An experimental device and method for evaluating performance of liquid carbon dioxide fracturing fluid

Abstract

The application discloses a kind of experimental device and method for evaluating the performance of liquid carbon dioxide fracturing fluid, belong to the technical field of oil and gas exploitation. Including reaction components, including visual sand suspension cavity and rectangular surrounding block, the cavity is provided in rectangular surrounding block, visual sand suspension cavity is placed in rectangular surrounding block, rectangular surrounding block is provided with interlayer, interlayer is passed into surrounding pressure medium to form surrounding pressure loading cavity;Surrounding pressure loading cavity is uniformly wrapped around visual sand suspension cavity, observation port is opened on the cavity wall of visual sand suspension cavity, and high-pressure-resistant visual window is sealingly installed at observation port;Carbon dioxide pressurized liquefaction assembly and injection assembly;High-speed camera assembly is arranged opposite to high-pressure-resistant visual window, surrounding pressure medium is passed into the interlayer of rectangular surrounding block to form surrounding pressure loading cavity which uniformly wraps around visual sand suspension cavity, which can accurately simulate formation closure stress, and avoid the problem of uneven stress distribution caused by traditional single-point pressure or flexible rubber sleeve pressure.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, specifically to an experimental apparatus and method for evaluating the performance of liquid carbon dioxide fracturing fluid. Background Technology

[0002] Low-permeability and ultra-low-permeability oil and gas reservoirs, due to the extremely low porosity and permeability of their reservoir media, require relevant reservoir stimulation technologies for commercial development. With the application of hydraulic fracturing technology, carbon dioxide fracturing technology has been widely utilized.

[0003] The viscosity of liquid carbon dioxide fracturing fluid determines its sand-carrying and filtration capacity. However, due to its extremely low viscosity, liquid carbon dioxide has poor sand-carrying capacity when used as a fracturing fluid, often leading to sand blockage in near-wellbore fractures and failing to achieve the expected fracturing results. Generally, a thickener compatible with it is needed to increase viscosity and improve its sand-carrying performance. To accurately evaluate the performance of this system, it is essential to precisely replicate downhole high-pressure conditions and sand-carrying morphology in laboratory experiments.

[0004] However, liquid carbon dioxide needs to operate at pressures ranging from several megapascals to tens of megapascals. Existing experimental setups typically use all-metal or transparent cavities for experiments. While all-metal cavities can withstand pressure, they cannot be used to observe the morphology of sand-carrying materials, and can only be indirectly estimated based on pressure differences, leading to inaccurate data. Transparent cavities, on the other hand, are limited by material strength and sealing performance, and are prone to bursting and leakage under high pressure, resulting in phase changes. Meanwhile, to simulate formation closure stress, existing experimental setups often use confining media to directly wrap the sample or use flexible rubber sleeves for isolation. The former is prone to media intrusion and contamination of the sample, while the latter suffers from low-temperature aging and uneven stress. This results in inaccurate measured rheological and sand-carrying data, making it difficult to replicate real downhole conditions. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems in the prior art and provide an experimental apparatus and method for evaluating the performance of liquid carbon dioxide fracturing fluid.

[0006] This invention provides an experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid, including a reaction component for simulating downhole temperature and pressure environment testing, assessing the rheological properties and proppant carrying capacity of the liquid carbon dioxide fracturing fluid. The apparatus includes a visualization proppant-carrying chamber and a rectangular containment block. The rectangular containment block has a cavity within it, and the visualization proppant-carrying chamber is placed within the rectangular containment block. The rectangular containment block has an interlayer, into which a confining pressure medium is introduced to form a confining pressure loading chamber. The confining pressure loading chamber uniformly surrounds the visualization proppant-carrying chamber circumferentially. An observation port is provided on the wall of the visualization proppant-carrying chamber for observation. A high-pressure resistant viewing window is sealed at the opening; a carbon dioxide pressurization and liquefaction component is connected to the first inlet on the visualization suspended sand chamber (5) through a first delivery pipe, used to pressurize gaseous carbon dioxide to the target pressure and liquefy it before delivering it into the visualization suspended sand chamber; an injection component is connected to the second inlet on the visualization suspended sand chamber (5) through a second delivery pipe, used to quantitatively inject thickener and co-solvent additives into the visualization suspended sand chamber; a high-speed camera component is arranged facing the high-pressure resistant viewing window, used to collect images of proppant migration and sedimentation in the visualization suspended sand chamber.

[0007] Preferably, the housing of the reaction assembly is a Hastelloy pressure-bearing housing.

[0008] Preferably, the high-pressure resistant viewing window is a sapphire transparent plate, and a metal sealing surface and an annular elastic sealing element are provided between the sapphire transparent plate and the reaction component housing.

[0009] Preferably, the visualized suspended sand chamber is equipped with a rotating rotor, which is fixed at the lower end of a rotating shaft. The rotating shaft extends upward through the top cover of the chamber and is driven to rotate by an external drive mechanism to forcibly stir and mix the liquid carbon dioxide, additives and proppant in the chamber.

[0010] Preferably, the confining pressure loading chamber is provided with a water inlet, the water inlet is connected to the water outlet of the water bath liquid storage tank through a pipeline, the water outlet of the confining pressure loading chamber is connected to the water inlet of the water bath liquid storage tank, and the water bath liquid storage tank is connected to a water bath through a pipeline.

[0011] Preferably, the confining pressure medium is selected from water or antifreeze.

[0012] A preferred experimental method for evaluating the performance of liquid carbon dioxide fracturing fluid involves setting target temperature and pressure, pressurizing water into the confining pressure loading chamber to simulate formation closure stress, pumping thickener / co-solvent into the visualized suspended sand chamber via an injection assembly, and then pressurizing carbon dioxide to the target pressure via a carbon dioxide pressurization and liquefaction assembly before pumping it into the visualized suspended sand chamber. The mixture is then subjected to rheological scanning according to a set shear rate program, and the apparent viscosity data of shear rate and shear stress are recorded. Quartz sand proppant is quantitatively added into the visualized suspended sand chamber, and a high-speed camera assembly facing the visualized suspended sand chamber records the entire process of proppant suspension and sedimentation, simultaneously acquiring pressure, temperature, and image data.

[0013] Compared with the prior art, the beneficial effects of the present invention are: By introducing confining pressure medium through the interlayer of a rectangular enclosing block, a confining pressure loading chamber is formed that uniformly surrounds the visualized suspended sand cavity. This fully enclosed pressure application method can accurately simulate formation closure stress, avoiding the uneven stress distribution problems caused by traditional single-point pressure application or flexible sleeve pressure application. At the same time, the confining pressure loading chamber and the experimental chamber are physically isolated, and with the metal seal and annular elastic seal of the high-pressure resistant viewing window, the risk of the confining pressure medium mixing into the carbon dioxide system and contaminating the sample is eliminated, ensuring the purity of the chemical system. Furthermore, through the high-speed camera component positioned directly opposite the high-pressure resistant viewing window, microscopic images synchronized with rheological parameters can be captured, allowing macroscopic rheological data and microscopic suspended sand morphology to correspond frame by frame, improving the confidence of experimental data and providing a solid theoretical basis for optimizing fracturing fluid formulations in the field. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the overall structure of the experimental apparatus of the present invention.

[0015] Figure 2 This is a three-dimensional structural diagram of the reaction component of the present invention.

[0016] Figure 3 This is a schematic diagram of the explosion structure of the reaction component of the present invention.

[0017] Figure 4 This is a front view of the reaction component of the present invention.

[0018] Figure 5 This is a schematic diagram of the water bath liquid storage tank structure of the present invention.

[0019] Figure 6 This is a schematic diagram of the sand storage silo structure of the present invention.

[0020] Explanation of reference numerals in the attached diagram: 1. Gas cylinder; 2. Constant pressure and constant speed displacement pump; 3. Intermediate container; 4. Reaction assembly; 5. Visualized suspended sand chamber; 6. High pressure resistant viewing window; 7. Sand storage bin; 8. Water bath; 9. Confining pressure loading chamber. Detailed Implementation

[0021] The following is in conjunction with the appendix Figures 1-6 To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art.

[0022] The terms "first," "second," and similar words used in the patent application specification and claims of this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "inner," "outer," "upper," "lower," "far," "near," "front," and "rear" are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. The drawings in this invention are not strictly drawn to scale; the specific dimensions and quantity of each structure can be determined according to actual needs. The drawings described in this invention are merely structural schematic diagrams.

[0023] This invention provides an experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid, such as... Figures 1-6 As shown, the apparatus includes a reaction component 4, which is used to simulate downhole temperature and pressure environments to test the rheological properties and proppant carrying capacity of liquid carbon dioxide fracturing fluid. This component includes a visualization proppant chamber 5 and a rectangular containment block. The rectangular containment block has a cavity, and the visualization proppant chamber 5 is placed inside the rectangular containment block. The rectangular containment block has an interlayer, into which a confining pressure medium is introduced to form a confining pressure loading chamber 9. The confining pressure loading chamber 9 uniformly surrounds the visualization proppant chamber 5. Observation ports are opened on the walls of the visualization proppant chamber 5, and a high-pressure resistant viewing window 6 is sealed at the observation ports. A carbon dioxide pressurization and liquefaction component is used to pressurize gaseous carbon dioxide to the target pressure and liquefy it before delivering it to the visualization proppant chamber 5. An injection component is used to quantitatively inject thickeners and co-solvent additives into the visualization proppant chamber 5. A high-speed camera component is positioned directly opposite the high-pressure resistant viewing window 6 to acquire images of proppant migration and sedimentation within the visualization proppant chamber 5.

[0024] In this embodiment, a confining pressure medium is introduced through the interlayer of a rectangular enclosing block to form a confining pressure loading chamber 9 that uniformly surrounds the visualized suspended sand chamber 5. This fully enclosed pressure application method can accurately simulate formation closure stress, avoiding the uneven stress distribution problems caused by traditional single-point pressure application or flexible sleeve pressure application. Secondly, the confining pressure loading chamber 9 and the experimental chamber are physically isolated, and with the metal seal and annular elastic seal of the high-pressure resistant viewing window 6, the risk of the confining pressure medium mixing into the carbon dioxide system and contaminating the sample is eliminated, ensuring the purity of the chemical system. By integrating the carbon dioxide pressurization and liquefaction component and the injection component, online mixing of liquid carbon dioxide with thickener and co-solvent is achieved in a closed high-pressure environment. Through the high-speed camera component arranged directly opposite the high-pressure resistant viewing window 6, microscopic images synchronized with rheological parameters can be captured, allowing macroscopic rheological data and microscopic suspended sand morphology to correspond frame by frame, improving the confidence of experimental data and providing a solid theoretical basis for optimizing fracturing fluid formulations in the field.

[0025] Preferred, such as Figure 3 As shown, the housing of reaction component 4 is a Hastelloy pressure-bearing housing.

[0026] In this embodiment, liquid carbon dioxide exhibits weak acidity during pressurization and liquefaction, especially when containing trace amounts of moisture. This acidity strongly corrodes ordinary carbon steel or stainless steel, and long-term use can lead to thinning of the shell wall, intergranular corrosion, and even sudden brittle fracture. Hastelloy possesses excellent resistance to strong oxidizing chloride crevice corrosion, pitting corrosion, and stress corrosion cracking, ensuring the structural integrity and safety of the device during long-term contact with high-pressure carbon dioxide. Furthermore, liquid carbon dioxide fracturing experiments often involve ultra-high pressure conditions ranging from several megapascals to tens of megapascals. Hastelloy's extremely high yield strength and tensile strength allow for a more compact shell design, effectively resisting the circumferential stress generated by internal high pressure while ensuring a safety factor.

[0027] Preferred, such as Figures 2-5 As shown, the high-pressure resistant viewing window 6 is a sapphire transparent plate, and a metal sealing surface and an annular elastic sealing element are provided between the sapphire transparent plate and the housing of the reaction component 4.

[0028] In this embodiment, sapphire possesses extremely high hardness and compressive strength, high light transmittance, and excellent optical transmittance in the visible to near-infrared band. It can withstand internal pressures of tens of megapascals without cracking, meeting the material requirements for the observation window under high-pressure environments. More importantly, sapphire is chemically extremely stable, does not react chemically with carbon dioxide, thickeners, or co-solvents, and is not easily eroded or worn by solid particles in fluids, ensuring long-term optical clarity. The metal sealing surface undergoes plastic deformation under the preload of the high-pressure bolts, filling the microscopic gaps between the sapphire and the metal shell, providing an initial rigid seal. The annular elastic seal acts as an auxiliary seal and provides rebound compensation, adapting to differences in material thermal expansion and contraction caused by temperature changes during the experiment, preventing micro-leakage caused by pressure fluctuations.

[0029] Preferred, such as Figures 2-4 As shown, the suspended sand chamber 5 is equipped with a rotating rotor, which is fixed at the lower end of the rotating shaft. The rotating shaft extends upward through the top cover of the chamber and is driven to rotate by an external drive mechanism to forcibly stir and mix the liquid carbon dioxide, additives and proppant in the chamber.

[0030] In this embodiment, in the liquid carbon dioxide fracturing fluid system, the thickener is often a high-molecular-weight polymer, which is much more difficult to dissolve and disperse in supercritical or liquid carbon dioxide than in water-based solutions, and is prone to agglomeration. Simultaneously, high-density silica sand proppant also settles rapidly in the low-viscosity liquid carbon dioxide. Traditional static mixing or external pipeline stirring methods often fail due to energy dissipation after the fluid enters the high-pressure chamber, leading to stratification of the experimental samples. The forced stirring mechanism introduced in this invention generates strong shear force and axial circulation flow inside the chamber through a rotating rotor, instantly breaking up thickener agglomerates and accelerating their swelling and dispersion in liquid carbon dioxide, ensuring a uniform microstructure in the fracturing fluid system. After proppant injection, continuous gentle stirring effectively counteracts the gravitational settling effect, maintaining the proppant in a transient suspension state within the chamber. This facilitates researchers' observation and differentiation of the actual proppant suspension capacity under different rheological properties, rather than simply static settling.

[0031] Preferred, such as Figures 1-3 As shown, the confining pressure loading chamber 9 is provided with a water inlet, which is connected to the water outlet of the water bath liquid storage tank through a pipeline. The water outlet of the confining pressure loading chamber 9 is connected to the water inlet of the water bath liquid storage tank, and the water bath liquid storage tank is connected to the water bath pot 8 through a pipeline.

[0032] In this embodiment, by connecting the confining pressure loading chamber 9 in series with the water bath liquid storage tank and the water bath 8 to form a circulation loop, the limitations of traditional static water injection are broken. The water bath 8, as a heat source or cold source, can precisely control the temperature of the confining pressure medium, and the medium is continuously flowed in the confining pressure loading chamber 9 by a circulation pump, thus achieving active temperature control of the confining pressure medium and ensuring that the pressure and temperature applied to the outer wall of the visualized suspended sand chamber 5 are constant, thereby accurately simulating the confining pressure environment of the formation temperature.

[0033] Preferred, such as Figure 1 As shown, the confining pressure medium is selected from water or antifreeze.

[0034] In this embodiment, water is an ideal pressure transmission medium, possessing advantages such as low viscosity, good fluidity, small compressibility coefficient, low cost, and no pollution. It can provide extremely sensitive and stable pressure transmission in experiments at room temperature and medium-high temperatures. Antifreeze has a low freezing point, enabling it to maintain liquid flow characteristics in experiments simulating extremely cold formation conditions in deep wells, ensuring that the confining pressure loading chamber 9 still has good pressure transmission function at low temperatures.

[0035] The experimental method for the experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid of the present invention is as follows: The experimental temperature, pressure, and confining pressure are set according to the target reservoir conditions. The water bath 8 is started to preheat or precool the reaction assembly 4 through the insulated chamber; simultaneously, the confining pressure pump is turned on to inject the selected medium into the independent confining pressure loading chamber, pressurizing to the set value and stabilizing for 30 minutes. The pressure of the carbon dioxide cylinder 1 is checked, and it is confirmed that the pneumatic plunger booster pump and the constant pressure and constant speed displacement pump 2 are in standby mode. The high-speed camera assembly is focused on the high-pressure resistant viewing window 6.

[0036] Thickener / co-solvent is pumped into rheological measurement chamber 5 through the injection port using a precision injection assembly. A rotary rotor is then started for low-speed stirring. A booster pump is activated to pressurize carbon dioxide in cylinder 1 to the target pressure. After buffering in intermediate container 3, the carbon dioxide is pumped into rheological measurement chamber 5, and stirring continues for 5 minutes to form a homogeneous mixture. Rheological scanning is performed according to the set shear rate program, and viscosity data is recorded. Under stable pressure, the connecting channel between the two chambers is opened, and a constant-pressure, constant-speed displacement pump 2 is used to push the mixture isovolumetrically into the visualization suspended sand chamber. The channel is then closed. Quartz sand is quantitatively added into the suspended sand chamber through the sand-filling assembly. A high-speed camera assembly is immediately activated to record the entire process of proppant suspension and sedimentation, simultaneously acquiring pressure and temperature data.

[0037] After observation, open the drain port at the bottom of the visualization sand chamber to discharge waste liquid and sand particles into the collection bucket; purge the pipeline with carbon dioxide, clean the chamber three times with deionized water, and dry the inside of the chamber with ethanol. Turn off all power and gas sources, release the pressure in the confining chamber, organize the experimental data, and save it to the database for analysis.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid, characterized in that, include: The reaction assembly includes a visualization suspended sand chamber and a rectangular enclosure block. The rectangular enclosure block has a cavity inside, and the visualization suspended sand chamber is placed inside the rectangular enclosure block. The rectangular enclosure block has a sandwich layer, and a confining pressure medium is introduced into the sandwich layer to form a confining pressure loading cavity. The confining pressure loading cavity uniformly surrounds the visualization suspended sand chamber circumferentially. An observation port is opened on the cavity wall of the visualization suspended sand chamber, and a high-pressure resistant viewing window is sealed and installed at the observation port. The carbon dioxide pressurization and liquefaction component is connected to the first liquid inlet on the visualized suspended sand chamber through the first delivery pipe, and is used to pressurize gaseous carbon dioxide to the target pressure and liquefy it before delivering it into the visualized suspended sand chamber. The injection assembly is connected to the second liquid inlet on the visualization suspended sand cavity via the second delivery pipe, and is used to quantitatively inject thickener and cosolvent additives into the visualization suspended sand cavity. A high-speed camera assembly is positioned directly opposite the high-pressure resistant viewing window to acquire images of proppant transport and sedimentation within the visualized suspended sediment chamber.

2. The experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid as described in claim 1, characterized in that, The housing of the reaction assembly is a Hastelloy pressure-bearing housing.

3. The experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid as described in claim 1, characterized in that, The high-pressure resistant viewing window is a sapphire transparent plate, and a metal sealing surface and an annular elastic sealing element are provided between the sapphire transparent plate and the reaction component housing.

4. The experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid as described in claim 1, characterized in that, The visualized suspended sand chamber is equipped with a rotating rotor, which is fixed at the lower end of a rotating shaft. The rotating shaft extends upward through the top cover of the chamber and is driven to rotate by an external drive mechanism to forcibly stir and mix the liquid carbon dioxide, additives and proppant in the chamber.

5. The experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid as described in claim 1, characterized in that, The confining pressure loading chamber is provided with a water inlet, which is connected to the water outlet of the water bath liquid storage tank through a pipeline. The water outlet of the confining pressure loading chamber is connected to the water inlet of the water bath liquid storage tank, and the water bath liquid storage tank is connected to a water bath through a pipeline.

6. The experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid as described in claim 1, characterized in that, The confining pressure medium is selected from water or antifreeze.

7. The experimental method of the experimental apparatus for evaluating the performance of liquid carbon dioxide fracturing fluid as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Set the target temperature and pressure, and pressurize the confining pressure loading chamber with water to simulate the formation closure stress value; Thickener / cosolvent is pumped into the visualized sand-suspension chamber via the injection assembly, and then carbon dioxide is pressurized to the target pressure via the carbon dioxide pressurization and liquefaction assembly before being pumped into the visualized sand-suspension chamber. Perform rheological scanning on the mixture according to the set shear rate program, and record the apparent viscosity data of shear rate, shear stress and shear stress. Quartz sand proppant is quantitatively added to the visualized suspended sand cavity, and a high-speed camera component facing the visualized suspended sand cavity records the entire process of proppant suspension and sedimentation, while simultaneously collecting pressure, temperature and image data.

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