Patent Grant
10428638
Technical Field
This disclosure relates to methods and systems for drilling boreholes in the earth in general, and more specifically, to methods and systems for drilling blast holes of the type commonly used in mining and quarrying operations.
Background
Various systems and methods for drilling boreholes are known in the art and have been used for decades in a wide variety of applications, for example, from oil and gas production, to mining, to quarrying operations. In mining and quarrying operations, such boreholes are typically filled with an explosive that, when detonated, ruptures or fragments the surrounding rock. Thereafter, the fragmented material can be removed and processed in a manner consistent with the particular operation. When used for this purpose, then, such boreholes are commonly referred to as “blast holes,” although the terms may be used interchangeably.
A number of factors influence the effectiveness of the blast, including the nature of the geologic structure (i.e., rock), the size and spacing of the blast holes, the burden (i.e., distance to the free face of the geologic structure), the type, amount, and placement of the explosive, as well as the order in which the blast holes are detonated. Generally speaking, the size, spacing, and depth of the blast holes represent the primary means of controlling the degree of rupture or fragmentation of the geologic structure, and considerable effort goes into developing a blast hole specification that will produce the desired result. Because the actual results of the blasting operation are highly correlated with the degree to which the actual blast holes conform to the desired blast hole specification, it is important to ensure that the actual blast holes conform as closely as possible to the desired specification.
Unfortunately, however, it has proven difficult to form or drill blast holes that truly conform to the desired specification. First, a typical blasting operation involves the formation several tens, if not hundreds, of blast holes, each of which must be drilled in proper location (i.e., to form the desired blast hole pattern) and to the proper depth. Thus, even where it is possible to achieve a relatively high hole compliance rate (i.e., the percentage of blast holes that comply with the desired specification), the large number of blast holes involved in a typical operation means that a significant number of blast holes nevertheless may fail to comply with the specification. In addition, even where blast holes are drilled that do comply with the desired specification, a number of post-drilling events, primarily cave-ins, can make a blast hole non-compliant. Indeed, such post-drilling events can be major contributors to blast hole non-compliance.
Still further, because of the large number of blast holes that are typically required for a single blasting operation, methods are constantly being sought that will allow the blast holes to be formed or drilled as rapidly as possible. As with most endeavors, however, there is an inverse relationship between speed and quality, and systems that work to increase speed at which a series of blast holes can be drilled usually come at the expense of hole quality. Consequently, there is a need for methods and systems for forming blast holes that will ensure consistent blast hole quality while minimizing the adverse effects on the speed of blast hole formation.
There is a desired ratio of penetration rate per drill bit revolution where the drill bit carbides penetrate and fracture the rock efficiently, resulting in desirable drilling speed and bit-wear characteristics. This ratio is referred to as the depth of cut (DOC). An optimum rate of penetration (ROP) for drilling efficiency can be calculated by multiplying the maximum rotation speed by the DOC. Prior art methods have used a simple feedback loop to adjust the feed force applied to the bit to maintain an assumed optimum penetration rate. (Feed force applied to the bit being generally proportional to the achieved rate of penetration.) In this application the terms “feed force” and “weight-on-bit” or “WOB” are used interchangeably.
However, at times it may be desirable to sacrifice the efficiency of the ideal depth of cut to achieve a higher penetration rate. Conversely it may be desirable to sacrifice rate of penetration to achieve longer consumable life; that is, the life of the drill bit. Also, such prior-art methods give an optimum DOC at a single penetration rate. What is needed is a method of monitoring and adjusting these opposing goals to achieve optimum drilling efficiency over a wide range of penetration rates, depending on local drilling conditions. As used in this application, the term “drilling efficiency” is not a precisely-defined term, but refers to the optimum ratio of the rate of penetration of the bit to the energy expended for extraction of a given volume of rock, taking into consideration also the amount of bit wear in such extraction.
Although this application is focused on solving problems in blast hole drilling operations, the disclosure and claims are equally applicable to the drilling of boreholes in other fields, such as oil and gas drilling.
Non-limiting embodiments of the present disclosure are described by way of example in the following drawings, which are schematic and are not intended to be drawn to scale:
Generally, the system and method of the present disclosure enhances drilling efficiency and borehole quality by monitoring one or more drilling parameters while the boreholes are being drilled. The monitored drilling parameters are compared with predetermined specifications for the parameters. If the monitored drilling parameter or parameters is outside the specification, the system selects and executes one or more procedures to adjust to ensure that drilling is carried out to the desired specification.
A graphical program or graphical model is a diagram comprising a plurality of interconnected nodes or icons, wherein the plurality of interconnected nodes or icons visually indicate functionality of the program. The interconnected nodes or icons are graphical source code for the program. Graphical function nodes may also be referred to as blocks. Exemplary graphical program development environments which may be used to create graphical programs include LabVIEW from National Instruments or Simulink from MathWorks. Many of the figures in this application are illustrations adapted from Simulink graphical models, but such figures are merely illustrative examples and do not limit the claims to any particular graphical program or depiction. The claimed methods could be implemented, for example, in C or C++ code directly. The meaning of the Simulink symbols shown in the drawings should be known to those skilled in the art, but if needed, descriptions of such symbols may be found at the Simulink web site, https://www.mathworks.com, and the links there to the relevant symbol libraries.
Referring now to
The system 100 comprises a control system 170 that is operatively associated with the drilling rig 110, as well as with the various systems thereof, e.g., a motor system 150, a hoist system 160, or an air injection system and water injection system (not shown in
The drill motor system 150 is connected to the drill string 130 and may be operated by a control system 170 to provide a rotational force or torque to rotate the drill bit 140 provided on the end of the drill string 130. The control system 170 may operate the drill motor system 150 so that the drill bit 140 rotates in either the clockwise or counterclockwise directions. The drill motor system 150 may also be provided with various sensors and transducers (not shown in
The drill hoist system 160 is also connected to the drill string 130 and may be operated by control system 170 to raise and lower drill bit 140. As was the case for the drill motor system 150, the drill hoist system 160 may also be conventionally provided with various sensors and transducers (not shown) to allow the control system 170 to monitor or sense the hoisting forces applied to the drill string 130, and thus the weight-on-bit (WOB), as well as the vertical position or depth of the drill bit 140.
In
The control system 170 also may include a display 210 with a graphical user interface, and an operator's control console 220, connected to the computer 200 to receive inputs from an operator during a drilling operation, and provide information to the operator. The operator's console 220 may include a keyboard, keypad, joystick, mouse, or other input device. In this application, the collective input mechanisms of the operator's console 220 and the display 210 may be referred to generally as a graphical user interface, or GUI. The display 210 of the GUI may of course provide one or more pages of information and input fields to an operator. The operator console 220 may not necessarily be located on the drilling rig 110, but may be remotely connected to the control system.
As further discussed below, the computer 200 of control system 170 is operatively connected to a database 250 of predetermined drilling parameters.
In the drilling system 100 and methods claimed here, a database 250 is provided having predetermined settings and parameters for achieving optimum performance of the drilling system 100. Such settings and parameters can include drill-bit class codes provided by the International Association of Drilling Contractors (IADC), as well as physical characteristics, such as drill bit diameter and cutting-tooth height. In the operation of one embodiment of the drilling system 100, an operator chooses the IADC code of the bit being used from a dropdown menu on the operating system GUI of the control console 220. The drill bit data and drill pipe diameter values are similarly entered. From these inputs, calculations are performed as described below, and the optimum operating range for the bit chosen is used for automatic control of drilling, and also displayed as a reference for manual drilling.
Further, in one embodiment, a maximum rotation speed for the drill bit 140 is stored the database 250 for each IADC code, and also a minimum rotation speed for all bit types. The desired operating window for the range of rotation speed is displayed on the GUI and used by the control system 170 for automatic control, as further explained.
A maximum rotation torque value per unit drill bit diameter is also stored within the database 250. A maximum drilling torque is calculated by multiplying this value by the entered drill bit diameter, as explained more fully below. The maximum drilling torque may also be calculated as a percentage of the torque capability of the drilling rig 110 to prevent rotation stall. The lesser value of the bit maximum drilling torque or rig maximum drilling torque is used. This value is displayed on the GUI and used as the point where the control system 170 will begin to reduce feed force to regulate torque. In some embodiments a recommended bit air pressure range is stored in the database 250 and displayed on the GUI based on good drilling practice for rotary bits.
An ideal depth-of-cut (DOC) for each IADC code and a maximum feed rate for that depth of cut is then calculated as explained below. The cutting-tooth height for a range of drill bit sizes and IADC codes is provided in the database 250, and this data is extrapolated to estimate the cutting-tooth height for any size rotary drill bit of each IADC code (typically, cutting-tooth height is not published by bit manufacturers, but must be measured). When an operator chooses the IADC code and bit size in the GUI, the ideal depth of cut is calculated as a fraction of estimated cutting tooth height. It has been found preferable to set the ideal depth of cut to approximately 66% of the estimated cutting tooth height.
This ideal DOC may then be used in the calculation for commanded rotation speed by the control system 170. This ideal DOC is also used in the calculation for feed force command used by the control system 170. This ideal DOC is further used in the calculation for maximum feed rate command of the control system 170, in which case the maximum feed rate is displayed on the GUI. The maximum feed rate is set by multiplying the ideal DOC by the maximum rotation speed and a predetermined factor, for example 400%. We have found the latter factor to be a reasonable for a wide variety of drill bit types. The maximum feed rate is relevant to the control system 170 when operating in voids or very soft ground, where feed force control is no longer an effective means of controlling feed rate. For example, if the feed rate of drilling is too fast because of very soft formations, cuttings will not be removed from the borehole fast enough.
Further, in one embodiment, a weight-on-bit (WOB) maximum value for a given unit drill bit diameter is stored within the database 250 for each IADC code. The operating maximum WOB is then calculated by multiplying this maximum value stored in the database 250 by the diameter of the chosen bit. A weight-on-bit minimum is calculated by multiplying the operating maximum by some fraction, for example 33%. The desired operating WOB range is displayed on the GUI and used by the control system 170 for automatic control, as further explained below.
The model of
In this application, “aggressiveness” refers to a consumable-life vs. rate-of-penetration scale, preferably chosen by the operator in the GUI. The “consumable” would generally be the drill bit, drill pipe, fuel for running the drilling rig 110 and water used in the drilling process. The aggressiveness may be adjusted by the user to balance the cost of drilling time against the cost of drill bits. The aggressiveness is scaled from 0-10 with 0 being the least aggressive and 10 being the most aggressive.
The system will target the maximum feed force between penetration rates of zero and a percentage of optimum penetration rate. The optimum penetration rate is the fastest we can drill at maximum drilling efficiency. At the most aggressive setting, the percentage of optimum penetration rate is set at about 125%. The system will target minimum feed force when the penetration rate exceeds another percentage of optimum penetration rate; at the most aggressive setting, this percentage of optimum penetration rate is set at about 300%. The feed force target decreases linearly from maximum at about 125% of optimum feed rate to minimum at about 300% of optimum feed rate. These values for the most aggressive setting provide maximum rate of penetration while exception controllers (described below) prevent undue waste of consumables or damage to the drilling rig 110.
As described in more detail below, the feed force, minimum air pressure and bailing velocity values are directly adjusted by the aggressiveness setting. (Bailing velocity is the velocity of the flushing traveling from the cutting surface to the top of the borehole.) The maximum feed force is reduced at lower aggressiveness settings, typically to a minimum of about 50% at the lowest aggressiveness setting. The percentage of optimum penetration rate also decreases at less aggressive settings down to a minimum of about zero.
Regarding control of air pressure, the minimum air pressure target increases linearly with increased aggressiveness. The bailing velocity target increases linearly with aggressiveness. Generation of airflow is large consumer of power in the drilling process therefore operating at lower airflow at less aggressive settings will reduce fuel burn. Reduced airflow will also decrease abrasion wear on drill pipe. In addition, at lower aggressiveness settings, the operating rotation speed, and water flow rates will generally be reduced, because in this system the targets for these are proportional to feed rate. In addition to the user selecting an aggressiveness setting, the system may adjust the aggressiveness setting automatically. Each time drilling parameters exceed a jam value, the aggressiveness is reduced by one increment. After a distance or time without exceeding a jam value, the aggressiveness automatically increases back to the operator setpoint.
A feedback loop compares the actual feed force as measured by sensors and monitors the calculated target feed force. If error is present, the controller increases or decreases the weight-on-bit actuator output to reduce the error and meet the calculated target weight-on-bit.
Water is used in the blast hole drilling process for dust suppression and hole stabilization. Water is injected into the drill string and flows with flushing air out of the bit where it mixes with cuttings from the drilling process. Water can have a negative effect on drilling bit life and can slow drilling penetration rate. It is desired to use the minimum amount of water necessary to achieve the dust suppression and hole stabilization goals.
As described below, this control of the amount of water injected by the control system 170 is performed with a water flow strategy that injects water in proportion to the amount of material being removed in the drilling process. The amount of material being removed is calculated by multiplying the borehole area by the current rate of penetration, or, (Pi/4)*Dbit{circumflex over ( )}2*R, where Dbit is the bit diameter, and R is the rate of penetration. For normal drilling a low proportion of water to cuttings is used, for example the volume of water would preferably be equal to about 5% of the volume of cuttings. Less water will be used as drilling slows and more water will be used as drilling speed and the amount of cuttings increases, so dust can be suppressed with a minimum amount of water.
In one embodiment, the control system 170 commands an output from the water injection system 240 to achieve the calculated water-flow target. If there is no water-flow sensor present, the commanded water flow is in proportion to the maximum output of the water-injection system 240. If a water-flow sensor is present, a feedback loop is used to measure error between commanded and actual water flow output and adjustments are made to reduce the error.
In unstable ground it can be beneficial to use increased water so cuttings will clump together and fill voids. The start of a blast hole is generally drilled through ground that has been fractured by the previous blast of the material above it, and the ground is therefore less stable. The control system 170 is programmed to use the same proportional strategy as just described, but with an increased ratio of water, for example, about 15%, to stabilize the ground while in hole collaring mode (i.e. starting the hole).
It is further desirable to stabilize the blast hole and cuttings pile generated while drilling so the borehole 180 will remain intact and drill depth remain accurate until the borehole 180 is loaded with explosives. To achieve this, the control system 170 again uses the same proportional strategy, but a uses much higher ratio of water, for example, about 50%, while near the bottom of the hole, for example, within one meter of target depth. This water mixes with the cuttings and forms a layer of mud in the borehole 180 and over the top of the cuttings pile. As this mud layer dries, it forms a hard stable cap to the borehole 180. As shown below, the control system 170 automatically switches between the three described water flow targets based on the vertical position of the drill bit 140 in the borehole 180.
Control of compressed air flow control is illustrated in
Table 1 following lists definitions for the various identifiers shown in the graphical models shown in
Rotation speed control model 300 receives the parameters as input shown in
The reader should note that the exception control model is generic to other functions in this disclosure, and also appears with differently-named input parameters in
In the rotation speed control model 300, if the jam prevention control is active, as set by parameter VBon, then the value from the exception controller will be used instead of the normal output target rotation speed.
The output value of the PIV control model 600 shown in
Continuing with
A threshold for jam prevention is preferably monitored by detecting lateral vibration of the drilling rig 110, which vibration can be measured with a sensor, such as an accelerometer, mounted to the drilling rig 110 support structure. Optionally, the sensor would output the vibration as a root-mean-squared G-force.
Exception control model 500 receives as input parameters KpVB, KiVB, KvVB, VBMax, and VBTarget, and also sensor value VBplant, representing the vibration magnitude. The VBTarget value is the setting where jam prevention begins. The VBMax value is the setting where retraction is started to escape a jam. The target is subtracted from the maximum, and the resulting value is used to scale the controller response. The VBplant value is subtracted from the VBTarget value. If the VBplant value is higher than VBTarget, the result will be negative. The resulting error value is divided by the range between max and target to calculate a scaled error.
The scaled error value is multiplied by a proportional gain, and also multiplied by an integral gain, which latter result is then integrated over time. The sensor value Vbplant is multiplied by a derivative gain, and the derivative of the sensor value is taken. Proportional and integral values are added and derivative value is subtracted from the target value to create an adjustment value.
Further, with regard to
Table 2 following lists definitions for the various identifiers shown in the graphical models shown in
Referring to
Further in
Referring to
A graph of the calculation in the WOB limiting-line calculation model 800 is displayed in
Returning to
The minimum value is the lower horizontal line which is common to all aggressiveness settings. While retracting, or during retraction anti-jam, the WOB setpoint is used directly, so that feed force will not then be reduced based on penetration rate or measured torque. The PIV feedback controller 715 is used to adjust the output so the plant value matches the target. Finally, in the scaling block 720 shown in
Referring to
The Regulate Rset block 930 is shown in the graphical model of
The R_position block 1010 shown in
Returning to
Referring to
Referring to
Further, as shown in
None of the description in this application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope; the scope of patented subject matter is defined only by the allowed claims. Moreover, none of these claims are intended to invoke paragraph six of 35 U.S.C. Section 112 unless the exact words “means for” are used, followed by a gerund. The claims as filed are intended to be as comprehensive as possible, and no subject matter is intentionally relinquished, dedicated, or abandoned.
This application claims the priority of U.S. Provisional Patent Application, Ser. No. 62/430,568, filed Dec. 6, 2016.
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