WO1981001168A1

WO1981001168A1 - Monitoring equipment for drilling operations

Info

Publication number: WO1981001168A1
Application number: PCT/GB1980/000170
Authority: WO
Inventors: A Miles; J James
Original assignee: Structural Dynamics Ltd; A Miles; J James
Priority date: 1979-10-17
Filing date: 1980-10-17
Publication date: 1981-04-30
Also published as: DK261481A; GB2075093A; EP0037821A1; NO812005L; JPS56501410A

Abstract

Monitoring equipment for ensuring a well being drilled (18) does not go close to existing production wells (12) comprises transducers coupled to the well being drilled and to the production wells and processing means for determining the attenuation or transfer function between the monitored vibrations from the transducers. Analogue processing circuitry is provided where attenuation is to be determined. Digital processing circuitry is provided where transfer function is to be determined.

Description

MONITORING EQUIPMENT FOR DRILLING OPERATIONS

Technical Field

This invention relates to monitoring equipment for drilling operations, particularly though not exclusively for oil and natural gas in offshore installations.

Background Art In offshore operations, a number of wells are usually drilled from the same rig, the wells extending underground in directions having horizontal and vertical components Ln order to locate pockets of oil and gas in the vicinity of the drilling rig. In such circumstances it is necessary when drilling a well that the drill should not puncture nor go close to an existing production well in order to avoid the risk of blow out of the well. Government regulations specify that in the event of a drill string coming within 20 feet of a production well, the production well should be closed until the path of the drill string is established in a direction away from the production well or wells. Remedial action, where a puncture does occur can be extremely expensive in terms of lost production during rework.

For this reason alone, it is necessary when drilling wells to monitor the position of the well. This is normally done by stopping the drilling process at intervals and lowering into the drill string gyroscopic, inertial or magnetic platforms, by which means it is possible to chart the position of the drill. The accuracy of this method is not good, depending on the skill of the operator and the types of rock formations through which the borehole is made and other local anomalies, and this necessarily increases the frequency with which drilling is stopped and chartering measurements are made. The accuracy of such measurements is sometimes not more then the required Government limits on spacing between wells. .

Disclosure of Invention

With this in mind, the present invention was devised and provides in one aspect a first transducer means for monitoring vibrations for coupling to a well being drilled, a second or plurality of transducer means coupled to an existing production well or wells in the vicinity of the well to be drilled in order to monitor vibration in the production wells arising from the operation of said drill, and processing means for coupling to said first and second transducer means for determining a function dependent on the values of the signals from said first and second transducer means and being related to or representative of the attenuation or transfer function between the monitored vibrations from said wells.

In a further aspect, the invention provides a method of monitoring drilling operations characterised by the steps of monitoring vibration from a well being drilled, monitoring vibration from one or more production wells arising from the operation of said drill, and determining a function dependent on the values of the monitored vibrations and related to or representative of the attenuation or transfer function between the monitored vibrations. Said transducer means may conveniently be located on the casings or coupled to the casings of the existing wells and of the well being drilled, approp riate comppensation being made, if necessary for the transfer coefficient of the coupled installation comprising drill floor and well conductors and the medium being drilled. Said transducer means may conveniently comprise an accelerometer which is suitable for rugged environments, or alternatively if conditions are suitable, a laser doppler device.

It has been found that the attenuation between the signals from the first and second transducer means can provide a realistic assessment of the distance between the wells, where attenuation is defined as the ratio of the averaged band limited power provided by the signals from the transducers. The attenuation represents the attenuation properties of the coupled structure and medium with increasing distance between well and drill string.

The transfer function is defined as the ratio of the magnitudes of the signals and takes account of the relative phase components of the signals, and is also a suitable measurement, but since the transfer function is more difficult to determine, and requires more complex processing the measurement of the attenuation of the signals may be preferred.

Any function representative of or related to attenuation or transfer function may be determined, for example it appears the antilog of the attenuation is a convenient measure since it appears empirically that such antilog is representative of the distance between the boreholes. The RMS acceleration of the drill string is given by the expression: a = 10 log ₁

T (v_d)² dt - dB_ATTN dB re Ig RMS

T being the measurement period in seconds. Similarly at the well b = 10 10g _{1 0} T

O

(VW)² dt - ^dBATTN ^dB re lS RMS

Where dB ATTN is the setting of the respective input attenuators, and v _d is the signal at the drill string transducer and v_w the respective signal at the well transducer or transducers.

Let x be the transfer attenuation between drill and well and x = (a - b) dB.

Therefore the relative distance = 10 where k is a scale factor related to transfer attenuation in the medium and structure and '1 unit' refers to the initial starting distance of the drill from the production well.

Where attenuation is selected as an appropriate function for determination, analogue signal processing circuitry is conveniently employed, as for example band -pass filters followed by root mean square detection circuits. If it is desired to determine the transfer function in order to take account of the relative phase components of the signals, it is preferred to employ digital signal processing techniques. Thus samples of the incoming signals from an A/D converter may be stored in a memory under microprocessor control. The microprocessor control. The microprocessor is arranged to control the input gain of the processing circuitry in dependence on the magnitude of the input samples to provide an autoraning facility. Subsequently the samples may be subject to fast fourier transform or discrete fourier transform analysis techniques by the microprocessor in order to compute the transfer function. In addition the coherence of the signal may be computed and cross -correlation techniques employed in order to remove signal components arising from echoes in order to increase accuracy.

The circuitry is preferably housed in a portable housing which can be located close to the drill operators console and connected to permanently fixed accelerometers. Where there are a large number of wells or drilling rigs it may in some circumstances be preferable to provide local signal processing circuitry close to the accelerometers communicating with a host computer system where the function and other required parameters may be determined.

Although specifically developed for offshore installations, the present invention may be practiced in land -based operations.

Brief Description of Drawings

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, wherein:-

Figure 1 is a schematic view of boreholes extending from a drilling rig of an offshore installation; Figure 2 is a perspective view of a vibration transducer coupled to a casing of a borehole being drilled from an offshore installation;

Figure 3 is a perspective view of a housing and control console for signal processing circuitry;

Figure 4 is a block schematic view of the signal processing circuitry; and

Figures.5 to 8 are circuit diagrams of elements of the processing circuitry.

Best Mode for Carrying Out the Invention

Referring to the drawings, Figure 1 is a schematic view of an offshore installation comprising an oil drilling rig or platform 2 mounted by means of a structure 4 to the seabed 6. The structure may be rigid and fixed to the seabed or semi -submersible and tethered to the sea floor, or stationed by navigational control. The drill 10 is such that it may be deviated at angles inclined to the vertical in order to reach pockets of oil or natural gas such as 14. The drill may either be rotary, in which case the whole string is turned, or turbine operated with the turbine located 'dowrihole', and driven hydraulically by mud which is also used to cool the drill and irrigate the hole. Existing wells such as 12 which may be in production may exist in the vicinity of the well being drilled. In order to maintain an adequate distance between well 12 and well 18 it has hitherto been necessary to stop the drilling operation at frequent intervals and to lower the gyroscopic, magnetic or inertia! platforms into the hole, so that the position of the wells can be charted and its position relative to existing well of known position can be calculated.

In accordance with the present invention, a means is provided to monitor the position of the drill string in relation to existing wells whereby the frequency at which interruptions in the drilling operations are necessary in order to chart the position of the drill path is reduced.

Referring to Figure 2, there is shown a drill string 20 of a well being drilled disposed on the deck of a drilling rig. A surrounding conductor 22 carries a vertically mounted accelerometer 24 for monitoring vibrations transmitted to the structure from the motions of the drill in the hole. The accelerometer is coupled to signal processing circuitry, the housing and control console of which is shown in Figure 3.

The circuitry is formed as three separate modules, an input conditioning module 30, a processor module 32, and a display module 34. Input conditioning module 30 includes a control switch 40 for determining which of three input channels for exuting wells will be operative. Controls 42, 44 provide a control for attenuating levels for the production well channel and the channel for the drill string conductor. Tape input sockets 46 are provided to enable the well channel and drill channel signals to be recorded. Control switch 40 may be replaced by a multiplexer means for sequentially offering a plurality of well channels to the input of the processor module.

Processor module 32 provides outputs 50 to a tape recorder for processed signals for the drill and well channels. A control switch 52 provides control over the output gain for the processor. A control switch 54 provides control of the input signal frequency band to be processed, 80 - 100 Hz, 100 - 125 Hz, 125 - 160 Hz and an overall frequency band 80 - 160 Hz, other frequencies being specified as dictated by special circumstances. The implementation of the processor module 32 may include a micro -computing device to control internal functions and extend the calculation ability to the measurement of transfer function or other such parameters. Where such computing means is implemented this would control the display device 34.

Display module 34 includes a digital display 60 providing a display of one or four functions, namely drill channel RMS level, well channel RMS level, attenuation and the antilog of attenuation, (providing an estimate of the distance between the drill head and the existing well). A control switch 62 determines which of these four functions appears on the digital display.

Referring now to Figure 4, there is shown a block diagram of the analogue processing circuitry. It will be understood that a plurality of similar channels may be provided for accelerometers connected to existing wells and the hole being drilled. The circuitry of the channel shown is coupled to an accelerometer on an existing well through a zener barrier which prevents ignition of any potentially explosive atmosphere which may be present. A preamplifier 84 feeds the vibration signals from the accelerometer to a filter 86 which rejects high slew rate signals. The purpose of filter 86 is to prevent the processing of signals arising from collision of the drill string with the well conductor when the drill is not centrally aligned within the casing or rotates accentrϊcally. A band-pass filter 88 separates the incoming signal into three third octave frequency bands over 60 - 400 Hz, this being the range at which the greater part of the incoming signal will be present. An output 50 to a tape recorder provides an historical record of the incoming signal. The frequency bands are separately rectified and averaged in unit 90, which also contains a log circuit and provides a signal representative of the logarithm of the averaged and rectified signal. These signals are represented as (a) and (b) in the accompanying diagrams and are referred to in equations (1), (2) and (3) previously. The log signal is fed at 92 to a chart recorder. The signals from each channel are compared in a differencing amplifier 94, the output from amplifier 94 being indicative of the attenuation of the signal from the drilling process relative to the signal received on the existing well. The attenuation signal may be processed as an antilog 95 and displayed on scale 60 (Figure 3) to provide an indication of the distance of the well being drilled from the existing borehole. Tape input sockets 46 are provided coupled to preamplifiers 84. A power supply unit 82 is provided. A lamp 83 is provided to indicate operation of the circuitry.

Referring to Figures 5 to 8, Figures 5 to 7 are diagrams of circuits located in the processor module, and Figure 8 is a diagram of a circuit in the display module.

Referring to Figure 5, there is shown a circuit diagram for the high slew rate filter 86 of Figure 4 which acts to reject high slew rate signals. Two separate filters 86a and 86b are shown, filter 86a acting on the drill channel, and filter 86b acting on the well channel. These non -linear filters may be implemented in a variety of ways including by digital processing means. Outputs A are provided for recording of the input signals in the well and drill channels. Aliasing and PSU filters 98a and 98b condition the input signals in the well and drill channels. Referring to Figure 6 the outputs from the filters of Figure 5 are fed to one third octave filters 102a, 102b, which each comprise charge coupled devices. These provide outputs 103 for frequency bands for the incoming signals of 80 - 100 Hz, 125 - 160 Hz and a summed output 105 of 10 - 160 Hz, although these may be changed by selection of other clocking frequencies, one of these outputs being selected by means of ganged switches 104a, 104b. The outputs of switches 'o4a, 104b are fed through gajn switches 52A, 52B to buffer amplifiers 106a, 106b. The outputs of amplifiers 106a, 106b are coupled to, as shown in Figure 7, rectifying and averaging circuits 90a and 90b (which contain log circuits). Switch 52 controls the output gain through buffers 92a and 92b to provide signals (a), (b). In Figure 8, there is shown an arrangement for summing the signals (a) and (b) in the drill and well channels in a differencing amplifier 110. The output x(a-b) of amplifier 110 provides a signal representative of the attenuation between the two signals. Circuit 112 coupled to the output of amplifier 110 provides an output representative of the antilog 10^(X/K) of the attenuation. Such antilog signal, the attenuation signal, the well and drill signals are selected for display by control switch 62.

Claims

WHAT IS CLAIMED IS:

1. Monitoring equipment for drilling operations, characterized by a first transducer means (24) for monitoring vibration for coupling to a well (14) being drilled, a second or plurality of transducer means for coupling to an existing production well or wells (12) in order to monitor vibration in the pro duction wells arising from the operation of said drill, and processing means (84-95) for coupling to said first and second transducer means for determining a function dependent on the values of said signals from said first and second transducer means and being related to or representative of the attenuation or transfer function between the monitored vibrations from said wells.

2. Equipment according to claim 1, characterized in that each of said transducers comprises an accelerometer.

3. Equipment according to claim 1, characterized by means (95) for determining the antilog of said attenuation.

4. Equipment according to claim 1, characterized by filter means (88) for providing a plurality of frequency bands and means (90) for determining the root mean square value of the signal in each frequency band.

5. Equipment according to claim 1, characterized in that said processing means comprises a gain control means, an analogue to digital converter, a processor for storing samples from said converter in a memory, said processor being arranged to control the attenuation of said gain control means in dependence on the magnitudes of said samples.

6. Equipment according to claim 1, characterized in that said processing means comprises an analogue to digital converter, a processor for storing samples from said converter in a memory and being arranged to compute said transfer function from said samples.

7. A method of monitoring drilling operations charaterized by the steps of monitoring vibration from a well being drilled, monitoring vibration from one or more production wells arising from the operation of said drill, and determining a function dependent on the values of the monitored vibrations and related to or representative of the attenuation or transfer function between the monitored vibrations.