WO2018039038A1

WO2018039038A1 - Measuring contact angles beteween a solid-fluid pair using x-ray imaging of the solid-fluid-fluid interface inside a capillary

Info

Publication number: WO2018039038A1
Application number: PCT/US2017/047379
Authority: WO
Inventors: Meinhard Bayani R. CARDENAS; Philip C. BENNETT; Kuldeep CHAUDHARY; Eric J. GUILTINAN
Original assignee: Board Of Regents, The University Of Texas System
Priority date: 2016-08-26
Filing date: 2017-08-17
Publication date: 2018-03-01

Abstract

A method for measuring contact angles between a solid-fluid pair, such as at reservoir pressure-temperature conditions, using X-ray images of a specific solid-fluid-fluid configuration. A column is formed out of a mineral or a rock. A core holder with a drilled capillary or a slot is placed vertically inside the column. A first and a second fluid is then injected within the capillary or slot. An X-ray scan of a solid-fluid-fluid interface in the capillary or slot is performed to generate image data, where the solid-fluid-fluid-interface corresponds to an interface of a material of the core holder, the first fluid and the second fluid. A contact angle at the solid-fluid-fluid interface is then calculated using the generated image data. As a result, contact angles defined by a solid-fluid pair interface under conditional typical of deep geologic environments can be measured in a fast and inexpensive manner.

Description

MEASURING CONTACT ANGLES BETWEEN A SOLID-FLUID PAIR USING X-RAY IMAGING OF THE SOLID -FLUID -FLUID INTERFACE INSIDE A CAPILLARY

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 62/379,914, entitled "Contact Angle Measurements for a Solid-Fluid-Fluid System," filed August 26, 2016, which is incorporated by reference herein in its entirety.

GOVERNMENT INTERESTS

[0002] This invention was made with government support under Grant No. DE-SC0001114 awarded by the Department of Energy. The U.S. government has certain rights in the invention.

TECHNICAL FIELD

[0003] The present invention relates generally to measuring contact angles between minerals/materials and two fluids, and more particularly to measuring contact angles between a solid-fluid pair, such as at reservoir pressure-temperature conditions, using X-ray images of a specific solid-fluid-fluid configuration.

BACKGROUND

[0004] Measuring contact angles between minerals/materials and two fluids is important for characterizing, predicting and modeling multiphase flow in a solid-multi-fluid system, such as in geologic porous media, which includes petroleum reservoirs and aquifers. However, in such underground environments, high temperatures and high pressures may be present. As a result, measurements of contact angles under ambient conditions are potentially not applicable to measurements of contact angles in such underground environments.

[0005] Subsurface multiphase fluid flow and transport is largely controlled by the wettability of the aquifer or reservoir matrix. Wettability is the measure of one fluid's affinity relative to another competing fluid to spread or contract on a solid surface. An increasingly relevant example of multiphase flow phenomena is that which occurs during the injection and storage of C0₂ in deep brine-saturated geologic reservoirs which is seen as a viable strategy for curbing anthropogenic C0₂ emissions to the atmosphere. The mechanisms for the permanent storage of C0₂ in subsurface brine reservoirs are: (a) structural or stratigraphic trapping, (b) residual or capillary trapping of CO?., (c) solubility trapping, and (d) mineral trapping. To understand the effectiveness of these mechanisms, fundamental insight regarding the controls on CQ₂ transport and its storage potential at the pore-scale (lO^"4 - 10^" ' m) is needed, and these are underpinned by wetting properties,

[0006] At the pore-scale, capillary forces typically control fluid displacement and trapping characteristics. The equilibrium force balance between fluids occupying a cylindrical mineral surface is described by the Young-Laplace equation:

where Pc is the capillary pressure, ju is interfacial tension between fluid 1 and fluid 2, r is the cylinder radius, and θ_β is the equilibrium contact angle, i.e., the measure of wettability.

[0007] The contact angle or the contact line of the two fluids' intersection with the solid surface is the macroscopic manifestation of the microscopic force balance between interfacial tension (or surface free energies) of the fluids and the solid (denoted by y) given by the Young equation:

[0008] Wetting fluids have 9_e <90° and fluids with 0_e >90° are nonwetting.

[0009] Wettability is one of the most significant factors controlling all four mechanisms for C0₂ storage outlined above. For example, a θ_ε >90° for seal or cap rocks will lead to negative capillar}' pressure and could potentially result in ineffective structural or stratigraphic trapping, C0₂-wet or C0₂-mixed-wet media is known to critically limit the C0₂ capillary trapping potential. Furthermore, the efficiency of mechanisms (c) and (d) is dependent on the success of mechanisms (a) and (b).

[0010] Experimental measurements of 9_e has generally been carried out using direct imaging, such as the conventional sessile drop method where a drop of a dense fluid is placed on a solid mineral surrounded by a lighter density fluid. The contact line of the fluid-fluid interface with the mineral surface is used to measure 6_e using axis symmetric drop shape analysis.

[0011] The fluid volume injected controls the drop size, and a similar injected volume may result in different drop sizes depending on pressure-temperature (P-T) conditions. However, different contact lengths/drop sizes can lead to differences in measured 6_e. Reproducibility of experimental results, i.e., recovering a drop with precisely the same volume and contact length, can be a challenge in the sessile drop method. Wettability measurements can be fraught with uncertainty leading to a wide range of values and typically poor agreement between different studies. Furthermore, the sessile drop method is subject to the effects of buoyancy and gravitational forces leading to inaccurate results. Thus, improvement of existing approaches or perhaps new robust techniques for measuring contact angles between minerals/materials and two fluids are welcome particularly for high P-T conditions representative of reservoirs.

SUMMARY

[0012] In one embodiment of the present invention, a method for measuring contact angles comprises forming a column out of a mineral or a rock. The method further comprises placing a core holder with a drilled capillary or a slot vertically inside the column. The method additionally comprises injecting a first fluid within the capillary or the slot. Furthermore, the method comprises injecting a second fluid within the capillary or the slot. Additionally, the method comprises performing an X-ray scan of a solid-fluid-fluid interface in the capillary or the slot to generate image data, where the solid-fluid-fluid-interface corresponds to an interface of a material of the core holder, the first fluid and the second fluid. In addition, the method comprises calculating a contact angle at the solid-fluid-fluid interface using the generated image data.

[0013] The foregoing has outlined rather generally the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the present invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which may form the subject of the claims of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which:

[0015] Figure 1 illustrates a system for measuring the contact angles between minerals/materials and two fluids, such as at reservoir pressure-temperature conditions, in accordance with an embodiment of the present invention;

[0016] Figure 2 is a flowchart of a method for measuring the contact angle defined by the solid- fluid pair interface using the system of Figure 1 in accordance with an embodiment of the present invention;

[0017] Figure 3A is a diagrammatic sketch of the setup for imaging the solid-fluid-fluid interface inside a column in accordance with an embodiment of the present invention;

[0018] Figure 3B is an image of a quartz core holder with a capillary in accordance with an embodiment of the present invention;

[0019] Figure 3C is an X-ray computed tomography (CT) image showing the magnified view of a quartz -brine-C0₂ interface inside the quartz capillary in accordance with an embodiment of the present invention;

[0020] Figure 3D is an image illustrating the definition and calculation of the contact angle, θ_ε, in accordance with an embodiment of the present invention.

[0021] Figures 4A-4E are X-ray images of fluid-fluid- sol id interfaces at room conditions (25°C and 0.1 MPa) for quartz-air-brine, borosilicate glass-air-brine, shale-air-brine, PTFE-air- deionized (DI) water and PTFE-air-brine, respectively, in accordance with an embodiment of the present invention; and

[0022] Figures 5A-5F are X-ray images of solid-fluid-fluid interfaces at reservoir conditions (60-71° C and 12.4-22.8 MPa) for quartz-C0₂-brine, muscovite plates-C0₂-brine, borosilicate glass-C0₂-brine, shale-C0₂-brine, PTFE-C0₂-brine and PEEK-C0₂-brine, respectively. DETAILED DESCRIPTION

[0023] As stated in the Background section, previous techniques for measuring the contact angles between a solid-fluid pair are subject to the effects of buoyancy and gravitational forces leading to inaccurate results. Furthermore, such techniques that measure contact angles under ambient conditions are potentially not applicable to measurements of contact angles in underground environments.

[0024] The principles of the present invention provide a means for measuring contact angles between minerals/materials and two fluids, such as at reservoir pressure-temperature conditions, using X-ray images of a specific solid-fluid-fluid configuration. The present invention ensures that capillary forces, whose balance controls the contact angle, dominate which makes the measurements using the present invention more accurate. The present invention is particularly suitable for situations where one fluid is "supercritical" (low density and high viscosity).

[0025] Referring now to the Figures in detail, Figure 1 illustrates a system 100 for measuring the contact angles between minerals/materials and two fluids, such as at reservoir pressure- temperature conditions, in accordance with an embodiment of the present invention.

[0026] System 100 includes an X-ray imaging system 101, such as a three-dimensional X-ray imaging system (e.g., computed tomography scanner, such as Xradia® MicroXCT-400 scanner) whose image data is sent to a computing system 102. A description regarding the internal staicture or functionality of X-ray imaging system 101 is not discussed herein for the sake of brevity as such knowledge is known in the art. The present invention may utilize any type of X- ray imaging system that is capable of rendering image data, such as in the form of a radiograph or three-dimensional cross-sectional images. Embodiments applying such X-ray imaging systems would fall within the scope of the present invention.

[0027] Computing system 102 may be any type of computing device (e.g., portable computing unit, Personal Digital Assistant (PDA), smartphone, laptop computer, mobile phone, navigation device, game console, desktop computer system, workstation, Internet appliance and the like) configured with the capability of computing the contact angle of a specific solid-fluid-fluid configuration using the X-ray image data provided by X-ray imaging system 101. A description regarding the internal staicture or functionality of computing system 102 is not discussed herein for the sake of brevity as such knowledge is known in the art. [0028] Figure 1 further illustrates forming a column 103 out of a mineral or rock 104, where a core holder 105 with a drilled capillary 106 is inserted within column 103. A discussion regarding such aspects is provided further below.

[0029] Figure 1 additionally illustrates the injection of a first fluid 107 and a second fluid 108 in capillary 106, where an X-ray scan of the solid-fluid-fluid interface (105/107/108), where the "solid" refers to the material of core holder 105, is performed to generate an image (image data), which is sent to computing system 102 to calculate the contact angle defined by the solid-fluid pair interface as discussed further below.

[0030] A description of a method for measuring the contact angle defined by the solid-fluid pair interface using system 100 of Figure 1 is provided below in connection with Figure 2.

[0031] Figure 2 is a flowchart of a method 200 for measuring the contact angle defined by the solid-fluid pair interface using system 100 of Figure 1 in accordance with an embodiment of the present invention.

[0032] Referring to Figure 2, in conjunction with Figure 1, in step 201, a column 103 is formed out of a mineral or rock 104 as shown in Figure 3 A. Figure 3 A is a diagrammatic sketch of the setup for imaging the solid-fluid-fluid interface inside column 103 in accordance with an embodiment of the present invention.

[0033] In step 202, a core holder 105 (e.g., quartz core holder) with a drilled capillary 106 (e.g., 1 to 1.5 mm inner diameter (ID)) is placed vertically inside column 103 as shown in Figures 3 A and 3B. Figure 3B is an image of a quartz core holder 105 with capillary 106 in accordance with an embodiment of the present invention. In one embodiment, core holder 105 is pervious to X- rays. In one embodiment, the material of core holder 105 consists of polyether ether ketone (PEEK), which is capable of handling potentially corrosive fluids, such as supercritical C0₂. In one embodiment, the material of core holder 105 consists of one of the following: quartz, muscovite, shale, silica glass, borosilicate glass or polytetrafluoroethylene (PTFE).

[0034] In one embodiment, capillary 106 is produced either entirely hollow or with one end plugged or solid, such that the capillary force that the fluids are subject to are dominant over gravitational or buoyancy forces, i.e., the Eotvos number or Bond number is small (e.g., < 1). Alternatively, two parallel planar surfaces can be used with a small slot between the planar surfaces so that the Bond number is < 1. The precision spacing of the slot or the capillary diameter allows for controlling the Bond number. By having the Bond number < 1, the influence of body forces (e.g., buoyancy and gravity) is removed thereby allowing for more accurate contact angle measurements.

[0035] In step 203, a first fluid 107 (e.g., brine, deionized water, sodium chloride brine) is injected within capillary 106 or the slot.

[0036] In step 204, a second fluid 108 (e.g., air, carbon dioxide) is injected within capillary 106 or the slot at a desired pressure to pressurize the system in core holder 105 so as to be able to withstand high pressure and temperature as shown in Figure 3C. Figure 3C is an X-ray computed tomography (CT) image showing the magnified view of a quartz-brine-air interface (105/107/108) inside the quartz capillary 106 in accordance with an embodiment of the present invention. As illustrated in Figure 3C, first fluid 107 corresponds to brine and second fluid 108 corresponds to air. Also, as illustrated in Figure 3C, the "solid" corresponds to quartz, which is the material of core holder 105.

[0037] In step 205, core holder 105 is heated at a desired temperature, such as by using a heating sleeve with precise temperature control.

[0038] In step 206, an X-ray scan of the solid-fluid-fluid interface (105/107/108) in capillary 106 or the slot is performed by X-ray imaging system 101 to generate an image (image data).

[0039] In step 207, the image data is sent to computing system 102 by X-ray imaging system 101.

[0040] In step 208, surfaces on the image (e.g., surfaces of an image of the solid-fluid-fluid interface (105/107/108)) are selected by a user of a computing system 101.

[0041] In step 209, computing system 102 calculates the contact angle between the selected surfaces. That is, computing system 102 calculates the contact angle at the solid-fluid-fluid interface (105/107/108) using the generated image data. An image illustrating the definition and calculation of the contact angle 301, 6_e, is shown in Figure 3D in accordance with an embodiment of the present invention.

[0042] A further description of method 200 is provided below. [0043] In one embodiment, the column setup discussed above was subject to X-ray imaging using an Xradia® MicroXCT-400 scanner. X-ray computed tomography (CT) and radiography were used to image the fluid-fluid-solid interfaces. A radiogram is a two-dimensional projection image of a three-dimensional object, whereas, X-ray CT provides three-dimensional cross- sectional images of an object from flat X-ray images. Radiography is much faster, as imagery can be obtained in seconds, but at a cost in clarity, as the interface is viewed through intervening material. Computed tomography provides clearer data, but may require several minutes to a few hours of imaging. Radiography requires that the interface be exactly orthogonal to the source- detector path to allow accurate measurement.

[0044] In the experimental design of capillaries 106, the fluid-fluid-solid interface (108/107/105) is expected to have axial symmetry, and a radiograph may be sufficient for accurate contact angle measurements. In the case of parallel planes, such as the muscovite flakes, X-ray CT scanning may be required. In one embodiment, the energy and power of the X- ray source along with the concentration of the contrasting agent in brine were optimized to obtain images with unique isolation of grayscale peaks for the various materials including silica glass, borosilicate glass, PEEK, polytetrafluoroethylene (PTFE), quartz, muscovite, C0₂, air, water, and brine. Radiography was conducted typically at 1-2 μπι resolution and X-ray CT scanning at ~ 10 μπι resolution.

[0045] The quantification of ()_e is described herein with the image processing all conducted in MATLAB® and is illustrated in Figures 3 A-3D. First, using the raw gray-scale image, the wall of capillary 106 is manually selected by placing a line on it. The image is then rotated so this line is vertical. Next, the image is smoothed and denoised using MATLAB® image processing functions. A search window that encompasses the interface 105/107/108 is defined by the selection of vertical pixels (rows) and horizontal pixels (columns). This window constrains the area to be searched for an interface and its size depends on the resolution of the image and the size of the interface. The window is placed a few column pixels away from the fluid-fluid-solid interface (107/108/105) since the denoising partly blurs this zone. Next, each column within the window can be scanned for the greatest pixel value change across some interval, usually 10 pixels (the average value of 5 pixels compared to the next 5 pixels). The length of this interval depends upon the resolution of the image, where "noisy" images may require larger intervals. Once found, a point is placed in the middle of the relatively narrow interval to mark the fluid- fluid interface (107/108). In this manner, a point along the interface is found for each column within the search window. When the surface tension forces are dominant, i.e., the Bond number Bo < \, the fluid interface successfully minimizes energy and takes the form of a spherical cap in three dimensions or an arc of a circle in two dimensions. Thus, a circle is fit to the selected points using the MATLAB® function circfit. The intersection of the wall of capillary 106 and the circle is then calculated and a tangent line to the circle at this point is plotted. Finally, the angle formed by the tangent line and the wall defines f)_e. This approach, which is illustrated in Figures 4A-4E, thus takes into account the shape of the entire interface which is also a check for the robustness of the experimental design, i.e., if the Bo condition is met. Figures 4A-4E are X- ray images of fluid-fluid-solid interfaces at room conditions (25°C and 0.1 MPa) for quartz-air- brine, borosilicate glass-air-brine, shale-air-brine, PTFE-air-deionized (DI) water and PTFE-air- brine, respectively, in accordance with an embodiment of the present invention. This potentially circumvents issues with manual measurements and perhaps algorithm errors when just focusing on fitting a tangent angle at the three-point contact.

[0046] The technique of the preent invention was tested against some well-known cases: borosilicate glass-water (or brine)-air and PTFEwater (or brine)-air under room conditions (0.1 MPa and -25° C), and two recently studied systems, quartz-C0₂-brine and PTFE-C0₂-brine, under varying but modest pressures and 23.3° C.

[0047] With respect to the materials for sample applications, the common minerals quartz and muscovite and the common laboratory materials PTFE, PEEK, and borosilicate glass, were used to measure wettability with respect to brine and C0₂ at 13.8 MPa and 60° C conditions. At these conditions C0₂ is in a supercritical state, and a brine solution was obtained by admixing deionized water with NaBr, NaCl, or NaBr + NaCl, which are contrast-enhancing agents for X- ray imaging and a surrogate for formation brines.

[0048] For the sample preparation, in one embodiment, a cylindrical core (6 mm x 20 mm) was obtained by mechanically drilling in the direction perpendicular to the c axis of a quartz crystal. A high-precision diamond-bit drill press was later used to form a capillary 106 (~ 1 mm) in the quartz 105 or shale core as shown in Figure 3B. The high-precision drill press created a smooth- surface capillary at the μιη-scale that was cleaned by an air pump. [0049] Monoclinic muscovite crystals have a well -developed platy cleavage along the [001] plane and posed a challenge to obtain a core or drill capillary 106. Alternatively, two rectangular muscovite flakes (7 mm x 20 mm) cleaved parallel to the [001] plane were obtained and arranged them to be parallel with each other with ~1 mm spacer along their long edges, i.e., a narrow slot form. The cleaved muscovite flakes were smooth and the flat surfaces had a vitreous luster. The slot between the parallel plates was used the same way as capillary 106 in core holder 105. Other laboratory materials, i.e., PTFE, PEEK, and glass were available in a capillary form (~1 mm ID) and used for experiments similar to the description above.

[0050] The column used to house the capillaries is made of PEEK, a material that is pervious to X-rays and can withstand pressures of up to 27.6 MPa. The exterior of the column consists of a carbon fiber heating sleeve powered by a DC voltage modulator, which helps optimize the voltage to maintain a constant temperature of 60°C ±2°C in the column. Brine is injected from the bottom of the column using a manual syringe and C0₂ is injected from the top of the column using a supercritical C0₂ pump until a constant pressure of 13.8 ±0.1 MPa is attained. The column is then set aside for about 4 hours for C0₂ dissolution equilibration in the brine. The brine volume injected was on the order of 2 mL and was optimized to position the interface of fluids in capillaries or the slit of muscovite flakes.

[0051] The ID of capillaries and the spacing between the parallel muscovite flakes was chosen, such that gravitational effects on the fluid interface were negligible. The Bond number (Bo), a metric for the importance of gravitational force relative to surface tension, is:

where Ap is the density difference between the fluid pair, g is acceleration due to gravity, the length-scale L is the capillary ID or the spacing between the muscovite flakes, and r is the interfacial tension of the fluids. A Bo < 1 indicates the dominance of surface tension over the gravity force. At experimental P-T conditions, a capillary ID of 1 mm leads to a Bo ~ 0.2 and ensures that gravity had negligible influence on the fluid interface.

[0052] Once the brine inside the column had achieved equilibrium with respect to C0₂ dissolution, the column setup was taken for X-ray imaging. [0053] The X-ray imaging of the column setup provided gray-scale images with distinct fluid- fluid and fluid-solid interfaces of the solid-water/brine-air and solid-CC -brine systems within capillaries and between muscovite surfaces as shown in Figures 4A-4E and 5A-5F. Figures 5A- 5F are X-ray images of solid-fluid-fluid interfaces at reservoir conditions (60-71° C and 12.4- 22.8 MPa) for quartz-C0₂-brine, muscovite plates-C0₂-brine, borosilicate glass-CC -brine, shale-C0₂-brine, PTFE-C0₂-brine and PEEK-CC -brine, respectively. The high-precision drill press created a smooth surface and thus a smooth capillary, showing that this method can be readily adopted for most minerals in geologic porous media.

[0054] Carefully choosing the diameter of capillaries or the spacing between muscovite flakes, i.e., ensuring that Bo « 1, resulted in fluid interfaces that follow an arc of a circle (Figures 4A- 4E and 5B), which in turn indicates that the systems were dominated by surface tension and had negligible gravity effects. The latter is necessary for robust G_e measurements.

[0055] Majority of the surfaces tested, except for PTFE and PEEK, exhibited a convex brine interface and are therefore brine-wet or water-wet (Figures 4A-4C and 5A-5D). PTFE and PEEK on the other hand are C0₂-wet with a concave brine interface (Figures 5E-5F). The quartz-C0₂-brine system is C0₂ nonwetting. Figure 5 A shows capillary 106 in quartz core 105 inside the column. The brine interface is convex with quartz-CC , and resulted in a G_e of 26° (Figure 5A). The muscovite-CC -brine system is also CO₂ nonwetting, with a convex fluid interface and a G_e of 58° (Figure 5B).

[0056] Figures 4A-4E also display the difference between imaging modes. Figure 4B is a radiograph image, whereas, Figure 4A is a vertical reslicing through a CT volume. The radiograph is a proj ection through the entire experimental setup, and thus incorporates spurious material leading to a noisier image, while the CT reslice image isolates the region of interest.

[0057] The borosilicate-air-brine system at ambient room condition is brine or water-wetting with a convex liquid interface and a G_e of 9° (Figure 4B). In contrast, borosilicate-CC^-brine system at 13.8 MPa and 60° C shows decreased brine or water-wetting characteristics, yet with a convex fluid interface and a Q_e of 54° (Figure 5C). The PTFE-C0₂-brine system is C0₂ wetting, with a concave brine interface and a G_e of 140° (Figure 5E). The PEEK-C0₂-brine system is also CO₂ wetting, with a concave brine interface and a G_e of 127° (Figure 5F). [0058] The examples above demonstrate the utility of the method of the present invention for quantifying wettability of minerals and materials that can be configured in a capillary form or parallel planes. The method of the present invention is fast to setup, uses little fluid volume, and can provide rapid measurements for changing thermodynamics conditions. For example, X-ray imaging can be done with stepwise change in P-T conditions of the column. Another advantage of the method of the present invention is the fixed spacing between fluid and solid surfaces which allows a constant external or body force on the interface of fluids. This, however, remains a challenge for the sessile drop method likely due to inconsistency in obtaining similar volume and contact length of drops for repeated experiments. The method of the present invention can be adapted for advancing and receding contact angle measurements. X-ray radiographs can be obtained at a frequency of 1 image per 2 seconds, thus allowing transient scanning of the advancing or receding interface. Furthermore, because the column setup consists of PEEK, the method of the present invention can also be applied to contact angle measurement of corrosive fluids with low pH and various salinities. Such a column can also be left saturated with such fluids for aging purposes.

[0059] The present invention measures wettability of reservoir and seal/cap rock minerals and laboratory materials at elevated P-T conditions. The present invention is based on constructing reservoir material (rocks or minerals) into a capillary (1 mm ID) or slot form (1-1.5 mm ID) and placing this vertically inside a high P-T column. Two fluids are then injected such that their interface is within the solid's interspace. The solid-fluid-fluid interfaces are imaged by X-ray radiography and/or CT scanning, and the images are later processed for the contact angle measurement.

[0060] The wettability of reservoir rocks and minerals is conventionally measured using the sessile drop method, in which recovering the same volume for the drop with the same contact length can be a challenge. In the method of the present invention, the spacing for the fluid-solid interface remains constant and can be easily optimized for precluding gravitational effects, i.e., precise control of the Bond number.

[0061] Using the method of the present invention, contact angles of air or C0₂ and water or brine interfaces with quartz, muscovite, shale, PTFE, PEEK, and borosilicate glass surfaces can be measured at room and reservoir P-T conditions. Thus, CT scanning (e.g., high resolution X- ray computed tomography) has rapidly emerged as a visualization tool for studying microscale multiphase fluid distribution in porous media, and the method of the present invention provides a new application for this technology which is also an alternative to the sessile drop method. The present invention allows for fast and inexpensive measurement of contact angles.

[0062] The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

CLAIMS: 1. A method for measuring contact angles, the method comprising:

forming a column out of a mineral or a rock;

placing a core holder with a drilled capillary or a slot vertically inside said column;

injecting a first fluid within said capillary or said slot;

injecting a second fluid within said capillary or said slot;

performing an X-ray scan of a solid-fluid-fluid interface in said capillary or said slot to generate image data, wherein said solid-fluid-fluid-interface corresponds to an interface of a material of said core holder, said first fluid and said second fluid; and

calculating a contact angle at said solid-fluid-fluid interface using said generated image data.

2. The method as recited in claim 1, wherein a material of said core holder comprises one of the following: quartz, muscovite, shale, silica glass, borosilicate glass, polytetrafluoroethylene (PTFE ), and polyether ether ketone (PEEK).

3. The method as recited in claim 1, wherein said capillary has an inner diameter between 1 and 1.5 mm.

4. The method as recited in claim 1, wherein said slot is a slot between parallel plates,

5. The method as recited in claim I, wherein said first fluid comprises one of the following: brine, deionized water and sodium chloride brine.

6. The method as recited in claim I, wherein said first fluid comprises brine.

7. The method as recited in claim 1 , wherein said second fluid comprises one of the following: air and carbon dioxide.

8. The method as recited in claim 1, wherein said second fluid comprises carbon dioxide.

9. The method as recited in claim 1, wherein said generated image data comprises a radiogram.

10. The method as recited in claim 1, wherein said generated image data comprises three- dimensional cross-sectional images of an object from flat X-ray images.

11. The method as recited in claim 1 further comprising:

defining a search window encompassing said solid-fluid-fluid-interface depicted in an image from said image data; and

scanning each column within said window for a greatest pixel value change across an interval.

12. The method as recited in claim 11 further comprising:

placing a point in a middle of said interval to mark a fluid-fluid interface of said solid- fluid-fluid interface resulting in points being selected along said fluid-fluid interface of said solid-fluid-fluid interface for each column within said search window.

13. The method as recited in claim 12 further comprising:

fitting a circle to said selected points; and

calculating an intersection of said circle and a wall of said capillary.

14. The method as recited in claim 13 further comprising:

plotting a tangent line to said circle at said intersection, wherein an angle formed by said tangent line and said wall of said capillary defines said contact angle.

15. The method as recited in claim 11, wherein said interval comprises 5 to 15 pixels.