind stick-slip motion is purely elastic and hence stick-slip motion occurs at a faster pace than true plastic creep.  FIG. 12  shows that the near wellbore fracture gradient change is tremendously high. The fracture gradient change occurs during the hydraulic fracturing process. When pumping stops, the near wellbore opening can collapse so as to rapidly and significantly reduce stresses, as shown in  FIG. 14 . The horizontal axis and vertical of axis of  FIG. 14  are the same as those shown in  FIG. 12 . The difference between  FIG. 12  and  FIG. 14  is that the time factor is normalized in order to fit the distance curve perfectly. 
     FIG. 14  shows that initially frac gradient changes substantially, but also elastically as represented in the first step in  FIG. 10(   b ). At this time, the near wellbore rock has not yet deformed plastically, although some plastic deformation occurs throughout a certain distance from the fracture (see the bottom of line  1415 ). If no time delay is taken for a major plastic deformation to occur and pumping is stopped, the fracture immediately collapses, even though some minor frac gradient change occurs nearby (see line  1430 ). With time, the deformation front moves away from the wellbore as a result primarily of the stick-slip process as shown by lines  1405 ,  1410 , and  1415 . The maximum slip distance can be limited by some “max change limit” which basically represents the true elastic limit for the formation. For example, assume that the stress gradient difference is represented by line  1435  and that the pumping stops at a the time depicted by line  1420 . Then, since every position away from the wellbore has been deformed plastically, stress differences remain high with the exception of the near wellbore which drops considerably. This drop could fall below the “Min/Max Stress Difference” level  1435  and hence, fracturing using conventional fracturing processes would re-open the first fracture. However, using a hydrajet fracturing process, deep hydrajetting could cause the perforation to bypass the near-wellbore stress effects and respond to the far-field stress condition. 
     FIG. 15  is a graphical representation of maximizing the second fracture length based on the first fracture gradient change in order to achieve maximum fracturing. As the first fracture opens (starting from line  1505 ) the stress effects of the first fracture jump down from the first line  1505  to the right. This is due to the “stick-slip” process plus some of the pure “Maxwell” type creep effects. The stress effects of the first fracture continue to move to the right (lines  1510  through  1540 ). If pumping is stopped when stresses are as shown by line  1545  and no other fracturing is performed, the stress lines will continue to move to the right while dying off as shown by lines  1550 - 1555 . Observing the Min/Max stress difference (line  1560 ), it is desirable to start the second fracture on or before the line  1540  condition. As  FIG. 15  shows, line  1540  starts crossing the Min/Max difference line  1560 . It is theorized, that even though line  1540  is slightly below the Min/Max difference line  1560 , when using SurgiFrac techniques, an orthogonal fracture can be created because the method could extend a little beyond the near wellbore condition. The condition depicted by line  1550  is quite too low for any process and the redirection technique will fail. On the other hand, it may be safe to start the second fracture to follow the condition depicted by line  1525 . Using the condition depicted by line  1525 , however, the second fracture is completed too early resulting in only a short fracture extension before the fracture bends to the natural fracture direction. The conditions depicted in  FIG. 15  illustrate that compressional effects translate to upward shift in the rock which provides some condition that is detectable using tilt meters, microseismic receivers, and other equipment known to one skilled in the art. By detecting the upward shift in real time, the extension of the fracture can be sped up or slowed down to provide a maximum length second fracture. 
   In one embodiment, the second fracture length is less optimized by inducing the second fracture at a time delay from the inducement of the first fracture as shown by line  1540 . 
   In another embodiment obtaining a maximum length fracture for the formation requires inducing the second fracture at a time delay from the inducement of the first fracture as shown by line  1550  in order to achieve maximum extension of the fracture of the formation. 
   In yet another embodiment, in order to obtain the maximum fracture length the second fracture length is optimized by inducing the second fracture at a time delay from the inducement of the first fracture as shown by line  1540  but then slowing down the fracture tip to wait for the condition depicted by line  1550  to occur. 
   Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.