APPARATUS AND METHOD FOR FILTERING DATA INFLUENCED BY A DOWNHOLE PUMP

Abstract

Disclosed is a method for transmitting data from a tool disposed in a borehole penetrating the earth to a receiver. The method includes disposing the tool in a borehole and receiving a series of measurements using a processor disposed at the tool. A telemetry system transmits a latest received measurement that meets acceptance criteria to the receiver after completion of transmission of a previously transmitted measurement.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of an earlier filing date from U.S. Provisional Application Ser. No. 61/467,262 filed Mar. 24, 2011, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The invention disclosed herein relates to filtering data obtained from a downhole environment and, in particular, to data related to using a downhole pump.

2. Description of the Related Art

Drilling apparatus used for geophysical exploration often includes one or more sensors for performing measurements on ambient subsurface materials. In performing measurements referred to as measure-while-drilling or MWD, the sensors are disposed in a bottomhole assembly located in a drill string in the vicinity of a drill bit. The measurements can be performed while drilling a borehole through the subsurface materials or during a temporary halt in drilling.

Data related to the measurements is typically transmitted to the surface of the earth using mud-pulse telemetry. Mud-pulse telemetry is usually very slow (a few bits per second) taking several seconds to minutes to transmit a whole data package. Because of the low data transmission rate, problems can arise when all the acquired data cannot be transmitted. Usually the latest acquired data available is used for transmission to the surface. However, not all of the latest acquired data is useful and transmission of such data wastes time and bandwidth and can prevent more useful data from being transmitted.

One type of sensor used to MWD is a formation tester tool. The formation tester tool is configured to draw formation fluid from a wall of the borehole and to perform one or more tests on the formation fluid sample. A positive displacement pump such as a dual action pump using a piston is typically used to draw the formation fluid sample. The sample is drawn by the piston reducing pressure within a chamber causing the formation fluid, which is at a higher pressure, to flow into the chamber. However, when the piston reverses its stroke, inlet flow stops and the sample chamber pressure rises towards the formation pressure. Sample pressure or a parameter related to sample pressure is generally one type of data required to properly evaluate the sample. Sometimes the pressure is transmitted while the piston is moving and sometimes the pressure is transmitted while the piston is reversing (i.e., stopped). Transmitting a value measured during pump reversing is a waste of time and bandwidth because the value it is transmitted at non-predictable intervals. Hence, it would be well received in the drilling industry if the transmission of data from a MWD tool could be improved.

BRIEF SUMMARY

Disclosed is a method for transmitting data from a tool disposed in a borehole penetrating the earth to a receiver. The method includes disposing the tool in a borehole and receiving a series of measurements using a processor disposed at the tool. A telemetry system transmits a latest received measurement that meets acceptance criteria to the receiver after completion of transmission of a previously transmitted measurement.

Also disclosed is an apparatus for transmitting data from a tool configured to be disposed in a borehole penetrating the earth to a receiver. The apparatus includes: a telemetry system disposed at the tool; and a processor disposed at the tool and configured to receive a series of measurements and to identify those measurements that are latest received and meet an acceptance criterion for transmission by the telemetry system to the receiver after completion of transmission of a previously transmitted measurement.

Further disclosed is a non-transitory computer-readable medium having computer-executable instructions for transmitting data from a tool disposed in a borehole penetrating the earth to a receiver by implementing a method that includes: receiving a series of measurements from a sensor disposed in a borehole; and transmitting a latest received measurement that meets an acceptance criterion to the receiver after completion of transmission of a previously transmitted measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 illustrates an exemplary embodiment of a downhole tool disposed in a borehole penetrating the earth;

FIG. 2 illustrates an exemplary embodiment of a dual-action sample pump;

FIG. 3 depicts aspects of sample chamber pressure in the sample pump;

FIGS. 4A and 4B, collectively referred to as FIG. 4, depict further aspects of sample chamber pressure in the sample pump;

FIGS. 5A and 5B, collectively referred to as FIG. 5, depict aspects of sensor output influenced by pump pressure variation; and

FIG. 6 presents one example of a method for transmitting data from a downhole tool to a receiver.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosed apparatus and method presented herein by way of exemplification and not limitation with reference to the Figures.

FIG. 1 illustrates an exemplary embodiment of a downhole tool 10 disposed in a borehole 2 penetrating the earth 3, which includes an earth formation 4. The downhole tool 10 is conveyed through the borehole 2 by a carrier 5. In the embodiment of FIG. 1, the carrier 5 is a drill string 6 for measurement-while-drilling (MWD) operations. In another embodiment, the carrier 5 can be a wireline for wireline operations. A telemetry system 7 is provided in order to transmit data from the downhole tool 10 to a receiver such as a computer processing system 13 disposed at the surface of the earth 3. In one embodiment, the telemetry system 7 is a mud-pulse telemetry system 8. In order to operate the downhole tool 10 and/or provide a communications interface with the telemetry system 7, the downhole tool 10 includes downhole electronics 11.

Still referring to FIG. 1, the downhole tool 10 includes a formation fluid tester 12 configured to perform one or more measurements on fluid extracted from the formation 4. The formation fluid tester includes a probe 14 configured to extend from the downhole tool 10 and seal with a wall of the borehole 2. A pump 15 coupled to the probe 14 is configured to lower the pressure internal to the probe 14 in order to draw a sample of formation fluid from the formation 4 and discharge the sample into a sample chamber 16 for analysis. Various sensors 17 are configured to perform various types of measurements on the sample. Non-limiting examples of the measurements include pressure, temperature, density, viscosity, compressibility, radiation, and spectroscopy.

Still referring to FIG. 1, the downhole electronics 11 includes a filter 18 configured to process data/measurements from the various sensors 17. The processing can include a filtering function and/or an associating function where each measurement received is associated with some other data such as a measurement of some aspect of the pump 15. The downhole electronics 11 also includes memory 19 configured to store measurements from the sensor 17 as the measurements are received. The memory 19 provides for storing measurements that cannot be immediately transmitted to the computer processing system 13 because of limited bandwidth of the telemetry system 7.

Reference may now be to FIG. 2 illustrating an exemplary embodiment of the pump 15. In the embodiment of FIG. 2, the pump 15 is a dual-action pump (i.e., pumping fluid on both strokes of a piston). A piston in pump 15 is used to displace fluid to cause the pumping. While pumping, valves 21 and 22 act as inlet valves and valves 23 and 24 act as outlet valves. Valves 21-24 can be check-valves or externally driven valves. Coupled to the pump 15 is a pump sensor 20. The pump sensor 20 is configured to measure one or more aspects of the pump 15. As non-limiting examples, the pump sensor 20 can measure inlet pressure, outlet pressure, piston position, pump flow rate, and/or volume pumped.

One property of a piston based dual-action pump is that it cannot generate a continuous flow. When the piston has reached an end stop, the direction must be reversed and optionally some valves must be actuated. Pump reversal takes some amount of time during which no flow is generated. In a fluid sampling application, the stopping of flow leads to increasing pressure on the inlet side. The pressure rises towards formation pressure (and is referred to as build-up). FIG. 3 presents a pressure curve of a dual-action pump for one of the inlet sides of the pump.

As noted in FIG. 3, pressure is relatively constant when the piston is moving. Hence, in one embodiment, transmission of the latest data acquired is the transmission of the latest data obtained while the piston is moving. If a telemetry data request is received by the tool 10, the returned data is either (case 1) the latest value if the piston is currently moving or (case 2) an older value (stored in memory) that was acquired while the piston was moving if the piston is currently reversing. Directly after pump reversal, the pressure needs some time to stabilize again. A further improvement to the above method is to include some time for piston movement after piston reversal such as in case 2. This additional time can be defined by a specific or set time, a volume pumped, a flow rate, or data stability of some sensor data. If the piston position is known, there is no need to detect if the piston has stopped. Case 2 can be entered when pump piston reversal is imminent. Each of the required conditions for data to be transmitted to the receiver may be referred to as an acceptance criterion.

The techniques for determining which data to transmit can be extended from pump inlet pressure measurement to other data. Downhole fluid sampling tools may contain fluid sensors for fluid contamination estimation or fluid identification or characterization. The output of these sensors can be pressure dependent. If a pressure variation is caused by the pump and influences the sensor data, an algorithm can be used to determine and transmit consistent data (i.e., data taken under approximately the same conditions). This way, a tool operator can better assess if variation in sensor data is caused by a change in fluid properties. It reduces the probability for misinterpretation because the transmitted data shows less variation and is known to be more consistent and, thus, yield more accurate data.

In general, the operator must make sure that the inlet pump pressure does not get below a threshold pressure (e.g., bubble point) at which the fluid properties change irreversibly. Hence, the tool operator is usually interested in the lower pressures. For this reason, one additional type of data to transmit is the lowest pump inlet pressure, which has occurred in a certain timeframe. This value helps the tool operator to decide if the pump speed must be adjusted to stay above the bubble point. The timeframe can be defined by a time interval, volume, or telemetry update rate as non-limiting examples. The idea of sending additional data to help interpret the primary data sent can be extended to other sensor data that is influenced by pressure or flow rate variation and where minimum, maximum, or other statistical values are important for the tool operator to know when the data transmission rate is too low to determine these values after transmission of raw data.

If pump speed is low, the time to fill a pump chamber can be long. Fluid entering the pump chamber may contain immiscible components or components featuring high difference in density. A long staying time in the pump chamber can lead to segregation of the fluid components. When the segregated fluid is pushed out of the chamber, the components may leave the chamber successively, influencing the fluid sensors successively as well. Usually, this leads to random noise in the telemetry data. In order to compensate for measurements of the different components, the measured data can be separated into data acquired at the beginning of a pump stroke from the data acquired at the end of the pump stroke. Thus, consistent data for the individual fluid components is transmitted.

Extraction and transmission of data acquired while the pump is reversing can give information about mobility (i.e., higher mobility leads to higher pressure or faster pressure stabilization at formation pressure during stopping of flow). Pressure rising above formation pressure during stopping of flow is an indicator for loss of seal with the formation. This information is very important because the loss of seal usually cannot be remedied except by aborting tool operation, releasing the seal element, moving the tool to a different location and trying to achieve a seal at the new location. Hence, for these reasons it may be desirable to transmit data obtained during reversal of the pump piston.

Some sensors are influenced by the pressure or flow rate variations caused by the pump. Some measurements take a long time to deliver a result, or long time response filters are involved in post-processing of the measurements. If this timeframe overlaps with pump piston reversal, the sensor data quality will suffer.

In a first example, a sensor is influenced by the pressure or flow rate variations caused by the pump. Its data is acquired at a high rate and filtered by a filter with a filter response time of several seconds. The pressure change during pump piston reversal generates biased acquired data and the filtered data will still be biased for some time after the pump piston reversal has been executed because of the filter delay.

In a second example, a sensor is influenced by pump pressure variation. A measurement takes several seconds. The sensor might feature a variation of a resonance frequency as response to a parameter of interest. To measure the parameter of interest, the resonance has to be determined by applying a frequency sweep. This can take several seconds. If a pressure variation occurs during the sweep, the acquired spectrum is distorted (maybe showing several resonance peeks or none at all) and the result can be of limited value or useless.

In order to accommodate sensors with long acquisition time windows and filters with long response times, sensor data acquisition can be paused during pump piston reversal. Sensor data acquisition is then resumed after pump piston reversal when the pump inlet pressure is stable again. If the pump piston position is known, the data acquisition can already be paused when the pump piston reversal is imminent. Pausing can include (1) stopping data acquisition completely and stopping the associated filtering as well (such as when using digital filters), (2) feeding the last good value (i.e., stable constant value) into the filter, (3) stopping a measurement sequence and resuming it later (for example, stopping the frequency sweep at the current frequency and resuming the frequency sweep at that frequency later), and (4) discarding already acquired data of a measurement sequence and restarting the sequence later.

It can be appreciated that the methods described above for data acquisition and transmission can be used for data post-processing and data display. Separating data acquired during flow and no-flow pump phases leads to less noisy and more clear and accurate data curves by separating the relevant information. FIG. 4A shows one example of original (i.e., unfiltered) data for pump pressure versus time while FIG. 4B shows that data after filtering (i.e., cleaned-up post processing data). FIG. 5A shows another example of original unfiltered data, in this case sound speed versus time, while FIG. 5B shows that data after filtering.

Combination of data acquired during flow and no-flow phases of the pump can be used to estimate additional fluid properties. If the pressure (or flow rate) change is known and the response of an additional sensor to pressure (or flow rate) change is also known, then properties such as fluid compressibility or viscosity related properties or thermal properties can be estimated. For example, fluid pressure during flow and during no-flow phases of the pump can be acquired. Additionally, fluid sound speed as well as refractive index during flow and no flow phases can also be acquired, while the density is determined only during flow condition. The fluid's compressibility and density determine the sound speed of a fluid according to equation (1) where κ is compressibility.

$\begin{array}{cc}{c}^2=\frac{1}{\kappa \rho }& \left(1\right)\end{array}$

The fluid's density, sound speed and refractive index ρ₁, c₁ and n₁, respectively, during flow phase are given as are the fluid's sound speed and refractive index c₂ and n₂ during no-flow phase. Because the polarizability of the fluid is not changed during the short flow stop, the density ρ₂ can be calculated following Clausius-Mosotti equation, as explained in patent U.S. Pat. No. 7,016,026 B2 using equation (2).

$\begin{array}{cc}{\rho }_2={\rho }_1\frac{n_2^2-1}{n_2^2+2}·\frac{n_1^2+2}{n_1^2-1}& \left(2\right)\end{array}$

The compressibility for both flow conditions can therefore be calculated using equations (3) and (4).

$\begin{array}{cc}{\kappa }_{\mathrm{flow}}=\frac{1}{c_1^2{\rho }_1}& \left(3\right)\\ {\kappa }_{\mathrm{no}\text{-}\mathrm{flow}}=\frac{1}{c_2^2{\rho }_1}·\frac{n_2^2+2}{n_2^2-1}·\frac{n_1^2-1}{n_1^2+2}& \left(4\right)\end{array}$

Additionally, significant changes in fluid compressibility between the flow and no-flow condition can be used as an indicator for bubble point pressure undershoot.

FIG. 6 presents one example of a method 60 for transmitting data from a tool disposed in a borehole penetrating the earth to a receiver. The method 60 calls for (step 61) disposing the tool in a borehole using a carrier. Further, the method 60 calls for (step 62) receiving a series of measurements using a processor disposed at the tool. Further, the method 60 calls for (step 63) transmitting a latest received measurement that meets an acceptance criterion to the receiver after completion of transmission of a previously transmitted measurement using a telemetry system.

In support of the teachings herein, various analysis components may be used, including a digital and/or an analog system. For example, the downhole electronics 11, the computer processing system 13, or the filter 18 may include the digital and/or analog system. The system may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, pulsed mud, optical or other), user interfaces, software programs, signal processors (digital or analog) and other such components (such as resistors, capacitors, inductors and others) to provide for operation and analyses of the apparatus and methods disclosed herein in any of several manners well-appreciated in the art. It is considered that these teachings may be, but need not be, implemented in conjunction with a set of computer executable instructions stored on a computer readable medium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), or any other type that when executed causes a computer to implement the method of the present invention. These instructions may provide for equipment operation, control, data collection and analysis and other functions deemed relevant by a system designer, owner, user or other such personnel, in addition to the functions described in this disclosure.

Further, various other components may be included and called upon for providing for aspects of the teachings herein. For example, a power supply (e.g., at least one of a generator, a remote supply and a battery), cooling component, heating component, magnet, electromagnet, sensor, electrode, transmitter, receiver, transceiver, antenna, controller, optical unit, electrical unit or electromechanical unit may be included in support of the various aspects discussed herein or in support of other functions beyond this disclosure.

The term “carrier” as used herein means any device, device component, combination of devices, media and/or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and/or member. Other exemplary non-limiting carriers include drill strings of the coiled tube type, of the jointed pipe type and any combination or portion thereof. Other carrier examples include casing pipes, wirelines, wireline sondes, slickline sondes, drop shots, bottom-hole-assemblies, drill string inserts, modules, internal housings and substrate portions thereof.

Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The terms “first” and “second” are used to distinguish elements and are not used to denote a particular order.

It will be recognized that the various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed.

While the invention has been described with reference to exemplary embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method for transmitting data from a tool disposed in a borehole penetrating the earth to a receiver, the method comprising:

disposing the tool in a borehole using a carrier;

receiving a series of measurements using a processor disposed at the tool; and

transmitting a latest received measurement that meets an acceptance criterion to the receiver after completion of transmission of a previously transmitted measurement using a telemetry system.

2. The method according to claim 1, further comprising storing each measurement in the series of measurements in memory disposed in the tool.

3. The method according to claim 1, further comprising associating each measurement with an acceptance criterion measurement performed by a first sensor.

4. The method according to claim 3, further comprising comparing the acceptance criterion measurement to the acceptance criterion in order to determine if the associated measurement should be transmitted to the receiver.

5. The method according to claim 4, further comprising transmitting the series of measurements from a second sensor disposed at the tool.

6. The method according to claim 5, wherein the second sensor is configured to sense a downhole property of interest.

7. The method according to claim 6, wherein in the downhole property of interest is a formation fluid property.

8. The method according to claim 7, further comprising extracting the formation fluid from an earth formation using a pump.

9. The method according to claim 8, further comprising performing the acceptance criterion measurement on the pump using the first sensor.

10. The method according to claim 9, wherein the acceptance criterion measurement comprises a selection from a group consisting of a pump piston stroke position, a time after a pump piston travel reversal, a pump flow rate, a volume pumped, or some combination thereof.

11. The method according to claim 10, wherein the pump piston stroke position comprises a position approximately half way between two stroke reversing positions.

12. The method according to claim 10, wherein the pump flow rate is approximately constant for a certain amount of time.

13. The method according to claim 10, further comprising separating first measurements associated with a first value of a selected acceptance criterion measurement from second measurements associated with a second value of the selected acceptance criterion measurement.

14. The method according to claim 13, wherein the first value is related to a stable flow rate of fluid through the pump and the second value is related to a flow rate of fluid through the pump that is less than the stable flow rate.

15. The method according to claim 14, further comprising determining the compressibility of the pumped fluid using the first measurements and the second measurements.

16. The method according to claim 8, wherein the pump comprises a piston configured to pump a fluid by displacement, the method further comprising separating first measurements performed when the piston is approximately reversing direction from second measurements performed when the piston is moving and pump inlet pressure is stabilized.

17. The method according to claim 16, further comprising associating a first component of the pumped fluid with the first measurements and a second component of the pumped fluid with the second measurements.

18. An apparatus for transmitting data from a tool configured to be disposed in a borehole penetrating the earth to a receiver, the apparatus comprising:

a telemetry system disposed at the tool; and

a processor disposed at the tool and configured to receive a series of measurements and to identify those measurements that are latest received and meet an acceptance criterion for transmission by the telemetry system to the receiver after completion of transmission of a previously transmitted measurement.

19. The apparatus according to claim 18, wherein the processor is further configured to store each measurement in the series of measurements in memory disposed at the tool.

20. The apparatus according to claim 18, further comprising a first sensor configured to provide to the processor an acceptance criteria measurement associated with each measurement in the series of measurements.

21. The apparatus according to claim 20, further comprising a second sensor configured to provide the series of measurements, wherein the measurements are of a downhole property of interest.

22. The apparatus according to claim 21, further comprising a pump configured to extract a formation fluid from an earth formation, wherein the second sensor is further configured to perform a measurement of a property of the extracted formation fluid.

23. The apparatus according to claim 22, wherein the first sensor is coupled to the pump and configured to measure a parameter of the pump.

24. The apparatus according to claim 18, wherein the telemetry system is a mud-pulse telemetry system.

25. The apparatus according to claim 18, wherein the tool is disposed at a carrier configured to be conveyed through the borehole.

26. The apparatus according to claim 25, wherein the carrier comprises at least one of a drill string, coiled tubing, a wireline, and a slickline.

27. A non-transitory computer-readable medium comprising computer-executable instructions for transmitting data from a tool disposed in a borehole penetrating the earth to a receiver by implementing a method comprising:

receiving a series of measurements from a sensor disposed in a borehole; and

transmitting a latest received measurement that meets an acceptance criterion to the receiver after completion of transmission of a previously transmitted measurement.