GB2024895A - Monitoring system for well drilling - Google Patents

Abstract

A monitoring system for parameters of a well drilling operation (e.g. mud flow rate, mud level, pump rate) comprises a central processor 29 having a transceiver 31, and a plurality of parameter sensors 20, 25, 22 having respective transceivers 26, 27, 28. The central processor periodically emits coded interrogation signals which cause a transceiver identified by the coded signals to be energized to transmit back to the central processor signals indicative of its respective sensed parameter. Each transceiver is interrogated every 7-15 seconds. In addition, signals are transmitted to the central processor every time certain events (e.g. pump strokes or rotary table rotations) occur. Monitored parameters are displayed on an instrumentation panel 35. <IMAGE>

Description

SPECIFICATION Monitoring system for well drilling The present invention relates to the art of drilling, and more particularly to a drilling rig instrumentation system for monitoring and controlling the drilling of a well.

In drilling a well for oil and gas or the like, a rotary drill bit is supported in a borehole by a rotary drill string. The drill string is composed of a plurality of individual lengths of drill pipe connected together. The drill string carries drilling fluid in its interior down to and through the rotary drill bit. Once the drilling fluid reaches the bottom of the borehole it passes upwardly in the annulus between the exterior surface of the drill string and the interior surface of the borehole. The drilling fluid continues upward to the surface of the earth and then through a return pipe to storage pits commonly referred to as mud pits. Various paramaters are monitored during the drilling operation and suitable control functions are employed based upon the information obtained from the monitoring procedure.Examples of the parameters monitored are pressure, flow rate, rotary speed, torque, hook load, depth of mud in pit, etc.

In order to understand the need for monitoring and controlling procedures during the drilling operation, the following problems routinely encountered during drilling will now be considered. The weight of the drilling fluid in the borehole is used to help maintain a high pressure at the bottom of the borehole and prevent undesired lighter materials such as gas, water and the like from intruding into the borehole. The intrusion of these materials would force drilling fluid from the borehole through the return pipe and a dangerous and expensive blowout could occur because of the reduced pressure in the borehole. Should high pressure gas from an underground reservoir enter the borehole a potential blowout could occur. The intrusion of gas into the borehole is manifested by the forcing of an equivalent amount of drilling mud out of the borehole and into the mud pits.The loss of mud from the borehole decreases the pressure opposite the underground reservoir and allows more gas to enter the borehole. A blowout occurs when the gas blows most of the mud out of the borehole and gas itself appears at the surface. Fire and accompanying loss of life and property can result from the uncontrolled blowing of gas at the surface.

If too much pressure is exerted upon the upper portion of the borehole while attempting to control the gas, fracturing of the formation surrounding the borehole can occur and the gas will then escape in an unctrolled manner upward through the earth. This may manifest itself by the gas blowing in an uncontrolled manner around the drilling rig once it has worked its way to the surface. In both of the foregoing cases, in addition to the loss of equipment and possible loss of life there is an economic loss from the loss of potential fuel.

Particularly porous geological formations can -be encountered during drilling. Substantial amounts of drilling fluid can be lost by being diverted into these formations. This is a lost circulation situation which can be expensive and harmful to the overall drilling operation. Also, under some circumstances it may be desirable to monitor gas-cut mud returning to the mud pits because of the danger of gas being released at the surface.

Systems have been provided in the prior art for monitoring oil and gas drilling operations and providing warning or preferably controlling the dangerous conditions previously mentioned. The prior art monitoring systems while being an improvement over unmonitored oil and gas drilling operations have weaknesses and a need exists to advance the state of the art. Prior art systems have utilized electronic systems having wires connecting various sensors and measuring devices with a central control panel. These systems have serious drawbacks in that electrical power must be provided at the drilling site to the sensing unit and the receiving and/or processing units and to carry signals between them.Further, the use of electrical equipment at a drilling site wherein explosive gases may be generated is dangerous and often runs counter to regulations enforced by governments and the drilling contractors. Further, the problem of stringing electrical wires and maintaining such wires at the drilling site is an important consideration. It is also known in the prior art to provide pneumatic lines connecting the sensors and measuring devices to a central control panel. Whereas the pneumatic measuring systems avoid the problems of creating sparks that would ignite an explosive gas, they compound the problem of lines criss-crossing the drilling site and being difficult to install and maintain.

Various monitoring systems for monitoring potential blowouts and lost circulation are shown in U.S. Patent No.3,614,761; U.S. Patent No.

3,608,653 and U.S. Patent No. 3,740,739.

Systems for automatically filling earth boreholes with drilling fluid and automatically controlling drilling equipment are shown in U.S. Patent No.

3,833,076; U.S. Patent No. 3,552,502 and U.S.

Patent No. 3,746,102.

According to the present invention there is provided a rig instrumentation system for monitoring a process parameter during the drilling of a well, comprising: a sensor for sensing the process parameter; a receiver-transmitter unit connected to said sensor; an interrogation unit for supplying an interrogation radio signal to said receivertransmitter and receiving a radio data signal from said receiver-transmitter; and a switch receiver in said receiver-transmitter unit for receiving said interrogation radio signal and energizing said receiver-transmitter to transmit said radio data signal to said interrogation unit.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings, wherein: Figure 1 is an illustration of an embodiment of a monitoring system constructed in accordance with the preserit invention; Figure 2 is an illustrative block diagram of the interaction of portions of the monitoring system shown in Figure 1; Figure 3 is a block diagram of a central processor; Figure 4 is a block diagram of a transmifter receiver; and Figure 5 is an illustrative diagram of a real time event transmitter.

Referring now to the drawings and to Figure 1 in particular, an embodiment of a drilling rig instrumentation system constructed in accordance with the present invention is shown. A well bore 11 is shown having the usual casing 15. The well bore 11 contains the rotary drill string 13. The rotary drill string 13 is provided with a bit 14 at its lower end. The drill string 13 is turned by a rotary table 16 mounted in the derrick 10. Drilling mud is pumped from a mud pit 19 by a positive displacement pump 22 through a mud delivery line 23 and flexible hose into the drill string 13 and is discharged out of the bit 14 into the well bore 11 and returned from the top of the casing 15 by a mud flowline 17 to the mud pit 19.An openable and closeable blowout preventer or rotary drill head 12 of any suitable conventional type is provided at the upper end of the casing 15.

An embodiment of the present invention provides a system for monitoring one or more parameters during the drilling operation. A particularly good application for a preferred embodiment of the invention is the monitoring of the well drilling process utilizing process parameters relating to the drilling mud being employed. For example, parameters which can be monitored during the drilling of an oil or gas well and the like are the flow rate of the liquid drilling mud returning from the well bore to the mud pits and the liquid level of the drilling mud in the mud pits. Variations in these parameters can be used as a warning of an impending blowout of the well and therefore this invention is applied to these parameters is extremely useful as a blowout control monitoring approach for the drilling of a well.Increases in drilling mud flow rate from the well bore and in the liquid level height of the drilling mud in the mud pits can indicate an impending blowout before the blowout occurs thereby allowing time for the drilling crew to take action to prevent the blowout from actually occurring. Also decreases in the above-mentioned flow rate and liquid height can indicate lost circulation in the well thereby requiring attention of the drilling crew in order to resume normal drilling operation before the loss of drilling mud circulation causes any substantial amount of damage or work stoppage.

An embodiment of the present invention provides transmission of data from a variety of sensors at the drill site and the reception of such transmitted data in one or more receiving and processing units without physical connections such as tubing, wires or mechanical linkage. This permits installation of the sensors in locations where such linkage interferes with other operations or causes hazards or maintenance problems. The transmissions of data are reliable and free from interference from other sources.An embodiment of the invention is useful in substantially any drilling operation wherein at least one process paramater can and desirably should be monitored to keep track of the dynamic state of the process and to provide warnings or allow suitable action to be taken when this dynamic state threatens to fall below a predetermined minimum value and/or exceed a predetermined maximum value. In the preferred embodiment sensor signals are transmitted by radio frequency through a long-life, batteryoperated unit. The system eliminates the need for direct contact between the sensor and the recorder-display, improves reliability and eliminates explosion-proofing problems associated with external wiring.

A conventional flow sensor 20 is mounted on outlet pipe 17 with a paddle means 18 extending down into the interior thereof to sense the flow rate of the drilling mud in pipe 17. For example, if the flow rate increases, the paddle 18 is moved toward the outlet end of pipe 17 whereas if the flow rate decreases the paddle 18, being spring biased or counter-weighted in that direction, moves toward the inlet of pipe 17. Flow sensor 20 can be any conventional device which is commercially available such as the "Flo-Sensor" produced by SWACO Division, Dresser Industries, Inc., Houston, Texas, which has both high and low set points to allow the presetting of minimum and maximum tolerable flow rate variation. Flow sensor 20 has a signal output which passes to a micro-power radio frequency receiver-transmitter 26.

The mud pit 19 contains drilling mud therein and has associated therewith a conventional liquid level sensor 25 which has a float on an arm extending to and floating on the drilling mud surface in pit 19. The liquid level sensor 25 can, for example, be as described in U.S. Patent No.

3,086,397. The signal output from level sensor 25 is processed in a signal processor and passed to a micro-power radio frequency transmitter which is included in receiver-transmitter 27.

Pump 22 is a conventional piston-type reciprocating pump which pumps a known volume of liquid each time the piston passes through one reciprocation cycle, i.e., movement forward to the full extended position and then movement backward to the original starting position. This known volume is provided by the manufacturer of the pump so that the number of reciprocation cycles (pump strokes) of the pump required to deliver a desired volume of drilling fluid can be readily ascertained in a conventional manner well known in the art. The pump 22 carries a sensing device such as a microwswitch which will register each reciprocation cycle of the pump piston. A signal representative of each reciprocation cycle is passed to a micro-power radio frequency receivertransmitter 28.

A central processor 29 is located remote from the flow sensor 20, liquid level sensor 25 and pump and sensor 22. The central processor obtains data from the units 20, 22 and 25. An antenna 30 is mounted on the RF panel 31 of the central processor 29. Readout devices such as units 32, 33 and 34 are provided on the instrumentation panel 35 of the central processor 29.

Referring now to Figure 2, the central processor 29 and receiver-transmitter 27 interaction is illustrated. A system is provided in which data from mud level sensor 25 is transmitted only on receiving a coded signal to do so from the RF panel 31. This also has the effect of lengthening battery life by leaving the basic sensor system including a transmitter and sensor encoder shut down except when "interrogated" by the central processor 29. A micro-power radio frequency receiver included in transceiver 37 receives and identifies unique codes sent by the interrogation transmitter and responds to the identifying code by switching on a telemetry data link. The aforementioned micro-power radio frequency receiver can operate continuously up to three years on C-size 1.5 volt alkaline batteries.The signal processor 36 acts upon the analog signal from mud level sensor 25 to place the signal in a form for transmission by transreceiver 37.

In operation, the monitoring system uses a number of low powered transmitters to send data from the sensors 20, 22 and 25; these transmitters have sufficient power to cover an entire drilling rig site with reliable transmissions.

In order to minimize cost and parts inventory and maximize battery life, all of these sensor transmitters will operate on the same frequency but be time multiplexed so that only one is on at a given time. This approach requires two .RF links; the first link is referenced as the "Interrogation Link." This link is a crystal controlled transmitter, typically operating at 174 MHz with 100 mW of power, amplitude-modulated by a 950 Hz sinusoidal carrier pulsed on and off by a pulse code modulator.An AM transmitter of this type can be found in Markus, Source Book of Electronic Circuits, P. 730 "60 mWTransmitter." The 950 Hz modulation signal is developed with a local phase-shift oscillator which is gated on or off by a string of long or short duration pulses representing 1 's and O's, generated from the selected address in the controlling micro-processor, such as a Fairchi Id F-8 micro-processor. The Interrogation Link signal is then transmitted through an antenna coupler to the antenna 30, whence it propagates to the remote interrogated sensor packages 26, 27 and 28 and associated equipment.

At the remote interrogated receiver-transmitter 27 the interrogation signal is received through the antenna and an antenna coupler. A 174 MHz switch receiver is located in the transceiver 37. It is a passive receiver with a tuned RF preselector diode detector and video amplifier. The output stage detects the 950 Hz envelope and decodes into a serial-to-parallel converter which is a commercially available integrated circuit (IC) shift register, such as the one or more cascaded Motorola MC 14015 four bit shift registers. An address for the sensor is detected by plug-in jumpers or a switch array and compared to the parallel output of the shift register by a comparator. The comparator is functionally available as cascaded IC four bit comparator circuits such as Motorola Semiconductor's My 14585.

When the decoded address agrees with the unit's preselected address, a power switch is activated. This consists of a monostable vultìvìbrator (such as Motorola's MC14538) which generates a short pulse to trigger a PNP transistor which conducts power from the battery to the circuitry which is normally quiescent. The short pulse is enough to make a measurement and transmit the reading so that battery power is conserved.

The switch provides power to circuitry that makes up part of the second link, the "Data Link." A position or parameter measuring circuit such as a potentiometer thus has power applied; it sends its output to a voltage-to-frequency (V-F) converter such as Analog Devices Inc. AD537 scaled for 0--1 OKHz output. The frequency output of the V-F is used to frequency-modulate a 217 MHz transmitter which is simultaneously switched on.This transmitter can be similar to the "460 KHz F-M wireless microphone" described in Markus, Source Book of Electronic Circuits, P.800; however, the transmitter has a crystalstabilized carrier frequency and a frequency deviation of 75~100 KHz. The output of the transmitter is fed to the antenna coupler and from there to the antenna to transmit back to the central processor 29.

The remainder of the "Data Link" is contained in the central processor 29. The "Data Link" signal (only one at a time is selected by the address) will be detected by a 217 MHz receiver and F-M demodulator. This receiver can be similar to the "460 KHz F-M Receiver for Wireless Microphone" found in Markus, Source Book of Electronic Circuits, page 571. The presence of a 217 MHz carrier frequency triggers a AGC line to a microprocessor, which then recognizes valid frequency data. The microprocessor is programmed to measure the frequency and do scaling of the data according to constants calculated by the microprocessor and stored in a memory. Pit area and sensor gain used for constant calculation are programmed into the memory by means of a keyboard and feedback display when the system is first set up at the drilling site.The memory consists of Semiconductor RAM such as Signetics 2102 and ROM such as Intel 2708.

The scaled data for the address is output through the microcomputer's data port to a digital-to-analog (D/A) converter such as Motorola's MC1408. Simultaneously, the address is presented in binary form to a decoder such as Motorola's MC 14515. The decoder drives individual lines to sample-and-hold units such as National Semiconductor's LF198, which then present individual analog data outputs for display or activating alarms. Each address is scanned.

Programming in the microprocessor can give precedence to any channel. Time between interrogations is normally 7-1 5 seconds, to keep the sample-and-hold outputs refreshed and up to date. Data of the nature that these sensors monitor on a drilling rig do not change significantly during this time period.

A preferred embodiment of the present invention having been described with reference to Figures 1 and 2, a description of another embodiment of the present invention will now be considered with reference to Figures 3-5. This embodiment of a Radio Frequency (RF) monitoring system for oilfield use includes three different physical components: component one is the central processor (see Figure 3), component two is one or more remote interrogated transmittersreceivers (see Figure 4) and component three is a remote event sensor for real-time events (see Figure 5). The system usually includes one central processor, one or more interrogated transmitterreceivers and one or more real-time event transmitters.

In operation, the RF monitoring system uses a number of low powered transmitters to send data from the sensors: these transmitters have sufficient power to cover an entire drilling rig site with reliable transmissions. In order to minimize cost and parts inventory and maximize battery life, all of these sensor transmitters will operate on the same frequency but be time multiplexed so that only one is on at a given time. This approach requires two RF links, the first link is referenced as the "Interrogation Link." This link is a crystal controlled transmitter 39, typically operating at 174 MHz with 100 mW of power, amplitudemodulated by a 950 Hz sinusoidal carrier pulsed on and off by a pulse code modulator 38.An AM transmitter of this type can be found in Markus, Source Book ofElectronic Cfrcuits, P. 730 "60 mWTransmitter". The 950 Hz modulation signal is developed with a local phase-shift oscillator 73, which is gated on or off by a string of long or short duration pulses representing l's or O's generated from the selected address 37 in the controlling microprocessor 36, such as a Fairchild F-8. The Interrogation Link signal is then transmitted through the antenna coupler 40 to the antenna 47, whence it propagates to the remote interrogated sensors.

At the remote interrogated transmitter (see Figure 4), the interrogation signal is received through the antenna 53 and the antenna coupler 54. The 174 MHz switch receiver 55 is a passive receiver with a tuned RF preselector, diode detector and video amplifier. The output stage detects the 950 Hz envelope and decodes into a serial-to-parallel converter 56 which is a commercially available integrated circuit (IC) shift register, such as the one or more cascaded Motorola My 14015 four bit shift registers. An address for the sensor is selected by plug-in jumpers or a switch array 57 and compared to the' parallel output of the shift register 56 by a comparator 58. The comparator is functionally available as cascaded IC four bit comparator circuits such as Motorola Semiconductor's MC14585.

When the decoded address agrees with the unit's preselected address, a power switch 59 is activated. This consists of a monostable multivibrator (such as Motorola's MC14538) which generates a short pulse to trigger a PNP transistor which conducts power from the battery 60 to the circuitry 61, 62 and 63 which is normally quiescent. The short pulse is enough to make a measurement and transmit the reading so that battery power is conserved.

The switch 59 provides power to circuitry that makes up part of the second link, the "Data Link".

A position or paramater measuring circuit such as a potentiometer 63 thus has power applied; it sends its output to a voltage-to-frequency (V-F) converter 62 such as Analog Devices inc. AD537 scaled for O~1 OKHz output. The frequency output of the V-F converter is used to frequency modulate a 217 MHz transmitter 61 which is simultaneously switched on. This transmitter is similar to the "460 KHz F-M wireless microphone" described in Markus, Source Book of Electronic Circuits, P, 800; however, the transmitter 61 has a crystal-stabilized carrier frequency and a frequency deviation of 75-100 KHz.The output of the transmitter is fed to the antenna coupler 54 and from there to the antenna 53 to transmit back to the central processor.

The-remainder of the Data Link is contained in the central processor. The Data Link signal (only one at a time is selected by the address) will be detected by the 217 MHz receiver and F-M demodulator 41. This receiver is similar to the "460 KHz F-M Receiver for Wireless Microphone" found in Markus, Source Book of Electronic Circuits, Page 571. The presence of 217 MHz carrier frequency triggers the AGC line 71 to the microprocessor 36, which then recognizes valid frequency data through line 72.

The microprocessor 36 is programmed to measure the frequency and do scaling of the data according to constants calculated by the microprocessor and stored in the memory 51. Pit area and sensor gain used for constant calculation are programmed into the memory by means of a keyboard and feedback display 74 when the system is first set up at a drilling site. The memory consists of a Semiconductor RAM such as Signetics 2102 and ROM such as Intel 2708.

The scaled data for the address is output through the microcomputer's data port 45 to a digital-to-analog (D/A) converter 43 such as Motorola's MC1408. Simultaneously, the address is presented in binary form 44 to a decoder 42 such as Motorola's My 14515. The decoder drives individual lines to sample-and-hold units 46 such as National Semiconductor's LF198, which then present individual analog data outputs for display or activating alarms. Items 42, 43 and 46 comprise what is commonly called an analog demultiplexer.

Each address is scanned. Programming in the microprocessor can give precedence to any channel. Time between interrogations is normally 7-1 5 seconds, to keep the sample-and-hold 46 outputs refreshed and up to date. Data of the nature that these sensors monitor on a drilling rig do not change significantly during this time period.

In addition to the interrogated Data Link, a number of data channels are provided for real time event sensing, such as pump strokes or rotary table rotations. Normally, there are two channels with dedicated frequencies. On this system, 21 6.5 MHz and 217.5MHz are used.

Figure 5 shows a block diagram of the dedicated transmitters. The unit is powered by a battery 68 which has long life due to the low power consumption and short duty cycle. When the event, such as a pump stroke, is sensed by a switch 64, a one-shot 65, such as Motorola's MC14538 monolithic IC monostable multivibrator, is fired. This drives a power switch 69, basically a transistor used as a switch, which applies the battery power to an oscillator 66 and the 216.5 or 217.5 MHz transmitter 67, similar to that used in the interrogated transmitters 61 (see Figure 4). The oscillator frequency-modulates the transmitter at a fixed frequency, about 15 KHz, during the time specified by the one-shot's 65 ontime. The output data is transmitted through the antenna 70.

This signal from the event sensor is detected back at the central processor through (see Figure 3) the antenna 47, the antenna coupler 40 and the appropriate receiver 48 or 52. The demodulated F-M signal from the receiver is then tonedetected for the presence of the correct 1 5 KHz tone by a phase-locked-loop (PLL) frequency detector 49 and 50 using a Signetics 567 tone decoder, as described in Signetic's PLL Application literature 1974, Chapter 6.

Claims (5)

1. A rig instrumentation system for monitoring a process parameter during the drilling of a well, comprising: a sensor ror sensing the process parameter; a receiver-transmitter unit connected to said sensor; an interrogation unit for supplying an interrogation radio signal to said receivertransmitter and receiving a radio data signal from said receiver-transmitter; and a switch receiver in said receiver-transmitter unit for receiving said interrogation radio signal and energizing said receiver-transmitter to transmit said radio data signal to said interrogation unit.

2. A rig instrumentation system according to claim 1 for monitoring a plurality of process parameters during the drilling of a well, comprising a respective sensor for sensing each of the process parameters; a respective receivertransmitter unit connected to each said sensor; means in said interrogation unit for supplying an interrogation radio signal to each said receivertransmitter and receiving a radio data signal from each said receiver-transmitter; and a switch receiver in each said receiver-transmitter unit for receiving said interrogation radio signal and selectively energizing a receiver-transmitter to transmit said radio data signal to said interrogation unit.

3. A rig instrumentation system according to claim 1 or claim 2 including means for continuously monitoring at least one further process parameter during the drilling of the well, the continuous monitoring means comprising a further sensor for sensing said at least one further process paramater; a radio transmitter unit connected to said further sensor; and circuit means in said interrogation unit for receiving a radio data signal from said radio transmitter.

4. A rig instrumentation system according to any preceding claim wherein the interrogation radio signal is a coded interrogation radio signal, and the switch receiver in the or each receivertransmitter unit is operative to energize its associated receiver-transmitter to transmit only upon recognizing a coded interrogation signal indicative of that receiver-transmitter.

5. A rig instrumentation system, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.