GB2162882A

GB2162882A - Encoding and transmission system for mud pulse telemetry of tool face angle data

Info

Publication number: GB2162882A
Application number: GB08519722A
Authority: GB
Inventors: Richard Frederick Roesler
Original assignee: NL Industries Inc
Current assignee: NL Industries Inc
Priority date: 1984-03-30
Filing date: 1985-08-06
Publication date: 1986-02-12
Also published as: GB8504675D0; BR8501430A; GB2156878A; NL8500949A; JPS60223593A; AR241609A1; AU4046585A; GB8519722D0; FR2562153A1; NO851151L; DE3511867A1

Abstract

Orthogonal indicia of orientation of a drilling tool 22 at the end of a drill string 18 within a borehole 12 are measured by a pair of sensors at intervals of a first frequency. Pressure pulses indicative of the tool face angle are generated in the mud flow passing along the drill string 18 by means of a mud flow valve in response to each measurement, and the pressure pulses are sensed at the surface in the vicinity of the well head 28 so that the tool face angle data can be obtained and used by the drilling operator. When the drilling tool 22 requires rapid reorientation following the addition of a section of drill pipe to the drill string 18, the reduction in the pressure of the mud flow due to the interruption of the mud flow necessitated by such addition is sensed by a mud pressure sensor. The sensor in turn provides a transmission rate selector signal which changes the interval of tool face angle measurement from the first frequency to a second, higher frequency, with the result that a more rapid updating of tool face angle is possible for reorientating the drilling tool 22 following addition of a drill pipe section. <IMAGE>

Description

1 GB 2 162 882A 1

SPECIFICATION

Encoding and transmission system for mud pulse telemetry of tool face angle data The invention relates to the telemetry of information related to drilling bit orientation in a 5 measuring while drilling system, and more particularly, to a system for encoding and transmitting data for determining tool face angle in a pulse position modulation mud pulse telemetry system.

In the drilling of boreholes into formations in the earth, it is highly desirable to obtain information related to the position and direction of the borehole while drilling is in progress. 10 Being -able to provide information to the drilling operator related to the inclination and azimuth of the borehole as well as the orientation of the drilling bit within the borehole while drilling is in progress enables corrective action and correction modifications during the drilling process.

Furthermore, systems for providing real time information as to bore hole configuration and drilling tool position renders the drilling operation much more efficient. Such information eliminates the need to stop the drilling process, remove the drill string from the hole and make measurements in order to ascertain the direction and angle of the borehole.

Toolface, orientation is measured in two ways. The first way is by the use of an array of three orthogonally mounted accelerometers which measure the gravitational acceleration in each of three sensors orthogonally positioned with respect to one another and oriented with respect to 20 the drilling tool. The second way is by the use of similar data obtained from three orthogonally mounted magnetometers which measure the orientation of the borehole tool with respect to the magnetic north of the earth. These well known techniques provide a relatively high degree of accuracy in measuring toolface orientation in virtually any position. For example, when the bore hole is closely approaching vertical with respect to the earth's axis, the accelerometer measurement becomes inaccurate and magnetometer data is used. Similarly, as the angle of the bore hole approaches that of alignment with the magnetic axis of the earth, the magnetometer data becomes inaccurate and requires reliance upon the accelerometer data. At all orientations between these two, the accelerometer and magnetometer information should be closely correlatable as a check one upon the other. 30 In a what is referred to as 'steering mode' of a measuring while drilling toolface orientation monitoring system, it is desirable to provide periodic indications of the precise angular orientation of the drilling too[ at the end of the drill string which is forming the borehole. This requires a system for the telemetry of data from the location of measurement at the lower end of the drill string up the borehole to the surface where it can be. utilized by the drilling operator. 35 Many different systems of the telemetry of information up a borehole have been proposed. The most generally successful has been that of utilizing pressure pulses imposed upon the flow of drilling mud down the central opening in the drill string to encode and convey information from the point of measurement to the drilling operator at the surface. Even among mud pulse telemetry systems there are a number of different techniques for encoding information into pressure pulses superimposed on the flowing drilling fluid stream. One system involves a pressure pulse to be imposed upon the system for each bit of information which is encoded on the stream of fluid. However, in order to generate pressure pulses downhole the rriud flow path must either be temporarily blocked or vented to the borehole annulus for inducing a pressure variation in the stream. Either technique of inducing pressure pulses requires large amounts of 45 energy to actuate a valve and introduce a pressure variation into the high pressure flowing stream. Power consumption and power requirements of equipment often- several thousand feet below the surface of the earth and subjected to tremendously hostile environmental conditions of pressure, temperature and vibration are quite severe. Therefore, it is desirable to minimize the consumption of power required to operate a mud pulser valve. Thus, the system of the present 50 invention contemplates the use of a pulse position modulation scheme to encode data onto the flowing stream of drilling mud as will be described and which requires fewer mud pulses to telemeter a given quantity of data.

Pulse position modulation involves the periodic production of a pressure pulse in the mud flowstream with the time between pulses being indicative of the data being transmitted. If, for 55 example, a time period of 10 milliseconds per unit of numerical value is assigned to the modulation scheme, the numerical value indicated by each time period between pulses would be the sum of the 10 millisecond intervals comprising the time between pulses. A time period of 4 seconds between pulses in such a scheme would represent a count of 400.

One of the parameters of evaluating the orientation of a bent sub used to perform directional 60 drilling operations is referred to as tool face angle. This measurement is the angle with which the plane defined by the bent axis of the bent sub makes with respect to a vertical plane, i.e., the angle of twist. In general, the tool face angle is measured by means of a pair of x and y sensors mounted with the bent sub, either accelerometers or magnetometers, which sensors each produce a voltage value. The ratio of the two voltage values is directly related to the value 65 2 GB2162882A 2 of tool face angle. However, as with all sensors, the voltage values vary as a function of temperature and must be corrected in accordance with certain bias voltages and certain scale factors prior to utilizing them as a direct indication of tool face angle. In conventional systems, this requires that two values one for each of the x sensor voltage value and one for the y sensor voltage value must be sent to the surface separately for correction for bias and scale factors prior to taking the ratio therebetween and obtaining a value of tool face. This requires two separate data words, one for each of the two values to be sent to the surface separately which requires an increased quantity of data to be handled by the mud pulse telemetry valve and an increased consumption of power to actuate that valve. The method and system of the present invention includes a technique by which the ratio between the x and y voltage values may be formed 10 downhole -and then simply the ratio telemetered to the surface and there corrected for bias and scale factors.

In addition, prior art data handling techniques provide for synchronization of data words being telemetered to the surface by sync pulses which are separate from the data frames, which contain no other information and which are basically "dead time". This again requires an 15 increased quantity of data bits to be transmitted by the mud pulse telemetry valve and the consumption of an increased quantity of power to perform this transmission. The system of the present invention utilizes a data format which eliminates any "dead time" between frames and thereby decreases the power requirements for telemetering the data. The data format of the present invention additionally minimizes the power requirements by providing an encoding 20 format which transmits two words per data frame by means of a single pulse position indication per frame.

Certain problems are inherent in the operation of a mud pulse telemetry system in the steering mode so as to provide a continuous indication of borehole tool position to a drilling operator.

For example, every 30 feet or so of drilling string it is necessary to briefly interrupt the drilling operation and interrupt the mud flow by stopping the mud pumps at the surface to add an additional 30 foot section of drilling pipe can be added to the drill string. During the process of adding the drill string section it is necessary to twist the drill pipe wherein the string becomes - torqued as an inherent part of the drill section addition process. Once the section of drill string has been added, the orientation of the drilling too[ is no longer the same as far as the tool face 30 angle is concerned as it was before the drilling was interrupted and the additional section of drill string added. Thus, the drilling operator must reorient the drilling tool to the same tool face angle prior to resuming the drilling operation so as to drill with consistency and in the desired direction. During the reorientation of the drilling too[ process, it is desirable to provide the substantially higher rate of data flow from the tool face angle sensors in the drilling tool than 35 during the remainder of the drilling operaton. An increased data flow rate enables the drilling operator to position the tool much more quickly to its original position and thereby resume drilling operations with a minimum of down time of the drilling equipment.

While prior art drilling information telemetry systems have included provision for a variable rate of data transmission, it has generally been only in response to a signal from the drilling operator at the surface. One such example is under conditions where the bore hole is becoming so deep that the telemetry data is insufficiently defined. For example, as taught in U.S'. Patent No. 3,863,203, addresses this problem with an adjustable transmission rate acoustic telemetry system for a logging while drilling mode. Surface to downhole communication channels, are used to control the data rate of-the acoustic signals sending information uphole. The system of 45 the present invention, however, monitors the parameters associated with the need more rapid - updating of tool face angle data and automatically switches the rate of data flow to the higher value and provides an indication within the encoded data format as to the rate of data transmission. Moreover, the system of the present invention provides a variable rate of transmission of tool face angle data in a measuring while drilling system within a tool face data 50 encoding format which maximizes the efficiency of a mud pulse position telemetry system.

More particularly, the invention includes a method and system for telemetering data indicative of the tool face- angle of a drilling tool to the surface of the earth in a logg ing-wh ile-d ri [ling system where the tool face angle of a drilling tool is measured at intervals at a first frequency and a data signal is generated in response to each measurement indicative of the measured too] 55 face angle. A pressure pulse signal is generated on a mud pulse telemetry system in response to each generated data signal to transmit a pressure pulse modulated indication of the measured tool face angle to the surface. The invention includes measuring the pressure of the downwardly flowing mud stream at a downhole location and changing the interval of tool face angle measurement from said first frequency to a second higher frequency in response to the measurement of a sequential interruption and reestablishment of mud pressure indicative of the addition of section of drill pipe to the drill string to provide a more rapid updating of tool face angle for reorienting the drilling tool.

In another aspect the invention includes a system for telemetering data indicative of the tool face angle of a drilling tool to the surface of the earth in a logg i ng- whi le-dril ling system which 65 3 GB2162882A 3 includes a pair of sensors for generating a first and a second voltage indicative of the orientation of the drilling tool in a pair of orthogonal planes. A frame of binary data is generated which includes a first and a second binary word, the first word of which has at least one bit position indicative of each of (a) the sign of the first voltage, (b) the sign of the second voltage ' (C) whether the first or second voltage is larger, and (d) whether the sensor pair are accelerometers 5 or magnetorneters, and the second word of which has a plurality of bit positions indicative of the absolute value of the ratio of the first and second voltage which is between zero and one. The system also includes means for translating the value of each of the first and second binary words into a pair of equivalent first and second time values, and means for generating a series of three pressure pulses in the downwardly flowing mud stream of the drilling system, the time 10 between the first and second pulses being equal to first time value and the time between the second and third pulses being equal to the second time value. Further, the system includes means located at the surface and responsive to the time between the first and second pulse for regenerating the first binary data word and responsive to the time between the second and third pulse for regenerating the second binary data word and means responsive to the components of 15 the first and second data words and previously measured values of borehole inclination and azimuth and temperature dependent bias and scale factors for calculating tool face angle.

In a still further aspect the invention relates to a mud pulse telemetry system- for transmitting data in:dicative of tool face angle from a drilling tool within a borehole to the surface wherein a pair of orthogonal x and y sensors each develop a voltage indicative of the orientation of the 20 drilling tool and pulse position modulation is used. The invention includes a tool face data format for each measurement of angle comprising a binary data frame which includes a pair of binary words, the first word containing an indication of (a) the sign of the x voltage, (b) the sign of the y voltage (c) which voltage is larger and, (d) whether the sensors are accelerometers or magnetometers, and the second word containing an indication of the absolute value of the ratio of the x voltage and the y voltage between zero and one.

Brief Description of the Drawing

For a-more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction 30 with the accompanying drawing in which:

Figure 1 is a diagrammatic side-elevational view of a borehole drilling operation illustrating the steering mode of a mud pulse telemetry system which incorporates a data handling and encoding format in accordance with the principles of the present invention; Figure 2 is a top plan illustration of a borehole drilling operation illustrating the azimuth of a 35 directional borehole; Figure 3 is a perspective illustration of a bent sub drilling tool and the tool face angle associated therewith in conjunction with a sub incorporating an encoding and transmission system for mud pulse telemetry tool face data constructed in accordance with the present invention; Figure 4 is a schematic illustration of a format for encoding mud pulse telemetry tool face data for transmission in a pulse position modulation system all in accordance with the teachings of the present invention; and Figure 5 is a block diagram of a system for encoding and transmission of tool face data constructed in accordance with the teachings of the present invention.

Detailed Description

Referring to Fig. 1, there is shown a drilling rig 11 disposed above a borehole 12. One embodiment of a system 10 for encoding and transmitting too[ face data is carried by a. sub 14 comprising a portion of a drill collar 15 positioned within the borehole 12. A drill bit 22 is disposed at the lower end of the drill string 18 and is attached to the lower end of a bent sub 21 affixed to the lower end of the drill collar 15. The drill bit 22 carves the borehole 12 out of the earth formations 24 while drilling mud 26 is pumped from the well head 28. Metal surface casing 29 is shown to be positioned in the borehole 12 at the top thereof for maintaining the integrity of the borehole 12 near the surface. The annulus 16 between the drill string 18 and 55 the borehole wall creates a theoretically closed return mud flow path. Mud is pumped from the well head 28 by a pumping system 30 through a supply line 31 coupled to the drill string 18.

Drilling mud is, in.this manner, forced down the central axial passageway of the drill string 18 and egresses at the drill bit 22 foir carrying cuttings comprising the drill sections of earth, rock and related matter upwardly from the drill bit to the surface as well as providing a force for rotating a mud turbine within the drill bit 22 causing the cutting surfaces of the bit to rotate and cut through the formations.

Within the region of the drill collar 15, there is incorporated into the drill string 18 a mud flow valve (not specifically shown) which is arranged to either interrupt or otherwise produce a perturbation in the pressure of the mud being forced down the central axial opening in the drill 65 4 GB 2 162.882A string 18 by the mud pump 30. This mud flow valve is used to encode pressure pulses onto the flowing stream of drilling mud and modulate pressure of that stream. In this manner information - -is transferred from the region near the drilling bit to the surface near the well head 28 so that the information can be obtained and used by the drilling operator.

As shown in Fig. 1, the borehole 12 which is being formed into the earth by the drilling rig 5 11 is not perfectly vertical. -That is, the lower end of the borehole is being formed at some angle between the axis of the borehole 25 and the vertical plane 26. This angle 27 is known as the inclination of the borehole.

Referring briefly to Fig. 2 a top plan illustration of the drilling rig 11 and borehole 12 of Fig.

1 is shown and there can be seen a second parameter associated with an angular borehole. The 10 angle which the axis of the borehole 28 makes with magnetic north 29 is referred to as the azimuth of the borehole and is designated by the arrows 31.

Referring now to Fig. 3, there is illustrated a perspective view of the lower end of the drill string 18 which includes a series of drill collars 15 which illustratively include equipment for sensing the orientation of the borehole, equipment for processing and encoding data with 15 respect to borehole parameters, and mud pulse telemetry equipment such as mud flow valves and actuators which are used to telemeter information from the lower end of the borehole to the well head for use by the drilling operator. As shown in Fig. 3, the bent sub 21 is attached to the lower end of the drill string and is terminated by the drilling bit 22. As can be seen, the central 30 axes of both segments of the bent sub 21 define and lie within a common plane. This plane 20 of the bent sub axes is generally not parallel with a vertical plane but, rather, lies at some angle with respect thereto and represents the twist of the bent sub relative to vertical. There is illustrated in Fig. 3 a line 32 which represents a line lying in a vertical plane and a line 33 which represents a line lying in the plane within which the axes 30 of both portions of the bent sub lie. Thus, these two lines define an angle 34, representing the twist of the bent sub, shown 25 - by arrow 34' and which is referred to the tool face angle. Other terms which are used with respect to this characteristic of the drilling tool is one which is called the "high-side" angle of the tool. Such nomenclature refers to the point on the uppermost surface of the drilling bit i.e., the "high-side" and the angle with respect to this point and a point which lies along the plane defined by the bent axes 30 of both the segments of the bent sub.

The high-side, or too[ face angle, is informaton of critical importance to the drilling operator because, along with the indications of azimuth and inclination, it tells him in which direction the tool is oriented and hence in which direction the borehole is being formed through the earth. It is critical that this information be provided on a periodic and regular basis to the drilling operator in an efficient measuring-while-drilling system in order for the operator to make 35 changes and continue to redirect the tool in the desired orientation.

The system of the present invention involves an algorithm and technique for computing both magnetic and high side tool face values as well as a method for encoding and transmitting magnetometer and accelerometer data to the surface in a compact and efficient format for providing an indication of tool face to the drilling operator. Tool face angle is conventionally 40 determined by the relative values of the output voltages of the x and y axis'accelerometer (or magnetometer) sensors within the borehole. The relationship between a sensor output voltage V and a physical quantity measured by that sensor is defined as:

- 45 V=mS+b where b is a temperature dependent bias voltage and m is a temperature dependent scale factor.

For the accelerometer data the value V is given in volts and the S term is related to gravitational acceleration while for the magnetometer data the value V is also in volts while the S term is in magnetic flux. In the present technique the procedure for a computing tool face involves the following:

1. Determine the relative value of V. and VY and form the ratio vj a = -where i, j = x,y such that 0< jul < 1.

Vi It should be noted that we must provide a way to remember the signs of V. and VY since the absolute value of ci will be transmitted to the surface.

2. Since S is a function of high-side tool face, we can write:

vj m,S,(0) + bi a= --- vi rnS,(4)) + bi GB 2 162 882A 5 Since we know that, the functional form of S(O) we can define a function, f, such that:

miSi((p) + bi m,S,(4)) + bi assuming that we know all of the variables except 0, we may solve for 0 using iteration procedures. These procedures are relatively straight forward wherein we choose initial guesses for 0 and then calculate different values so that as we reach the exact 0 it will cause f(O) to be equal to 0.

Thus, using this technique we may arrive at a value of tool face angle from the ratio of the two voltages rather than having to transmit the full value of both the x sensor voltage and y sensor voltage to the surface as discrete values. That is, by transmitting the value of the ratio between the two, the sign of the x voltage, the sign of the y voltage and the information as to which of the two values was greater as well as whether or not the information was derived from either accelerometers or magnetometers, all of the corrections for bias and scale factor may be made at the surface by the iteration technique. This data encoding format saves a tremendous quantity- of data handling capacity and lowers the power requirements in order to transmit a given volume of tool face data from within the bore hole to the surface.

Referring now to Fig. 4 there is shown an illustration of the data encoding format of the present invention. A data frame is identified within the boundaries of the bracket 41 and represents a single spacing between mud pulses in a mud pulse telemetry system. Within a single. frame of data 41, there are two data words contained 42 and 43. Each word contains two bit positions 44 and 45 assigned to information related to the rate at which data is being telemetered to the surface, as will be discussed below. The next position in each word 46 isassigned to a sync pulse. A "0" pulse is assigned to the first word in the frame while a -1 " is assigned to the second word in that frame so that if a word is dropped in process the next "0" sync pulse observed in the sync pulse position will indicate the beginning of a word. This eliminates the need for spacing between pulse frames and also saves data handling capacity.

The next-pulse position 47 in the first word indicates the sign of x; the next pulse position in the 30 first word 48 indicates the sign of y. The 6th pulse position 49 in the first word indicates which of the two values x or y is greater while the next pulse position 51 indicates whether or not the values were obtained from magnetometers or accelerometers, thus enabling the bias and scale factors. associated with the particular sensors to be applied at the surface. The 8th bit position 52 of-the first word contains the 5th bit of the absolute value of the ratio.of the x and y voltage 35 values. Similarly, the 4th through 8th bit positions 53 of the second word contain respectively the 4th through the Oth bit of the absolute value of the ratio x and y.

Thus, it can be seen how the data encoding format for tool face data maximizes the amount of information which can be contained within a single frame of data transmitted to the surface by a single pulse position modulation unit. This, of course, saves substantially in the power required 40 to transmit the data for a full reading of tool face value to the surface.

Referring now to Fig. 5, there is shown a block diagram of the overall system of encoding and transmitting too[ face data by means of mud pulse telemetry all constructed in accordance with the teachings of the present invention. As shown in the block diagram of Fig. 5, a mud transmission line 61 carries pulse position modulated tool face data to the surface. Each of the blocks below the mud transmission line 61 represent equipment located downhole while each of the blocks located above the mud transmission line represent equipment and processing which is located at the surface. First, it can be seen how a pair of accelerometers (or magnetometers) 62 and 63 are used to obtain values associated with the orientation of the drilling tool. The x - sensor 62 produces a voltage value associated with the x component of the earth's gravitational 50 field while the y sensor 62 produces a voltage associated with y component of the earth's gravitational field based upon the position of the sensors with respect to the earth. The output voltage of the xaccelerometer is represented at 63 while the y output voltage is represented at 64. BotKof these voltages are input to a processor which evaluates several parameters.

The processor 65 first evaluates what is the absolute value of the ratio of the value of one of 55 the output voltages with respect to the other. The absolute value is always taken so that the value is positive and greater than 0 and less than 1. In addition, the computational unit 65 determines the sign of each of the components of the voltage values V. and VY; which of the two values V, and V Y are greater, and in other words, which of the two values was the numerator and which was the denominator in order to produce a ratio having a value between O,and 1. 60 Finally, the unit denotes whether the V voltage values are obtained from accelerometers or magnetometers. The data determined by the computational unit 65 is then input to a binary frameassembly unit 66 which assembles a binary data frame from that information That is, this unit composes two 8 bit words in accordance with the data format shown and described in connection with Fig. 4 above. In addition to the input from the computational unit 65, the 6 GB2162882A 6 binary data frame asseTbly units 66 receives an input from a sync pulse source 67 as well as a transmission rate selector unit 68 which also provides a bit generator indicative of the transmission rate selected by the unit 68. The transmission rate selector is actuated in response to a mud pressure sensor 69 also mounted in the sub 15 along with the associated calculation and encoding equipment.

After the binary data frame assembly unit 66 has assembled the information from the computational unit 65, the sync pulse generator 67, the transmission rate selector and the bit generator 68 in accordance with the data format shown in Fig. 4, the value of this Word is then translated from a binary word value into a pair of time values. The translation is made in accordance with the particular pulse position modulation scheme used in the mud pulse 10 telemetry system being employed by a unit 70. That is, one time value is associated with the value of the first data word 71 while a second time value is associated with the data word 72(Fig, 4). Once the two values are determined, the mud flow control valve which forms part of the pulse position modulation mud pulser 73 produces a series of three pulses in the mud transmission line 61. The space between the first pulse and the second pulseis indicative of the 15 value of the first data word while the space between the second pulse and third pulse is indicative of the second data word. Thus it can be seen how a large quantity of data indicative of tool face has been encoded into the format which only requires the expenditure of energy necessary to produce a series of three mud pressure pulses. This format is in contrast to prior art s stems wherein many pulses must be encoded into the mud flow stream in order to convey all 20 of the bits.of information necessary to specify the sensor voltage values and enable the calculation of tool face angle therefrom at the surface.

The-pulses placed upon the mud transmissions line 61 are demodulated at the surface by a pulse position demodulator unit 75 and which provides an input to a unit which reconstructs the binary word values of the data frame -originally assembled by the downhole unit 66. The binary 25 word value reconstruction unit 76 furnishes output to a calculation unit 77 which performs the iterative calculation in order to correct the value of tool face for bias and scale factor parameters.

This is done in accordance, with the iteration technique utilizing the data of ratio of sensor - voltage values, the signs of the respective voltages and information as to which voltage is greater as well as whether or not the sensor was a- magnetometer or accelerometer all in accordance with known techniques.

The iterative calculation in unit 77, of course, relies upon previous values of inclemation azimuth, temperature variation bias and scale factors stored in the memory unit 78 and furnished to the iterative calculation unit 77. Finally, the output from the calculation provides a tool face value to the operator which has been corrected for bias and scale factors but which has 35 been provided with a minimum of expenditure of power to telemeter the information to the surface.

As discussed above, the tool face value is required to be updated with a much greater frequency immediately following the addition of a section of drill pipe to the drillstring. In order to add a section of drill pipe, the mud pumps located at the surface and the well head are interrupted which reduces the pressure of the mud stream down hole. As discussed above, the mud pressure sensor 69 detects this interruption in mud flow pressure as well as the subsequent repressurization of the system caused by restarting of the mud pumps following the addition of the drill string -section and the recommencement of drilling. The repressurization of the system is detected by the mud pressure sensor 69 which provides a transmission rate selector signal which indicates that a much higher rate of tool face data is now required at the surface by the drilling operator in order to reorient his drilling too[ in a minimum amount of time. Thus, the rate at which voltage values are sampled and tool face calculation made in the computational unit 65 is increased by a preselected value, for example on the order of a factor of 4, so that rather than providing a tool face indication every 20 seconds in this interval for a 50 preselected period of time tool face value is recalculated and transmitted every 5 seconds. This continues for a surfficient period of time for the drilling operator to have reoriented the tool and begun full scale drilling operations, after a "time out", the transmission rate selector returns to the standard rate at which information is sampled and transmitted to the surface. This of course, only requires increased power to operate the mud position modulation mud pulser 78. at an increased rate for a brief period of time to provide the additional information when it is most - critically needed. When the transmission rate selector 68 is actuated in response to the mud pressure sensor, it also provides a coded bit indication into positions 44 and 45 of the data frame format of Fig. 4 to indicate the rate.at which the data is being transmitted uphole to the surface equipment.

Thus, it can be seen from the foregoing that the system for encoding and the transmission of tool face data format in a pulse position modulation mud pulse telemetry system is greatly enhanced in efficiency and maximizes the utilization of power downhole to transmit a maximum amount of information to the surface with a minimum expenditure of power. It is thus believed that the operation and construction of the present invention will be apparent from the foregoing 65 7 GB2162882A 7 description while the mpthod and apparatus shown and described has been characterized as being preferred it will bh obvious that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the following claims.

Claims

1. A method for telemetering data indicative of the tool face angle of a drilling tool within a borehole to the surface of the earth in a loggingwhile-dril ling system comprising the steps of:

measuring the orthogonal indicia of orientation of a drilling tool at intervals of a first frequency; generating a data signal indicative of the tool face angle in response to each measurement; 10 generating a pressure pulse signal on a mud pulse telemetry system in response to each generated data signal to transmit a pressure pulse modulated indication of the measured tool face angle; measuring the pressure of the downwardly flowing mud stream at a downhole location; and 1.5 changing the interval of tool face angle measurement from said first frequency to a second 15 higher frequency in response to the measurement of a sequential interruption and reestablish ment of mud pressure indicative of the addition of a section of drill pipe to the drill string to provide a more rapid updating of too[- face angle for reorienting the drilling tool.

2. A method for telemetering data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-wh i le-dril ling system as set forth in claim 1 wherein said data 20 signal generating step includes generating a component of said data signal which is indicative of the frequency of said interval of measurement.

3, A method for telemetering data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-while-drilling system as set forth in claim 1 wherein said second frequency is higher than said first frequency by a factor of four.

4. A method for telemetering data indicative of the tool face angle of a drilling too[ to the surface of the earth in a logging-while-drilling system as set forth in claim 1 wherein said pressure pulse signal generating step includes modulating a series of mud pressure pulses in accordance with a pressure pulse position scheme.

5. A method for telemetering data indicative of the tool face angle of a drilling tool to the 30 surface of the earth in a logging-while-drilling system as set in claim 1 wherein said measuring step comprises the steps of:

generating a first voltage indicative of the position of an x axis sensor mounted in the drilling tool; generating a second voltage indicative of the position of a y axis sensor mounted in the 35 drilling tool;, and wherein said data signal generating step comprises:

assembling a frame of binary data including a pair of binary words, the first word containing an indication of the frequency of tool face angle measurement, the sign of the first voltage, the sign of the second voltage, which voltage is greater and whether the sensors are accelerometers 40 or magnetometers, and the second word containing an indication of the absolute value of the ratio of the first and second voltages between 0 and 1.

6. A method for telemetering data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-while-drilling system as set forth in claim 5 wherein said mud pulse telemetry system is of the pulse position modulation type and wherein said pressure pulse 45 signal generating step includes generating three mud pressure pulses, the time spacing between the first and second pulses being indicative of the value of said first binary word in said frame of binary data and the time spacing between the second and third pulses being indicative of the value of said second binary word in said frame of binary data. 50

7. A system for telemetering data indicative of the too[ face angle of a drilling tool within a 50 borehole to the surface of the earth in a logging-whiledrilling system, comprising: a pair of sensors for generating a first and a second voltage indicative of the orientation of the drilling tool in a pair of orthogonal planes; 'means for generating a frame of binary data including a first and a second binary word, said first word having at least one bit position indicative of (a) the sign of the first voltage, (b) the sign of the second voltage, (c) whether the first or second voltage is larger, and whether said sensor pair are accelerometers or magnetometers, and a second word having a plurality of bit positions indicative of the absolute value of the ratio of the first and second voltages which is between zero and one; means for translating the value of each of the first and second binary words into a pair of 60 equivalent first and second time values; means for generating a series of three pressure pulses in the downwardly flowing mud stream of the drilling stream, the time between the first and second pulses being equal to first time value and the time between the second and third pulses being equal to the second time value; means located at the surface and responsive to the time between the first and second pulse 65 8 GB2162882A 8 for regenerating said firt binary data word and response to the time between the second and third pulse for regenerating said second binary data word; and means responsive to the components of said first and second data words and previously measured values of borehole inclination and azimuth and temperature dependent bias and scale 5 factors for calculating too[ face angle.

8. A system for telemetry data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-while-drilling system as set forth in claim 7 wherein each of said first and second binary words has a bit position for a sync pulse and wherein the sync pulse bit in each word is of opposite polarity.

9. A system for telemetry indicative of the tool face angle of a drilling tool to the surface of 10 the earth in a logging-while-dril ling system as set forth in claim 7 which also includes means for varying the frequency with which frames of binary data are generated from said first and second voltages.

10. A system for telemetry of data indicative of the tool face angle of a drilling too[- to the surface of the earth in a logging-while-dril ling system as set forth in claim 9 wherein said 15 frequency varying means increases the frequency of generation of frames of binary data from said first and second voltages in response to a sequence of a substantial decrease in the pressure of the downwardly flowing mud stream and reestablishment of that pressure indicating the addition of a section of drill pipe to the drill string,

11. A system for telemetry of data indicative of the tool face angle of a drilling tool to the 20 surface of the earth in a logging-wh ile-dril ling system as set forth in claim 10, wherein -both -said first and second data words include at least one bit position indicative of the frequency at which frames of binary data are generated.

12. A system for telemetry of data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-wh ile-dril ling system as set forth in claim 7 wherein said 25 calculating means computes too[ face angle by means of an iteration technique.

13. In a mud pulse telemetry system for transmitting data indicative of tool face angle from a drilling tool within a borehole to the surface wherein a pair of orthogonal x and y sensors each develop a voltage indicative of the orientation of the drilling too[ and pulse position modulation is used, a tool face data format for each measurement of angle, comprising:

a binary data frame which includes a pair of binary words, the first word containing an indication of (a) the sign of the x voltage, (b) the sign of the y voltage, and (c) which of said voltages is larger and the second word containing an indication of the absolute value of the ratio of the x voltage and the y voltage between zero and one.

14. A method for telemetering data indicative of the tool face angle of a drilling tool, the method being substantially as hereinbefore described with reference to the accompanying drawings.

-- 45 Printed in the United Kingdom for Her Majesty's Stationery Office. Dd 8818935, 1986, 4235. Published at The Patent Office, 25 Southampton Buildings. London, WC2A lAY. from which copies may be obtained.

14. The mud pulse telemetry system for transmitting data indicative of the tool face angle of 35 a drilling tool to the surface of the earth in a logging-while-drilling system as set forth in claim 13 wherein both the first and second binary words comprising the binary data frame contain a sync bit.

15. The mud pulse telemetry system for transmitting data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-while-drilling system as set forth in claim - 40 13 wherein both the first and second binary words comprising the binary data frame contain an indication of the frequency with which tool face angle measurements are made and telemetered to the surface.

16. A system for telemetering data indicative of the tool face angle of a drilling tool within a borehole to the surface of the earth in a logging-while-drilling system comprising: - means for measuring the orthogonal indicia of orientation of a drilling too[ at intervals of a first frequency; means for generating a data signal indicative of the tool face angle in response to each measurement; means for generating a pressure pulse signal on a mud pulse telemetry system in response to 50 each generated data signal to transmit a pressure pulse modulated indication of the measured tool face angle; means for measuring the pressure of the downwardly flowing mud stream at a downhole location; means for changing the interval of tool face angle measurement from said first frequency to a - 55 second higher frequency in response to the measurement of a sequential interruption and reestablishment of mud pressure indicative of the addition of section of drill pipe to the drill string to provide a more rapid updating of tool face angle for reorienting the drilling tooL 17. A system for telemetering data indicative of the tool face angle of a drilling too[ to the surface of the earth in a logging-while-drilling system as set forth in claim 16 wherein said data 60 signal generating means includes means for generating a component of said data signal which is indicative of the frequency of said interval of measurement.

18. A system for telemetering. data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-while-drilling system as set forth in claim 17 wherein said second frequency is higher than said first frequency by a factor of four.

9 GB2162882A 1 9 A system for telepetering data indicative of the tool face angle of a drilling tool to the surface of the earth in a togging-while-drilling system as set forth in claim 17 wherein said pressure pulse signal generating means includes modulating a series of mud pressure pulses in accordance with a pressure pulse position scheme.

20. A system for telemetering data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-while-dril ling system as set forth in claim 16 wherein said measuring means comprises:

means for generating a first voltage indicative of the position of an x axis sensor mounted in the drilling too[; means for generating a second voltage indicative of the position of a y axis sensor mounted in 10 the drilling tool; and wherein said data signal generating means comprises:

means for assembling a frame of binary data including a pair of binary words, the first word containing an indication of the frequency of tool face angle measurement, the sign of the first voltage, the sign of the second voltage, which voltage is greater and whether the sensors are 15 accelerometers or magnetometers and the second word containing an indication of the absolute value of the ratio of the first and second voltages between 0 and 1.

21. A system for telemetering data indicative of the tool face angle of a drilling tool to the surface of the earth in a logging-while-drilling system as set forth in claim 20 wherein said mud pulse telemetry system is of the pulse position modulation type and wherein said pressure pulse 20 signal generating step includes means for generating three mud pressure pulses, the time spacing between the first and second pulses being indicative of the value of said first binary word in said frame of binary data and the time spacing between the second and. third pulses being indicative of the value of said second binary word in said frame of binary data.

22. A method. for telemetering data indicative of the tool face angle of a drilling tool, the 25 method being substantially as hereinbeforedescribed with reference to the accompanying drawings.

23. A system for the telemetering of data indicative of the tool face angle of a drilling tool, the system being substantially as hereinbefore described with reference to the accompanying drawings.

CLAIMS Claims 1 to 23 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. A method for telemetering data indicative of the too[ face angle of a drilling tool within a 35 borehole to the surface of the earth in a logging-while-drilling system comprising the steps of:

measuring the orthogonal indicia of orientation of a drilling too[ at intervals of a first frequency; generating a data signal indicative of the tool face angle in response to each measurment; generating a pressure pulse signal on a mud pulse telemetry system in response to each 4G generated data signal to transmit a pressure pulse modulated indication of the measured tool face angle; measuring the pressure of the downwardly flowing mud stream at a downhole location; and changing the interval of tool face angle measurement from said first frequency to a second, higher frequency in response to the measurement of a sequential interruption and reestablish- 45 ment of mud pressure indicative of the addition of a section of drill pipe to the drill string to provide a -more rapid updating of too[ face angle for reorienting the drilling tool.

2. A method according to claim 1, wherein said data signal generating step includes generating a component of said data signal which is indicative of the frequency of said interval of measurement.

3. A method according to claim 1 or 2, wherein said second frequency is higher than said first frequency by a factor of four.

4. A method according to claim 1, 2 or 3, wherein said pressure pulse signal generating step includes modulating a series of mud pressure pulses in accordance with a pressure pulse position scheme.

5. A method according to any preceding claim, wherein said measuring step comprises the steps of:

generating a first voltage indicative of the position of an x axis sensor mounted in the drilling tool; generating a ssecond voltage indicative of the position of a y axis sensor mounted in the 60 drilling tool; and wherein said data signal generating step comprises:

assembling a frame of binary data including a pair of binary words, the first word containing an indication of the frequency of tool face angle measurement, the sign of the first voltage, the sign of the second voltage, which voltage is greater and whether the sensors are accelerometers 65 GB2162882A 10 or magnetometers, and the second word containing an indication of the absolute value of the ratio of the first and second voltages between 0 and 1.

6. A method according to claim 5, wherein said mud pulse telemetry system is of the pulse position modulation type and wherein said pressure pulse signal generating step includes generating three mud pressure pulses, the time spacing between the first and second pulses. being indicative of the value of said first binary word in said frame of binary data and the time spacing between the second and third pulses being indicative of the value of said second binary word in said frame of binary data.

7. A method according to claim 5 or 6, wherein both said first and second data words include at least one bit position indicative of the frequency at which frames of binary data are - 10 generated.

8. A system for telemetering data indicative of the tool face angle of a drilling tool within a borehole to the surface of the earth in a loggingwhile-drilling system comprising:

means for measuring the orthogonal indicia of orientation of a drilling tool at intervals of a first frequency; means for generating a data signal indicative of the tool face angle in response to each measurement; means for generating a pressure pulse signal on a mud pulse telemetry system in response to each generated data signal to transmit a pressure pulse modulated indication of the measured tool face angle; means for measuring the pressure of the downwardly flowing mud stream at a downhole location; and means for changing the interval of tool face angle measurement from said first frequency to a second, higher frequency in response to the measurement of a sequential interruption and - reestablishment of mud pressure indicative of the addition of a section of drill pipe to the drill 25 string to provide a more rapid updating of too[ face angle for reorientating the drilling tool.

9. A system according to claim 8, wherein said data signal generating means includes means for generating a component of said data signal which is indicative of the frequency of said interval of measurement.

10. A system according to claim 8 or 9, wherein said second frequency is higher than said 30 first frequency by a factor of four.

11. A system according to claim 8, 9 or 10, wherein said pressure pulse signal generating means includes means for modulating a series of mud pressure pulses in accordance with a pressure pulse position scheme.

12. A system according to any preceding claim, wherein said measuring means comprises: 35 means for generating a first voltage indicative of the position of an x axis sensor mounted in the drilling tool; means for generating a second voltage indicative of the position of a y axis sensor mounted in the drilling too[; and wherein said data signal generating means comprises:

means for assembling a frame of binary data including a pair of binary words, the first word containing an indication of the frequency of too[ face angle measurement, the sign of the first voltage, the sign of the second voltage, which voltage is greater and whether the sensors are accelerometers or magnetometers, and the second word containing an indication of the absolute value of the ratio of the first and second voltages between 0 and 1.

13. A system according to claim 12, wherein said mud pulse telemetry system is of the pulse position modulation type and wherein said pressure pulse signal generating means includes means for generating three mud pressure pulses, the time spacing between the first and second pulses being indicative of the value of said first binary word in said frame of binary data and the time spacing between the second and third pulses being indicative of the value of 50 said second binary word in said frame of binary data.