Patent Application
20070278008
The foregoing objects, features and advantages of the present invention will be more clearly understood by those of skill in the art from the following detailed description of preferred embodiments thereof, taken with the accompanying drawings, in which:
Turning now to a more detailed description of the present invention, there is illustrated in
The reference well 10 is drilled using conventional drilling tools, which usually consist of a drilling motor and a rotatable, steerable drilling assembly with an electronics control package, such as is found in a measurement while drilling (MWD) system. This first well is drilled along a prescribed course using conventional guidance techniques and is then cased with steel tubing, generally indicated at 16. In accordance with a preferred form of the present invention, during the casing operation one or more electromagnetic beacons 18, each incorporating a casing coupler, to be described, are installed between lengths of casing in this well at prescribed locations. A “casing crew” installs these beacon couplers in the same way that ordinary pipe couplings are installed, although the beacon couplers may have a specified “down hole” polarity orientation. These couplers may be installed as permanent sections of the reference well casing 16 or as couplings in a temporary “work string” of tubing, to be described, installed inside the reference well.
Within a few months after casing has been installed in the reference well, the second well 12 of the pair is drilled along a specified parallel path with respect to well 10. The electromagnetic beacons of the invention are energized while drilling this second well to give the driller periodically measured, updated, location ties to the reference well to keep the new well from veering off course. In drilling a borehole it is standard practice for the driller to periodically make drill bit orientation and direction determinations using MWD measurements of the Earth's magnetic field and the direction of gravity while a new length of drill pipe is being attached to the drill string. It is during such times that an electromagnetic beacon in the reference well can be given a start signal to briefly turn it on to allow measurements of the beacon's electromagnetic field components at the well being drilled to be made at the same time that other measurements are being made. Measurements of this beacon electromagnetic field may utilize the techniques disclosed in U.S. Pat. No. 6,814,163. After making a determination of relative position and drilling direction based on these measurements, the drilling direction for the next drilling interval for well 12 is adjusted to make course corrections, as needed.
An electromagnetic beacon 18 for use in a SAGD application is illustrated in cross-section in
In one example, the main electromagnetic field generating coil 28 was about 20 inches long, and consisted of a single layer with 500 turns of #18 gauge magnet wire wound on the 7 inch diameter coupling 19 to form a solenoid. The coil was thoroughly impregnated with epoxy and was covered with a protective fiberglass layer approximately ⅛ of an inch thick. If desired, a Kevlar layer could be used instead of the fiberglass. A further, non-magnetic stainless steel cover 34 was installed, although in most cases this will not be necessary. The lengths of steel casing 23 and 24 extending from respective ends of the coupling become an integral part of the ferromagnetic core of the solenoid so that the electromagnetic pole separation of the solenoid is much greater than the coupling length.
Transmission of a “start” signal to cause a selected beacon unit to begin operation may employ any one of a number of methods. A simple one is to provide a sonic source in the MWD equipment in the well being drilled. As illustrated in
In many SAGD drilling operations, an electromagnetic communication system is used instead of a pressure pulse system to communicate data between the Earth's surface and the MWD unit in the well being drilled. In this case, electrical signals are transmitted along the drill stem 52 and are detected by the MWD unit. If desired, these signals may be used to start a beacon by encoding them to activate a corresponding sonic transmitter in the MWD unit to produce a pulse, or burst, 56 for detection by the beacons in the reference well 10 and to activate a selected beacon.
Alternatively, it is a relatively simple matter to incorporate a magnetic field sensor in each beacon to permit activation of a selected beacon by magnetic fields produced by current in the drill stem 52 in well 12, or to permit activation of a selected beacon by signal currents in the casing string 58 of the reference well 10, which is made up of end-to-end coupled casing segments such as the segments 23 and 24, as described above. For this purpose, and as illustrated in
When a coded “start” signal is sent electromagnetically along the drill stem 52 from the driller's console 54, it is detected by the MWD apparatus 48 (
Instead of integrating the electromagnetic communication circuitry for controlling the operation of the beacon with the software of the MWD instrument 48, it may often be advantageous to have an independent beacon communication system, such as that illustrated at 80 in
An overall drilling system 100 incorporating a coupler beacon 102, which is similar to the beacons described hereinabove in accordance with the present invention, is illustrated in
A sonic transducer 112 in the down hole equipment 105 is connected to the MWD package 110, for example by way of an electronics package 114 that includes a sound generator and sound sensor, as well as electromagnetic field sensors for detecting the field generated by the beacon 102. The electronics package 114 includes a processor that responds to the coded signals received from the control console 104 by the MWD package 110 to produce a corresponding sonic pulse 120. The sonic pulse, or burst 120, that is initiated from the down hole equipment 105 in the well being drilled travels through the intervening geologic formations, is detected by a transducer 122 on the beacon 102, and is received by a receiving amplifier and processor 124 at the beacon. A sonic burst about 1 second long will, in many cases, be sufficiently long to communicate with the beacon. This enables the use of a very low power receiver 124 that will have a narrow bandwidth for rejecting the broad band, intense noise generated by the drill bit while drilling is actually in progress. In the preferred form of the invention, each of the beacon receivers remains in standby continuously from the time the beacon is installed in the casing string, waiting for an initiating burst. In most cases it is advantageous to have simple encoding in this burst to ensure that only a specified beacon is turned on.
As described above, the sonic burst 120 is initiated by the driller from the driller's console 104 by turning the drilling fluid pumps on and off in a prescribed way. This sends pressure pulses 106 from transducer 107 down the drilling fluid in the drill string, which are sensed by the down hole transducer 108 connected to the MWD unit 110 and the electronics package 114 to produce corresponding sonic signals 120. The selected beacon responds to the sonic burst to briefly energize the solenoid windings 28 on the beacon with encoded polarity and solenoid current as described above, to produce a corresponding electromagnetic field 44. Electromagnetic sensors in the MWD package 110 or in the electronics package 114 connected to the MWD package receive, signal average, and process three vector components of the alternating electromagnetic field 44 produced by the solenoid. Measurement while drilling tools manufactured by Vector Magnetics LLC, Ithaca, N.Y., incorporate the required electromagnetic field sensing elements for AC field measurements; however, most off the shelf standard MWD packages are programmed to only measure the Earth's magnetic field and the three vector components of the gravity. Therefore, to incorporate the AC capability required to measure the AC field 44 produced by the beacon, it is necessary either to reprogram the processing electronics of such standard tools or to provide the “add-on” AC unit as schematically indicated at 114 in
An electronics package 126 is carried by the beacon 102, for example in cavities 38 or 40 as described above, and includes a standard Peripheral Interface Circuit (PIC) and a field effect transistor (FET) circuit to put about 1 ampere of current into the solenoid coil 28 for about 10 seconds at a current reversal frequency of about 2 Hertz. The number of field reversals is conveniently made inversely proportional to the current injected into the coil so that the product of the magnetic moment generated and the time of excitation is constant, thereby keeping the integrated electromagnetic signal a fixed quantity even though the battery voltage may vary with current load and age. The current polarity of the first current flow half cycle can be used to define the polarity of the electromagnetic field.
Four or five “AA” alkaline batteries are capable of generating a magnetic moment of about 200 amp meters2; this is ample for range determination to at least 30 meters away. An ampere of current flow from an “AA” alkaline battery loads it from an open circuit voltage of about 1.56 volts to about 1.3 volts. Such a battery is rated at about 0.5 ampere-hours. Tests also indicate that such batteries and the integrated circuits being used can operate while subject to at least 3,000 psi of pressure without a protective sonde enclosure. Thus the typical requirements for many SAGD applications are readily met.
Once a beacon comes into range so that its magnetic field can be detected by the MWD tool of a well being drilled, relative distance determinations between the well bores are made to establish a surveying tie point. Then drilling continues, preferably using conventional drilling techniques, to the next beacon, which may be 100 or more meters down hole.
The signal averaged electromagnetic field vector components detected at the MWD package, along with the Earth field and accelerometer data obtained by the MWD tool and used to determine the azimuth, inclination and roll angle of the drilling assembly, are sent up-hole to the driller's console, using transducers 108 and 107 to send and receive pressure pulses 106 in the drilling fluid in known manner.
In general, the design of battery-powered beacons using the principles described herein to provide an alternating magnetic field and AC detection methods is much easier than using DC methods; in addition, AC methods give much greater range for a given amount of electrical power than would a DC beacon. DC beacon excitation using battery power is feasible, however, for it is often advantageous to use standard, off the shelf MWD drilling equipment, which has the capability of measuring only Earth magnetic field vectors.
The use of a DC magnetic field source in a drill guidance system is described in U.S. Pat. No. Re 036,569, wherein a direct current generated electromagnetic field is activated for a short time interval at one polarity and then for a short time interval at the other. The apparent Earth magnetic field is measured during each time interval. By subtracting the three vector components of the apparent Earth field measurements in the two cases, the electromagnetic field vector received from the DC magnetic field can be found. The processed three vector components of the received electromagnetic field are incorporated into the data stream of the standard MWD package and are transmitted to the driller using standard drilling fluid pressure pulse technology where they are further processed.
Several variations of the invention that are particularly suited to DC solenoid excitation of the above-described apparatus are illustrated in
The work string 130 can carry communication signals such as those described with respect to the system of
Another embodiment is illustrated in
As illustrated in
An overall electronic and computer control system 150 for use with the apparatus of
As described above, each beacon thus has a self contained electronics package which includes not only the peripheral interface controller (PIC), but solenoid current regulating and measuring circuitry and telemetry that is capable of applying to the solenoid the excitation currents that are required. In this way, either alternating current may be applied directly to the beacon or a “positive” direct current of a few amperes may be applied for approximately 10 seconds, during which time the MWD unit on the drilling assembly makes an apparent Earth field measurement. This is followed by a similar “negative” current excitation and measurement. Subtracting the measured apparent Earth magnetic field measurements from each other yields the vector components of the electromagnetic field generated by the beacon, while averaging the two measurements gives the vector components of the Earth's magnetic field. The measurements are transmitted to a data processor, which may be a part of the driller's control console 54, where the location and drilling direction of the well 12 are then computed and the drilling direction adjusted for the next course length, after which similar measurements are made. After a given beacon lies too far behind the drilling location to give precise enough results, drilling proceeds using the usual non-beacon guided methods until the next beacon comes in range, whereupon the procedure is repeated.
Although several systems for beacon deployment, beacon communication and beacon excitation and magnetic field sensing have been disclosed, it will be understood that they can be used in various combinations with one another to suit detailed drilling requirements.
For the SAGD application of the present invention, the detailed mathematics of the methods usefully employed for location and direction determination are well known and have been disclosed in numerous publications, such as, for example, U.S. Pat. No. 6,814,163. Algebraic manipulation of the mathematical details outlined in this patent is readily applied to the present configuration by those conversant in physics and mathematics. The following description of the salient features of this process will provide a general understanding of the method.
The overall considerations are illustrated in
An important feature in
If the three vector magnitudes, M, R and H are specified to be positive numbers, then the associated direction vectors m, r and h have the unique directions illustrated in
The field direction and magnitude at two points P and P1, at diametrically opposite locations from the source 170, are equal. They are on separate coplanar field line lobes 1 and 1a, respectively. It is necessary to know at the outset which of these lobes is the correct one in order to obtain a unique location determination from the measurement of the three vector components of the electromagnetic field. For the SAGD application disclosed herein, knowing that the observation point lies above the source is a sufficient condition.
Thus, given the directions of the vectors m and h and knowledge that the observation point is at a vertical elevation higher than the elevation of the source, the direction vector r is uniquely determined. The direction vector r lies in the plane of m and h and the field line lobe in that plane must lie above the source. The angle Amr from m to r on that lobe is uniquely related to the angle Amh, i.e., the angle from m to h. Furthermore the magnitudes of R, H, M and the angle Amr are related through the relationship
H=(M/(4*pi*R3))*sqrt(3*(cos(Amr))2+1)
Thus, knowing M, H, and the angle Amr, the magnitude of R is readily found from the above equation. Important points to note are that the field magnitude H is proportional to the source strength M, and is the inverse cube of the distance R and an angle factor, which varies between 2 and 1 depending upon the angle Amr. The moment M is proportional to the current flow in the solenoid, which is proportional to the battery voltage. Since the measurement will be time integrated over the duration of the excitation, varying the length of the excitation burst inversely with the current flow compensates for this, in addition to providing a direct, remote measurement of the battery condition.
Implicit in the above discussion is not only that it is desirable to know the directions of m and h; it is usually desirable to know the sense of each, i.e., the “sign” of each. The primary purpose of the standard MWD measurements made by drillers is the precise determination of borehole direction and MWD tool roll angle at each point in the borehole and to determine these quantities at closely spaced points in the boreholes. Thus, the axial direction of the electromagnetic field direction and its sign is readily determined. The axis of the source is known, since the reference well was also surveyed at the time of drilling. Constructing the source and installing it so that, e.g., the first positive current excitation of the source generates a local field pointing down, the axis of the reference well will specify the sign of the source moment direction. The sign of the source can usually be indirectly inferred, since the along-hole depth of each borehole is precisely known. Thus, the driller usually knows whether the current observation point lies “before” or “beyond” the source. Indeed, the driller usually knows the approximate relative location of a beacon before making a measurement, based on the previous drilling history. Thus, if need be, in many cases it is not necessary to know the sign of m.
The above discussion demonstrates that the relative location of the well being drilled and the beacon can be found from measurements at each station. In practice, electromagnetic field measurements will be made and analyzed whenever the beacon is within range. Using well-known methods of data analysis and an ensemble of measurements, together with the known distance along the borehole being drilled, drilling direction data can be optimized and relative location determination of the two boreholes made more precise.
Although the invention has been described in terms of various embodiments, it will be understood that these are exemplary of the true spirit and scope of the invention as set forth in the accompanying claims.
This application claims the benefit of U.S. Provisional Application No. 60/810,696, filed Jun. 5, 2006 and of U.S. Provisional Application No. 60/814,909, filed Jun. 20, 2006, the disclosures of which are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60810696 | Jun 2006 | US | |
| 60814909 | Jun 2006 | US |
