Formation sampling apparatus

Abstract

 An apparatus and method for taking fluid samples from earth formations surrounding a borehole while minimizing the erosion of the formations which occurs during such sample-taking, in which a specialized tool is brought into communication with the desired formation and the fluid pressure which exists within the formation prior to taking a sample is used to restricttheflow of fluids into the tool. This restriction is however opposed with a pre-determined biasing force in combination with the dynamic fluid pressure during the sample-taking process. These opposing forces control the rate of flow of formation fluids into the tool in a manner diminishing the erosion which occurs.

Description

Background of the Invention

[0001] The present invention relates to a device for sampling earth formations and, more particularly to a device for taking fluid samples within a borehole, by laterally piercing the earth formations of interest surrounding the borehole and sampling the fluids which are within such formations.

[0002] The -conventional manner of collecting fluid samples within the formations surrounding a borehole involves lowering a specialized tool into borehole on a wireline or similar conveyence device. This tool includes sample collection means such as are described in U. S. Patent 3,530,933, the contents of which are incorporated herein by reference, in which a specialized projection on the tool is extended into contact with an adjacent earth formation in order to establish communication with any connate fluids situated therein. The collection means also includes one or more sample chambers for receiving separate samples of the formation fluid when collected. These sample chambers are typically at atmospheric pressure which is substantially less than the pressure of the connate fluids. The connate fluids are therefore caused to flow into the sample chambers as long as an open passage-way exists between the chambers and the formations, in which such fluids can flow. 'The pressure of the sampled fluid in each chamber is generally measured, and the projection is then withdrawn from the formation and the fluid sample is either expelled or carried to the surface with the tool.

[0003] Although such tools are generally effective, there continues to be a problem in certain earth formations which consist of loosely or unconsolidated formation materials which can be eroded by the relatively high velocity flow of fluids which occurs during the sample-taking process. The erosion of these loosely consolidated materials not only causes the eroded materials to be included within the sample taken, thereby potentially clogging the fluid passageways within the sample taking device; it also interferes with the sealing engagement that the projection on the tool makes with the borehole wall. Since various gases are also present within the borehole, any leaks with in the engagement between the tool and the formation can potentially introduce such gas in the samples being taken. The inclusion of this gas can contaminate the sample as well as introduce errors into the pressure measurements being made.

[0004] In order to minimize the occurrence of erosion, modifications have previously been made to the tool in order to control the rate of flow of the fluid as the samle is being taken. The conventional manner of controlling this rate is to employ a water cushion system within the tooL This water cushion includes a slideable piston that is operatively arranged within the sample receiving chamber so as to divide this sample chamber into two compartments. Prior to using the tool, this piston is disglaced to the end of the sample chamber which is proximate the sampling entrance to the sample chamber. The compartment created on the other side of the piston is then filled with water. The opposing end of the chamber contains a psssageway with a predetermined diameter orifice that leads into an adjacent chamber that has been kept at atmospheric pressure. As the sample is being taken, the slideable piston moves within the sample chamber and causes the expulsion of the water through the orifice and into the adjacent atmospheric chamber. Since the rate of the flow of water through the orifice is predetermined by the size of the orifice chosen, the rate at which the sample is admitted can be controlled.

[0005] Although the use of a water cushion has diminished the problem of erosion during the taking of the sample, there are still some difficulties. For example, at such high pressures as are present within a borehole, there is a finite compression of the water within the water cushion during the initial moments of the sample-taking process. This compression is enough to cause an initial erosion of the loosely consolidated material adjacent the sampletaking passageway. In addition, the space occupied by the water cushion system necessitates a longer tool This added length can introduce problems in the loweriug or removing of the tool into or from the borehole.

[0006] One aspect of the present invention is directed to an apparatus for obtaining samples of connate fluids from earth formations that are located peripheral to a borehole, said apparatus comprising: sample collection means for establishing communication between the apparatus and a peripheral earth formation, said sample collection means including at least one control valve controlling the admission of fluids from the earth formation into the sampling apparatus; means for applying the pressure of the connate fluids within the formation prior to the collection of a sample to bias said control valve toward its closed position thereby tending to restrict the admission of fluids into said sampling apparatus; means for applying the pressure of the connate fluids within the formation as a sample is being taken to bias said control valve toward its open position, and means for applying a differential force to said control valve, whereby said control valve will open and remain open as long as the force of the pressure of the connate fluids within the formation during the collection of a sample exceeds a fraction of the force due to the pre-collection pressure, thereby affording the controlled admission of formation fluids into the sampling apparatus.

[0007] Another aspect of the present invention is directed to a method for obtaining samples of connate fluids from earth formations that are located peripheral to a borehole, said method comprising: establishing comnunication between an apparatus adapted to obtain such fluid samples and a peripheral earth formation; applying the pressure of the connate fluids within such formation prior to the collection of a sample in a manner restricting the admission of fluids into the apparatus; applying the pressure of the connate fluids within such formation as a sample is being taken in a manner opposing said restriction of the admission of fluids into the apparatus, and applying a differential force in a manner affecting the admission of fluids into the apparatus, whereby fluids will be admitted into the apparatus as long as the force of the pressure of the connate fluids within the formation during the collection of a sample exceeds a fraction of the force due to the pre-collection pressure, thereby affording the controlled admission of formation fluids into the sampling apparatus.

[0008] The formation sampling apparatus of the present invention therefore affords a control on the flow of the formation fluids into the sample-taking apparatus based on the change of the pressure of the connate fluids within the formation during the sample taking process. This invention further minimizes the problem of erosion of any adjacent formations as well as the multiplicity of difficulties associated therewith. Furthermore the present invention minimizes the problem of erosion without substantially lengthening the tool.

Brief Description of the Drawings

[0009] The present invention will be further described hereinafter with reference to the accompanying drawing wherein:

Figure I illustrates a fluid sampling apparatus of the present invention as it might appear within the borehole;

Figure 2 is a partial schematic representation of the fluid sampling apparatus according to the present invention;

Detailed DescriDtion

[0010] A fluid sampling apparatus 10 according to the present invention is illustrated in Figure 1 as it appears within a borehole 12. The fluid sampling apparatus 10 Is suspended from a multi-conductor cable 11 which not only supports the apparatus 10 but which also contains the various electrical conductors necessary to operate the fluid sampling apparatus 10. Typically this cable 11 is referred to as a wireline. The apparatus 10 is lowered into a borehole 12 on the wireline 11 until it is positioned adjacent a particular formation interval 13 in which it is desired to collect a sample of the connate fluids that are located within that formation 13. The opposing end of the cable 11 is in turn spooled in the usual manner and suspended from a winch 14 at the earth's surface. Some of the conductors within cable 11 are connected to switch 15 for the selective connection of the apparatus 10 to a power source 16. Others conductors within cable 11 are connected to conventional indicating and recording apparatus 17 which are used to monitor the operation of the apparatus 10. To afford a number of tests to be made during a single trip into the borehole 12, the fluid sampling apparatus 10 typically comprises a corresponding number of tandomly arranged sample collection means 20. Each of these sample collection means 20 is generally capable of independent operation for recovering such multiple samples as are desired. Some of the standard components and operation of such sample collection means 20 have already been described in the Background section of this application. For example, as has been noted the sample collection means 20 include an extendable projection 18 capable of achieving a sealed interface with the formation 13, i.e., in order to avoid sampling borehole (as opposed to formation) fluids and gases in addition to or instead of the connate fluids within the formation 13. As has also already been described, it is important that the sample be taken in a manner minimizing the erosion of the formation 13 adjacent the sample collection means 20 in order to maintain this sealed interface between the projection 18 and the formation 13. The components of the present invention making this controlled collection of a sample possible are schematically illustrated in Figure 2.

[0011] The sample collection means 20 includes a passageway 21 therein leading from the projection 18 toward two valves. One of these valves is a reference pressure valve 22 and the other is a flow line valve 23. The sample collection means 20 also includes a control valve 26 connected to valves 22 and 23 via passageways 24 and 28 respectively, and at least one sample chamber 35 connected to control valve 26 via passageway 33. The control valve 26 has three chambers 25, 29 and 32. The passageway 24 from the reference pressure valve 22 opens into chamber 25. The passageway 28 from the flow line valve 23 opens into chamber 29 and the passageway 33 leading to the sample phamber 35 opens into chamber 32. Boundaries exist between the various chambers 25, 29. and 32 preventing the flow of fluid there between. Thus for example, chamber 25 can be used to trap the reference pressure of the formation as will be described. The houndary between chambers 29 and 32 however contains an orifice 31 which when open permits the passage of fluid between these chambers. This orifice 31 can be closed by the movement of a shuttle 30 which is mounted within the control valve 26. The shuttle 30 and the various chambers 25, 29, and 32 are operatively disposed withinthe control valve 26 such that any fluid pressure within chamber 25 will tend to force the shuttle 30 in a direction closing orifice 3L Contrastingly any fluid pressure within chamber 29 will tend to force the shuttle 30 in a direction opening orifice 3L The control valve 26 also contains a spring 34 which is positioned to bias the shuttle 30 in a direction tending to open orifice 3L

[0012] When the tool 10 has been lowered into the borehole 12, and the projection 18 has established contact with the formations 13, the reference pressure valve 22 is opened. This permits a small quantity of the formation fluid to pass through line 21, valve 22, line 24, and into chamber 25 of control valve 26. The dimensions of line 21, valve 22, line 24, and chamber 25 are chosen to minimize the volume of formation fluid which actually flows while this initial pressure measurement is being made, while still providing sufficient compressible fluid volume to afford the movement of the shuttle 30. A pressure sensor 27 is also in communication with line 21. This pressure sensor 27 is able to sense the static pressure of the fluids within the formation 13 that exists prior to taking a sample of these fluids. The pressure as sensed by sensor 27 is communicated to the recording apparatus 17 on the surface by the wireline 11. This initial static or pre-collection pressure also serves as a reference pressure for the present invention.

[0013] As the tool 10 is being lowered into the borehole 12 flow line valve 23 is normally closed and remains closed during the initial sensing of the static pressure of the connate fluids within the formation by sensor 27. Line 28 and chamber 29 of valve 26 are therefore at atmospheric pressure, which is substantially less than the typical static pressure of the fluids within the formation. Thus the pressure within chamber 25 is typically substantially greater than the pressure within chamber 29. Although the shuttle 30 of control valve 26 is biased toward its open position by a spring 34, this spring 34 is chosen such that the force it exerts is insignificant when compared to the difference between the static formation pressure and atmospheric pressure. For this reason control valve 26 typically closes when the reference pressure valve 22 is opened, with the shuttle 30 of control valve 26 being driven into sealing engagement with the orifice 31 that exists between chambers 29 and 32.

[0014] In. order to take a sample, switch 15 is closed and the appropriate solenoids (not snown) within the tool 10 are actuated by power source 16 to close the reference pressure . valve 22 and open flow line valve 23. The closing of valve 22 traps the static reference pressure in chamber 25 of valve 26. The opening of the flow line valve 23 causes the dynamic pressure of the fluid within the formation to be present within chamber 29 of control valve 26. This pressure when combined with the force exerted by the spring 34 is typically greater than the initial static reference fluid pressure of the formation as trapped within chamber 25. The shuttle 30 of valve 26 therefore moves to its open position, compressing the fluid trapped within the reference pressure circuit, and formation fluid is allowed to pass through the orifice 31 and from chamber 29 to chamber 32 and into line 33 leading from chamber 32 to the sample chamber 35. Since the volume of the sample chamber 35 is large compared to the volume of formation fluids contained within the various flow lines and valves thus far described, there is typically a slight decrease in the pressure that is present within chamber 29 of valve 26. This decrease in pressure occurs as a result of the flow of formation fluids through the formation, and within the various lines and valves and into the sample chamber 35. When the pressure in the chamber 29 decreases to the extent that the combined force of the pressure within chamber 26 plus the force due to the spring 34 is less than the force due to the trapped static formation pressure in chamber 25, the control valve 26 will close. The control valve 26 will remain closed until the formation fluid pressure in chamber 29 increases to the minimum pressure necessary for the combined force of the pressure and the spring 34 to again open the valve 26.

[0015] In practice the control valve 26 will either remain open at such a position that the opposing forces are in balance or rapidly shuttle between its open and closed positions till the sample chamber 35 is eventually filled. The filling of the sample chamber 35 can be sensed by means such as gressure sensor 27. This pressure information can again be communicated to the recording equipment 17 on the surface by the cable 11. When the sample chamber 35 is filled, the reference pressure valve 22 is opened and the flow line valve 23 is again closed in order that the sample can be released or transported to the surface.

[0016] It is therefore possible with the present invention to control the flow of formation fluids into the sample chamber 35 based upon the selection of spring force exerted by spring 34. This construction minimizes the initial pressure surges which were otherwise present with the water cushion of the existing tools. The present invention also affords a control of the pressure drop which occurs as formation fluids flow into the sample chamber 35.

[0017] Having thus described one embodiment of the present invention, it will be understood that changes may be made in the size, shape, or configuration of some of the parts or fluid circuits described herein without departing from the present invention as recited in the appended claims. One such modification for example is the replacement of spring 34 and shuttle 30 with a shuttle having a slightly increased surface area exposed in chamber 29 than is exposed in chamber 25.

Claims

1. An apparatus for obtaining samples of connate fluids from earth formations that are located peripheral to a borehole, said apparatus characterized by:

sample collection means for establishing communication between the apparatus and a peripheral earth formation, said sample collection means including at least one control valve controlling the admission of fluids from the earth formation into the sampling apparatus;

means for applying the pressure of the connate fluids within the formation prior to the collection of a sample to bias said control valve toward its closed position thereby tending to restrict the admission of fluids into said sampling apparatus;

means for applying the pressure of the connate fluids within the formation as a sample is being taken to bias said control valve toward its open position; and

means for applying a differential force to said control valve, whereby said control valve will open and remain open as long as the force of the pressure of the connate fluids within the formation during the collection of a sample exceeds a fraction of the force due to the pre-collection pressure, thereby affording the controlled admission of formation fluids into the sampling apparatus.

2. An apparatus as claimed in claim 1 characterized in that said sample collection means further comprises a projection adapted to be extended from said apparatus into contact with the formation, said projection including at least one passageway therein which establishes communication with the formation once said projection is extended.

3. An apparatus as claimed in claim 1 characterized in that said control valve comprises a housing and a shuttle mounted within said housing in a manner affording the movement of such shuttle between an open position affording the passage of formation fluid through said control valve and a closed position where the passage of fluid is obstructed.

4. An apparatus as claimed in claim 3 characterized in that said control valve further comprises wall portions defining a first chamber within said housing which is oriented within said control valve such that any pressure within said first chamber biases said shuttle of said control valve toward its closed position, and wherein said means for applying the pre-collection pressure comprises a reference pressure valve in comnunication with said passageway and said first chamber of said control valve.

5. An apparatus as claimed in claim 3 or claim 4 characterized in that said control valve further comprises wall portions defining a second chamber within said housing which is oriented such that any pressure within said second chamber biases said shuttle of said control valve toward its open position, and wherein said means for applying the pressure of the fluids during the collection of a sample comprises a flow line valve in communication with said passageway and said second chamber of said control valve.

6. An apparatus as claimed in any one of claims 3, 4 and 5 characterized in that said means for applying a differential force comprises a spring positioned between said housing of said control valve and said shuttle within said control valve.

7. An apparatus as claimed in any one of claims 3, 4 and 5 characterized in that said means for applying a differential force comprises shuttle end portions of different surface areas included in said shuttle.

8. A method for obtaining samples of connate fluids from earth formations that are located peripheral to a borehole, said method characterized by:

establishing communication between an apparatus adapted to obtain such fluid samples and a peripheral earth formation;

applying the pressure of the connate fluids within such formation prior to the collection of a sample in a manner restricting the admission of fluids into the apparatus;

aplying the pressure of the connate fluids within such formation as a sample is being taken in a manner opposing said restriction of the admission of fluids into the apparatus; and

applying a differential force in a manner affecting the admission of fluids into the apparatus, whereby fluids will be admitted into the apparatus as long as the force of the pressure of the connate fluids within the formation during the collection of a sample exceeds a fraction of the force due to the pre-collection pressure, thereby affording the controlled admission of formation fluids into the sampling apparatus.

9. A method as claimed in claim 8 characterized in that the step of establishing communication comprises extending a projection from the apparatus into contact with the peripheral formation.

10. A method as claimed in claim 8 characterized in that the step of appling the pre-collection pressure includes the step of admitting a small quantity of formation fluid into a portion of the apparatus prior to the collection of a sample.

11. A method as claimed in claim 10 further characterized by trapping the small quantity of formation fluid within a portion of the apparatus so as to provide a reference pressure.

Drawing