A METHOD FOR REAMING IN THE CONSTRUCTION OF A WELL

The present invention relates to a method for reaming in the construction of a well and preferably, but not exclusively, in the construction of an oil or gas well .

In the construction of a well, a borehole is drilled using drilling apparatus . The drilling apparatus generally incorporates a drill bit forming part of a Bottom Hole Assembly (BHA) attached to a lower end of a drill string. The drill bit is rotated by a motor to drill the borehole . The motor may be arranged at the top of the drill string in a drilling rig. There are two common types of drilling rig: a top drive drilling rig; and a rotary table drilling rig. A top drive drilling rig comprises a top drive having a hydraulic or electric motor arranged on vertical rails in a derrick. The top drive is suspended from a wire rope over a crown block for lifting and lowering the top drive along the rails . A rotary table drilling rig comprises a rotary table arranged in a floor of the drilling rig and is driven by a hydraulic or electric motor. When drilling deep wells utilizing very long drill strings and/or in directional drilling in which the well can be curved, horizontal in parts and occasionally inclined, prohibitively large torque is required to be applied by the rotary table or top drive to turn the drill bit. One way of overcoming this problem is to use a downhole motor. The downhole motor is provided in the BHA and may be an electric motor or more commonly a mud motor utilizing the flow of drilling mud. An example of a mud motor is disclosed in US-A-6, 527 ,513. During drilling, drilling mud is pumped through the drill string to the BHA and back through an annulus formed between the drill string and the borehole

and/or casing lining the borehole. Drilling mud is primarily used to cool and lubricate the drill bit, provide a carrier fluid to carry drill cuttings to the top of the well and to control the pressure in the well to prevent the well from collapsing and for controlling the relative pressure between the pressure in the formation and the pressure in the well for controlling underbalanced or overbalanced drilling. Another use for the drilling mud is to power the mud motor. At least a part of the pressurized drilling mud is pumped into the drill string at a predetermined flow rate and at least a part of the drilling mud flows out through passages between a rotor and a stator of the mud motor and out into an annulus formed between the drill string and the bore hole or continues to flow through an annulus in the BHA to and through the drill bit. The arrangement of the passages and various components in the mud motor causes the rotor to rotate. The rotor is coupled to the drill bit and rotates therewith or through a gearbox. The BHA may also comprise a check valve, drill collars to add weight to the drill bit, stabilzers, a percussion hammering section and Measurement Whilst Drilling (MWD) tools. The drill string may be formed of sections of drill pipe connected together, usually with threaded connectors or may be coiled tubing.

Boreholes are usually drilled along predetermined paths and the drilling of a typical borehole proceeds through various layers of formations . The drilling operator typically controls the surface-controlled drilling parameters, such as the Weight On Bit (WOB) , drilling mud flow through the drill string, the drill string rotational speed (rpm of the surface motor coupled to the drill pipe) and the density and viscosity of the

drilling mud to optimize the drilling operations . The downhole operating conditions continually change and the operator must react to such changes and adjust the surface-controlled parameters to optimize the drilling operations. For drilling a borehole in a virgin region, the operator typically has seismic survey plots that provide a macro picture of the subsurface formations and a pre-planned borehole path. For drilling multiple boreholes in the same formation, the operator also has information about the previously drilled boreholes in the same formation. Additionally, various downhole sensors and associated electronic circuitry (MWD tools) deployed in the BHA continually provide information to the operator about certain downhole operating conditions, condition of various elements of the drill string and information about the formation through which the borehole is being drilled.

The step of reaming takes place after the borehole has been bored. The step of reaming is usually carried out to "smooth" off the wall of the borehole and/or for widening the borehole. The step of reaming is carried out using a reaming tool known as a reamer. The reamer is lowered within the borehole on a drill string or tool string to a predetermined location. The drill string is usually rotated whilst lowering to inhibit the reamer from sticking in the borehole.

If the well comprises a borehole having a large diameter upper section and a smaller diameter lower section, a reamer can be lowered through the large diameter upper section and used to ream out the lower section to increase the diameter of the lower section. Thus, in this situation, the reamer need not have radially extending cutting elements . The cutting elements

may be bound by a circumference which has a smaller diameter than the upper section of the borehole and a larger diameter than the diameter of the lower section of the borehole. If the upper part of the well bore is of smaller diameter is desired in the lower section, the reaming tool is activated downhole to radially extend cutting elements from a body of the reamer. The reamer is then rotated at a predetermined rotational speed (rpm) on or with the drill string, the cutting elements ream the formation to enlarge the borehole . The cutting elements may be arranged on arms which may extend radially.

A borehole may be lined with casing. A reamer can be used to cut a section of casing from a string of casing lining the borehole. This is carried out by lowering the reamer on a drill string or tool string to a predetermined location within the casing lining the borehole. The reaming tool is activated to radially extend cutting elements from a body of the reaming tool . The reaming tool is then rotated on or with the drill string, the arms reaming radially extending into the casing to remove a section of casing. The reamer may also remove further formation to enlarge the diameter of the borehole whilst also cutting the section of casing. The step of reaming is may be carried out in a separate operation to drilling a virgin borehole.

The reamer can also be used to help stabilize the bit and/or straighten the wellbore if kinks or doglegs are encountered, and drill directionally . The reamer may be a drill bit incorporating drilling elements suitable for reaming.

Typically, the information provided to the operator during drilling includes drilling parameters , such as

WOB, rotational speed of the drill bit and/or the drill string, and the drilling fluid flow rate. In some cases, the drilling operator is also provided selected information about bit location and direction of travel, bottomhole assembly parameters such as downhole weight on bit and downhole pressure, and possibly formation parameters such as resistivity and porosity. Typically, regardless of the type of the borehole being drilled, the operator continually reacts to the specific borehole parameters and performs drilling operations based on such information and the information about other downhole operating parameters, such as bit location, downhole weight on bit and downhole pressure, and formation parameters, to make decisions about the operator controlled parameters .

Autodrilling controlling parameters include, but are not limited to Weight On Bit, Rate Of Penetration and mud motor delta pressure.

During tripping, i.e. lowering or raising of the drill string from the borehole, the driller's primary job is to know where the drill bit is in relation to the bottom of the borehole. During the initial part of a drilling operation, the bit is prone to damage. The BHA must be set down into the formation to be drilled as rotation of the bit is begun. Typically, the driller does this manually, simply counting the number of sections of drill pipe tripping-in and tripping-out to gauge. As such, the setting down process may be performed differently each time drilling is begun. If setting down and rotation is begun thereafter, the bit may be damaged by the suddenness of the contact with the rock, or the drill string may become overtorqued. If setting down and rotation are carried out too slowly, rig

time is wasted. This is especially true for a new bit, which must be ^λ drilled in' to establish a new pattern. Typically, a drill bit impacting a hard formation with a force of lOKlbs (44,500 Newtons) at a rate of 20 ft/min (6m/min) may not cause damage to the drill bit. However, a drill bit impacting a hard formation with a force of 20Klbs (89,000 Newtons) at a rate of 50 ft/min (15m/min) may cause damage to the drill bit. The driller slows down the bit as he thinks it is approaching bottom of the borehole to minimize the impact. Some examples of where this can fail and result in high-speed impact are drill is confused about distance bit is from bottom (such as error in pipe tally) , inattention as bit nears bottom, and being in too much of a hurry to follow proper practices .

US-A-7,100,708A co-owned by the present applicant, discloses a method for controlling the placement of weight on a bit of a drilling assembly during the start of a drilling operation, the method comprising the steps of: a) establishing a setpoint for a parameter of interest related to the placement of weight on the bit; b) monitoring the parameter of interest; and c) increasing actual weight on bit in a gradual manner until the setpoint is reached for the parameter of interest, wherein the weight on bit is increased in a gradual manner by establishing a plurality of intermediate setpoints below the setpoint and sequentially moving the weight on bit along the intermediate setpoints .

US-A-6,029,951, co-owned by the applicant for the present case, discloses inter alia, a system and method for use with a drawworks having a rotatable drum on which a line is wound, wherein the drawworks and the line are used for facilitating movement of a load suspended on the

line, includes a drawworks control system for monitoring and controlling the drawworks . A brake arrangement is connected to the rotatable drum for limiting the rotation of the rotatable drum and at least one electrical motor is connected to the rotatable drum for driving the rotatable drum. A load signal representative of the load on the line is produced and a calculated torque value based on the load signal and electrical motor capacity is provided. The drawworks control system provides a signal representative of the calculated torque value to the electrical motor wherein pre-torquing is generated in the electrical motor in response to the signal. Control of the rotation of the rotatable drum is transferred from the brake arrangement to the electrical motor when the electrical motor pre-torquing level is substantially equal to the calculated torque value.

A few other systems have been proposed for automated operation of portions of a drilling operation. In general, such systems establish a set point for WOB, and then control the drilling equipment to reach the setpoint quickly. This may be counterproductive. Attempting to achieve the setpoint quickly may cause a step change to the system that results in damage to the bit, overtorquing of the drill string and other problems. US-A-4,875,530 issued to Frink et al . , for example, describes an automatic drilling system wherein a required speed and bit weight is input into the system by an operator. A controller device electronically senses the weight on bit and provides instantaneous feedback of a signal to a hydraulically driven drawworks which is capable of maintaining precise bit weight throughout varying penetration modes. Frink 's system provides a setpoint for the bit weight. However, Frink also seeks

to achieve the setpoint quickly and without regard to protection of the bit.

US-A-6,382,331 issued to Pinckard describes a method and system for optimizing the rate of bit penetration while drilling. Pinckard ¹ S arrangement collects information on bit rate of penetration, weight on bit, pump or standpipe pressure, and rotary torque data during drilling. This information is stored in respective data arrays. Periodically, the system performs a linear regression of the data in each of the data arrays with bit rate of penetration as a response variable and weight on bit, pressure, and torque, respectively, as explanatory variables to produce weight on bit, pressure, and torque slope coefficients. The system calculates correlation coefficients for the relationships between rate of penetration and weight on bit, pressure, and torque, respectively. The system then selects the drilling parameter with the strongest correlation to rate of penetration as the control variable. Pinckard ¹ S system, however, does not attempt to solve the problems associated with the start of drilling or drilling in of a bit.

There is a need for a system that overcomes the problems associated with prior art systems as regards the starting of drilling, and, in particular situations, resuming drilling after reaming.

The inventors have noted that reaming is normally a low-energy process, since minimal rock is removed. However, some situations, such as drilling an under-gauge hole, can be challenging, due to drill bits being designed for drilling out a full-cross-section of rock, as opposed to drilling only the outer ring and encountering high side forces from the sloped sides of

the hole .

The present invention provides a method for controlling movement of a bit of a drilling assembly during reaming of an already-drilled hole, the method comprising the steps of a . ) determining a ream speed for downward movement of the bit in a hole, the hole having a hole bottom, b.) moving the bit downward in the hole at said ream speed, c.) determining a time period for deceleration of the downwardly moving bit to the hole bottom, d.) determining a value for a target drilling parameter for drilling beyond the bottom of the hole, e.) decelerating the bit for the time period, and f . ) achieving the value for the target drilling parameter when the bit reaches the bottom of the hole.

Advantageous and preferable steps in the method are set out in dependent claims .

In any method according to the present invention at some point in a reaming process one or more of a variety of drilling parameters (e.g., weight on bit, fluid differential pressure across a mud motor, drillstring rotation speed, ROP, and/or drillstring torque) can come into play in the sense of becoming an overarching parameter in terms of which the reaming process is then controlled; e.g., when a collapsed hole is encountered or bridging of the formation before hole bottom is reached.

Methods for controlling movement of a bit of a drilling assembly during reaming of a hole; the method, in one aspect, including determining a speed for downward movement of the bit, moving the bit downward in a hole at said speed, determining a time period for deceleration of the downwardly moving bit as it approaches the hole

bottom, determining a value for a target parameter related to the reaming of the hole to be achieved as the bit comes down to the bottom of the hole, decelerating the movement of the bit for the time period, and ending the period when the value is achieved at the bottom of the hole. "Reaming" includes moving a drillstring with a bit down into an already-drilled hole to advance the bit to the bottom of the hole whether additional widening of the already-drilled hole is accomplished or not by the downwardly advancing bit and whether or not the bit is rotating. The present invention discloses systems for and computer readable mediums programmed to effect such methods .

The present invention, in certain aspects, addresses and overcomes the foregoing disadvantages of the prior art by providing a system that optimizes the drilling process. The system and methods of the present invention seek to provide protection to the bit during the drilling process, and particularly during the initial portion of the drilling operation, when the bit is set down into the formation .

In certain embodiments , an autodriller device is provided according to the present invention that operates the drawworks for hoisting/lowering of and rotation of the drill string. The autodriller includes a controller that is programmed to provide an automatic bit protection sequence that can be initiated during the initial stage of set down of the bit within the formation. The automatic protection sequence establishes a setpoint for a parameter of interest that is associated with operation of the drilling system. This parameter of interest may be the actual WOB. It may also be measured torque on the drill string, ROP, or differential mud motor pressure.

At the start of drilling, the controller initiates a gradual increase in the parameter of interest in order to achieve the setpoint. The controller may automatically choose the bit protection process or it can be provided with an on/off switch so that the driller may selectively choose to use or not use bit protection. Additionally, the bit protection sequence may be adjustable so that varying degrees of gradualness may be selected.

In other aspects , the present invention provides a system and method in which the controller of the autodriller is provided with measured data for the torque on the BHA, rate of penetration (ROP) and/or the differential pressure of the mud motor of the drilling system. Each of these parameters is provided with a predetermined setpoint, and each may be selected as the controlling parameter for operation of the autodriller. In yet a further embodiment, the controller will automatically select a controlling parameter from among these parameters. Preferably, the method of the invention provides controlled deceleration of a reaming bit until it reaches a bottom of a hole being reamed.

For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings in which: the accompanying drawings , in which : Figure 1 is a schematic depiction of a drilling apparatus incorporating a rotary table drilling rig in accordance with the present invention for carrying out a method in accordance with the present invention;

Figure 2 is a chart illustrating controlled gradual achievement of a bit weight setpoint;

Figure 2a depicts an alternative technique for providing controlled gradual achievement of a bit weight setpoint;

Figure 3 illustrates portions of an exemplary display panel for the controller of the autodriller device ;

Figures 4a, 4b, 4c, and 4d illustrate operation of an exemplary display gauge for the automatic protection sequence ; Figure 5 is a flowchart illustrating steps in a method of control in accordance with the present invention;

Figure 6 is a chart illustrating control of parameter of interest associated with the drilling process wherein control is substantially continuous so as to use time steps that approach being infinitely small;

Figure 7 is a flowchart depicting steps in a further exemplary control method in accordance with the present invention wherein the controller selects a controlling parameter automatically from among several drilling parameters ;

Figure 8 is a schematic depiction of a top drive drilling rig provided with an apparatus of the present

invention for carrying out a method in accordance with the invention;

Figure 8A is a side schematic view in cross-section illustrating a method of reaming in accordance with the present invention;

Figure 8B is a side schematic view in cross-section illustrating a method of reaming in accordance with the present invention;

Figure 9 is a graph illustrating parameters of a method of reaming in accordance with the present invention; and

Figure 10 depicts a display panel useful in a method of reaming according to the present invention.

Figure 1 illustrates, in schematic fashion, an exemplary drilling rig 10 with an automatic drilling system. The rig 10 includes a supporting derrick structure 12 with a crown block 14 at the top. A traveling block 16 is movably suspended from the crown block 14 by a cable 18, which is supplied by draw works 20. A kelly 22 is hung from the traveling block 16 by a hook 24. The lower end of the kelly 22 is secured to a drill string 26. The lower end of the drill string 26 has a bottom hole assembly 28 that carries a drill bit 30.

The drill string 26 and drill bit 30 are disposed within a borehole 32 that is being drilled and extends downwardly from the surface 34. The kelly 22 is rotated within the borehole 32 by a rotary table 35. Other features relating to the construction and operation of a drilling rig, including the use of mud hoses, are well known in the art and will not be described in any detail herein .

A load cell assembly, generally shown at 36, is disposed below the travelling block 16. The load cell

assembly 36 is of a type known in the art and contains a sensor for measuring the entire weight of the drill string 26 and kelly 22 below it. It is noted that the load cell assembly 36 might also be located elsewhere, the location shown in Figure 1 being but an exemplary location for it. A suitable alternative location for the load cell assembly 36 would be to incorporate the load cell assembly into the cable 18 to measure tension upon the cable 18 from loading of the drill string 26 and kelly 22.

The load cell assembly 36 is operably interconnected via cable 38 to a controller 40. The controller 40 is typically contained within a housing (not shown) proximate the derrick structure 12. The controller 40 is preferably programmable and embodied within a drawworks control system, or autodriller, of a type known in the art for control of raising and lowering, rotation, torque and other aspects of drill string operation. One such autodriller, which is suitable for use with the present invention, is that described in U.S. Pat. No. 6,029,951, issued to Guggari. That patent is owned by the assignee of the present application and is herein incorporated by reference. The controller 40 is operably interconnected with the drawworks 20 for control of the payout of cable 18 which, in turn, will raise and lower the drill string 26 within the wellbore 32. Additionally, the controller 40 is operably associated with the rotary table 35 for control of rotation of the drill string 26 within the wellbore 32. Prior to lowering the drill string 26 into the wellbore 32 to engage the bottom of the wellbore 32 , the load cell assembly 36 provides a reading to the controller 40 that is a baseline "zero" WOB. This zero

reading is indicative of the load on load cell assembly 36 with just the hookload, i.e., the kelly 22, drill string 26 and BHA 28. In other words, with this hookload, the actual weight on the bit 30 is essentially zero since the bit is hanging free and has not yet been set down into the wellbore 32. The actual WOB is determined by subtracting the reference hookload value from the reading provided by the load cell assembly 36. As the bit 30 is lowered into the wellbore 32 , and prior to the bit 30 engaging the formation, mud pumps are started to flow drilling mud down through the drill string 26 for lubrication of the bit 30. Because this operation is well understood by those of skill in the art, it is not described in any detail herein. Additionally, rotation of the drill string 26 is started. As the drill string 26 and BHA 28 are further lowered into the wellbore 32 , the bit 30 eventually will be brought into contact with the bottom of the wellbore 32 , as the BHA 28 is set down. At this point, the reading on the load cell assembly 36 will be decreased as the weight of the hookload is born by the bit 30. The decrease in weight on the load cell assembly 36 provides a measurement of the increase in WOB. The controller 40 can selectively adjust the rate of increase of WOB by controlling the braking force provided by the drawworks

20 on cable 18. The controller 40 is preprogrammed with a WOB set point, which is typically selected by the driller prior to the commencement of drilling operations .

When in the "bit protection mode," the controller 40 seeks to adjust the WOB toward a WOB setpoint in a gradual manner. Figure 2 is a graph that illustrates gradual adjustment of the actual WOB toward the WOB setpoint in a gradual manner. Figure 2 depicts the

actual weight on bit (WOB) versus time for the setting down portion of a drilling operation. A WOB setpoint is shown at line 40, indicating a desired WOB for the drilling operation. The actual zero WOB, prior to set down, is indicated by line 42. Line 44 depicts a rapid, step change type adjustment of the WOB toward the setpoint 40. This is undesirable. Line 46 illustrates a gradual increase in the actual WOB 42 toward the setpoint WOB 40, in accordance with the present invention. As will be described in greater detail below, the controller 40 accomplishes this gradual increase by ensuring that weight is added to the bit 30 in discrete increments and that there is an increment of time (t.sub.min) between additions of each increment of added weight. The stair step appearance of the line 46 is due to the placement of the increment of time (t.sub.min) between each increase in weight.

Line 48 also illustrates a gradual increase in the actual WOB 42 to the setpoint WOB 40. As is apparent, there is a greater degree of gradualness in reaching the setpoint WOB 40 along the second line 48. This greater degree of gradualness is due to the use of a longer minimum time period (t . sub.min2) . In the latter instance, also, the controller 40 has been programmed to increase the actual WOB to the setpoint WOB 40 within a set period of time (max t) , or target time. The driller may specify a target time (max t) by inputting this parameter into the controller 40 for the actual WOB to be brought to the WOB setpoint. In this way, the degree of gradualness may be adjusted.

An alternative method for increasing the weight on bit in a gradual manner is illustrated by Figure 2A. According to this method, the controller 40 calculates

intermediate setpoints for the WOB at various points in time from the beginning of drilling to achievement of the setpoint. The controller 40 will control the drawworks 20 to maintain the actual WOB at the intermediate setpoints. Figure 2A shows an example. In this example, the setpoint 40 has been established prior to the start of drilling. At the start of drilling, t=0 in Figure 2A. The controller 40 then calculates an intermediate setpoint (shown as intermediate setpoint 41a in Figure 2A) for the actual WOB for a specific point in time

(i.e., t=l) after the start of drilling. The controller

40 then controls the drawworks 20 to increase the actual

WOB to this intermediate setpoint. The controller 40 will also calculate additional intermediate setpoints 41b, 41c, 4Id, etc. for subsequent time periods (t=2; t=3 ; t=4 , . . . ) and continuing until the actual WOB reaches the WOB setpoint 40. The intermediate setpoints 41a, 41b, 41c, . . . may be calculated using known mathematical techniques for determining intermediate values between two known endpoints . One suitable technique for making such a determination is the slope intercept form of linear equation:

y=mx+b where :

m=slope;

b=the value where the line crosses the y axis; and

x and y are the coordinates for the y intercept.

A display/control panel is associated with the controller 40 so that a driller may have actuation control over the controller 40 and to have a visual

indication of the actual WOB, WOB setpoint, and other parameters. Figure 3 illustrates a portion of an exemplary display/control panel 50. The panel 50 presents numerical representations of the actual WOB 52 and the WOB set point 54. The latter value is typically input into the controller 40 by a keyboard or other input device that is known in the art. The panel 50 also provides a control switch 56 for turning the bit protection feature on and off. Additionally, there is a bit protection gauge 58 that will graphically depict the increase in actual WOB toward the setpoint WOB. Additionally, the panel 50 provides a numerical display 60 for torque, as measured at the surface. As those of skill in the art recognize, torque may be measured at the bit by a sensor (not shown) located proximate the rotary table 35. Because the measurement and monitoring of torque upon the drill string is well understood in the art, it will not be described herein. The panel 50 also provides a numerical display 62 for the rate of penetration (ROP) of the bit 30 and a display 64 for the differential pressure of the mud motor (not shown) that is associated with the drilling rig 10 to supply drilling mud to the bit 30.

Figures 4A 4D illustrate operation of the bit protection gauge 58 during the initial portion of a drilling operation, principally during the time that the bit 30 is "set down" into the formation or earth for the start of drilling. In Figure 4A, the actual WOB is at the baseline or zero value, indicated by the top of the colored area 66, which represents the actual WOB. At this point, no WOB setpoint has been input into the controller 40. In Figure 4B, a WOB setpoint has been input into the controller 40 and is indicated by the graphical arrow

"SP" indicator 68. In addition, the driller has actuated the switch 56 to turn on the bit protection feature, and this is illustrated by the graphical arrow "BP" indicator 70, which is aligned with the top of the colored area 66. In Figure 4B, the bit 30 has not yet been set down. In Figure 4C, the controller 40 is setting the bit 30 down in a gradual manner, and the actual WOB indicator 66 rises. In Figure 4D, the actual WOB has reached the desired setpoint WOB. The "BP" indicator 70 then disappears, showing that the bit protect feature is no longer active.

The controller 40 is programmed to provide a "bit protection" operating sequence. The sequence protects the bit and other components from damage that might result during a too rapid increase in WOB during setdown. Figure 5 depicts a flowchart showing steps in an exemplary control method 80 that is performed by the controller 40 in accordance with the present invention during operation of the bit protect feature. According to the method 80, the controller first determines the actual WOB, which is provided by the load cell assembly 36. This is shown at step 82. In step 84, the controller 40 determines if the autodriller is on and there has been a WOB setpoint entered by the driller. If so, the controller 40 compares the two values in step 86. If the actual WOB is not less than the setpoint WOB, the controller 40 takes no action and the bit protection sequence is stopped. However, if the actual WOB is less than the setpoint WOB, the controller 40 proceeds to step 88 wherein it determines whether the minimum interval of time t.sub.min (or t . sub .min2) has passed before additional weight may be placed upon the bit 30. If not, the controller 40 places no additional weight on the bit.

If t.sub.min (or t.sub.min2) has occurred since additional weight was placed on the bit 30, the controller 40 proceeds to step 90 wherein the brake (not shown) for the drawworks 20 is released by the controller 40 to cause a predetermined increment of cable to be unwound, thereby placing an additional increment of weight on the bit 30. Depending upon the particular type of drawworks 20 that is used by the drilling rig 10, the controller 40 might adjust an on/off style brake, a continuous brake adjustment, or a motor control. This process 80 will continue in an iterative fashion until the actual WOB is at the setpoint WOB. It is noted that the use of a minimum interval of time between placements of additional weight on the bit 30 ensures that weight is added in a gradual manner. The controller 40 may, alternatively, implement the method described with respect to Figure 2A previously of establishing a plurality of intermediate setpoints and then controlling the drawworks 20 to achieve the intermediate setpoints until the WOB setpoint 40 is reached.

In an alternative embodiment, the processor 40 may be programmed to control the drilling rig 10 using a controlling setpoint that is selected from among other drilling parameters . These other drilling parameters are values that are typically measured and monitored during a drilling operation and include the torque, rate of penetration (ROP) and/or the differential pressure of the mud motor of the drilling system. If, for example, it is desired to use ROP as the controlling parameter, a desired setpoint is selected for ROP. The controller 40 then compares the actual rate of penetration to the ROP setpoint, in the same manner as the actual WOB was compared to the setpoint WOB via process 80 described

above. The controller 40 will adjust the payout of cable 18, as previously described, until the actual ROP matches the setpoint ROP. Figure 6 is a graph that depicts the use of a setpoint 81 and the gradual achievement of that setpoint for a parameter of interest 83. The parameter of interest 83 may be ROP, torque, or differential mud pump pressure, as well as WOB. As depicted generally in Figure 6, the parameter of interest 83 is increased from the start of drilling at t=0 to the setpoint 81 in a gradual manner, illustrated by line 85 until the setpoint 81 is reached. The gradual increase in the parameter of interest 83 is achieved by the controller 40 using methods previously described for gradual increase of the actual WOB (i.e., use of incremental increases spaced apart by time intervals or the establishment of a plurality of intermediate setpoints for the parameter of interest) .

In yet a further alternative embodiment of the invention, the controller 40 will automatically select from among the available drilling parameters to use as the controlling parameter of interest. During setdown, the controller 40 monitors each of several drilling parameters, such as WOB, ROP, torque, and mud motor differential pressure. Each of these drilling parameters is assigned a setpoint value. As the controller 40 increases weight on the bit 30, each of these parameters will begin to approach its pre-established, ultimate setpoint (i.e., as WOB is increased, the rate of penetration of the drill bit 30 will also increase) . The controller 40 will select the parameter to use as the system setpoint by determining which of the parameters first reaches its setpoint value. Figure 7 is a flowchart that illustrates an exemplary selection process

that might be employed by the controller 40. According to the process, generally designated as 92, the controller first determines whether the actual WOB has reached the WOB setpoint (step 94) . If so, the controller 40 selects the WOB setpoint as the setpoint for control of actual WOB (step 96) . If the controller 40 determines that the WOB setpoint has not been reached, it then determines whether the actual ROP has reached the ROP setpoint (step 98) . If so, then the ROP setpoint is selected as the setpoint for control of ROP (step 100) . If the actual ROP has not reached the ROP setpoint, the controller 40 then determines whether torque has reached its predetermined setpoint (step 102) . If it has, then the torque parameter is chosen by the controller as the parameter for control of torque (step 104) . If not, the controller 40 proceeds to determine whether the actual mud pump pressure has reached the selected setpoint for mud pump pressure (step 106) . If so, that parameter is chosen as the controlling parameter (step 108) . This process 92 will continue in an iterative fashion until a selection is made. Thus, the first parameter to reach its designated set point will be selected by the controller 40 as the controlling setpoint parameter for operation of the drilling rig 10. It is noted that the steps for the processes according to the present invention described above and below may be hardwired into the controller or provided by programming of the controller 40. Additionally, the. steps may be accomplished by using instructions that are provided to the controller via removable storage media, such as diskettes, CD ROMs and other known storage media. These computer readable media, when executed by the controller 40, will cause it to control operation of the

drilling rig 10 to perform the described methods.

A top drive drilling rig 210 shown in Figure 8 is provided with a controller of the invention. The top drive rig 210 has a derrick 211 and a rig floor 212 containing an opening 213 through which the drill string 214 extends downwardly into the earth 215 to drill a well 216. The drill string is formed of series of pipe sections interconnected at threaded joints 217 and having a bit at the lower end of the string. At vertically spaced locations, the string has stabilizer portions which may include stabilizer elements 218 extending helically along the outer surface of the string to engage the well bore wall in a manner centering the drill string therein. More commonly, a stabilizer is located close to the drill bit in the downhole assembly and centralizers are located along the length of the drill string.

The string is turned by a top drive drilling unit 219 which is connected to the upper end of the string and moves upwardly and downwardly therewith along the vertical axis 220 of the well, and which has a pipe handler assembly 221 suspended from the drilling unit. The drilling unit 219 has a swivel 222 at its upper end through which drilling fluid is introduced into the string, and by which the unit is suspended from a traveling block 223 which is suspended and moved upwardly and downwardly by a wire rope 224 connected at its upper end to a crown block 225 and actuated by the usual drawworks represented at 226. The drilling unit 219, pipe handler 221 and connected parts are guided for vertical movement along axis 120 by two guide rails or tracks 227 rigidly attached to derrick 211. The drilling unit 219 is attached to a carriage (not shown) having rollers (not shown) engaging and located by rails 227 and guided by

those rails for only vertical movement upwardly and downwardly along the rails parallel to axis 220.

A load cell assembly 228, is incorporated in the drawworks 226. The load cell assembly 228 is of a type known in the art and contains a sensor for measuring the entire weight of the drill string 217, BHA and top drive 219. It is noted that the load cell assembly 228 might be located elsewhere, including, but not limited to, between the wire rope 224 and the top drive or between the quill of the top drive and the saver sub (not shown) , or in the pipe handler assembly 221.

The load cell assembly 228 is operably interconnected via a cable (not shown) to a controller (not shown), like controller 40 shown in Figure 1. The controller 40 is of the type as described above.

Reaming is a method of re-introducing a drillstring with a reamer or drill bit into an already-drilled hole to move the bit down to the hole bottom to resume drilling from that point. In some cases, reaming is carried out to widen the already-drilled hole, as shown in Figure 8A. In other cases, reaming is carried out to "smooth" the wall of the borehole, such as that shown in Figure 8B.

Referring to Figure 8A, a reaming system 120 with a reamer 122 is reaming a previously-drilled hole 124 in a formation 128 to a reamed hole diameter of a new hole 126. In Figure 8B a reamer 132 on a drillstring 130 is reintroduced into an already-drilled hole 134 in a formation 138 and is moved down to a bottom 136 of the hole 134 to resume drilling. Often each new section of a drilled hole is reamed before adding another stand or joint to a drillstring for further drilling. Reaming, in certain aspects , is normally a low-energy process , since

minimal rock is removed. However, some situations, such as drilling an under-gauge hole, can be challenging, due to drill bits being designed for drilling out a full- cross-section of rock, as opposed to drilling only the outer ring and encountering high side forces from the sloped sides of the hole. In any method according to the present invention at some point in a reaming process one or more of a variety of drilling parameters (e.g., weight on bit, fluid differential pressure across a mud motor, drillstring rotation speed, ROP, and/or drillstring torque) can come into play in the sense of becoming an overarching parameter in terms of which the reaming process is then controlled; e.g., when a collapsed hole is encountered or bridging of the formation before hole bottom is reached.

In a reaming method according to the present invention, the drillstring is lowered so that the bit again encounters the bottom of an already-drilled hole and drilling again commences. The controller 40 (as disclosed above) is programmed to accept as inputs a "Ream Speed" and a defined "deceleration time." The "Ream Speed" is a speed at which the bit 122 or the bit 132 progresses downward in the hole (the hole 124 or 134, respectively) . The "deceleration time" is a period of time calculated by the controller 40 (or by some other computer on-site or remote in communication with the controller 40) during which the bit decelerates from the Ream Speed to a point at which a target rate of penetration is reached. This deceleration time period is calculated (by the controller 40 or another computer) based on the calculated distance of the bit from the bottom of the hole and on other factors, e.g., mass of the drillstring, capability of the brake system, kinetic

energy of the system or some combination of these factors . Based on this calculated deceleration time period, a time is calculated at which to begin deceleration and a time is calculated at which the bit should be at or just above the bottom of the hole.

In one particular aspect, the distance traversed during the deceleration time is calculated so that a deceleration occurs over a minimum distance. In this way the shortest time period is employed for deceleration so that the overall time for drilling the hole is optimized.

In one particular aspect, deceleration is constant to achieve a minimum safe reliable deceleration. In other aspects , deceleration is at different rates , depending on situations that may occur during reaming. Deceleration rate can, according to the present invention, be adjusted during reaming; e.g., but not limited to, when bit reliability is questionable or hole depth is uncertain.

When deceleration is not linear, it can occur in separate segments, each beginning with its own setpoint and continuing to the beginning of the next segment having its own setpoint. In certain aspects, in reaming methods according to the present invention, the methods include establishing a final setpoint for a parameter of interest, monitoring the parmeter of interest during reaming, establishing a plurality of intermediate setpoints and sequentially achieving the intermediate setpoints as reaming progresses, and proceeding with reaming until the final setpoint is reached. In certain systems for providing protection to a drill bit according to the present invetnion during reaming, the systems have a sensor for measuiring an operational parameter of interest, and a controller to

receive values for the measured parameter of interest from the sensor and to compare the values to a predetermiend setpoint. The controller further adjusts the reaming operation in separate discrete segments in separate predetermined time periods in response to valuse recevied for the parameter of interest. A final setpoint is reached in agradual manner. In certain embodiments and aspects, a controller according to the present invention has a computer readable medium with instructions that, when executed, cause the controller to: control operation of a drilling assembly with a bit according to a method; the method including establishing a final setpoint for a parameter of interest in a reaming operation, monitoring the parameter of interest during the reaming operation, changing the parameter of interest sequentially through a plurality of intermediate values during reaming, and reaching the final setpoint value.

In one particular aspect the driller inputs a target ROP to be achieved when the bit (122 or 132) encounters the bottom of the hole (124 or 134) so that at this point the bit is progressing at the target ROP, an ROP which typically is not suitable for reaming, but for drilling new hole . In any reaming method according to the present invention any drilling parameter can be used as the

"target" other than ROP.

In one particular aspect a reaming method according to the present invention is automatic. The controller 40 is preprogrammed with a Ream Speed and Deceleration Time so that when personnel, e.g. a driller, activates reaming (by pushing a "Start" button or by turning on an autodriller) , the drilling system automatically begins reaming at the pre-set Ream Speed and continues reaming

through the pre-set Deceleration Time period. The drilling system then decelerates for the deceleration time period until the Target ROP is reached at hole bottom. Once the Target ROP is achieved, the system automatically goes into the usual autodriller mode and continues drilling (e.g. continues drilling the hole 126, Figure 8A, or the hole 134, Figure 8B).

Figure 9 illustrates a drilling system reaming at a pre-selected bit lowering Ream Speed (vertical axis of graph) until the beginning of a pre-selected deceleration time period ("Decel Time") (Time on horizontal axis). Constant deceleration is indicated until the Target ROP is achieved at the hole bottom ("Bit Position equals Hole Depth") . [63. Figure 10 illustrates a system controller display panel 130 for preprogramming the controller 40 with a pre-selected Ream Speed and a pre-selected Deceleration Time (pre-selection is done via manual user input (on-site or remot) or automatically by the controller or by another computer) . In one aspect, as may be the case for every display panel herein, a touch screen display is used.

Pushing the "HELP" button presents an on-screen explanation of system operation, definitions of system paramters , and details of system procedures. In certain aspects, in methods according to the present invention when a drill system with a bit is reaming a hole or is performing any other operation in which a bit approaches a hole bottom to resume drilling, drilling is controlled in terms of any particular selected drilling parameter.

For example, as a bit approaches a hole bottom during a reaming process or other bit lowering process at a relatively high bit rotational speed (high RPM ¹ S), the

RPM's are decreased during a deceleration time period; then, as the bit comes to the hole bottom, the RPM's are increased so that further drilling of the hole can be commenced quickly and efficiently. Similarly, adjustments can be made regarding ROP, torque on bit, mud flow rate, , drillstring rotational speed, mud motor differential pressure, or mud motor rotational speed.

The present invention, therefore, provides in some, but not in necessarily all, embodiments a method for controlling movement of a bit of a drilling assembly during reaming of an already-drilled hole, the method including: determining a ream speed for downward movement of the bit in a hole, the hole having a hole bottom; moving the bit downward in the hole at said ream speed; determining a time period for deceleration of the downwardly moving bit to the hole bottom; determining a value for a target drilling parameter for drilling beyond the bottom of the hole; decelerating the bit for the time period; and achieving the value for the target drilling parameter when the bit reaches the bottom of the hole. Such a system may have one or some, in any possible combination, of the following: wherein the already- drilled hole is not widened during reaming; wherein the deceleration is constant; wherein the target parameter is rate of penetration; wherein the bit moves a first distance at the ream speed and then the bit moves a second distance during the time period, and the second distance is a minimum distance within which a linear deceleration is achieved for the bit to be brought to the bottom of the hole; wherein a controller automatically controls movement of the bit; wherein a controller controls movement of the bit, and the controller calculates the second distance; wherein a value for the

ream speed is input into the controller, a value for the time period is input into the computer, and the controller controls the movement of the bit in the hole; wherein the controller inputs the ream speed value and the time period value automatically; drilling the already-drilled hole with the bit past the hole bottom; wherein the controller automatically controls drilling by the bit after the bit is at the bottom of the hole to extend the hole past said bottom; the time period has a beginning and an end, and the decelerating occurs by sequentially decelerating to each of a plurality of intermediate setpoints between the beginning of the time period and the end of the time period, each intermediate setpoint corresponding to an intermediate value for the target drilling parameter; and/or wherein the target drilling parameter is weight on bit, differential fluid pressure across a mud motor, bit rotational speed or torque on the bit.

The present invention, therefore, provides in some, but not in necessarily all, embodiments a method for controlling movement of a bit of a drilling assembly during reaming of an already-drilled hole, the method including: determining a ream speed for downward movement of the bit; moving the bit downward in a hole at said ream speed; determining a time period for deceleration of the downwardly moving bit to the hole bottom; determining a value for a target drilling parameter for drilling beyond the bottom of the hole; decelerating the bit for the time period; achieving the value for the target drilling parameter when the bit reaches the bottom of the hole; the target drilling parameter is rate of penetration; the bit moves a first distance at the ream speed; the bit moves a second distance during the time

period; the second distance a minimum distance within which a linear deceleration is achieved for the bit to be brought to the bottom of the hole ; , and a controller controls movement of the bit. Such a method may include: drilling the already-drilled hole with the bit past the hole bottom.

The present invention, therefore, provides in some, but not in necessarily all, embodiments a system for controlling movement of a bit in reaming a hole, the system having: a sensor for measuring a target drilling parameter associated with drilling past a bottom of an already-drilled hole, the reaming done by a system with a bit; a controller to receive a measured target drilling parameter from the sensor and to compare the measured target drilling parameter to a predetermined setpoint for the measured target drilling parameter; and the controller adjusting deceleration of the bit as the bit approaches the setpoint. In such a system the measured target drilling parameter be rate of penetration; and/or the controller may decelerate the bit so that the decelerating occurs by sequentially decelerating to each of a plurality of intermediate setpoints between a beginning of the time period and an end of the time period, each intermediate setpoint corresponding to an intermediate value for the target drilling parameter.

The present invention, therefore, provides in some, but not in necessarily all, embodiments a computer readable medium containing instructions that, when executed, cause a controller to control operation of a drilling assembly with a bit according to the following method: determining a ream speed for downward movement of the bit in the hole, the hole having a hole bottom; moving the bit downward in a hole at said ream speed;

determining a time period for deceleration of the downwardly moving bit to the hole bottom; determining a value for a target drilling parameter for drilling beyond the bottom of the hole; decelerating the bit for the time period, and achieving the value for the target drilling parameter when the bit reaches the bottom of the hole. In such a medium with instructions for such a method, the target parameter may be rate of penetration; the bit may move a first distance during the time period, the first distance being a minimum distance within which a linear deceleration can be achieved for the bit to be brought to the bottom of the hole; and/or the method may include decelerating by sequentially decelerating to each of a plurality of intermediate setpoints between a beginning of the time period and an end of the time period, each intermediate setpoint corresponding to an intermediate value for the target drilling parameter.

This is a continuation-in-part of U.S. Application Serial No. 10/745,247 filed on 12/23/2003, issued as U.S. Patent 7,100,708 on 09/05/2006; all of said application and said patent are incorporated fully herein by reference for all purposes ; and from and based on said application and said patent the present invention claims priority under the Patent Laws . What is claimed is :