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METHOD AND ARRANGEMENT FOR OPERATING AN EXTRACTION IN A BOREHOLE

20170370207 · 2017-12-28

    Inventors

    Cpc classification

    International classification

    Abstract

    A method and an arrangement for operating a process for extracting a fluid in a borehole are optimized. In the case of deep wells, the location of an interface depth in the borehole is detected. A pressure measurement of the pressure at the head of the borehole is made. The pressure in the liquid in the borehole below the interface depth is determined from the measured pressure at the head of the borehole and the detected location of the interface depth. The determination of this pressure is used for regulating the performance of an extracting device for the liquid that is to be extracted.

    Claims

    1. Method for operating a process for the extraction of a fluid in a borehole in which the location of an interface depth in the borehole is detected in the case of deep wells, characterized in that a pressure measurement of the pressure at the head of the borehole is made, in that the pressure in the liquid below the interface depth in the borehole is determined from the measured pressure at the head of the borehole and the detected location of the interface depth and in that the determination of this pressure is utilised for regulating the performance of an extracting device for the liquid that is to be extracted.

    2. A method in accordance with claim 1, characterized in that an acoustic event which produces acoustic pressure waves is deliberately effected for the purposes of detecting the location of the interface depth in the borehole at the earth's surface in the case of deep wells, in that the pressure waves produced in the borehole by the event travel into the depths, in that pressure waves travelling into the borehole are also reflected at least at the interface depth, in that the pressure waves travelling out of the borehole at the earth's surface are captured there and the time that has elapsed since the acoustic event is measured, in that the captured and measured pressure waves are evaluated and are used together with the associated elapsed time for indicating the location of the interface depth, in that the acoustic event produces signal samples having a predetermined, time-varying frequency spectrum, in that the signal sample is emitted into the borehole as an oscillatory event, travels into the depths and is reflected, in that captured signals emanating from the borehole at the earth's surface are analyzed, in that oscillatory events which correlate to the emitted signal sample are filtered out from the captured signals during the analysis, and in that an estimate of the location of the interface depth is made from the oscillatory events which are correlated to the emitted signal sample amongst the captured signals and the time elapsing since the transmission of the signal sample.

    3. A method in accordance with claim 1, characterized in that the pumping performance of the pump is regulated in such a way that constant feed rates and/or a constant location of the interface depth and/or the pressure at the head of the borehole prevail.

    4. A method in accordance with claim 1, characterized in that for the purposes of determining the pressure in the liquid in the borehole, this is determined using the following equations: PI = q P r - P wf ( 1 ) q MAX = PI * P r ( 2 ) q = q MAX * [ 1 - ( P wf P r ) 2 ] ( 3 ) v sg = q MAX * [ 1 - ( P wf P r ) 2 ] * GOR * B g A F ( 4 ) f g = v sg ( C + D * TU OD CA ID ) * v sg + E * [ g * σ * ( ρ o - ρ g ) ρ o 2 ] 0.25 ( 5 )

    5. A method in accordance with claim 1, characterized in that the determination of the pressure at the bottom of the borehole is utilised for the regulation process in such a way that the pressure is always held above the boiling point or the bubble point or the beginning of the degassing process.

    6. A method in accordance with claim 1, characterized in that in the case of extraction process conditions using an intermittent mode consisting of cyclic running and switched-off periods, automatic adjustment of the switch-off and the switch-on time points of the extracting device situated in the borehole is effected as a function of the pressure at the bottom of the borehole.

    7. Arrangement for carrying out the method in accordance with claim 1, characterized in that a pressure measuring device is provided above the earth's surface for the purposes of measuring the pressure at the head of the borehole, in that a device is provided for detecting the location of the interface depth, in that there is provided an evaluating device to which the values of the pressure measuring device and the device for detecting the location of the interface depth are supplied, and in that the evaluating device supplies values determined from the input data to a control system of the extracting device.

    8. A method in accordance with claim 1, characterized in that an acoustic event which produces acoustic pressure waves is deliberately effected for the purposes of detecting the location of the interface depth in the borehole at the earth's surface in the case of deep wells, in that the pressure waves produced in the borehole by the event travel into the depths, in that pressure waves travelling into the borehole are also reflected at least at the interface depth.

    9. A method in accordance with claim 8 in that the pressure waves travelling out of the borehole at the earth's surface are captured there and the time that has elapsed since the acoustic event is measured.

    10. A method in accordance with claim 9 in that the captured and measured pressure waves are evaluated and are used together with the associated elapsed time for indicating the location of the interface depth, in that the acoustic event produces signal samples having a predetermined, time-varying frequency spectrum.

    11. A method in accordance with claim 10 in that the signal sample is emitted into the borehole as an oscillatory event, travels into the depths and is reflected.

    12. A method in accordance with claim 11 in that captured signals emanating from the borehole at the earth's surface are analysed.

    13. A method in accordance with claim 12 in that oscillatory events which correlate to the emitted signal sample are filtered out from the captured signals during the analysis.

    14. A method in accordance with claim 13 in that an estimate of the location of the interface depth is made from the oscillatory events which are correlated to the emitted signal sample amongst the captured signals and the time elapsing since the transmission of the signal sample.

    15. A system for the extraction of a fluid in a bore hole in which the location of an interface depth in the borehole is detected in the case of deep wells, and comprising: a pressure measuring device that is provided above the earth's surface for the purposes of measuring the pressure at the head of the borehole, a device is provided for detecting the location of the interface depth, an evaluating device to which the values of the pressure measuring device and the device for detecting the location of the interface depth are supplied, and an extracting device for extracting the fluid, wherein the evaluating device supplies values determined from input data to a control system of the extracting device.

    16. A system in accordance with claim 15 including a system of pipes or a pipeline is provided in order to transport the crude oil from the borehole to the earth's surface.

    17. A system in accordance with claim 16 wherein the pipeline runs vertically in the borehole.

    18. A system in accordance with claim 17 wherein the pipeline includes an inner tubular pipe and an outer tubular pipe which surrounds the inner tubular pipe concentrically and at the same time forms a pipe wall.

    19. A system in accordance with claim 18 wherein the crude oil is extracted upwardly through the inner tubular pipe and an annular space is formed between the inner tubular pipe and the outer tubular pipe.

    20. A system in accordance with claim 19 wherein, during the extraction process, crude oil is ascending in the inner tubular pipe, crude oil is likewise present in the annular space below the interface depth, but above it, it is substantially a gas which is ascending upwardly.

    Description

    [0042] FIG. 1 shows a schematic illustration of a borehole and of measuring and evaluating devices arranged at the borehole; and

    [0043] FIG. 2 a schematic illustration of exemplarily determined values.

    [0044] A borehole 10 is illustrated in FIG. 1. The borehole 10 extends into the depths from the earth's surface 11 down to deposits of mineral oil or crude oil 12 for example. Within the borehole 10, the crude oil 12 together possibly with water and other liquids forms a mixture which is separated by a boundary layer 13 from the various gases and gaseous media 14 forming above it. These gases are, inter alia, nitrogen, argon and other constituents of the atmosphere and in addition, methane and other gases that are forming above the crude oil 12. The composition varies in the course of time and also with the depth of the borehole 10.

    [0045] The precise location of the boundary layer 13 between the liquid substances including the crude oil 12 and the gaseous media 14 forms an interface depth. The precise location of this interface depth 13 i.e. the boundary layer or liquid surface varies in the course of time in dependence upon the rate at which the crude oil 12 and the other liquids flow into the borehole 10 from the side and from below.

    [0046] A system of pipes or a pipeline 20 is provided in order to transport the crude oil 12 from the borehole 10 to the earth's surface 11. This pipeline 20 which runs vertically in the borehole 10 consists of an inner tubular pipe 21 and an outer tubular pipe 22 which surrounds the inner tubular pipe concentrically and at the same time forms the pipe wall. The crude oil 12 is extracted upwardly through the inner tubular pipe 21. An annular space 23 is formed between the inner tubular pipe 21 and the outer tubular pipe 22. The pressure is balanced in the annular space 23. Thus, during the extraction process, crude oil 12 is ascending in the inner tubular pipe 21. Crude oil 12 is likewise present in the annular space 23 below the interface depth 13, but above it, it is substantially a gas which is ascending upwardly.

    [0047] A pump 30 is illustrated down below in the borehole 10. This pump may, for example, be an electrical submersible centrifugal pump or a beam-type borehole pump, but naturally, in dependence on the circumstances, there may be a plurality of pumps which can be arranged at varying heights and also be of different types.

    [0048] Further elements of the pumping system which appertain to the schematically indicated pump 30 could also be situated above the earth's surface 11 and serve there for the regulated removal of the extracted crude oil 12 which has been extracted upwardly through the inner tubular pipe 21 of the pipeline 20.

    [0049] These elements above the earth's surface 11 such as a pipeline 31 and further facilities for example, are only illustrated schematically here.

    [0050] Moreover, a pressure measuring device 41 is shown that measures the pressure at the head of the borehole 10 which is situated above the earth's surface 11.

    [0051] In particular, a device 42 for detecting the location of the interface depth in the borehole 10 is also situated here. Such a device which is known in particular from EP 2 169 179 B1 and U.S. Pat. No. 8,902,704 operates (not illustrated) with a vibration emitting device which emits an oscillatory signal downwardly into the borehole. The oscillatory signal in the form of pressure waves is reflected at the boundary layer 13 or at the interface depth and then recaptured in a measuring device in the device. This measuring device comprises a pressure sensor. By using such a device and in contrast to earlier ideas, extremely precise indications in regard to the exact location of the interface depth or the surface of the liquid in the borehole 10 and the aforementioned boundary layer 13 can be obtained.

    [0052] In addition to these measuring instruments 41, 42, a control system 43 for the pumping speed of the pump 30 and the further elements is also provided here above the earth's surface 11, whereby here, an appropriate connection between the measuring instruments 41, 42 and this control system 43 is provided.

    [0053] Furthermore, an evaluating device 44 is provided. The evaluating device 44 receives the measured values from the measuring instruments 41 and 42 in regard to the location of the interface depth 13 in the borehole 10 and the pressure at the head of the borehole 10 and then calculates therefrom control values which it passes on to the control system 43 for controlling the performance of the pump 30.

    [0054] Hereby, the evaluating device 44 functions by taking into consideration the Equations 1 to 5 as described hereinabove. Further data can also be supplied thereto and it also receives the data which otherwise results in the course of the activities associated with the extraction process such as the quantities extracted, the inflow rates, etc.

    [0055] Thus, the evaluating device 44 can inform the control system 43 that the location of the interface depth 13 should remain as constant as possible when this is desired as is the case in many practical applications. One can also prevent the pressure in the liquid below the interface depth 13 from falling under the boiling point pressure so that, as discussed above, the problems occurring thereby can also be avoided.

    [0056] Furthermore, the manner in which the different physical values and data can behave is illustrated in FIG. 2.

    [0057] Indicated here from left to right, is a time scale with different exemplarily used dates which are indicated in days and months and describe the behaviour at a borehole of certain values during these days.

    [0058] The pressure is entered upwardly on one side in hectopascal or in bar, namely, every 1,000 hectopascal, i.e. ascending from 0 to 60,000 hectopascal.

    [0059] On the right-hand side, there is provided a scale which indicates the location of the interface depth within the borehole in metres under the earth's surface.

    [0060] Three measured values are now entered on the diagram, namely, the measured pressure is indicated by line a when a pressure sensor is actually arranged in the borehole as must conventionally occur.

    [0061] The line b shows a value for the pressure in the liquid in the borehole computed in accordance with the invention.

    [0062] Finally, the line c shows the location of the interface depth during the measuring time which extended over approximately five weeks.

    [0063] Some changes in state were deliberately effected during these measurements and these are then also reflected accordingly in the measured values.

    [0064] Thus, a stable or else stationary state, i.e. a current extraction process is denoted by (1).

    [0065] A transient state was then caused to occur and is accordingly illustrated by (2).

    [0066] Hereby in (3), one can see different peaks which resulted due to pressure fluctuations in the pipeline above the earth's surface.

    LIST OF REFERENCE SYMBOLS

    [0067] 10 borehole [0068] 11 earth's surface [0069] 12 crude oil [0070] 13 boundary layer [0071] 14 gaseous media [0072] 20 piping [0073] 21 internal pipe [0074] 22 outer pipe [0075] 23 annular space [0076] 30 pump [0077] 31 piping above the earth's surface 11 [0078] 41 pressure measuring device [0079] 42 device for detecting the interface depth [0080] 43 control system for the pump 30 [0081] 44 evaluating device [0082] ρ density [0083] q supply rate [0084] B.sub.g volume factor of the gas formation [0085] f.sub.g gas bubble fraction [0086] GOR ratio of gas to oil [0087] IPR inflow performance relationship [0088] ID internal diameter [0089] OD external diameter [0090] P.sub.r pressure of the reservoir [0091] P.sub.wf flow pressure at the bottom of the borehole [0092] σ boundary surface tension [0093] ν.sub.sg empty tube gas speed [0094] A surface [0095] CA outer pipe (casing) [0096] TU inner pipe (tubing)