X-RAY TOMOGRAPHY DEVICE

Abstract

An X-ray tomography device for providing a 3D tomography image of a sample comprising a X-ray source, a cell, a photon detector and a processing unit. The X-ray source is monochromatic and has a photon beam solid angle higher than 0.1 degree. The processing unit computes the 3D tomography image on the basis of acquired images corresponding to a plurality of cell angles.

Description

PRIORITY CLAIM

The present application is a National Phase entry of PCT Application No. PCT/EP2012/060439, filed Jun. 1, 2012, which claims priority from U.S. Provisional Patent Application No. 61/492,268, filed Jun. 1, 2011, and U.S. Provisional Patent Application No. 61/492,272, filed Jun. 1, 2011, said applications being hereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention concerns an X-ray tomography device.

BACKGROUND OF THE INVENTION

The present invention concerns an X-ray tomography device adapted to petrophysics application, such as to study the flow of fluids into a porous medium. For example, the aim is to study the multiphase flow of a mix of two or three fluids inside a porous medium: a mix of any two of water, gas and oil or the three of them.

The known X-ray tomography systems are adapted to study the morphology of rock pores, to identify the minerals comprised into the rock sample (the porous medium) or the topology of various fluid phases present in the rock sample under static (ie non flowing) conditions.

Because of use of polychromatic X-ray source, these systems develop approximative results due to non linear absorption and therefore image artefacts. The quality of images is therefore strongly impacted, especially with respect to the identification of materials (fluid or rock). The laboratory sources used in these systems have a very low photon flux that requires a very long recording time for the acquisition of high resolution images. These systems thus do not provide an acquisition time compatible with the study of multiphase flow in porous media. These systems also use image reconstruction algorithms that must deal with large volumes of data to calculate only one 3D tomography image. Moreover the strong diverging angle of polychromatic X-ray microtomographs introduces artifacts in the 3D image reconstructions resulting from compromises in the complex reconstruction process in a very diverging geometry. These systems are unable to provide rapidly 3D tomography images for generating a movie of fluid transport within the porous medium sample.

Consequently, these devices are only able to provide static characteristic values inside the porous medium, such as irreducible water saturation or residual oil saturation. They are unable to visualise the flow of a fluid or the flow of a plurality of fluids inside the porous medium.

Synchrotron X-ray sources provide enough photon flux.

But, these devices provide a parallel photon beam having a very small focus spot size, varying about a few mm², that is incompatible with a large field of view needed to observe macroscopic flow of fluids inside a porous medium and especially in realistic porous media where dispersion, anisotropy, viscous fingering requires to be able to record the whole sample view. Additionally, these devices have huge size, are very expensive and they are for scientific use only. It is difficult to have access to such instrument for analysis of a petroleum porous medium where experimental time may require waiting for several weeks up to several months.

OBJECTS AND SUMMARY OF THE INVENTION

One object of the present invention is to provide an X-ray tomography device that can be used to analyse the flow of fluids inside a porous medium, such as a rock sample of a geological formation.

To this effect, the X-ray tomography device according to the invention is adapted for providing a 3D tomography image of a sample, and it comprises:

a X-ray source emitting a photon beam in the direction of a beam axis, said X-ray source being a near monochromatic source and said photon beam having a solid angle higher than 0.1 degree around said beam axis,
a cell adapted to include a porous sample to be imaged, said cell being situated inside the photon beam and being able to rotate around a cell axis that is substantially perpendicular to the beam axis, and being adapted to enable the porous sample to be flooded by at least one fluid,
a photon detector receiving a transmitted photon beam that is transmitted through said cell, said photon detector providing at least one acquired image for each angle of a plurality of cell angles, and said acquired images being taken during a length of time lower than ten minutes, and
a processing unit that computes the tomography image on the basis of the acquired images corresponding to the plurality of cell angles.

Thanks to these features, the X-ray tomography device is able to have simultaneously, a high level of photons and a large field of view.

It is also able to have a very high level of photons and a small field of view permitting to work in stitching mode or local tomography mode

The volume analysed can be imaged during a length of time lower than ten minutes, which is very competitive with what is achieved with a 3^rd generation synchrotron,

It is therefore possible to get a plurality of 3D tomography images showing a movie of the flow of fluids inside the porous medium of the sample. Moreover, it may possible to scan the whole volume and to identify areas of fluid fluctuations before to zoom in to reach the best resolution.

In various embodiments of the X-ray tomography device, one and/or other of the following features may optionally be incorporated.

According to an aspect, the monochromatic and highly brilliant X-ray source is a compact light source using a collision between a laser beam and an opposing electron beam.

According to an aspect, the length of time for the volume analysis is lower than one minute.

According to an aspect, the processing unit is computing the tomography image during a time period lower than the length of time of used for producing the acquired images corresponding to the plurality of cell angles.

According to an aspect, the cell has a size comprised in the range of 0.3 cm to 20 cm, and preferably in the range of 0.6 cm to 10 cm.

According to an aspect, the cell is made of a material in a list comprising the beryllium, beryllium alloys, and a carbon-carbon composite.

According to an aspect, the cell comprises means for heating the sample to a temperature higher than 650° Celsius and means for pressuring the cell to a pressure higher than 1000 bars,

According to an aspect, the photon detector comprises a CCD of at least ten megapixels.

According to an aspect, the X-ray tomography device further comprises a grating based interferometer situated between the cell and the photon detector.

According to an aspect, the X-ray tomography device further comprises a microscope situated between the cell and the photon detector.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be apparent from the following detailed description of one of its embodiments given by way of non-limiting example, with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic view of a X-ray tomography device according to the invention, and

FIG. 2 is an example of a 3D tomography image provided by the device of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

In the various figures, the same reference numbers indicate identical or similar elements. The direction Z is a vertical direction. A direction X or Y is a horizontal or lateral direction. These are indications for the understanding of the invention.

The X-ray tomography device 1 shown on the FIG. 1 comprises:

a X-ray source 2 emitting a photon beam PB in the direction of a beam axis BA,
a cell 3 comprising a porous sample 10 to be imaged,
a photon detector 4 receiving a transmitted photon beam TPB that is transmitted through said cell 3, and
a processing unit 5 computing the 3D tomography image on the basis of the acquired images provided by the photon detector 4.

The X-ray source 2 is preferably a monochromatic source, so that the cell is illuminated with a high level of brilliance by an X-ray beam of small diverging angle. The polychromatic sources spread their energy into a wide frequency bandwidth. It is possible to produce a natural monochromatic flux of photons or to filter the photon beam PB to obtain a quasi-monochromatic photon beam. However, this decreases a lot the photon flux. The monochromatic source concentrates the energy on a very narrow frequency bandwidth. The length of time needed by a detector for acquiring an image is then very low, and then it is compatible with multiphase flow tracking.

The photon beam PB generated by said X-ray source 2 is a diverging cone beam having a solid angle SA that is wide, and for example higher than 0.1 degree or a few mrad around the beam axis BA. It is possible to illuminate a complete cell having a size of 10 cm at a distance from the X-ray source 2 that is a small distance, for example lower than 25 m, and preferably lower than 10 m. The solid angle SA may be higher than 0.5 degree.

Preferably, the X-ray source is able to emit a photon beam having a high level of energy, for example comprised between 10 and 200 KeV. The photon flux may be higher than 10⁸ photons/s near the photon detector 4, and preferably higher than 10¹¹ photons/s. The device is then able to image thick cells and thick samples (between 0.3 cm and 10 cm). The X-ray source may have a tuneable X-ray energy level.

For example, the X-ray source 2 may be a compact photon source using collision between a laser beam and an opposing electron beam. Such X-ray source 2 preferentially uses Inverse Compton Effect (Thomson scattering) to generate a natural monochromatic photon beam PB having a high level of energy. The main advantage of such X-ray sources is that they are very compact compared to classical synchrotron devices. Known Table-top synchrotron device using such physical properties are the “Compact Light Source” (CLS) from Lyncean Technologies Inc., but filtering very brilliant polychromatic flux such “Mirrorcle” from Photon Production Lab may produce a quite similar result.

The X-ray source 2 may be tuneable according to the energy level (brilliance) so as to proceed to various experiments above the porous sample.

The cell 3 is situated inside the photon beam PB. The cell position can be controlled via a rotation mean 8 (Z rotation) and a translation mean 9 (XYZ translations).

Thanks to the rotation mean 8, the cell 3 can be rotated around a cell axis CA substantially parallel to axis Z and perpendicular to the X axis, the beam axis BA on FIG. 1. The cell 3 is rotated of a cell angle around the cell axis CA. The detector 4 can then provide images from the cell (sample) from various view angles and the processing unit 5 can compute a 3D tomography image of the sample.

Thanks to the translation mean 9, the cell 3 can be positioned inside the photon beam PB.

The cell 3 can be placed or positioned between a first distance from the source 2 and a second distance from the source 2. The first distance may be short and the cell 3 is close to the X-ray source 2 (see position P1 on FIG. 1). This configuration optimizes the maximal flux in high resolution (stitching mode or local tomography). The second distance is much higher than the first distance, the cell 3 being away from the X-ray source 2 In this configuration, it is possible to illuminate the whole region of interest permitting to easily switch from a global tomography mode to local tomography based on observed changes induced by the multiphase flow. The acquisition time in this last configuration is less performing than the first one but it permits to analyse the sample in interactive mode

For example, the cylindrical rock sample contained inside the cell 3 has a size comprised in the range of 0.3 cm to 10 cm. The size is preferably in the range 0.6 cm to 3 cm in diameter and in the range of 2 cm to 10 cm in length. The size of the rock sample is chosen big enough to study multiphase transport properties at a scale representative of macroscopic transport properties in the said rock and small enough to enable high resolution tomography of the sample in a length of time that allows imaging the whole sample in less than ten minutes: acquiring the images from the plurality of cell angles within said length of time.

The cell 3 is for example a tube extending along the cell axis CA, said tube receiving the sample of porous medium. The cell 3 comprises an input conduct 6 that input the fluid to the cell 3 and an output conduct 7 that outputs the fluid from the cell. The cell is adapted to be crossed by the fluid.

The X-ray tomography device 1 also comprises hydraulic devices to provide the fluid to the input conduct and to get back this fluid from the output conduct. These hydraulic devices can also add physical conditions to the fluid: temperature, pressure. To this end, these hydraulic devices include a thermal regulator, and a pressure regulator. The sample 10 inside the cell 3 can be tested according to the physical conditions of the geologic formation.

The thermal regulator can heat the sample up to a temperature of 650° Celsius.

The pressure regulator can pressurize the sample up to a pressure of 1000 bars.

The cell 3 is a sort of Hassler cell meeting the requirements of X-ray tomography imaging. The cell 3 is adapted to enable the porous sample 10 to be flooded by one or several fluids under controlled pressure and temperature conditions.

The cell 3 is made of a material that is transparent to the X-ray photon beam. Advantageously, it is made of beryllium, or beryllium alloy such beryllium aluminium alloy, or a carbon-carbon composite.

The photon detector 4 can be tuned to have a sensitivity corresponding to the sample and fluids. Small variations of fluid densities can be therefore detected. Oil and water can be distinguished in the acquired images provided by the photon detector 4 using very fast classical absorption mode, or phase mode or dark field mode.

The photon detector 4 is providing at least one image for each angle of a plurality of cell angles. All these acquired images are taken during a length of time lower than ten minutes for the whole volume to analyse. It is assumed that the state of the sample does not change much during this length of time: the fluid movements inside the porous medium remain very small. All the acquired images from various cell angles are then supposed to represent a unique state of the sample.

Advantageously, the length of time is lower than one minute. The images represent more precisely a unique state of the sample, and the tomography device is acquiring images in real time and stores all these images for the processing unit 5.

The photon detector 4 can be a flat panel, or an X-ray CCD (Charge-Coupled Device) or a CMOS. The photon detector 4 has a high resolution. It is for example a CCD having at least ten megapixels. The acquired images are enough accurate to visualise at the same time (simultaneously) the complete field of view of the sample or very small details inside the sample thanks to a stitching mode or local tomography process. In this way several ways are possible to scan the sample, and the acquired image can be taken in a very short length of time and the acquired image is enough exposed to photon flux to show small details and small variations of densities.

The processing unit 5 is computing the 3D tomography image on the basis of the acquired images corresponding to the plurality of cell angles. Such reconstruction method is known and efficient (fast and providing a very good image quality) benefiting from the quasi parallel approximation. Examples of reconstruction methods can be found in the following document:

A. C. Kak and Malcolm Slaney, Principles of Computerized Tomographic Imaging, IEEE Press, 1988.

In the present invention, the processing unit 5 may comprise parallel computing means so that the 3D tomography image can be computed during a very short time period. This high performance for reconstruction time and imaging are mainly due to the quasi parallel beam geometry. The time period can be lower than the length of time for acquiring the images from various cell angles of the sample. The X-ray tomography device is therefore generating real time 3D tomography images, and can visualize a real time movie showing the fluids movements inside the porous medium.

The tomography device 1 may comprise a microscope to obtain high (accurate) resolutions. In that case, the resolution may reach 200 nm of voxel size which is the theoretical limit of microscopes due to Rayleigh criterion.

The tomography device 1 may also comprise a grating based interferometer, situated between the cell 3 and the microscope or the photon detector 4. Such gratings improve the contrast of the acquired images by adding absorption contrast image, phase contrast image and dark field contrast image: materials having similar densities can be distinguished on the acquired images by photon detector 4. In that case, the same resolution than obtained only by the microscope can be obtained.

The gratings, the microscope and the detector 4 compose an optical station of the X-ray tomography device 1.

The FIG. 2 is showing an example of a projection of 3D image 20 provided by the X-ray tomography device 1 of the invention. The 3D tomography image comprises various gray levels or various colours, each representing a constituent of the sample. The reference 21 represents the porous medium. The reference 22 represents a first fluid having a first density. The reference 23 represents a second fluid having a second density.

The embodiments above are intended to be illustrative and not limiting. Additional embodiments may be within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention.

Claims

1. An X-ray tomography device for providing a 3D tomography image of a sample, said device comprising:

a X-ray source (2) emitting a photon beam in the direction of a beam axis, said X-ray source being a near monochromatic source and said photon beam having a solid angle higher than 0.1 degree around said beam axis,

a cell (3) adapted to include a porous sample to be imaged, said cell being situated inside the photon beam and being able to rotate around a cell axis that is substantially perpendicular to the beam axis, and being adapted to enable the porous sample to be flooded by at least one fluid,

a photon detector (4) receiving a transmitted photon beam that is transmitted through said cell, said photon detector providing at least one acquired image for each angle of a plurality of cell angles, and said acquired images being taken during a length of time lower than ten minutes, and

a processing unit (5) that computes the tomography image on the basis of the acquired images corresponding to the plurality of cell angles.

2. The X-ray tomography device according to claim 1, wherein the monochromatic and highly brilliant X-ray source is a compact light source using a collision between a laser beam and an opposing electron beam.

3. The X-ray tomography device according to claim 1, wherein the length of time for the volume analysis is lower than one minute.

4. The X-ray tomography device according to claim 1, wherein the processing unit is computing the tomography image during a time period lower than the length of time of used for producing the acquired images corresponding to the plurality of cell angles.

5. The X-ray tomography device according to claim 1, wherein the cell has a size comprised in the range of 0.3 cm to 20 cm, and preferably in the range of 0.6 cm to 10 cm.

6. The X-ray tomography device according to claim 1, wherein the cell is made of a material in a list comprising the beryllium, beryllium alloys, and a carbon-carbon composite.

7. The X-ray tomography device according to claim 1, wherein the cell comprises means for heating the sample to a temperature higher than 650° Celsius and means for pressuring the cell to a pressure higher than 1000 bars,

8. The X-ray tomography device according to claim 1, wherein the photon detector comprises a CCD of at least ten megapixels.

9. The X-ray tomography device according to claim 1, further comprising a grating based interferometer situated between the cell and the photon detector.

10. The X-ray tomography device according to claim 1, further comprising a microscope situated between the cell and the photon detector.