WO2004019029A1

WO2004019029A1 - Device and method for petrophysical analysis of a rock sample

Info

Publication number: WO2004019029A1
Application number: PCT/NO2003/000292
Authority: WO
Inventors: Gudmund Hafstad; Svein Erling Johnstad; Karstein Monsen; Harald Westerdahl
Original assignee: Norsk Hydro Asa
Priority date: 2002-08-23
Filing date: 2003-08-22
Publication date: 2004-03-04
Also published as: AU2003263683A1; NO20024045D0

Abstract

The invention relates to a pressure cell for petrophysical examination of a cylinder-shaped oil-bearing rock sample (3). The cell comprises: a cylindershaped fiber reinforced pressure mantle (7) with end portions (7a,7b) and caps (2a,2b); a pressurising channel (12) through the caps (2a,2b) from a pump (122) for pressurising by means of a pressurising fluid (124) in a space inside the pressure mantle (7); a rubber sleeve (131) enveloping the sample's (3) cylinder surface against the pressurising fluid (124); flow channels (13a, 13b) through the caps (2a,2b) with an injection flow pump (132) for flowing flow gas (134) through the rock sample's (3) end surfaces (38a,38b) and within the rubber sleeve (131) to a receiving flow pump (136). The novel features of the invention comprise the following features: acoustic transducers (14a) arranged in either end (38a,38b) of the rock sample (3) for generating and reception respectively of P (pressure) and S (shear) waves; a circumferential central portion (7c) of the pressure mantle (7) being transparent to X-rays (81); so as to conduct simultaneous CT-X-ray examination of gas content and gas distribution after flowing of the flow gas (134} through the rock sample (3), for examining the rock sample's seismic properties under various pressures from the pressurising fluid (124) and gas content of the flow fluid (134) or degree of oil content.

Description

DEVICE AND METHOD FOR PETROPHYSICAL ANALYSIS OF A ROCK SAMPLE

Introduction

This invention relates to a device and a method for petrophysical analysis of a rock sample. More specifically, the invention relates to a pressure cell for analysing acoustic, i.e. seismic velocities through the rock sample, both as S- (shear) waves and P (compression) waves, in which the rock sample may be subject to various pressures to simulate a reservoir pressure.

Statement of problem

At seismic exploration of geological prospects, knowledge of P- and S- wave velocities are important during the interpretation of the seismic data. In a similar manner, it is known that the relation between gas and oil, or gas and water, affects the seismic P- and S- wave velocities, particularly at a transition between total oil or water saturation, to a relatively little content of gas. However, laboratory experiments with a gas/oil mixture in a rock sample under atmospheric pressure would not be able to tell much about prevailing seismic velocities down in a reservoir with natural lithostatic and hydrostatic pressure, said reservoir residing several hundreds or thousands of meters below the Earth's surface. Due to this, it is desirable to analyse the seismic velocities in drilled core samples from boreholes, in which the seismic velocities are a function of the pressure that corresponds to the depths of which the rock samples have been taken. The seismic velocities are not only sensitive to pressure. An important aspect is whether the present gas in the rock is gathered in distinct channels in cracks or faults and otherwise does not reside in separate pore spaces between e.g. sedimentary particles, or whether it is more homogenously distributed in the rock, e.g. in a porous, more or less homogenous permeable sandstone. The P-wave velocity as a function of gas saturation decreases in a near-linear manner with an increasing gas saturation if the gas has a non-homogenous distribution, a so-called patchy distribution in the rock sample. The P-wave velocity contrarily decreases sharply with gas content increasing between zero and about 25%, and thereafter flattens out. It is therefore important to observe the gas distribution in the sample during acoustic measurements. Until now, no equipment exists that could perform such simultaneous observations of gas distributions and acoustic velocities during reservoir pressure conditions.

Solution to the stated problem, summary of the invention

The device of the invention: A solution to one or more of the above-mentioned problems appeared in that the inventors proposed a pressure cell for petrophysical analysis of a rock sample 3 in which one conducts a tomographic analysis of gas content and gas distribution simultaneously with the sample being subject to a confining pressure after being gas flushed.

The device according to the invention comprises the following features: a mainly cylinder-shaped pressure mantle having a first and a second end portion and two caps arranged at the first and the second end portion, respectively; one or more pressurising channels through one or more of said caps, for connection to a pump for pressurising the volume inside of said pressure mantle by means of a pressurising fluid (preferably silicon oil), and a fluid-proof sleeve, preferably of rubber, said sleeve enveloping said rock sample's cylindrical sidewall surface toward said pressurising fluid.

The novel and surprising effect of the invention comprises: a first and a second high pressure flow channel arranged through the cell, preferably through the caps, with a first injection flow pump for flushing of flushing gas (preferably nitrogen) and/or oil, through the rock sample's preferably cylindrical end surfaces (so that no pipes run parallel with the cylindrical sample), and inside of the flexible sleeve (so that the flushing gas does not mix with the pressurizing fluid) to a second receiving flow pump; that the pressure cell has acoustic transducers arranged at either end of the rock sample for generation and reception of P- (pressure) and S- (shear) waves, respectively; that the pressure mantle has a circumferential central portion being generally transparent to X-rays (which will not be disturbed by metallic high pressure channels through the central portion); for simultaneous computer tomographic X-ray examination of gas content and gas distribution after flushing of the flushing gas through the rock sample, in order for the rock sample's seismic properties under various pressures from the pressurizing fluid and gas content of the flushing fluid or degree of oil content may be examined.

Results from such acoustic measurements under pressures that may be compared to reservoir pressures, may be included in interpretation of in-situ gas saturation based on repeated seismic exploration of a reservoir using the same

3-D acquisition configuration, so-called 4-D seismics.

The method according to the invention:

The invention comprises also a method for petrophysical examination of a preferably cylindrical rock sample, comprising the following steps: arranging of said rock sample in a generally cylinder-shaped pressure mantle having one or more pressurising channels for connection to a pump for pressurising a space inside said pressure mantle by means of a pressurising fluid; enveloping said rock sample's cylinder sidewall surface in a fluid-proof flexible sleeve, preferably of rubber, enveloping said rock sample in a fluid-proof way against said pressurising fluid; connecting a first flow channel from a first injection flow pump and a second flow channel to a receiving second flow pump for flushing of flushing gas, preferably nitrogen and/or oil, through the rock sample's preferably cylindrical end surfaces, and inside of said flexible sleeve; connection of acoustic transducers in either ends of said rock sample and generation, and reception, respectively, of acoustic, i.e. seismic waves; computer tomographic x-ray reception of said rock sample's gas content after flushing said flushing gas through said rock sample, by means of X-rays through a generally X-ray transparent central portion of said pressure mantle; in order for examining seismic properties of said rock sample under various degrees of gas content of said flushing fluid or degree of oil content.

Short figure captions

Fig. 1 is a principal illustration of a pressure cell according to the invention, in which a fibre reinforced composite sleeve is shown enclosing a rock sample being subject to pressure from a system illustrated on the left side, and being examined by an acoustic system illustrated on the right side while the rock sample is being examined by a CT-X-ray scanner straight through the sleeve portion of the cell.

Fig. 2a is a longitudinal view of the pressure cell.

Fig. 2b is a section of a first end of said pressure cell and its first end flange at the end of the composite material sleeve, and shows a convex geodome on an insert sleeve in the end flange, at which the geodome is wound around by the fiber reinforced composite sleeve's end portion in order to take up longitudinal forces during pressurising of the cell.

Fig. 2c is a section of a transition between an end cap and an end flange and the O-ring washers and rubber packers used for proofing the pressure cell.

Fig. 2d is a section through the pressure tolerant composite sleeve's transition between the end flange's geodome and the transparent central portion of which the CT scanning shall take place. Fig 2e is an end view of said cap on the end flange, and shows a pressure setting channel and a flow channel in the cap.

Fig. 3a shows calculated computer tomographic sections of a gas distribution through the rock sample. X/L is the section's distance from the first end of said sample, i.e. the end that is situated closest to the source of the flow gas, and is constantly 1/10 of the sample's length in this figure. Sg is the gas saturation and varies in the figure between 5%, 10%, 25% and 50%.

Fig. 3b shows calculated computer tomographic sections of the gas distribution through said rock sample, in which x/L is set for the section taken through 3/10 of the sample's length in this figure. Sg varies as in the previous figure. The gas distribution is homogenous, and neither formation of channels with large concentrations of gas, nor enveloped portions without gas penetration, has been avoided.

Fig. 3c shows calculated computer tomographic sections of gas distribution through said rock sample, in which x/L is 5/10 (i.e. halfway) of the sample's length in this figure. Sg varies as in the previous figure.

Fig. 3d shows calculated computer tomographic sections of the gas distribution through the rock sample, in which x/L is through 7/10 (i.e. more than halfway) of the sample's length in this figure. Sg varies as in the previous figure.

Fig. 3e shows calculated computer tomographic sections of the gas distribution, in which x/L is through 9/10 of the sample's length in this figure. Sg varies as in the previous figure. The gas distribution is still homogenous and not separated between channels and empty areas.

Fig. 4 is an image of a cap with a column that shall extend inwards almost to the middle of the pressure cell, with a cylindrical acoustic end piece that simultaneously allows influx of flow fluid through the circular end of the rock sample. The rock sample and the corresponding cylindrical portion of the acoustic end piece is covered by a rubber sleeve that separates the pressure fluid (usually silicon oil) that confines the entire columnar structure shown in the image, from the gas that flows through the rock. A corresponding end piece (arranged oppositely) with acoustic equipment is arranged at the top of the shown column.

Fig. 5a shows the underside of the acoustic end piece and illustrates how the flow lines run into the rear side of the acoustic end piece. Additionally two acoustic transducers are shown, one for P-waves and one for S-waves.

Fig. 5b shows a side view of the first acoustic end piece (upside down in the image) with the connector to the flowline. The threaded bolt is fixed in the top of the bottom column, the cylinder shaped end (here lowest upper part).

Fig. 6 shows P-wave arrivals in an expanded view of measurements between 32 and 38 milliseconds. Six diagrams are shown with P-wave traces of which the upper one is measured under a confining pressure of 1 MPa and zero gas saturation, and the other five diagrams with P-wave traces are conducted under 5 MPa confining pressure and a gas saturation of 0%, 10%, 20%, 30%, and 40%.

Description of a preferred embodiment of the invention

Fig. 1 shows a system with a pressure cell for rock geophysical or so-called petrophysical analysis. The system is used for analysing a preferably cylinder- shaped oil-bearing rock sample 3. The system with the pressure cell comprises the following features:

The pressure cell comprises a generally cylinder-shaped pressure mantle 7 having a first and a second end portion 7a,7b with caps 2a,2b arranged in the first and the second end portion 7a,7b, respectively. The pressure cell is provided with one or more pressurising channel 12 through one or more of the caps 2a,2b, for connection to a pump 122 for pressurising of the volume space 71 inside of the pressure mantle 7 by means of a pressure fluid 124.

It would hardly be necessary to provide more than one single pressurising channel, as this is not the channel that shall create flow but only for setting pressure on the sample. For enveloping the sample a fluid-proof flexible sleeve 131 (not shown) is made, preferably of rubber, for preventing the pressurising fluid to penetrate into the sample, and for discriminating between a flux through the sample and the pressurising fluid that confines the sample. The rubber sleeve 131 envelopes the rock sample's cylinder sidewall surface 39 toward the pressurising fluid 124.

At least one first and one second flow channel 13a, 13b are arranged through the caps 2a,2b, respectively. An injection pump 132 injects, and a receiving pump 136 receives at the opposite side of the sample and the cell, for flowing flow gas 134 and/or oil, through the rock sample's 3 preferably cylindrical end surfaces 38a,38b and inside of the flexible sleeve 131. The flow gas 134 may in the experiments be nitrogen, and the oil of which the sample is saturated may be decane by means of vacuum pumping techniques or by injecting decane through the measurement system.

The pressure cell has acoustic transducers 14a, 14b arranged in either end 38a,38b of the rock sample 3. These are illustrated in Fig. 5a and are situated inside a cylindrical connecting piece of which an outer cylinder circular end surface is adjacent to the circular end of the cylindrical rock sample. The transducers 14a, 14b generate P- (pressure) and S- (shear) waves through their respective end walls toward and through the sample. In Fig. 1 is shown an electronics unit 140 with a signal generator that transmits electrical signals to the transducer 14a that converts the electrical signals to acoustic P- and/or S- waves. Correspondingly the transducer 14b receives acoustic P- and/or S- waves and converts these to electrical signals that are transmitted back to the electronics unit 140. The electronics unit 140 may be of any kind that may generate and store signals with respect to acoustic measurements using P- and/or S- waves in rock samples. The set-up may be calibrated by means of a sample having known velocities because the acoustic waves run some distance through the connection pieces.

The pressure mantle 7 of the pressure cell has a circumferential central portion 7c being transparent to X-rays 81 ; the pressure cell may thus be arranged in a computer tomograph for simultaneous computer tomographic X-ray examination of gas content and gas distribution during flowing of flow gas 134 through the rock sample 3, so that the rock sample's seismic properties under different pressures of the pressurising fluid 124 and gas content of the flow fluid 134, or degree of oil content, may be examined.

In a preferred embodiment the pressure cell according to the invention is designed so as at least the central portion 7c of the pressure mantle 7 and preferably the entire pressure mantle 7,7a,7b,7c is made in carbon fiber reinforced composite material. The end flanges 102a,102b and the caps 2a,2b are, in the preferred embodiment, made of steel.

The pressure cell according to the embodiment is provided with one or more pressure-proof liner 5,4 preferably made of rubber, along the inner surface of the cylinder-shaped pressure mantle 7, see Fig. 2b, Fig. 2c, and Fig. 2d. The fiber reinforced pressure mantle's end portions 7a,7b envelope each of their corresponding sleeve portion 104a, 104b respectively, with flanges 102a, 102b respectively, constituting attachments for the caps 2a,2b respectively, see Fig. 2b. The sleeve portion 104a,104b comprises in the preferred embodiment of the invention a geodome 106a, 106b respectively, constituting an evenly curved concave portion of the sleeve portion 104a,104b respectively, in a desired distance between the flange 102a,102b respectively and the pressure mantle's transparent central portion 7c, in which the geodome 106a, 106b, respectively at either end of the pressure mantle 7 may be enveloped by the fiber reinforced mantle's end portions 7a,7b respectively. The fiber reinforced mantle's end portions may be cross-wound and somewhat thicker from outside of the place where the geodome starts decreasing in its diameter.

The pressurising fluid 124 is, in the preferred embodiment, a silicon oil having little expansion if it is subject to a sudden drop in pressure.

In the preferred embodiment of the invention, the fluid-proof flexible sleeve 131 which envelopes the rock sample 3 and is proof with respect to the pressurising fluid 124, is also arranged to extend over and for covering the two cylinder portions 142a,142b adjacent to the rock sample's end surfaces 38a,38b. The cylinder portions 142a, 142b respectively, comprise the first flow channel 13a and the second flow channel 13b so as for the flow channels' mouths are arranged adjacent to the rock sample 3 and at the same time situated inside of the flexible sleeve 131 so as for the flowing to be conducted through the sample.

Fig. 4 shows an image of a cap 2a with a column that shall extend almost into the middle of the pressure cell, with a cylindrical acoustic end piece having a circular end portion that simultaneously allows influx of flow fluid through the circular end of the rock sample. A rubber sleeve is pulled over the rock sample and the adjacent cylindrical portion 142a, 142b of the acoustic end pieces, said rubber sleeve separating the pressurising fluid (usually silicon oil) that envelopes the entire columnar structure illustrated in the image, from the gas that flows through the sample. The corresponding end piece with acoustic equipment is arranged oppositely on top of the illustrated column.

In a preferred embodiment of the invention the adjacent cylinder portions 142a, 142b is designed so as to comprise the first flow channel 13a and the second flow channel 13b respectively. The cylinder portions 142a, 142b have a cavity having an inner wall that preferably is parallel with its adjacent end portion 38a,38b respectively, and contains the acoustic transducers 14a, 14b at either end 38a,38b of the rock sample 3. As explained above, transducers are used for generating and reception respectively of acoustic, i.e. seismic waves through the inner wall, through the sample and through the opposite adjacent wall of the opposite cylinder portion.

The pressurising fluid 124 is, in the preferred embodiment of the invention, a silicon oil.

Description of a preferred method according to the invention

According to the preferred embodiment of the invention it comprises a method for rock geophysical examination of a rock sample 3, that comprises the following steps:

* The rock sample 3 is arranged in the above described cylinder-shaped pressure mantle 7 with the pressurising channel 12 connected to the pump 122 for pressurising the volume 71 inside of the pressure mantle 7. A pressurising fluid 124 is used, which may be a silicon oil. ^* The rock sample's 39 is enveloped by a fluid proof flexible sleeve 131 that envelopes the rock sample in a fluid-proof manner toward the pressurising fluid 124. The sleeve 131 preferably is of rubber.

^* The first flow channel 13a from the injection flow pump 132, and a second flow channel 13b to the receiver flow pump 136 are connected for flux of flow gas 134, preferably nitrogen and/or oil, through the rock sample's 3 preferably cylindrical end surfaces 38a,38b, and inside the flexible sleeve 131. The injection flow pump 132 is set to deliver a desired, constant pressure. The receiving flow pump 136 is set to receive a desired, constant amount of flow gas per time unit, under a given pressure, and thus regulates the amount of flow gas being flowed through the rock sample.

* Inside the pressure cell, before the pressure cell is closed and pressure is set, acoustic transducers 14a, 14b are connected to either end 38a,38b of the rock sample 3 for generating and reception respectively of acoustic, i.e. seismic waves. * The pressure cell is placed in a CT-scanner. One may e.g. utilise a CT- scanner usually used for scanning of human beings or animals. A computer tomographic x-ray exploration is conducted, by means of X-rays 81 through the X-ray transparent circumferential central portion 7c of the pressure mantle 7, of the rock sample's gas contents after flushing by flow gas 134 through the rock sample 3.

* Thus the rock sample's seismic properties under different degrees of gas content of the flow fluid (134) may be examined, as shown in Figs. 3a, b, c, d, and e.

The rock sample should be prepared as a straight cylindrical sample because this provides good contact with the connecting pieces with the acoustic transducers with flow channels.

The rock sample, which may be a porous sandstone, is prepared by partially saturating with decane before mounting it in the pressure cell.

In a preferred embodiment of the invention, series of acoustic and computer tomographic measurements may be conducted under different pressures from the pressurising fluid 124.

Fig. 6 shows P-wave arrivals in an expanded section of P-wave traces between 32 and 38 microseconds. Six diagrams are shown, with P-wave traces of which the upper is measured under a confining pressure of 1 MPa and zero gas saturation, and the additional five P-wave traces are measured under 5 MPa confining pressure and gas saturation of 0%, 10%, 20%, 30%, and 40%. This is shown as two traces in each diagram; one with raw data (the more uneven), and a filtered smoother curve. Please notice that the resolution in each diagram increases downwardly due to decreasing maximum amplitude for the P-wave arrival. The plots show that there is a distinct delay of the P-wave arrival with increasing gas saturation (together with an attenuation of the P-wave amplitude). With the invention one has achieved to conduct measurements of seismic wave velocities in geological samples from a reservoir while, by means of CT-scanning, observing the gas distribution in the sample after flushing with a desired degree of gas saturation, all under pressures that may simulate reservoir pressures. These measurements may be included in interpretations of in-situ gas saturation based on repeated seismic explorations of a reservoir by use of so-called 4-D seismics in which is utilised a fixed 3-D acquisition configuration with long time intervals, e.g. several months or years, along with production from a gas-bearing reservoir. A better comprehension of the distribution of P-wave velocities and S-wave velocities provides improved processing of the seismic data, and thus a better image of the reservoir during production. The measurements of P- and S- wave velocities at gas saturations being equal to the expected gas saturation of the reservoir and at the expected reservoir pressure is also important if seismic data shall be related to wells of which geological samples are available in the form of drill cuttings or core samples, particularly while an image of a probably representative gas distribution in the sample now may be available.

Claims

1. A pressure cell for petrophysical analysis of a preferably cylindrical oil petroleum-bearing rock sample (3), comprising the following features: a mainly cylinder-shaped pressure mantle (7) with a first and a second end portion (7a,7b) and two caps (2a,2b) arranged at said first and said second end portion (7a,7b) respectively; one or more pressurising channel (12) through one or more of said caps (2a,2b), for being connected to a pump (122) for pressurising the volume (71) inside said pressure mangle (7) by means of a pressurising fluid (124); a fluid-proof flexible sleeve (131), preferably of rubber, enveloping the rock sample's cylinder sidewall surface toward the pressurising fluid (124); a first and a second flow channel (13a, 13b) arranged thro the caps (2a,2b) respectively, with an injection flow pump (132) for injecting and a receiving flow pump (136) for reception, for flowing of flow gas (134) and/or oil, through the rock sample's (3) preferably cylindrical circular end surfaces (38a, 38b) and inside the flexible sleeve (131); characterized in that the pressure cell has acoustic transducers (14a) for being arranged in either end (38a, 38b) of said rock sample (3) for generating and reception of P (pressure) and S (shear) waves; said pressure mantle (7) has a circumferential central portion (7c) being generally transparent to X-rays (81); for simultaneous computer tomographic X-ray examination of gas content and gas distribution after flowing of said flow gas (134) through said rock sample (3), so as for said rock sample's seismic properties under various pressures from said pressurising fluid (124), and gas contents of said flow fluid (134) or degree of oil content, may be examined.

2. The pressure cell of claim 1 , in which said central portion (7c) of said pressure mantle (7) and preferably the entire of said pressure mantle (7,7a,7b,7c) is formed in a carbon fiber reinforced composite material.

3. The pressure cell of claim 1 , with one or more pressure-proof lining (5,4) preferably of rubber, along the inner surface of said cylinder-shaped pressure mantle (7).

4. The pressure cell of claim 1 , of which said end portions (7a,7b) envelope each their sleeve portion (104a, 104b respectively) with flanges (102a, 102b respectively) constituting an attachment for said caps (2a, 2b respectively).

5. The pressure cell of claim 4, of which said sleeve portion (104a, 104b) comprises a geodome (106a, 106b respectively) constituting an evenly convex portion of said sleeve portion (104a, 104b) in a desired distance between said flange (102a, 102b respectively) and said pressure mantle's transparent central portion (7c), in which said geodome (106a,106b respectively) is enveloped by said pressure mantle's end portions (7a,7b respectively).

6. The pressure cell of claim 1 , in which said pressurising fluid is a silicon oil.

7. The pressure cell of claim 1 , in which said fluid proof flexible sleeve (131) enveloping said rock sample (3) and being fluid proof toward said pressurising fluid (124) is also arranged for extending over to cover said two cylindrical portions (142a, 142b) adjacent to said end surfaces (38a,38b) of said rock sample, said adjacent cylinder portions (142a, 142b) comprising said first flow channel (13a) and said second flow channel (13b), respectively, so as for said flow channels' mouths toward said rock sample (3) also are situated inside said flexible sleeve (131).

8. The pressure cell according to claim 7, in which said adjacent cylinder portions (142a, 142b) comprising said first flow channel (13a) and said second flow channel (13b) have a cavity with an inner wall parallel to its adjacent corresponding end surface (38a,38b respectively), and contains acoustic transducers (14a, 14b) by either end (38a,38b) of said rock sample (3) for generating and reception respectively of acoustic, i.e. seismic waves through said inner wall.

9. The pressure cell according to claim 1 , in which said pressurising fluid (124) is a silicon oil.

10. A method for petrophysical examination of a preferably cylinder-shaped rock sample (3), comprising the following steps: arranging said rock sample in a generally cylinder-shaped pressure mantle (7), having one or more pressurising channels (12) for connection to a pump (122) for pressurising a volume (71) inside said pressure mantle (7) by means of a pressurising fluid (124); enveloping said rock sample's cylindrical side surface in a fluid proof flexible sleeve (131), preferably of rubber, enveloping said rock sample in a proof manner toward said pressurising fluid (124); connecting a first flow channel (13a) from an injection flow pump (132) and a second flow channel (13b) to a reception flow pump (136) for flowing of flow gas (134), preferably nitrogen and/or oil, through said rock sample's (3) preferably cylindrical end surfaces (38a,38b), and inside said flexible sleeve (131); characterized by connecting acoustic transducers (14a, 14b) at either end (38a,

38b) of said rock sample (3) and generating and receiving, respectively, of acoustic, i.e. seismic waves; conducting a computer tomographic examination of said rock sample's gas content after flowing a flow gas (134) through said rock sample (3), by means of

X-rays (81) through a generally X-ray transparent circumferential central portion

(7c) of said pressure mantle (7); so as for examining said rock sample's seismic properties under various degrees of gas content of said flow fluid (134), or degree of oil content.

11. The method of claim 10, in which series of acoustic and computer tomographic measurements are conducted under various pressures from said pressurising fluid (124).

12. The method of claim 11 , in which said pressure of said pressurising fluid (124) is generally like a reservoir pressure in a petroleum reservoir.

13. The method of claim 10, in which said fluid proof flexible sleeve (131) enveloping said rock sample (3) and is fluid-proof against said pressurising fluid (134) is also arranged for extending over to cover two cylinder portions (142a, 142b) adjacent to said rock sample's end surfaces (38a,38b), of which said cylinder portions (142a, 142b) comprise said first flow channel (13a) and said second flow channel (13b) so as for said flow channels' (13a, 13b) mouths towards said rock sample (3) are situated within said flexible sleeve (131).

14. The method according to claim 10, in which said adjacent cylinder portions (142a, 142b) comprising said first flow channel (13a) and said second flow channel (13b) respectively, has a cavity having an inner wall parallel with one of the adjacent end surfaces (38a,38b respectively) and contains acoustic transducers (14a, 14b) at either end (38a,38b) of said rock sample (3) for generation and reception respectively of acoustic, i.e. seismic waves through said inner wall.

15. The method according to claim 10, in which emission and reception of P- waves is made, i.e. so-called longitudinal or pressure waves.

16. The method according to claim 10, in which emission and reception of S- waves is made, i.e. so-called transversal or shear waves.