FIELD

The invention relates generally to fixed-cutter drill bits that, in addition to drilling a borehole, create a core that is ejected into the annulus and returned to the surface in the drilling mud to be captured and analyzed, and methods of using the same.

BACKGROUND AND SUMMARY

Well drilling is the process of drilling a hole in the ground for the extraction of a natural resource such as ground water, brine, natural gas, or petroleum, for the injection of a fluid from the surface to a subsurface reservoir, or for subsurface formation evaluation and monitoring. One type of drilling tool uses fixed cutters to shear rock with a continuous scraping motion, known as a fixed-cutter or drag bit. Fixed-cutter bits are configured having a cutting portion disposed along a face and shoulder portion of the bit. The cutting portion may also extend a distance into a central opening in the face portion of the bit. The cutting portion may include a plurality of cutting elements that project outwardly away from the bit face and shoulder surfaces.

Rate of penetration ("ROP"), or the speed at which a drill bit breaks the rock under it to deepen the borehole, normally measured in feet per hour or meters per hour, is a major challenge in drilling deep reservoirs. A fixed-cutter bit exhibiting improved rates of penetration would be well received in the industry.

In one aspect, embodiments disclosed herein relate to a drill bit including a bit head having a front face, a plurality of blades extending along at least a portion of the front face, the blades comprising cutters, a cavity for forming a core, the cavity being approximately centrally located in the front face of the bit between adjacent end portions of the plurality of blades, and a removable core breaking device disposed within the cavity. The core breaking device is configured to project toward the front face a distance to engage and destroy the so formed core into multiple smaller fragments prior to a core length exceeding a core diameter, or project toward the front face a distance to engage and break the so formed core into a substantially unitary core sample.

In other aspects, embodiments disclosed herein relate to a method of using a drill bit including providing a drill bit including a bit head having a front face, a plurality of blades extending along at least a portion of the front face, the blades comprising cutters, a cavity for forming a core, the cavity being approximately centrally located in the front face of the bit between adjacent end portions of the plurality of blades, and a removable core breaking device disposed within the cavity and configured to project toward the front face a distance to engage and destroy the so formed core into multiple smaller fragments prior to a core length exceeding a core diameter, or a removable core breaking device disposed within the cavity and configured to project toward the front face a distance to engage and break the so formed core into a substantially unitary core sample. The method further includes operating a drillstring having the drill bit on a distal end for a first period of time, the drill bit having the removable core breaking device disposed within the cavity configured to project a distance toward the front face for destroying the so formed core into multiple smaller fragments, or operating the drillstring having the drill bit for a second period of time, the drill bit having the removable core breaking device disposed within the cavity configured to project a distance toward the front face for breaking the so formed core into a substantially unitary core sample.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a perspective view of an embodiment of a fixed-cutter bit.

Figure 2 illustrates a front view of an embodiment of a fixed-cutter bit.

Figure 3 illustrates an embodiment of a fixed-cutter bit drilling a formation.

Figure 4A illustrates a cross-section view of an embodiment of a fixed-cutter bit including a core breaking device. Figure 4B illustrates a cross-section view of an embodiment of a fixed-cutter bit including a core breaking device.

Figure 5 illustrates a cross-section view of an embodiment of a fixed-cutter bit including a core breaking device.

DETAILED DESCRIPTION

A fixed-cutter bit that, in addition to drilling a full borehole, creates cores that are ejected into the annulus and returned to the surface in the drilling mud to be captured and analyzed is disclosed. The fixed-cutter bit may be suitable for drilling in any subterranean formations in any downhole environment. The bit may have an end (e.g., a threaded end) which can be attached to a joint of drill pipe making up a drillstring. The bit may include a bit head having a longitudinal axis extending therethrough, and a plurality of cutters disposed around a front face (e.g., facing a bottom of the wellbore being drilled), shoulder portion, and gauge portion of the bit head. The cutters may be polycrystalline diamond compact (PDC) cutting elements. Alternatively, the cutting elements may be formed from hard materials other than PDC, such as tungsten carbide, or tungsten carbide with enhanced diamond coating, or any other suitable hard materials. Cutters may be arranged on a number of blades disposed on the front face of the bit, some or all of which extend away from the front face, and over the shoulder to the gauge portion of the bit. The bit may include any number of blades, the blades being evenly or unevenly spaced or oriented about the longitudinal axis, to accommodate drilling under a variety of drilling conditions. The bit may have an even or odd number of blades. For example, the front face of the bit may have two, three, four, five, six, eight, or more blades, depending upon the hardness of the formation to be drilled. The blades may be any height and width.

The fixed-cutter bit includes a number of openings or nozzles that extend through the front face portion of the bit. The nozzles serve to dispense drilling fluid from inside the bit to the surface of the particular formation being drilled. The dispensed fluid facilitates the drilling operation by cooling the bit and removing drilling debris from the working area of the bit (e.g., the front face, shoulder and gauge portions), and the core forming cavity described below.

The fixed-cutter bit includes a core forming cavity approximately centrally located in the face portion of the bit and that is formed between adjacent end portions of the blades. Alternatively, the cavity may be formed from a recessed portion in the face portion of the bit itself. However, preferably the cavity is formed from end portions of the blades because the placement of one or more cutters on adjacent the end portion of the blade serve to cut a diameter of the drilled formation, thereby generating a core within the cavity. For example, the diameter of a core formed in the cavity may range between 5mm and 50mm, and preferably between 10mm and 25mm. Additionally, the use of adjacent blade end portions to form the cavity provides openings in the cavity between each end portion to allow for broken, crushed, cut or trimmed core portions to be directed outwardly away from the cavity. The cavity may include an opening towards an evacuation channel, the opening having a width greater than or equal to a diameter of the core sample formed to render possible the evacuation of a unitary core sample towards the evacuation channel. For example, an evacuation channel or opening may be provided between blades to allow a unitary core sample or multiple smaller core fragments to be carried away. The evacuation channel may be configured to be a deeper channel than other spaces between the blades for evacuating drilled cuttings and other debris from the front face of the bit. The evacuation channel may also extend along the front face, preferably deeper than other standard spaces between the blades, for evacuating the core. A unitary core sample or multiple smaller core fragments may be allowed to pass from the cavity along the face portion of the bit to the bore of the hole to join other drilling debris and thereby not interfere with the cutting action of the bit. The fixed-cutter bit may include one or more core breaking devices disposed within the core forming cavity. The core breaking devices may be slightly off-center within the cavity and angled at any angle with respect to the longitudinal axis of the bit head. The angle at which the core breaking device may be positioned is often dictated by access from the front face of the bit for inserting and removing the core breaking device. Sizing (e.g., diameter) of the core breaking device may be dependent upon the bit size. Core breaking devices may be removable and interchangeable within the cavity.. For example, the core breaking devices may be threaded into a threaded hole, or could alternatively be press fit, or any other means of rigidly attaching the core breaking devices within the cavity.

In an embodiment, the core breaking device may include an extended cutter of any hardened material. For example, the extended cutter may be tungsten carbide. Or the extended cutter may be tungsten carbide with a diamond-enhanced coating. Still further, the extended cutter may be a PDC material. The extended cutter is configured to extend or project toward the front face of the bit and destroy the core being formed within the cavity before the core reaches a predetermined length. That is, the cutter extends toward the front face a distance to expose an edge or tip on a distal end of the cutter to engage the core proximate or near the core base and destroy the so formed core into multiple smaller fragments. In one embodiment, the extended cutter may be configured having a length such that it destroys the core before the core reaches a 1 :1 length to diameter ratio. That is, the extended cutter may destroy the core before a core length exceeds the core diameter. Destroying the core at or before the core reaches a 1 : 1 length to diameter ratio has been shown to improve ROP of the drill bit in a variety of formation types.

In another embodiment, the core breaking device may include a nozzle through which hydraulic fluid exits the bit head to impinge upon the core base and destroy the core being formed within the cavity. For example, softer and unconsolidated formations may be damaged more easily with hydraulic energy from a nozzle than harder, more dense formations. However, nozzles may be used ^' in some formations with or without complementary formation breaking devices. The nozzle may be any type of fluid nozzle, for example^ any type of fluid nozzle configured to direct a high-velocity jet of hydraulic fluid, or any fluid in any direction. When installed, the nozzle is in fluid communication with a hydraulic channel within the bit head receiving hydraulic fluid from a hydraulic source. For example, the hydraulic source may be the same as for the nozzles in the front face of the bit for cooling the bit and removing debris. Pump pressures may range between 1,000 psi and 4,000 psi, depending upon hole size, rig capability, and other factors. The nozzle includes an exit orifice having a certain diameter located at a distal end of the nozzle. In one embodiment, the nozzle may be configured so that fluid exiting the nozzle impinges on a core being formed at a distance from the distal end of the nozzle of approximately eight times the exit orifice diameter, or less. Distances beyond approximately eight times the exit orifice diameter have been found to have minimal or no effect for destroying the core. In other embodiments, the nozzle may be configured so that fluid exiting the nozzle impinges on a core being formed at a distance from the distal end of the nozzle of approximately six times the exit orifice diameter, or less. In yet other embodiments, the nozzle may be configured so that fluid exiting the nozzle impinges on a core at a distance from the distal end of the nozzle of approximately four times the exit orifice, or less.

In yet other embodiments, the core breaking device may be any type of standard breaking device or cutter used for causing a core being formed within the cavity to break by shearing. For example, the core breaking device may be a standard cutter. The core brealdng device may be a cutter configured to extend toward the front face a distance to expose a substantially flat surface at an angle with respect to a core axis to engage and break the so formed core into a substantially unitary core sample. As used herein, "unitary" may refer to substantially a single unit. The core breaking device may be configured to allow a length of the core being formed within the cavity to be approximately the same diameter as or exceed the core diameter, oftentimes by a substantial amount. For example, using the core breaking device, a core length may exceed twice the core diameter, or more.

In yet other embodiments, more than one core breaking device may be disposed within the cavity. For example, two or more extended cutters may be used. In another example, two or more nozzles may be used. In yet another example, a combination of extended cutters and nozzles may be used. In still further embodiments, a combination of extended and standard cutters may be used.

Figures 1 and 2 illustrate a fixed-cutter bit 100 in accordance with an embodiment. The fixed-cutter bit 100 may be suitable for drilling in any subterranean formations in any downhole environment. The bit may have an end 102 (e.g., a threaded end) which can be attached to a joint of drill pipe (not shown). The bit 100 may include a bit head 104 having a longitudinal axis 103 extending therethrough, and a plurality of cutters 110 disposed around a front face 105 (e.g., facing a bottom of the wellbore being drilled), shoulder portion 106, and gauge portion 107 of the bit head 104. The cutters 110 may be polycrystalline diamond compact (PDC) cutting elements. Alternatively, the cutters 110 may be formed from hard materials other than PDC. Cutters 110 may be arranged on a.number of blades 108 disposed on the front face 105 of the bit 100, some of which extend away from the front face 105, and over the shoulder portion 106 to the gauge portion 107 of the bit 100. The fixed-cutter bit 100 also includes a number of openings or nozzles 112 that extend through the front face 105 portion of the bit 100. The nozzles 112 serve to dispense drilling fluid from inside the bit to the surface of the particular formation being drilled. The dispensed fluid facilitates the drilling operation by cooling the bit and removing drilling debris from the working area of the bit. The fixed-cutter bit includes a core forming cavity 114 substantially centrally located in the face portion 105 of the bit 100 and that is formed between adjacent end portions of the blades 108. An evacuation channel 116 may be provided between blades 108 to allow core or core fragments to be carried away. As illustrated in Figure 3, the broken core sample 150 may be allowed to pass from the cavity along the face portion of the bit to the bore of the hole to join other drilling debris and thereby not interfere with the cutting action of the bit 100.

Figures 4A and 4B illustrate cross-section views of the bit 100 showing core breaking devices disposed within the core forming cavity 114. Figure 4A illustrates an extended cutter 120 of any hardened material. For example, the extended cutter 120 may be tungsten carbide. Or the extended cutter 120 may be tungsten carbide with a diamond-enhanced coating. Still further, the extended cutter 120 may be a PDC material. Or the extended cutter 120 may be any hard material other than PDC.

The extended cutter 120 is configured to extend a certain distance toward the front face 105 of the bit and destroy the core 150 being formed within the cavity 114 when the core 150 reaches a predetermined length X. That is, the extended cutter 120 extends toward the front face a distance to expose an edge or tip on a distal end of the cutter 120 to engage the core 150 proximate or near the core base and destroy the so formed core 150 into multiple smaller fragments. The extended cutter 120 may be configurable to destroy the core 150 being formed within the cavity 114 at any predetermined length. In one embodiment, the extended cutter 120 may destroy the core 150 before the core reaches a length X that exceeds the core diameter, that is, at or before a 1 :1 core length to core diameter ratio. In still further embodiments, the extended cutter 120 may destroy the core 150 before the core reaches a length X that is three-fourths the core diameter, that is, at or before a 0.75:1 core length to core diameter ratio. The extended cutter 120 may be configured to break the core 150 at predetermined lengths that are shorter still than those examples described above. The axis of the extended cutter 120 may be slightly off-center and disposed at a radial distance from the longitudinal axis 103 within the cavity 114. The axis of the extended cutter 120 may be angled within the cavity 114 at any angle a with respect to the longitudinal axis 103. The angle a at which the extended cutter 120 may be positioned is often dictated by available access from the front face 105 of the bit for inserting and removing the extended cutter 120. For example, the angle a of the extended cutter 120 may be less than 5 degrees, at least 5 degrees, 10 degrees, or 20 degrees with respect to the longitudinal axis 103, and up to 45 degrees, 60 degrees, or 75 degrees, or more. A diameter of the extended cutter 120 may be dependent upon the bit size. A longitudinal profile of the extended cutter 120 may be any geometry. For example, the extended cutter 120 may be tapered longitudinally, or have a constant diameter. The extended cutter 120 is removable and interchangeable within the cavity 114. For example, the extended cutter 120 may have threads 125 that engage a threaded hole in the bit 100.

Figure 4B illustrates a nozzle 121 through which hydraulic fluid 123 exits the bit head 104 to impinge upon the core 150 being formed within the cavity 114. The nozzle 121 may be any type of fluid nozzle, for example, any type of fluid nozzle configured to direct a high- velocity jet of hydraulic fluid, or any fluid in any direction, but generally in the direction of front face 105. The nozzle 121 is arranged however to avoid impinging upon any cutter or other structural component of the bit to avoid erosion of those components. When installed, the nozzle 121 is in fluid communication with a hydraulic channel (not shown) within the bit head 104 receiving hydraulic fluid from a hydraulic source. For example, the hydraulic source may be the same as for the nozzles 112 in the front face 105 of the bit for cooling the bit and removing debris. The nozzle 121 includes an exit orifice 122 located at a distal end having a certain diameter, which may be any diameter. In one embodiment, the nozzle 121 may be configured to direct fluid 123 exiting the nozzle to impinge on a base or near a base of a core 150 at a distance from the distal end of the nozzle of approximately eight times the exit orifice diameter, or less. In other embodiments, the nozzle 121 may be configured to direct fluid 123 exiting the nozzle 121 to impinge on a base or near a base of a core 150 at a distance from the distal end of the nozzle of approximately six times the exit orifice diameter, or less. In yet other embodiments, the nozzle 121 may be configured to direct fluid 123 exiting the nozzle 121 to impinge on a base or near a base of a core 150 at a distance from the distal end of the nozzle of approximately four times the exit orifice diameter, or less. As such, the nozzle 121 may destroy the core 150 before the core reaches a length X that exceeds the core diameter, that is, at or before a 1 : 1 core length to core diameter ratio. In still further embodiments, the nozzle 121 may destroy the core 150 before the core reaches a length X that is three-fourths the core diameter, that is, at or before a 0.75:1 core length to core diameter ratio. The nozzle 121 may be configured to destroy the core 150 at predetermined lengths that are shorter still than those examples described above.

The axis of the nozzle 121 may be slightly off-center and disposed at a radial distance from the longitudinal axis 103 within the cavity 114. The axis of the nozzle 121 may be angled within the cavity 114 at any angle a with respect to the longitudinal axis 103. The angle a at which the nozzle 121 may be positioned is often dictated by available access from the front face 105 of the bit for inserting and removing the nozzle 121. For example, the angle a of the nozzle 121 may be less than 5 degrees, at least 5 degrees, 10 degrees, or 20 degrees with respect to the longitudinal axis 103, and up to 45 degrees, 60 degrees, or 75 degrees, or more. Diameter of the exit orifice 122 may be dependent upon the bit size and may be any diameter. The nozzle 121 is removable and interchangeable within the cavity 114. For example, the nozzle 121 may have threads 125 that engage a threaded hole in the bit 100.

Figure 5 illustrates a core breaking device 130 installed within the core forming cavity 114 in accordance with alternative embodiments. The core breaking device may be any type of standard breaking device or cutter used for causing a core being formed within the cavity to break by shearing. For example, the core breaking device may be a standard cutter. The core breaking device may be a cutter configured to extend toward the front face a distance to expose a substantially flat surface at an angle with respect to a core axis to engage and break the so formed core into a substantially unitary core sample. The core breaking device may be configured to allow a length of the core being formed within the cavity to be approximately the same diameter as or exceed the core diameter, oftentimes by a substantial amount. For example, using the core breaking device, a core length may exceed twice the core diameter, or more.

Methods of using the fixed-cutter bit described herein include interchanging core breaking devices within the cavity at the well site depending upon whether a user wishes to recovery and analyze substantially unitary formation core samples, or increase the bit rate of penetration by destroying the core, with no interest in formation recovery and analysis.

Advantageously, embodiments disclosed herein provide a fixed-cutter bit with interchangeable core breaking devices that allow the user to decide whether generating substantially unitary core samples is desired or not. The core breaking devices are field interchangeable. Accordingly, the bit is modifiable to either focus on formation recovery and analysis (e.g., returning unitary core segments up a- well annulus), or on increasing the bit rate of penetration (e.g., destroying the core segment and returning multiple core fragments up the annulus)-. Core breaking devices may be selected at the rig depending on the objective of the bit run. Using the core breaking device, the bit rate of penetration may be increased by as much as 30%, or in some cases 50%, or higher. By using hydraulic energy with the nozzle to destroy the core being formed at the center of the bit, bit cleaning is improved and the incidence of formation packing and bit balling is reduced.

The claimed subject matter is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the appended claims.