CN111855502A - Apparatus and method for measuring wettability of reservoir rock under the action of electric current - Google Patents

Abstract

The invention discloses a device and method for measuring the wettability of reservoir rocks under the action of electric current. The device comprises: a light source, which forms an outgoing light path along a first direction; a camera, which is located in the outgoing light path and is used for capturing the contact angle an image; a container, located between the light source and the camera and used for accommodating a solution of a predetermined ratio, the container as a whole extends longitudinally along a second direction perpendicular to the first direction; a support, located in the container and capable of fixing the rock sample in the solution , the support is made of insulating material; the syringe is used to inject crude oil into the lower surface of the rock sample; the first electrode and the second electrode with one end protruding into the solution, the first electrode and the second electrode face away from each other along the second direction Distribution; a power source, which is electrically connected to the first electrode and the second electrode for providing an electric field, and the first electrode and the second electrode after electrification are electrically connected through the solution. The invention can measure the wettability change of reservoir rock under the action of electric current and at different positions and different times.

Description

Apparatus and method for measuring wettability of reservoir rock under the action of electric current

technical field

The invention relates to the technical field of tight oil reservoir development, in particular to a device and method for measuring the wettability of reservoir rocks under the action of electric current.

Background technique

The descriptions in this section merely provide background information related to the present disclosure and do not constitute prior art.

Recent exploration shows that the proven reserves of tight oil in my country are huge. How to effectively develop this type of reservoir is a key problem that the country needs to solve urgently. The study found that the tight oil reservoirs in China are dominated by continental deposits, with poor reservoir physical properties, small pore throats, poor connectivity, and low reservoir pressure coefficient. of submicron pore throats. Due to the particularity of the pore throats of tight oil reservoirs, it is difficult to achieve supplementary energy by general water injection. During the production process, the formation pressure and single well production decline rapidly, and the recovery rate is low. The recovery degree that relies on natural energy production is generally less than 10%. .

Among them, wettability is a major factor affecting the distribution and flow of oil and water in rock pores, and directly restricts the relative permeability of oil and water, capillary force and oil recovery. It is crucial for the development of reservoirs.

Chinese patent CN104697902B describes a method for determining the wettability of rocks in an electric field, the method includes: a. A three-phase system is formed by a sample rock, an environmental liquid and a test liquid in a sample cell made of insulating materials; b. . Observe the initial wettability and contact angle characteristics of the sample rock when no electric field is applied; c. After applying an electric field to the three-phase system in the sample cell through the electrode plate located outside the sample cell, observe the test liquid on the surface of the sample rock. Changes in contact angle.

Since this method uses a sample cell made of insulating material, the electrode plate is outside the sample cell and is not in direct contact with the solution. As a result, only an electric field is applied during the measurement process, but no current can be generated, thus directly excluding the electrokinetic factor. effect of wettability, and therefore cannot describe the determination of reservoir wettability under the action of electric current.

SUMMARY OF THE INVENTION

In order to solve at least one of the above problems, the present invention provides a device and method for measuring the wettability of reservoir rock under the action of electric current, which can realize the change of the wettability of reservoir rock under the action of electric current at different positions and different times.

The embodiment of the present application discloses a device for measuring the wettability of reservoir rock under the action of electric current, and the device for measuring the wettability of reservoir rock under the action of electric current includes:

a light source, forming an outgoing light path along the first direction;

a camera, located in the outgoing light path, for capturing contact angle images;

a container, which is located between the light source and the camera and is used for accommodating a solution in a predetermined ratio, the container as a whole extends longitudinally along a second direction perpendicular to the first direction;

a holder located in the container and used to hold the rock sample in the solution, the holder being made of insulating material; the rock sample having opposing upper and lower surfaces;

a syringe for injecting a predetermined amount of crude oil into the lower surface of the rock sample;

a first electrode and a second electrode with one end protruding into the solution in the container, the first electrode and the second electrode are distributed away from each other along the second direction;

A power supply is electrically connected to the first electrode and the second electrode, and is used for providing an electric field, and the first electrode and the second electrode after being energized form electrical communication through the solution.

In a preferred embodiment, the device for measuring the wettability of reservoir rock under the action of electric current further comprises a controller, the controller is electrically connected to the camera, and is determined based on the contact angle image obtained by the camera Contact angle.

In a preferred embodiment, the material of the stent includes: polytetrafluoroethylene.

In a preferred embodiment, the container is a cuboid water tank, the direction of the long side of the cuboid is the second direction, and the material of the container is plexiglass.

In a preferred embodiment, the power source is a DC power source, and when the power source is turned on, an anode area is formed around the first electrode, a cathode area is formed around the second electrode, and the cathode area is connected to the anode. Between the regions is the middle region.

In a preferred embodiment, the device further comprises an adjusting member, the adjusting member can at least adjust the position of the container along the second direction.

In a preferred embodiment, the electric field strength formed by the DC power source between the first electrode and the second electrode is not greater than 500 V/m.

A measuring method based on the measuring device for the wettability of reservoir rock under the action of the above-mentioned current, comprising:

Place the holder with the rock sample fixed at the predetermined position in the container; determine the positions of the container, light source and camera;

Use a syringe to inject a predetermined amount of crude oil on the lower surface of the rock sample;

Periodically capture a contact angle image, and determine the contact angle based on the contact angle image; when the contact angle remains unchanged, the rock sample, crude oil and solution reach equilibrium, and the contact angle at this time is the contact angle of the reservoir;

The power is turned on, and a contact angle image is periodically captured, and the contact angle of the reservoir obtained in each cycle is determined based on the contact angle image, so as to form data of the change of the contact angle with time under a predetermined electric field.

In a preferred embodiment, the determination method further comprises: changing the voltage of the power supply to obtain data of the change of the contact angle with time under different currents.

In a preferred embodiment, the measurement method further comprises: changing the position of the rock sample in the container, and obtaining data of the contact angle changing with time of the rock sample in different positions; the rock sample is in the container The positions include: an anode region close to the first electrode, a cathode region close to the second electrode, and an intermediate region between the anode region and the cathode region.

In a preferred embodiment, before performing the measurement, the method further comprises cutting the rock sample into slices, grinding at least the lower surface for adhering the crude oil, and placing the polished rock sample in a solution Soak.

The DC electric field can improve the recovery factor of the reservoir, but it is currently unclear how the DC electric field works on the reservoir and its influence on the properties of the reservoir, which greatly limits the large-scale application of this technology in oil fields. Wettability is an extremely important surface property of a reservoir. The patent CN104697902B invented the wettability study of the reservoir under the action of the electric field, but this invention patent ignores the effect of the current on the reservoir, which will produce electrokinetic phenomena (electroosmosis, electrophoresis and electrolysis), and at the same time violate the tested liquid ( The objective law that the density of crude oil) is smaller than that of the ambient liquid (salt water, water) and floats. It cannot accurately describe the wettability change of the reservoir under the action of the objective law of the electric field.

The features and advantages of the present invention are as follows: in order to study the change of the wettability of the reservoir under the action of a direct current electric field. Provide a new measuring device for the wettability of reservoir rock under the action of electric current. By adding platinum electrode, plexiglass water tank, polytetrafluoroethylene support and DC power supply instrument, it can study the reservoir under different electric current for different time. Segment (real-time) wettability changes. This kind of device can greatly promote the research of DC electric field to enhance the oil recovery of reservoirs, so as to develop reservoirs more efficiently, especially tight reservoirs.

With reference to the following description and drawings, specific embodiments of the present application are disclosed in detail, indicating the manner in which the principles of the present application may be employed. It should be understood that the embodiments of the present application are not thereby limited in scope.

Features described and/or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, in combination with, or instead of features in other embodiments .

It should be emphasized that the term "comprising/comprising" when used herein refers to the presence of a feature, integer, step or component, but does not exclude the presence or addition of one or more other features, integers, steps or components.

Description of drawings

1 is a schematic structural diagram of a device for measuring the wettability of reservoir rock under the action of an electric current provided in an embodiment of the application;

FIG. 2 is a schematic diagram of the relative positional relationship among the power supply, electrodes, containers, and rock samples in a device for measuring the wettability of reservoir rocks under the action of electric current provided in the trial method of this application;

FIG. 3 is a flowchart of steps of a method for real-time determination of the wettability of reservoir rock under the action of an electric current provided in the embodiment of the present application.

Description of reference numbers:

100, stage; 10, rock sample; 1, light source; 2, camera; 3, container; 4, syringe; 5, adjustment piece; 6, bracket; 7, power supply; 81, first electrode; 82, second electrode.

Detailed ways

The details of the present invention can be more clearly understood with reference to the accompanying drawings and the description of the specific embodiments of the present invention. However, the specific embodiments of the present invention described herein are only for the purpose of explaining the present invention, and should not be construed as limiting the present invention in any way. Under the teaching of the present invention, the skilled person can conceive any possible modifications based on the present invention, and these should be regarded as belonging to the scope of the present invention. It should be noted that when an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection, or it can be the internal communication between two components, it can be directly connected, or it can be indirectly connected through an intermediate medium, For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific situations. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for the purpose of illustration only and do not represent the only embodiment.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein in the specification of the present application are for the purpose of describing particular embodiments only, and are not intended to limit the present application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The method of enhancing the oil recovery of the reservoir by direct current has been applied in some heavy oil reservoirs abroad, and good application results have been achieved. Such as the Santa Maria Basin oil field in California, the Lloydminster heavy oil belt in Saskatchewan and Alberta in Canada, and the St. George Basin oil field in Argentina. Relevant experiments have demonstrated that direct current can significantly improve the recovery factor of tight oil reservoirs. Direct current can change the interfacial properties of the reservoir through the movement of electric charges, thereby improving the seepage capacity of oil and water, while electrolysis and electrothermal effects can effectively improve the connectivity of the reservoir, thereby enhancing the recovery factor. The use of direct current method has unique advantages for tight oil reservoirs where it is difficult to use ordinary enhanced oil recovery methods, and has huge economic and environmental advantages. Therefore, DC electric field enhanced oil recovery has extremely important practical significance for the effective development of tight oil reservoirs.

At present, the main research methods of the effect of direct current on the reservoir are the experimental method and the theoretical simulation method. The experimental method is mainly aimed at carbonate reservoirs and Berea sandstone reservoirs. The insulating core holder is used to carry out displacement experiments with an external electric field on the reservoir cores. (Chilingar et al., 1970) and other related electric indoor experiments, the results show that low power can help improve the Berea sandstone recovery. (Aggouret al., 1992) studied the effect of electroosmosis on relative permeability through dynamic displacement experiments. The results showed that the voltage gradient would increase the relative permeability of oil phase and decrease the relative permeability of water phase, reservoir recovery factor and applied voltage. The gradients show a positive correlation. (Shalabi et al., 2012) used constant voltage combined with brine flooding to study the flow effect of Berea sandstone. The results showed that when the hydraulic and electroosmotic directions were the same, the core permeability increased by 223%; when the hydraulic and electroosmotic directions were opposite , the core permeability did not change significantly. (Ghosh et al., 2012) studied the changes of the permeability and recovery factor of Berea sandstone reservoir under the applied DC electric field. Forward permeability increased by 59%, oil displacement increased by 11.6%, reverse permeability increased by 10%, and oil displacement increased insignificantly. (Ansari et al., 2015) conducted research on the effect of different acid concentrations and voltage gradients on carbonate rocks under DC electric field. % penetration.

Some scholars use theoretical simulation methods to simplify the actual flow, which also proves that DC power can improve reservoir recovery. (Zhang Ningsheng et al., 1998) and others believed that the electroosmotic flow in the capillary is proportional to the square of the capillary radius. As the capillary radius decreases, the electroosmotic flow has a significant effect, thereby starting the fluid that cannot be activated by hydrodynamics. (Guan Jiteng et al., 1999) established an oil-water two-phase seepage model under an external DC electric field based on the capillary electric double layer theory and the pore medium seepage theory. The results show that the DC electric field can effectively improve the relative seepage relationship between oil and water. With the increase of the potential gradient, the permeability of the oil phase increases and the permeability of the water phase decreases. (Wang Yudou et al., 2000) started from the capillary model of porous media seepage and established the electrodynamic hydrodynamic coupling formula under reservoir conditions. yield. (Huang Liubin et al., 2007) used the finite element method to simulate the unidirectional fluid seepage velocity in porous media under an applied DC electric field, and the results showed that the fluid seepage velocity increased by 1-7.5 times under an applied DC electric field. (Peraki et al., 2018) used the implicit pressure display saturation method to simulate the flow of two-phase immiscible liquids under an applied DC electric field.

(Zhang et al., 2019) applied direct current to tight oil reservoirs, and the experimental results showed that there is an optimal voltage gradient and ionic solution concentration. Under the optimal voltage gradient, with the increase of the voltage gradient, the experimental flooding Oil efficiency increases. In summary, both experimental and simulation literatures demonstrate that DC power enhances the recovery of reservoirs. Therefore, under the circumstance that unconventional energy (tight sandstone) has been paid more and more attention, it is very important to carry out the research of direct current electric field to enhance the oil recovery of tight oil reservoirs.

Chinese patent CN104697902B describes a method for measuring rock wettability under electric field. Since the electric field provided by the electric field is set on both sides of the insulating container, it does not constitute electrical connection, and the current does not have various effects on the liquid-rock system, such as electroosmosis. , Under the premise of electrophoresis and electrolysis effect, the invention patent for the determination of rock wettability under the action of electric field is proposed. The system to which this patent is directed does not include the effect of electrical current on the reservoir-rock system. In fact, it is precisely due to the various electrokinetic phenomena after the current is applied that the oil recovery factor is significantly enhanced. The following section describes the electrical mechanism of DC electric field to enhance reservoir recovery. Contains electroosmotic, electrophoretic and electrolytic effects.

The main electrical mechanisms of direct current to enhance reservoir recovery are as follows:

①Electrothermal, electroosmotic and viscous force. Electrothermal effect means that under an external DC electric field, the action of ohmic heat will cause the fluid viscosity in the reservoir to change and increase the fluid seepage. Electroosmosis means that in a water-wet porous medium, the direct current passes through the pore space, and the electroosmotic flow of substances (water, ions) will occur, which will increase the flow of substances in the porous medium. The electroosmotic flow generated by the electric double layer generates momentum in the wetting phase (water), which is transferred to the non-wetting phase (oil) by viscous force, which is the viscous momentum transfer. The interfacial transport of species and the resulting "viscous forces" are the main driving forces for the transport of hydrocarbon compounds near the interface.

② Change effect of clay mineral structure. Electrophoretic transport occurs when hydrophobic molecules attach to colloidal particles or when relatively large hydrocarbon molecules form colloid-micelles. Electrophoresis washes out the colloidal particles and enlarges the pore throat of the porous matrix, so that more fluid can be transported under the action of the DC electric field. (Zhang Ningsheng et al., 1998) and others believed that under the action of DC electric field, the clay minerals at the pore throat that play a major role in the resistance to the fluid are often destroyed and released, and the fluid seepage resistance is reduced. (Shalabiet al., 2012) analyzed the experimental results of direct current to improve the Berea sandstone recovery factor, and the clay decomposed and moved in the form of colloid, resulting in an increase in the effective pore throat diameter. (Ghosh et al., 2012) and others showed that the structure and content of clay minerals changed after applying direct current through mass spectrometry and X-ray diffraction.

③ The role of electrolysis and electrowetting. In the reservoir/brine/oil system, the reaction between the electrolysis products of the brine and the carboxylic acid of the oil will form a surfactant at the water/oil interface, which will significantly reduce the oil-water interfacial tension and change the wettability, thereby enhancing the recovery factor. (Fleurea et al., 1988) et al. pointed out that the electrolysis products of brine and acidic impurities in oil generate surfactants in the oil layer, and the interfacial tension decreases. The electrowetting phenomenon is that under an external DC electric field, the interfacial tension of the solid-liquid interface decreases, the contact angle decreases, and the wettability increases. (Kariminezhad et al., 2018) studied the effect of different applied DC electric fields on the properties of solid interfaces, and found that the contact angle after electrokinetic treatment was smaller than that of centrifugal control (109.4°), indicating that the electrokinetic effect would effectively change the solid interface. wettability. (Karna et al., 2018) studied the change mechanism of the contact angle under an external DC electric field by molecular simulation technology, and found that the change of the interface hydrogen bond structure and the increase of the viscous force of the interface layer will lead to the decrease of the contact angle.

Because wettability is crucial for reservoir development. When using a DC electric field to enhance the oil recovery of tight reservoirs, it is necessary to have an accurate and specific description of the change in the wettability of the reservoir under the applied DC electric field.

The relevant research results show that the DC electric field can improve the oil recovery of the reservoir, and it is a very promising technical means to enhance the oil recovery. However, at present, it is unclear how the DC electric field affects the reservoir and its influence on the properties of the reservoir, which greatly limits the application of this method in oil fields. However, as an extremely important property of the reservoir, the change of wettability under the action of DC electric field has not been studied. The main reason is the lack of relevant experimental instruments. The previous patent CN104697902B invented a method for measuring reservoir wettability under the action of electric field, but this method excludes the effect of electrokinetic phenomena (such as electroosmosis, electrophoresis and electrolysis) on reservoir rocks.

Based on this, a device that can measure the wettability of reservoir rock in real time under the action of electric current and a corresponding test method are invented. Based on this measuring device and method, it can be realized: monitoring the influence of the current on the wettability of the reservoir rock at different times. This device takes into account the effect of electrokinetic phenomena on the reservoir. It is also possible to accurately describe the wettability of the reservoir at different locations (anode region, intermediate region and cathode region) after electrolysis. The device and method have a great impetus to the research on the DC electric field to improve the oil recovery of the reservoir and the application of the technical means related to the DC electric field to the oil field.

Due to the need to measure rock wettability under an external DC electric field, the insulation requirements of the device are relatively high. In the air state, due to the existence of pores in the reservoir, the shape of the droplets changes continuously on the surface, and finally spreads out completely, and a stable rock-liquid-air system cannot be formed, which greatly interferes with the contact angle test. Based on this, the determination of the wettability of reservoir rocks under the action of electric current provided in this application is to test the contact angle in a liquid environment.

As shown in FIG. 1 to FIG. 2 , the device for measuring the wettability of reservoir rock under the action of electric current provided in the embodiment of this specification may include: a light source 1, a camera 2, a container 3, a support 6, a syringe 4, a first Electrode 81 and second electrode 82 and power source 7 .

In addition, the device for measuring the wettability of the reservoir rock under the action of the current may further include a stage 100, and the light source 1, the camera 2, the syringe 4, the container 3, etc. can be installed on the stage 100. The stage 100 can be a platform capable of realizing three-dimensional manual fine adjustment, and is flexible in operation and accurate in positioning during use.

In this embodiment, the light source 1 forms an outgoing light path along the first direction, and is used for cooperating with the camera 2 to improve the definition of the photographed boundary when photographing the contact angle image for the camera 2 . Specifically, the light source 1 can use dense LED cold light, which emits uniform light, has clear graphics, and has a long service life.

In this embodiment, the camera 2 is located in the outgoing light path formed by the light source 1 for capturing a contact angle image. The camera 2 has a lens whose focal length can be adjusted. During use, the focal length of the lens is adjusted to make the image of the rock sample-brine-crude interface clear, and then the contact angle image of the crude oil is captured. Specifically, the camera 2 can use a CCD camera, which is stable in shooting, clear in image, true and reliable.

In this embodiment, the holder 6 is located in the container 3 and is used to fix the rock sample 10 in the solution. The bracket 6 is made of insulating material. To realize the function of measuring rock wettability under the action of electric current, it is necessary to connect to an external DC electric field. The metal support 6 in the solution environment is easily chemically reacted under the action of the current, resulting in chemical precipitation, thereby contaminating the solution and causing the failure to measure the contact angle. Therefore, the support 6 made of polytetrafluoroethylene is used to avoid the effect of the DC electric field and at the same time play a supporting role.

In the present embodiment, the rock sample 10 for testing may be in the shape of a thin sheet with a certain thickness, which may be obtained by cutting a columnar core. The thin rock sample 10 has opposite upper and lower surfaces, wherein the lower surface of the rock sample 10 is used for attaching oil droplets. Therefore, at least the lower surface of the rock sample 10 needs to be polished many times to make it have less roughness.

In this embodiment, the container 3 is located between the light source 1 and the camera 2, and the interior is used for accommodating a solution with a predetermined ratio. The solution can be a solution composed of different ions, and the specific ratio can be set according to actual needs, which is not specifically limited in this application. For example, the solution may be a saline solution including sodium chloride, magnesium chloride, and the like.

The container 3 as a whole extends longitudinally along a second direction perpendicular to the first direction. The container 3 can be a sink with an open upper end. Further, considering that the actual laboratory measurement core is generally cylindrical, the water tank is changed to a cuboid water tank, which is more suitable for laboratory measurement of wettability. When the container 3 is a cuboid water tank with an open upper end, the extending direction of its long side is the second direction of the water tank.

In addition, in the embodiment of the present application, the material of the water tank is also optimized. Glass water tanks commonly used in general experiments generally contain silica. A DC electric field can have an effect on silica such as surface charge. Because silica undergoes different equilibrium reactions in different acid-base environments. Specifically, the chemical formula of silicon dioxide is SiO ₂ . Since the silanol (≡Si-OH) group on the glass surface is acidic, the silanol (≡Si-OH) group will dissociate in the solution. And the quartz surface groups will change with the pH value of the aqueous solution. When the hydrogen ion concentration decreases to a certain extent, the electrically neutral silanol (≡Si-OH) groups can be converted into positively charged silanols (≡SiO- ) group When the hydrogen ion concentration rises to a certain extent, the neutral silanol (≡Si-OH) group can be converted into a positive silanol (≡SiOH ²⁺ ) group again. )

In order to make the DC electric field act on the sample perfectly without affecting the surrounding glass, in the embodiment of the present application, the glass water tank is replaced with transparent organic glass (acrylic) to better retain the insulating properties. The chemical name of this polymer transparent material is polymethyl methacrylate, which is a polymer compound formed by the polymerization of methyl methacrylate, and is an important thermoplastic that was developed earlier.

In this embodiment, the injector 4 is used to inject a predetermined amount of crude oil into the lower surface of the rock sample 10 . Wherein, the syringe 4 can be a U-shaped micro-injector 4 . The lower end of the syringe 4 is provided with a U-shaped injection head. When the injector 4 is used to inject crude oil into the lower surface of the rock sample 10 , the outlet end of the U-shaped injection head can be accurately positioned to the position where the lower surface of the rock sample 10 needs to be dripped. Since the density of crude oil is lower than that of water, it will gradually float up. When encountering the sample, due to the action of the molecular force (van der Waals force, structural force, electrostatic force) of the rock-solution-crude oil system, the shape of the crude oil droplet changes, and finally reaches state of balance. Wherein, the injection amount of the crude oil may be one drop, about 2.5 microliters. Specifically, the syringe 4 can be electrically connected to the controller, and the controller controls the injection speed and injection volume of the syringe 4, thereby ensuring stable dripping and dripping precision.

In this embodiment, two electrodes are provided on both sides of the container 3 , which are a first electrode 81 and a second electrode 82 respectively. One ends of the first electrode 81 and the second electrode 82 protrude into the solution in the container 3 . Specifically, the first electrodes 81 and the second electrodes 82 are distributed away from each other along the longitudinal direction (ie, the second direction) of the rectangular parallelepiped water tank. Specifically, the first electrode 81 and the second electrode 82 are respectively fixed on the side walls of the two short sides by means of fixing members.

In this embodiment, the power source 7 is electrically connected to the first electrode 81 and the second electrode 82 for providing an electric field, and the first electrode 81 and the second electrode 82 after being energized pass through the The solution forms electrical communication. Specifically, the power source 7 can be a DC power source 7, and the power source 7 is a DC power source 7. When the power source 7 is turned on, an anode area is formed around the first electrode 81, and a cathode area is formed around the second electrode 82 , between the cathode region and the anode region is an intermediate region. The voltage of the power supply 7 can be a lower voltage value, such as 10V or the like. Of course, the specific value of the supply voltage of the DC power supply 7 is not specifically limited in this application.

In the prior art, for example, the patented electrode plate described in CN104697902B is on the outside of the insulating cell, and is not in direct contact with the solution and the sample, so that the circuit path cannot be generated. Therefore, in the process of applying the voltage, a large electric field strength is required. As the applied electric field in the example is 3478V/m, the abscissa of Figure 3 in this patent extends to 7000V/m. In the actual oilfield production process, if a comparison setting is made based on the CN104697902B patent, the required voltage is extremely large, and the corresponding power consumption cost is very high.

Specifically, the strength of the electric field formed between the first electrode 81 and the second electrode 82 by the DC power supply 7 provided in the present application is not greater than 500 V/m.

In the present invention, since the circuit path is realized, the actual required DC voltage is relatively low. At the same time, the current literature shows that the optimal voltage gradient for electric drive in tight sandstone is 2V/cm, equivalent to 200V/m, during the laboratory test. The optimal voltage gradient of the electric drive for carbonate rocks in the room is 1V/cm, which is equivalent to 100V/m. In the electric drive experiment of artificial core, the maximum voltage gradient is 4V/cm, which is equivalent to 400V/m. Considering the practical operability of applying the DC electric field to the oilfield site, the power consumption required for the application of the patent described in CN104697902B is larger. In addition to the consideration of electrical mechanism, the possibility of practical application of the channel DC electric field of the present invention is greater in terms of economic cost. Therefore, the present invention has a stronger impetus to the research on improving the recovery factor of the reservoir by the direct current electric field.

Because other non-inert electrodes can produce chemical precipitation under the action of solution and current. In one embodiment, in order to be able to provide a stable DC electric field, a DC power source 7 and an inert electrode are selected. Specifically, the inert electrode can be a platinum electrode. During specific installation, two platinum electrodes can be placed on both sides of the inner wall of the cuboid plexiglass water tank and connected by electrode clips. At the same time, the length and width of the rectangular water tank are perpendicular to the position of the light source 1 when the contact angle is measured. Due to the DC electric field, different chemical reactions are produced in the electrolysis of the two electrodes. The anode produces oxidation to produce hydrogen ions, and the cathode produces reduction to produce hydroxide ions. This method can still describe the wettability change of the reservoir under the action of DC electric field for different locations. To measure the change of the reservoir wettability in the anode region under an applied DC electric field, it is only necessary to place the PTFE support 6 and the sheet on the anode region. To measure the change of the reservoir wettability in the middle region under the applied DC electric field, it is only necessary to place the PTFE support 6 and the sheet in the middle region. To measure the change of the reservoir wettability in the cathode area under the applied DC electric field, it is convenient to only place the PTFE support 6 and the sheet in the cathode area. Therefore, to measure the wettability of the reservoir at different positions under the action of an external DC electric field, it is only necessary to place the different positions of the cuboid water tank (anode area, middle area and cathode area) respectively perpendicular to the direction of light source 1 of the contact angle measuring instrument.

In one embodiment, the measuring device may further include an adjustment member 5, the cuboid water tank can be prevented from being on the adjustment member 5, and the adjustment member 5 can at least accurately adjust the position of the water tank along the second direction, so as to facilitate the Measure the contact angle images of the rock sample 10 at different positions in the water tank. Specifically, the adjusting member 5 can also change the height position of the water tank along the third direction. The third direction is perpendicular to the first and second directions, respectively.

Before taking an image with the camera 2, the focal length of the lens of the camera 2 can be adjusted until the image of the sample-brine-crude interface is clear. The measuring device may further include a controller, which is electrically connected to the camera 2 and determines the contact angle based on the contact angle image obtained by the camera 2 . In this case, the capture period of the contact angle image can also be set by the controller.

Use camera 2 to capture images of the crude oil and record the shape of the oil droplets at intervals. Then, the droplet profile was analyzed using the image analysis software that comes with the contact angle measuring instrument, and the contact angle was calculated. Water phase contact angle = 180° - oil phase contact angle. Keep recording until the value of the contact angle no longer changes, the rock-solution-crude oil system reaches equilibrium at this time, and the water phase contact angle at this time is the contact angle of the reservoir sample. Contact angles are classified into water-wet, neutral-wet and oil-wet characteristics.

It should be added that the sum of the contact angles of oil and water is 180°. The contact angle of water is between 0 and 75 degrees for water wetting, between 75 and 105 degrees for neutral wetting, and between 105 and 180 degrees for oil wetting. If the contact angle of the oil is between 0 and 75 degrees it is oil wetting, between 75 degrees and 105 degrees it is neutral wetting, and between 105 and 180 degrees it is water wetting. According to the size of the contact angle, the wettability of the rock sample 10 can be determined and the specific type of the wettability of the rock sample 10 can be determined.

As shown in FIG. 3 , based on the above-mentioned device for measuring the wettability of reservoir rock under the action of electric current, the present application also provides a method for measuring the wettability of reservoir rock under the action of electric current. The determination method mainly includes the following steps:

Step S10: place the support 6 with the rock sample 10 fixed at a predetermined position in the container 3; determine the positions of the container 3, the light source 1, and the camera 2;

Step S12: injecting a predetermined amount of crude oil on the lower surface of the rock sample 10 by using the syringe 4;

Step S14: Periodically capture the contact angle image, and determine the contact angle based on the contact angle image; when the contact angle remains unchanged, the rock sample 10, the crude oil and the solution reach equilibrium, and the contact angle at this time is the reservoir the contact angle;

Step S16: Turn on the power supply 7, periodically capture the contact angle image, and determine the contact angle of the reservoir obtained in each cycle based on the contact angle image, so as to form data of the change of the contact angle with time under a predetermined electric field.

The assay method is described below in conjunction with the specific operation flow.

(1) Cut the rock sample 10 to be measured into thin slices, and place it in the solution to be measured for immersion, in order to achieve sufficient contact and reaction between the rock and the solution.

(2) Place the rock sheet on the Teflon support 6 and adjust the position (cathode area, middle area and anode area). Specifically, in which region the change of the wettability of the reservoir sheet in the DC electric field needs to be measured, the polytetrafluoroethylene support 6 can be placed in the corresponding region.

(3) Adjust the light source 1 to obtain the position of the sample piece. The crude oil was injected using a U-shaped micro-syringe 4 (the amount of crude oil in this experiment was 2.5 microliters), the contact angle image was captured every 5 minutes, and the contact angle was calculated using the analysis software that comes with the contact angle measuring instrument. Continue recording until the contact angle remains unchanged, at which time the rock-crude oil-solution reaches equilibrium, and the stable contact angle at this time is calculated and defined as the contact angle of the reservoir (the contact angle of the reservoir itself before the application of the DC electric field is also wettability).

(4) Turn on the DC power source 7, add an external DC electric field, such as 10V, capture a contact angle image every 5 minutes, and use the analysis software that comes with the contact angle measuring instrument to calculate the contact angle. Continuous recording can obtain the change of the contact angle of the reservoir at different times under a certain DC electric field, that is, the change of the wettability of the reservoir rock under the DC electric field is measured in real time.

(5) By changing the voltage, the contact angle data measured in real time under different currents can be obtained. The change of reservoir rock wettability in different time periods can be studied under the action of different currents.

The measurement experiment shows that the present application can realize the function of real-time measurement of reservoir wettability under the action of a DC electric field. Specifically, the experimental verification shows that when the test time reaches about half an hour, the contact angle decreases by 6.938°, and the hydrophilicity of the rock sample 10 is enhanced. The experimental data verifies that under the action of DC electric field, the wettability of the reservoir rock decreases with the increase of treatment time, and also verifies that the DC electric field reduces the contact angle of the material surface.

It should be emphasized that the present application has the following differences compared with the prior art, for example (patent CN104697902B):

First, the existing patent CN104697902B directly excludes the effect of current. Specifically, in this patent, the sample rock, the ambient liquid and the test liquid share a system in a sample cell made of insulating material. The sample cell has insulating properties. The change of the contact angle of the liquid on the sample surface is achieved by applying an electric field by adding electrode plates on the outside of both sides of the insulated sample cell. One of the problems is that the electrodes cannot generate electrokinetic reactions, such as electrolysis, because the electrodes are not in contact with the solution and the sample rock.

Because of the sample cell of insulating material, the circuit is not a path and cannot generate current, so it is only the effect of applying an electric field. At present, the application of DC electric field to the reservoir to enhance oil recovery mainly uses electroosmosis, electrophoresis and electrolysis generated by electric current. Electroosmosis and electromigration are the movement of water and ions in solution from the anode direction to the cathode direction under the action of an electric field. Electrolysis is an oxidation reaction at the anode to generate hydrogen ions, and a reduction reaction at the cathode to generate hydroxide ions. Electrophoresis is the movement of charged colloids in solution under the action of an electric field.

One of the main purposes of this application is to realize the electrokinetic phenomenon by realizing the circuit path, and to study the effect of the current on the wettability of the reservoir rock.

In addition, the patent CN104697902B sample is placed at the bottom of the sample cell, and crude oil or other hydrocarbon liquids are used to attach the sample surface. However, the density of crude oil and hydrocarbons is generally lower than that of water (including brine, etc.). If crude oil or hydrocarbon droplets are dropped into the solution, they will float on the surface of the ambient liquid (salt water), and the droplets cannot adhere to the surface of the sample.

The present invention uses a liquid water tank, uses an insulating support 6, uses a U-shaped micro-syringe 4 to take crude oil, uses a camera 2 to capture the oil droplet image, and uses the computer's own analysis software to analyze the contact angle. Using this method is more simple, convenient, efficient and accurate.

Under the action of the DC electric field, the cathode and anode will have different chemical reactions due to the generation of the path. The anode loses electrons and undergoes an oxidation reaction to generate hydrogen ions, and the cathode gains electrons and undergoes a reduction reaction to generate hydroxide ions. The patent CN104697902B does not take into account that the current will change the environment of the rock reservoir at different locations, especially in the oil and gas field development project, the application of the DC electric field will cause the reservoir to be subjected to environmental changes. The change in wettability of the core at different locations (anode region, intermediate region and cathode region) after DC electric field treatment could not be detected.

In conclusion, the methods described in the prior art are suitable for the determination of the wettability of reservoir rocks by electric fields, excluding electrokinetic effects (such as electroosmosis, electrophoresis and electrolysis). In fact, the mechanism of using DC electric field to enhance reservoir recovery is mainly electrokinetic action. Therefore, the prior art cannot describe the determination of reservoir wettability in the case of electrokinetic phenomena (current). Moreover, the problem that crude oil is less dense than water and easily floats on the water surface is ignored. At the same time, considering that there is currently no method to measure the wettability of reservoir cores at different positions under the action of electric current. Based on this, by inventing a method for measuring the wettability of rocks under the action of electric current, it is possible to realize the measurement of the wettability of rocks under the action of electric current, taking into account the electromechanical mechanism (electroosmosis, electrophoresis and electrolysis), at different positions (anode region, Reservoir rock wettability changes at different times in the middle and cathode regions.

In general, the present application has achieved at least the following technical effects relative to the prior art:

(1) Realize the electrokinetic phenomena (electroosmosis, electrophoresis and electrolysis) of the current-action reservoir, which can accurately describe the change of the wettability of the reservoir under the action of current.

(2) The device and method can detect the wettability changes of reservoir rocks at different locations (anode region, intermediate region and cathode region) at different times.

Any numerical value recited herein includes all values of the lower value and the upper value in one unit increments from the lower value to the upper value, there being a separation of at least two units between any lower value and any higher value That's it. For example, if the number of components or process variables (eg, temperature, pressure, time, etc.) are stated to have values from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, the intent is to illustrate that the The specification also explicitly lists values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32, and the like. For values less than 1, one unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1. These are merely examples of what is intended to be express, and all possible combinations of numerical values recited between the lowest value and the highest value are considered to be expressly set forth in this specification in a similar fashion.

Unless otherwise stated, all ranges include the endpoints and all numbers between the endpoints. "About" or "approximately" used with a range applies to both endpoints of the range. Thus, "about 20 to 30" is intended to cover "about 20 to about 30," including at least the indicated endpoints.

All articles and references disclosed, including patent applications and publications, are hereby incorporated by reference for all purposes. The term "consisting essentially of" describing a combination shall include the identified element, ingredient, component or step as well as other elements, components, components or steps that do not materially affect the essential novel characteristics of the combination. Use of the terms "comprising" or "comprising" to describe combinations of elements, ingredients, components or steps herein also contemplates embodiments consisting essentially of those elements, ingredients, components or steps. By use of the term "may" herein, it is intended to indicate that "may" include any described attributes that are optional.

A plurality of elements, components, components or steps can be provided by a single integrated element, component, component or step. Alternatively, a single integrated element, component, component or step may be divided into separate multiple elements, components, components or steps. The disclosure of "a" or "an" used to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

It should be understood that the above description is for purposes of illustration and not limitation. From reading the above description, many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art. The scope of the present teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated herein by reference for the purpose of being comprehensive. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended to disclaim such subject matter, nor should it be construed that the inventor did not consider such subject matter to be part of the disclosed subject matter.

Each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.

The above-mentioned embodiments are only intended to illustrate the technical concept and characteristics of the present invention, and the purpose thereof is to enable those who are familiar with the art to understand the content of the present invention and implement accordingly, and cannot limit the protection scope of the present invention by this. All equivalent changes or modifications made according to the spirit of the present invention should be included within the protection scope of the present invention.

Claims (11)

1. An apparatus for determining wettability of reservoir rock under the action of electric current, comprising:

a light source forming an exit light path along a first direction;

a camera located in the exit light path for capturing a contact angle image;

a container located between the light source and the camera and used for containing a solution with a preset proportioning, wherein the container extends lengthways along a second direction which is vertical to the first direction;

a holder located in the container and for fixing a rock sample in the solution, the holder being made of an insulating material; the rock sample having opposing upper and lower surfaces;

an injector for injecting a predetermined amount of crude oil to a lower surface of the rock sample;

the first electrode and the second electrode extend into the solution in the container at one end, and are distributed along the second direction in a mode of deviating from each other;

and the power supply is electrically connected with the first electrode and the second electrode and is used for providing an electric field, and the first electrode and the second electrode after being electrified form electric communication through the solution.

2. The apparatus for determining wettability of a reservoir rock by an electric current according to claim 1, further comprising a controller electrically connected to said camera for determining the contact angle based on contact angle images acquired by said camera.

3. An apparatus for determining wettability of reservoir rock by an electric current according to claim 2, wherein the material of said support comprises: polytetrafluoroethylene.

4. The device for measuring wettability of reservoir rock under the action of electric current according to claim 2, wherein the container is a rectangular parallelepiped water tank, the direction of the long side of the rectangular parallelepiped is the second direction, and the material of the container is organic glass.

5. The apparatus for determining wettability of reservoir rock by electric current as set forth in claim 4, wherein said power source is a DC power source, and when said power source is turned on, an anode region is formed around said first electrode, a cathode region is formed around said second electrode, and an intermediate region is formed between said cathode region and said anode region.

6. Apparatus for determining wettability of reservoir rock by an electric current as set forth in claim 5, wherein said apparatus further comprises an adjustment member capable of adjusting at least a position of said container along the second direction.

7. An apparatus for determining wettability of reservoir rock by an electric current according to claim 5, wherein said DC power source provides an electric field strength of not more than 50V/m between said first and second electrodes.

8. A method for measuring wettability of a reservoir rock by an electric current according to claim 2, comprising:

placing the holder with the rock sample fixed thereon at a predetermined position in the container; determining the positions of the container, the light source and the camera;

injecting a predetermined amount of crude oil into the lower surface of the rock sample using an injector;

periodically capturing a contact angle image, determining a contact angle based on the contact angle image; when the contact angle is kept unchanged, the rock sample, the crude oil and the solution reach equilibrium, and the contact angle at the moment is the contact angle of the reservoir;

the power is turned on, contact angle images are periodically captured again, and contact angles of the reservoir obtained in each period are determined based on the contact angle images to form data of the change of the contact angle with time under a predetermined electric field.

9. The assay method of claim 8, further comprising: and changing the voltage of the power supply to obtain the data of the change of the contact angle along with time under different currents.

10. The assay method of claim 8, further comprising: changing the position of the rock sample in the container to obtain the data of the change of the contact angle of the rock sample in different positions along with time; the position of the rock sample in the container comprises: an anode region adjacent the first electrode, a cathode region adjacent the second electrode, and a region intermediate the anode and cathode regions.

11. The assay of claim 8 wherein prior to conducting the assay, the method further comprises slicing the rock sample, grinding at least the lower surface for attachment of crude oil, and placing the ground rock sample in a solution for immersion.

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