Patent Application
20050133259
1. Field of the Invention
The invention relates generally to systems for drilling boreholes for the production of hydrocarbons. More particularly, the invention relates to devices and methods for protecting the bit during the initial stages of the drilling operation in order to extend the lifetime of the bit.
2. Description of the Related Art
To obtain hydrocarbons such as oil and gas, boreholes are drilled by rotating a drill bit attached at a drill string end. Modem drilling systems generally employ a drill string having a bottomhole assembly (BHA) and a drill bit at end thereof that is rotated by a drill motor (mud motor) and/or the drill string. Pressurized drilling fluid (commonly known as the “mud” or “drilling mud”) is pumped into the drill pipe to rotate the drill motor and to provide lubrication to various members of the drill string including the drill bit. The drill pipe is rotated by a prime mover, such as a rotary table, to facilitate directional drilling and to drill vertical boreholes.
Boreholes are usually drilled along predetermined paths and the drilling of a typical borehole proceeds through various formations. The drilling operator typically controls the surface-controlled drilling parameters, such as the weight on bit, drilling fluid flow through the drill pipe, the drill bit rotational speed (rpm of the surface motor coupled to the drill pipe) and the density and viscosity of the drilling fluid 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 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.
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.
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. As such, the setting down process may be performed differently each time drilling is begun. If setting down and rotation is begun too quickly, 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 done too slowly, rig time is wasted. This is especially true for a new bit, wherein it must be “drilled in” to establish a new pattern.
A few 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.
U.S. Pat. No. 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.
U.S. Pat. No. 6,382,331 issued to Pinckard describes a method and system for optimizing the rate of bit penetration while drilling. Pinckard'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'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.
The system and methods of the present invention overcome 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 a preferred embodiment, an autodriller device is provided 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 be provided with an on/off switch so that the driller may selectively choose to use or not use the bit protection process. Additionally, the bit protection sequence may be adjustable so that varying degrees of gradualness may be selected.
In a further embodiment of the present invention, 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.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.
For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals, wherein:
a depicts an alternative technique for providing controlled gradual achievement of a bit weight setpoint.
a, 4b, 4c, and 4d illustrate operation of an exemplary display gauge for the automatic protection sequence.
A load cell assembly, generally shown at 36, is disposed below the traveling 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
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 the 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.
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 (tmin2). 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
y=mx+b where:
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.
a-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
In accordance with the present invention, 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.
In an alternative embodiment, the processor 40 may be programmed to control the drilling rig 10 using utilize 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.
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 preestablished, 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.
It is noted that the steps for the processes described above 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.
The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes.
