Fracture mold, method and apparatus for preparing a fractured saturated oil shale core sample

Abstract

The application provides a crack mold, a preparation method and a device for a saturated oil shale core sample containing cracks, and the crack mold comprises a pipe body and a crack simulation layer wrapping the outer sidewall of the pipe body. The crack simulation layer is made of a soluble material. An overcurrent channel is formed in the inside of the pipe body. A plurality of through holes are arranged in the sidewall of the pipe body and pass through the outer sidewall of the pipe body to the inner sidewall of the pipe body and communicate with the overcurrent channel. The crack simulation layer is dissolved by introducing a solvent for dissolving the crack simulation layer into the overcurrent channel. The space left in the core after the crack simulation layer is dissolved is the simulated crack. The application solves the problems of difficulty in manufacturing cracks, difficulty in saturating oil in the core and difficulty in obtaining a shale core sample in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oilfield development, and particularly relates to a fracture mold, a preparation method and device of a saturated oil shale core sample containing fractures. BACKGROUND

[0002] With the gradual expansion of shale oil reservoir mining scale, the research on the seepage mechanism of shale oil is more and more in-depth. Because the permeability of shale is extremely low (less than 0.1 mD), the conventional methods such as water injection and gas injection all have different degrees of difficulty. Initially, it relies on natural energy decay mining, but the oil production rate of this method is extremely slow, and the wellbore pressure decreases rapidly, and the recovery degree is very low. In order to improve the recovery degree, the common method is the fracturing method, which creates fractures in the shale oil reservoir to exploit the crude oil near the fractures and the affected area. Although the recovery degree is improved to a certain extent, the remaining oil is still very rich.

[0003] At present, the method of carbon dioxide huff and puff mining is tried, but the effect is still not ideal. Since there is no experimental capability, reliable basic data cannot be obtained through experiments to analyze the reasons and propose countermeasures.

[0004] The existing prominent problems include: (1) It is difficult to obtain core samples with reservoir characteristics. When the permeability is low to very low (permeability less than 1 mD), even if the reservoir rock is sampled, the change of rock stress affected by pressure drop has changed its pore structure. When the pore diameter is less than 1 micron, the change has a significant impact on seepage. (2) It is difficult to saturate water / saturate oil of core. Due to the small pore size, the fluid injection pressure is greatly increased. Although high pressure can be provided, the effect of core saturation of water / oil is still poor, and the small pores that fluid is difficult to enter are still more than 30%. (3) There is a lack of effective fracturing experimental simulation method. In the oilfield field, proppants maintain high permeable channels after fracturing, but in indoor experiments, if the fractures are made in advance, it will increase the difficulty of saturating oil; if the fractures are made after saturating oil, the technology is not available. SUMMARY

[0005] The present application aims to provide a fracture mold, a preparation method and device of a saturated oil shale core sample containing fractures, to solve the problems of difficulty in obtaining core samples with reservoir characteristics, difficulty in saturating oil of core, and difficulty in making fractures in the prior art.

[0006] To achieve the above object, the present application provides a crack mold, which comprises a pipe body and a crack simulation layer wrapping the outer sidewall of the pipe body, the crack simulation layer is made of a dissolvable material, the inside of the pipe body forms a flow channel, a plurality of through holes are arranged in the sidewall of the pipe body, the through holes penetrate the outer sidewall of the pipe body to the inner sidewall of the pipe body and communicate with the flow channel, and the crack simulation layer is dissolved by introducing a solvent for dissolving the crack simulation layer into the flow channel.

[0007] The crack mold as described above, wherein the crack simulation layer is made of sodium sulfate, and the crack simulation layer is formed by melting sodium sulfate powder.

[0008] The crack mold as described above, wherein the crack mold further comprises a plurality of steel needles, the steel needles are fixed on the outer sidewall of the pipe body, the steel needles are perpendicular to the axial direction of the pipe body, and the crack simulation layer wraps the steel needles.

[0009] The crack mold as described above, wherein the plurality of steel needles are respectively fixed at the plurality of through holes.

[0010] The crack mold as described above, wherein the plurality of through holes are arranged at intervals along the axial direction and the circumferential direction of the pipe body.

[0011] The crack mold as described above, wherein the pipe body is a steel pipe.

[0012] The present application also provides a preparation method of a saturated oil shale core sample containing cracks, which comprises the following steps: uniformly mixing sand particles and solid-phase cementing material having water absorption to obtain a solid-phase raw material, wherein the particle size of the solid-phase cementing material is smaller than that of the sand particles; diluting a cementing agent with water to obtain a cementing agent solution; spraying the cementing agent solution on the solid-phase raw material and uniformly mixing to obtain a to-be-pressed raw material; placing the crack mold into a pressing cavity of a pressing mold; filling the pressing cavity with oil; adding the to-be-pressed raw material into the pressing cavity; pressing the to-be-pressed raw material in the pressing cavity to obtain a saturated oil shale core sample containing the crack mold; introducing a solvent for dissolving the crack simulation layer into the flow channel of the crack mold, and the space left after the crack simulation layer is dissolved is a crack, thereby obtaining a saturated oil shale core sample containing cracks.

[0013] The preparation method of a saturated oil shale core sample containing cracks as described above, wherein the solid-phase cementing material comprises the following components in percentage by weight: aqueous calcium carbonate: 80% to 90%; clay: 10% to 15%; and gypsum: 5% to 10%.

[0014] The preparation method of the saturated oil shale core sample with cracks as described above, wherein the content of the sand particles accounts for 85-90% of the total weight of the solid phase raw materials, and the content of the solid phase cementing material accounts for 10-15% of the total weight of the solid phase raw materials.

[0015] The preparation method of the saturated oil shale core sample with cracks as described above, wherein the particle size of the sand particles is less than 100 μm, and the particle size of the solid phase cementing material is 15-25 μm.

[0016] The preparation method of the saturated oil shale core sample with cracks as described above, wherein the cementing agent is a water-based epoxy resin.

[0017] The preparation method of the saturated oil shale core sample with cracks as described above, wherein the preparation method further comprises a method for preparing the crack mold, and the method for preparing the crack mold comprises the following steps: machining through holes on a pipe body, and fixing steel needles at the through holes of the pipe body to obtain a crack mold core; manufacturing a forming mold with a receiving cavity for accommodating the crack mold core; placing sodium sulfate powder and the crack mold into the receiving cavity so that the sodium sulfate powder wraps the crack mold core; and placing the forming mold into a heating furnace to heat the forming mold at a temperature at which the sodium sulfate powder can be melted, so that the sodium sulfate powder melts and wraps the crack mold core to obtain the crack mold.

[0018] The present application further provides a preparation device for a saturated oil shale core sample with cracks, which comprises the crack mold as described above, and further comprises: a pressing cylinder comprising a cylinder body, an upper end cover and a lower end cover respectively arranged at the upper end and the lower end of the cylinder body, and an upper piston and a lower piston arranged in the cylinder body, the upper piston and the lower piston being in sealing connection with the cylinder body in an up-and-down sliding manner, a pressing cavity being formed between the upper piston and the lower piston, an upper pressurizing cavity being formed between the upper piston and the upper end cover, and a lower pressurizing cavity being formed between the lower piston and the lower end cover, the crack mold being arranged in the pressing cavity, one end of the pipe body of the crack mold extending to form a liquid injection extension, the other end of the pipe body of the crack mold extending to form a liquid outlet extension, the liquid injection extension penetrating through the upper piston and the upper end cover and extending out of the pressing cylinder, and the liquid outlet extension penetrating through the lower piston and the lower end cover and extending out of the pressing cylinder; an upper pressurizing pipe penetrating through the upper end cover and being in communication with the upper pressurizing cavity; a lower pressurizing pipe penetrating through the lower end cover and being in communication with the lower pressurizing cavity; an upper communication pipe penetrating through the upper end cover and the upper piston and being in communication with the pressing cavity; a lower communication pipe penetrating through the lower end cover and the lower piston and being in communication with the pressing cavity; a pressurizing container for accommodating pressurizing liquid, which is connected with the upper pressurizing pipe and the lower pressurizing pipe; and a pressurizing pump connected with the pressurizing container and capable of pumping the pressurizing liquid in the pressurizing container into the upper pressurizing cavity and the lower pressurizing cavity.

[0019] The preparation device for the fractured saturated oil shale core sample as described above, wherein the inner wall of the cylinder comprises an upper cylindrical section, an upper conical section, a lower conical section and a lower cylindrical section connected in sequence from top to bottom, the upper piston is arranged in the upper cylindrical section, the lower piston is arranged in the lower cylindrical section, the inner diameter of the upper conical section gradually decreases from top to bottom, and the inner diameter of the lower conical section gradually decreases from bottom to top.

[0020] The preparation device for the fractured saturated oil shale core sample as described above, wherein the upper pressurizing pipe is provided with a first on-off valve, the lower pressurizing pipe is provided with a second on-off valve, the upper communication pipe is provided with a third on-off valve, and the lower communication pipe is provided with a fourth on-off valve.

[0021] The preparation device for the fractured saturated oil shale core sample as described above, wherein the preparation device further comprises a displacement container for containing a displacement fluid, the displacement container is connected with the upper communication pipe or the lower communication pipe, the displacement container is connected with the pressurizing pump, and the pressurizing pump can pump the displacement fluid in the displacement container into the pressing cavity.

[0022] The preparation device for the fractured saturated oil shale core sample as described above, wherein the preparation device further comprises a back pressure controller, and the back pressure controller is connected with the upper communication pipe and the lower communication pipe.

[0023] The preparation device for the fractured saturated oil shale core sample as described above, wherein the preparation device further comprises a fluid metering device, and the fluid metering device is connected with the upper communication pipe and the lower communication pipe.

[0024] The preparation device for the fractured saturated oil shale core sample as described above, wherein the preparation device further comprises a first multi-way valve, the upper pressurizing pipe and the lower pressurizing pipe are connected with the pressurizing container through the first multi-way valve; a second multi-way valve, the upper communication pipe is connected with the fluid metering device, the displacement container and the back pressure controller through the second multi-way valve; and a third multi-way valve, the lower communication pipe is connected with the fluid metering device, the displacement container and the back pressure controller through the third multi-way valve.

[0025] The preparation device for the fractured saturated oil shale core sample as described above, wherein the first multi-way valve is connected with the pressurizing container and the displacement container through an inlet pipeline, and the second multi-way valve and the third multi-way valve are connected with the displacement container through the first multi-way valve and the inlet pipeline respectively.

[0026] The preparation device for the fractured saturated oil shale core sample as described above, wherein the first multi-way valve is connected with a gas guide main pipe, the gas guide main pipe is connected with the second multi-way valve through a first gas guide branch pipe, the gas guide main pipe is connected with the third multi-way valve through a second gas guide branch pipe, the fifth switch valve is arranged on the gas guide main pipe, the sixth switch valve is arranged on the first gas guide branch pipe, and the seventh switch valve is arranged on the second gas guide branch pipe.

[0027] The preparation device for the fractured saturated oil shale core sample as described above, wherein the second multi-way valve is connected with a first liquid guide pipe, the third multi-way valve is connected with a second liquid guide pipe, the eighth switch valve is arranged on the first liquid guide pipe, the ninth switch valve is arranged on the second liquid guide pipe, the second multi-way valve is connected with the fluid metering device and the back pressure controller through the first liquid guide pipe, and the third multi-way valve is connected with the fluid metering device and the back pressure controller through the second liquid guide pipe.

[0028] The preparation device for the fractured saturated oil shale core sample as described above, wherein the tenth switch valve is arranged on the liquid injection extension section, and the eleventh switch valve is arranged on the liquid outlet extension section.

[0029] The preparation device for the fractured saturated oil shale core sample as described above, wherein the preparation device comprises two fracture molds, i.e., a horizontal fracture mold and a vertical fracture mold, the pipe body of the horizontal fracture mold is parallel to the axial direction of the barrel body, and the pipe body of the vertical fracture mold is perpendicular to the axial direction of the barrel body.

[0030] The preparation device for the fractured saturated oil shale core sample as described above, wherein the pressurizing pump is a high-pressure plunger pump.

[0031] The preparation device for the fractured saturated oil shale core sample as described above, wherein the preparation device further comprises a rotating support for supporting the pressing barrel, and the barrel body is rotationally connected with the rotating support.

[0032] The present application provides an experimental device for carbon dioxide huff and puff shale oil exploitation, which comprises the preparation device for the fractured saturated oil shale core sample as described above, and the liquid injection extension section is connected with a carbon dioxide gas supply source.

[0033] The experimental device for carbon dioxide huff and puff shale oil exploitation as described above, wherein the liquid outlet extension section is connected with the back pressure controller and the fluid metering device through a tee joint.

[0034] The experimental device for carbon dioxide huff and puff exploitation of shale oil as described above, wherein the experimental device further comprises two conventional well simulation tubes, one of the conventional well simulation tubes passes through the upper end cover and the upper piston and extends into the pressing cavity, the other conventional well simulation tube passes through the lower end cover and the lower piston and extends into the pressing cavity, the two conventional well simulation tubes are separated in the pressing cavity, and the two conventional well simulation tubes can be connected with the carbon dioxide gas supply source respectively.

[0035] The fracture mold, the method and the device for preparing the saturated oil shale core sample with fractures of the present application have the following characteristics and advantages:

[0036] 1. The fracture mold of the present application is placed in the core when the core is prepared, and the space left in the core after the fracture simulation layer is dissolved is the simulated fracture, which solves the problem of difficulty in manufacturing fractures in the prior art.

[0037] 2. According to the formation mechanism of shale oil, the present application adopts the method of pressing in an oil phase environment, so that the rock is formed and solidified, and the oil phase is naturally sealed in the pores, the saturated oil step is completed, and the distribution of the oil phase in the pores in the actual shale oil reservoir is completely simulated in mechanism, so that the oil phase can fill all levels of pores, and the saturation of oil reaches the maximum value of 100%. Compared with the method of injecting fluid into a shale core sample in the prior art, the problem of difficulty in entering the micro pores is solved, the effect of saturated oil is better, and the problem of difficulty in saturating oil in the core in the prior art is solved.

[0038] 3. The shale physical model of the present application uses water-absorbing solid cementing material. When pressing, the water-absorbing solid cementing material can absorb water in the cementing agent droplets in the form of molecularly combined water. The higher the pressure, the better the absorption effect. The solid cementing material after absorbing a certain amount of water also has cementing effect, that is, the local surface of the solid cementing material not covered by the cementing agent also has cementing ability. Since part of the cementing agent is adsorbed on the surface of the solid cementing material, the contact area between the cementing agent and the surface of the sandstone particles is significantly reduced. Under the double action of the cementing agent and the solid cementing material, not only the cementing quality is guaranteed, but also the effective pore space is guaranteed, forming a pore structure with shale characteristics, and solving the problem of difficulty in obtaining shale core samples in the prior art.

[0039] 4. The core sample preparation device of the present application has the functions of preparing core samples and conducting oil displacement experiments, and realizes the continuous operation of core preparation, saturated oil and displacement / development steps.

[0040] 5. The experimental device for carbon dioxide huff and puff exploitation of shale oil of the present application has the functions of preparing core samples and conducting CO2 huff and puff experiments, and realizes the continuous operation of core preparation, saturated oil and huff and puff experiments. BRIEF DESCRIPTION OF DRAWINGS

[0041] The following drawings are merely intended to schematically illustrate and explain the present application, and do not limit the scope of the present application. Among them:

[0042] Figure 1 is a structural schematic diagram of a crack mold of the present application;

[0043] Figure 2 is Figure 1 is a structural schematic diagram of a core in a crack mold;

[0044] Figure 3 is a schematic diagram of the cementing effect of a shale core sample prepared by the prior art;

[0045] Figure 4 is a schematic diagram of the cementing effect of a shale core sample prepared by the present application;

[0046] Figure 5 is a schematic diagram of an experimental device for carbon dioxide huff and puff recovery of shale oil according to an embodiment of the present application;

[0047] Figure 6 is a schematic diagram of a horizontal fracturing mold and a vertical fracturing mold installed in a pressing cylinder;

[0048] Figure 7 is a schematic diagram of carbon dioxide huff and puff during an experiment of carbon dioxide huff and puff recovery of shale oil;

[0049] Figure 8 is a schematic diagram of the cooperation of a cover and a plug according to the present application;

[0050] Figure 9 is a schematic diagram of a cover according to the present application;

[0051] Figure 10 is a schematic diagram of a plug according to the present application;

[0052] Figure 11 is a half sectional view of an upper piston according to the present application;

[0053] Figure 12 is a solubility comparison diagram of common inorganic salts.

[0054] Explanation of main element reference numerals:

[0055] 100, crack mold; 100', horizontal fracturing mold; 100'', vertical fracturing mold; 110, pipe body; 111, flow passage; 112, through hole; 120, crack simulation layer; 130, steel needle; 140, liquid injection extension section; 150, liquid outlet extension section; 200, sand particle; 300, solid phase cementing material; 400, cementing agent; 500, oil; 1, cylinder body; 101, upper cylindrical section; 102, upper conical section; 103, lower conical section; 104, lower cylindrical section; 2, upper end cover; 3, lower end cover; 4, upper piston; 401, piston through hole;

[0056] 5, lower piston; 501, piston through hole; 6, pressing cavity; 7, upper pressing cavity; 8, lower pressing cavity; 9, upper pressing pipe; 10, lower pressing pipe; 11, upper communication pipe; 12, lower communication pipe; 13, pressurizing container; 14, pressurizing pump; 15, cover; 151, large hole; 152, small hole; 153, annular insertion hole; 16, plug; 161, large diameter section; 162, small diameter section; 163, sealing through hole; 164, injection through hole; 17, first switch valve; 18, second switch valve; 19, third switch valve; 20, fourth switch valve; 21, displacement container; 22, back pressure controller; 23, fluid metering device; 24, first multi-way valve; 25, second multi-way valve; 26, third multi-way valve; 27, inlet pipeline; 28, gas guide main pipe; 29, first gas guide branch pipe; 30, second gas guide branch pipe; 31, fifth switch valve; 32, sixth switch valve; 33, seventh switch valve; 34, first liquid guide pipe; 35, second liquid guide pipe; 36, eighth switch valve; 37, ninth switch valve; 38, rotating support; 39, O-shaped sealing ring; 40, three-way pipe; 41, tenth switch valve; 42, eleventh switch valve; 43, conventional well simulation pipe. DETAILED DESCRIPTION

[0057] In order to have a clearer understanding of the technical features, objectives and effects of the present application, the specific embodiments of the present application will be described with reference to the drawings. In the drawings, the use of adjectival or adverbial modifiers "upper" and "lower", "top" and "bottom", "inner" and "outer" is only for the convenience of relative reference between multiple groups of terms, and is not intended to describe any specific directional limitation of the modified terms. In addition, the terms "first", "second", etc. are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second", etc. can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise stated, the meaning of "multiple" is two or more. In the description of the present application, unless otherwise stated, the term "connection" should be understood broadly, for example, it can be fixed connection, it can be detachable connection, it can be direct connection, it can be indirect connection through intermediate medium, and the specific meaning of the above-mentioned term in the present patent can be understood according to the specific circumstances by those skilled in the art.

[0058] Unless the direction indicated by the separate definition, the directions such as up, down, front, back, etc. mentioned in this article are based on the directions of up, down, right, left, etc. shown in the drawings of the present application, which are described herein. Figure 12 Unless the direction indicated by the separate definition, the directions such as up, down, front, back, etc. mentioned in this article are based on the directions of up, down, right, left, etc. shown in the drawings of the present application, which are described herein.

[0059] Embodiment one

[0060] As Figure 1As shown, the present application provides a fracture mold 100, which comprises a pipe body 110 and a fracture simulation layer 120 wrapping the outer sidewall of the pipe body 110, the material of the fracture simulation layer 120 is a dissolvable material, the inside of the pipe body 110 forms a flow passage 111, i.e. the center hole of the pipe body 110 is the flow passage 111, a plurality of through holes 112 are arranged in the sidewall of the pipe body 110, the through holes 112 penetrate from the outer sidewall of the pipe body 110 to the inner sidewall of the pipe body 110 and communicate with the flow passage 111, by introducing a solvent for dissolving the fracture simulation layer 120 into the flow passage 111, the solvent enters the fracture simulation layer 120 through the through holes 112, the fracture simulation layer 120 is dissolved, and the space formed after the fracture simulation layer 120 is dissolved is the simulated fracture.

[0061] The fracture mold of the present application is placed inside the core when the core is prepared, and the space left in the core after the fracture simulation layer is dissolved is the simulated fracture, solving the problem of difficult fracture manufacturing in the prior art.

[0062] Further, the material of the fracture simulation layer 120 is inorganic salt.

[0063] Further, the material of the fracture simulation layer 120 is sodium sulfate, and the fracture simulation layer 120 is formed by melting sodium sulfate powder. There are three principles for selecting the material of the fracture simulation layer 120, one is non-toxic and harmless, and no pollution to the environment; two is easy to dissolve in water; three is not decomposed under melting conditions.

[0064] After screening, sodium sulfate is selected as the preferred preparation material. The solubility of sodium sulfate in water is relatively high at room temperature, and the solubility in water at 25℃ is 80g / 100g. The solubility of sodium sulfate and other commonly used inorganic salts is compared as follows: Figure 12 The melting point of sodium sulfate is 884℃, and sodium sulfate is a very stable ionic crystal, which does not decompose even under melting conditions. By utilizing these characteristics of sodium sulfate, it can be cast into a specific fracture shape, and under the condition of water scouring, the space after dissolution can simulate the fracture morphology.

[0065] For example, the sodium sulfate powder can be high-temperature melted in a muffle furnace to reach a molten state, and the liquefied sodium sulfate gradually solidifies after slow cooling to form the fracture simulation layer 120. After the sodium sulfate solidifies, the outer layer has a crystal growth form, which is slightly rough, and the surface can be polished by sandpaper, and the roughness is controllable.

[0066] Further, the pipe body 110 is a steel pipe, for example, a stainless steel pipe.

[0067] For example, the outer diameter of the steel pipe is 3mm, and the inner diameter is 2mm.

[0068] For example, the fracture simulation layer 120 is a layer of sodium sulfate powder, and the fracture simulation layer 120 is formed by melting the sodium sulfate powder. Figure 1 , Figure 2As shown, in one embodiment of the present invention, the crack mold 100 further includes multiple steel needles 130. The steel needles 130 are fixed to the outer wall of the tube body 110 and are perpendicular to the axial direction of the tube body 110. The crack simulation layer 120 wraps around the steel needles 130. By setting the steel needles 130 to support the crack simulation layer 120, the shape of the crack simulation layer 120 can be made closer to the shape of a real crack. For example, the diameter of the steel needles 130 is 1 mm, the length of the steel needles 130 is 1 cm to 5 cm, and the steel needles 130 are welded and fixed to the tube body 110.

[0069] like Figure 2 As shown, further, multiple steel needles 130 are fixed at multiple through holes 112 respectively, and the solvent in the flow channel 111 enters the crack simulation layer 120 from each through hole 112 to dissolve the crack simulation layer 120.

[0070] like Figure 1 , Figure 2 As shown, in one embodiment of the present invention, a plurality of through holes 112 are arranged at intervals along the axial and circumferential directions of the tube body 110 to provide multiple spaced dissolution sites for the solvent, enabling the solvent to dissolve the crack simulation layer 120 more quickly. For example, the spacing between two adjacent through holes 112 is 5 cm to 10 cm.

[0071] Implementation Method 2

[0072] Please see Figure 4 The present invention also provides a method for preparing a fractured saturated oil shale core sample, which includes the following steps:

[0073] Sand particles 200 and water-absorbing solid binder 300 (or solidified microparticles) are mixed evenly to obtain solid raw materials, wherein the particle size of the solid binder is smaller than that of the sand particles.

[0074] Dilute the binder 400 with water to obtain a binder solution;

[0075] A binder solution is sprayed onto a solid raw material and mixed evenly to obtain the raw material to be pressed. For example, the spraying method is ultrasonic spraying.

[0076] Place the crack mold 100 of Embodiment 1 into the pressing cavity of the pressing mold;

[0077] Fill the pressing chamber with oil;

[0078] Add the raw material to be pressed into the pressing chamber;

[0079] The raw material to be pressed in the pressing chamber is pressed to obtain a saturated oil shale core sample containing a cracked mold 100 inside.

[0080] A solvent for dissolving the fracture simulation layer 120 is introduced into the flow channel 111 of the fracture mold 100. The space left after the fracture simulation layer 120 is dissolved is the fracture, thus obtaining a fractured saturated oil shale core sample.

[0081] Compared with the prior art, the preparation method of the present invention has at least the following advantages:

[0082] (1) In this invention, the crack mold 100 is placed into the pressing cavity of the pressing mold. After the saturated oil shale core sample is pressed and formed, the crack simulation layer 120 is dissolved to obtain the crack, which solves the problem of the difficulty in manufacturing cracks in the prior art.

[0083] (2) According to existing research results, the formation of shale oil is the direct transformation of organic matter in the pores of rocks, which is significantly different from the formation process of typical sandstone oil reservoirs, which involves transformation and migration. Based on this formation, this invention adopts a pressing method in an oil phase environment to solidify the rock and naturally seal the oil phase in the pores, thus completing the saturation oil step. In terms of mechanism, it completely simulates the distribution of the oil phase in the pores of actual shale oil reservoirs, so that the pores at all levels can be filled with the oil phase, and the saturation oil reaches a maximum of 100%. Compared with the existing technology of injecting fluid into shale core samples, it does not have the problem of fluid being unable to enter the micropores, and the saturation oil effect is better. It solves the problems of difficulty in obtaining core samples and difficulty in saturating core oil in the existing technology, and truly simulates the initial state of shale oil reservoirs.

[0084] (3) In this invention, when preparing core samples using a water-absorbing solid binder 300, sand particles 200 are first uniformly mixed with the solid binder 300, and then a water-diluted binder 400 (hereinafter referred to as binder solution) is sprayed on. Even if there is uneven adsorption of binder droplets on the surface of the sandstone particles at this time, during the subsequent pressing process, the water-absorbing solid binder 300 will absorb the water in the droplets in the form of molecularly bound water. The higher the pressure, the better the absorption effect. Figure 4 As shown, the solid binder 300, after absorbing a certain amount of moisture, also has a cementing effect; that is, the local surfaces of the solid binder 300 not covered by the binder 400 also have cementing ability, such as... Figure 4 As shown in position D, under ideal conditions, the cementitious agent 400 is gradually and uniformly adsorbed on the particle surface of the solid cementitious material 300. Since some of the cementitious agent 400 is adsorbed on the particle surface of the solid cementitious material 300, the contact area between the cementitious agent 400 and the sandstone particle surface is significantly reduced, thereby reducing the aforementioned problems in the preparation of shale physical models by existing technologies. Under the dual action of the cementitious agent 400 and the solid cementitious material 300, not only is the cementation quality guaranteed, but also the effective pore space is guaranteed, forming a pore structure with shale characteristics.

[0085] The prior art method for preparing the core sample is to directly spray the cementing agent 400 on the surface of the sand particles 200, which has the problem that, as shown in Figure 3 , even if the droplets are small, they are distributed in the form of local adsorption on the surface of the sand particles 200, and the cementing between the sand particles 200 is uneven during the pressing process; the cementing agent 400 is too thick between the pores (such as Figure 3 position A), and occupies more pore space; the cementing agent 400 is locally adsorbed (such as Figure 3 position B), and does not play a cementing role; the surface of the small particles is easily completely wrapped by the cementing agent 400 (such as Figure 3 position C), and loses the rock surface characteristics; therefore, the shale core sample prepared by the present application has the characteristics of a shale reservoir.

[0086] In an embodiment of the present application, the preparation method further comprises a method for preparing the fracture mold 100, and the method for preparing the fracture mold 100 comprises the following steps:

[0087] A through hole 112 is processed on the pipe body 110, and a steel needle 130 is fixed at each through hole 112 of the pipe body 110, to obtain a fracture mold inner core (as shown in Figure 2 ).

[0088] A forming mold with a containing cavity is made, and the containing cavity is used to contain the fracture mold inner core;

[0089] The sodium sulfate powder and the fracture mold 100 are placed into the containing cavity, so that the sodium sulfate powder wraps (completely covers) the fracture mold inner core;

[0090] The forming mold is placed into a heating furnace, and the forming mold is heated at a temperature at which the sodium sulfate powder can be melted, so that the sodium sulfate powder wraps the fracture mold inner core after being melted, to obtain the fracture mold 100.

[0091] Further, the specific method for making the forming mold is as follows: kaolin clay is used to make a mud blank, and a space around the fracture mold inner core is dug out, so that a space for wrapping the sodium sulfate outside the fracture mold inner core is left, and then the mud blank is dried for 24 hours, and then a muffle furnace is used to heat the mud blank to 2000 DEG C and keep the temperature constant for 2 hours, and after cooling, a pottery forming mold is formed.

[0092] Further, the specific operation steps of putting the sodium sulfate powder and the crack mold 100 into the accommodating cavity are as follows: firstly, half of the sodium sulfate powder is put into the accommodating cavity of the forming mold, then the core in the crack mold is put in, and then the other half of the sodium sulfate powder is used to cover the core in the crack mold, and the edge is arranged, and the upper surface of the sodium sulfate powder is required to be not less than 2mm away from the edge of the forming mold, and the sodium sulfate powder used is required to be a chemical reagent grade; then the muffle furnace is used to heat it to 950 DEG C, and the temperature is kept for 2 hours, so that the sodium sulfate powder is in a molten state and uniformly wrapped around the pipe body 110 of the core in the crack mold, because the area of the through hole 112 is small and the viscosity of the molten sodium sulfate is high, so the sodium sulfate will not enter the inside of the pipe body 110, that is, the flow channel in the inside of the pipe body 110 is unobstructed, and then the temperature is reduced again, and the temperature is reduced to the control range of the muffle furnace heat preservation material at a gradient of 200 DEG C / hour, and then the temperature is kept not to open the furnace and naturally reduced for not less than 24 hours; the crack mold 100 is taken out from the muffle furnace, and is carefully peeled to obtain the primary mold as shown in Figure 1 Fig. 1, and if it is required to trim the surface shape and roughness, it can be carefully polished with fine sandpaper, and the sandpaper grade is preferably higher than 2000 meshes.

[0093] In an embodiment of the present application, the solid phase cementing material 300 includes the following components in percentage by weight: water-based calcium carbonate: 80% to 90%; clay: 10% to 15%; gypsum: 5% to 10%; and other substances such as carbonates can also be added according to the specific reservoir geological conditions, accounting for 2% to 5%. The solid phase cementing material is composed of the above components mixed in proportion, and the specific proportion of each component can be determined according to the characteristics of the shale prepared. The water-based calcium carbonate has good water absorption, can quickly absorb the water in the cementing agent solution, the clay is an inorganic binder and plays a bonding role, and the gypsum mainly temporarily absorbs water and can release part of the water during the pressing process, and the main purpose is to enable the epoxy resin to be uniformly distributed on the surface of the solid phase cementing material particles.

[0094] Further, the content of the sand particles 200 accounts for 85% to 90% of the total weight of the solid phase raw materials, for example, 90%; and the content of the solid phase cementing material 300 accounts for 10% to 15% of the total weight of the solid phase raw materials, for example, 10%. The sand particles are selected according to the actual shale sand particle size and proportion, and the sand particles with good circularity are preferably selected, and the sand particles with this shape have high simulation degree to the characteristics of the actual shale sand particles. For example, the particle size of the sand particles 200 selected in the present application is less than 200μm (more than 150 meshes).

[0095] Further, the particle size of the solid phase cementing material 300 is 15μm to 25μm, that is, the particle size of the water-based calcium carbonate is 15μm to 25μm, the particle size of the clay is 15μm to 25μm, and the particle size of the gypsum is 15μm to 25μm.

[0096] Further, the binder 400 is a water-based epoxy resin, and the sand particles 200 and the solid-phase particles such as the solid-phase binder 300 are cemented and consolidated under the action of the water-based epoxy resin. Before spraying, the binder 400 is diluted with water into a fluid with low concentration and low viscosity, for example, the viscosity of the fluid is less than 2 cp, and the fluid is uniformly sprayed on the solid-phase particles by using the ultrasonic spraying method to form the to-be-pressed raw material, and then the to-be-pressed raw material is added into the shale pressing device for pressing and forming after being placed in the air for 30 minutes to 1 hour.

[0097] Embodiment three

[0098] As shown in Figure 5 , the application also provides a preparation device for a fractured saturated oil shale core sample, which comprises the fracture mold 100 of the embodiment one, a pressing cylinder, an upper pressurizing pipe 9, a lower pressurizing pipe 10, an upper communication pipe 11, a lower communication pipe 12, a pressurizing container 13 for containing pressurizing liquid, and a pressurizing pump 14.

[0099] The pressing cylinder is the pressing mold mentioned in the embodiment two, and the pressing cylinder comprises a cylinder body 1, an upper end cover 2 and a lower end cover 3 respectively arranged at the upper end and the lower end of the cylinder body 1, and an upper piston 4 and a lower piston 5 arranged in the cylinder body 1, the upper end cover 2 is detachably and sealingly connected with the cylinder body 1, the lower end cover 3 is detachably and sealingly connected with the cylinder body 1, the upper piston 4 and the lower piston 5 are sealingly connected with the cylinder body 1 and can slide up and down, a pressing cavity 6 (or a filling space) for containing the sand particles 100, the solid-phase binder 200, the binder solution and the oil liquid is formed between the upper piston 4 and the lower piston 5, an upper pressurizing cavity 7 is formed between the upper piston 4 and the upper end cover 2, a lower pressurizing cavity 8 is formed between the lower piston 5 and the lower end cover 3, and the fracture mold 100 is arranged in the pressing cavity 6, one end of the pipe body 110 of the fracture mold 100 extends to form a liquid injection extension 140, the other end of the pipe body 110 of the fracture mold 100 extends to form a liquid outlet extension 150, the liquid injection extension 140 penetrates through the upper piston 4 and the upper end cover 2 and extends out of the pressing cylinder, and the liquid outlet extension 150 penetrates through the lower piston 5 and the lower end cover 3 and extends out of the pressing cylinder.

[0100] The upper pressurizing pipe 9 passes through the upper end cover 2 and communicates with the upper pressurizing cavity 7, the lower pressurizing pipe 10 passes through the lower end cover 3 and communicates with the lower pressurizing cavity 8, the upper communicating pipe 11 passes through the upper end cover 2 and the upper piston 4 and communicates with the pressing cavity 6, the lower communicating pipe 12 passes through the lower end cover 3 and the lower piston 5 and communicates with the pressing cavity 6, the pressurizing container 13 is connected with the upper pressurizing pipe 9 and the lower pressurizing pipe 10, the pressurizing pump 14 is connected with the pressurizing container 13, for example, the pressurizing pump 14 is a high-pressure plunger pump, the pressurizing pump 14 can pump the pressurizing liquid in the pressurizing container 13 into the upper pressurizing cavity 7 and the lower pressurizing cavity 8, by injecting the pressurizing liquid (for example, water) into the upper pressurizing cavity 7 and the lower pressurizing cavity 8, the pressurizing liquid drives the upper piston 4 and the lower piston 5 to extrude the to-be-pressed raw material in the pressing cavity 6, so as to press and form the saturated oil shale core sample, in the pressing process, as the pressing cavity 6 is compressed, the oil liquid in the pressing cavity 6 is discharged from the upper communicating pipe 11 and the lower communicating pipe 12, when the fracture is manufactured, the solvent is introduced into the liquid injection extension section 140, and the solvent flows out from the liquid outlet extension section 150 after dissolving the fracture simulation layer 120.

[0101] The saturated oil shale core sample with the fracture is prepared by using the preparation device, and the operation is simple and convenient.

[0102] As shown in the drawings, Figure 6 in an embodiment of the present application, the preparation device includes two fracture molds 100, which are a horizontal fracture mold 100' and a vertical fracture mold 100", the pipe body 110 of the horizontal fracture mold 100' is parallel to the horizontal section of the axial direction of the barrel body, and is used for simulating a horizontal fracture, and the pipe body 110 of the vertical fracture mold 100" is perpendicular to the vertical section of the axial direction of the barrel body, and is used for simulating a vertical fracture.

[0103] As shown in the drawings, Figure 6 in an embodiment of the present application, the inner wall of the barrel body 1 includes an upper cylindrical section 101, an upper conical section 102, a lower conical section 103 and a lower cylindrical section 104 connected in sequence from top to bottom, the upper piston 4 is arranged in the upper cylindrical section 101, and the lower piston 5 is arranged in the lower cylindrical section 104, so as to slide up and down, the inner diameter of the upper conical section 102 is gradually reduced from top to bottom, and the inner diameter of the lower conical section 103 is gradually reduced from bottom to top, the advantage of the conical inner wall surface is that, when the model is pressed, the taper is beneficial to reduce the frictional resistance caused by the inner wall, and is beneficial to the close concentration between the solid-phase particles, for example, the taper angle of the upper conical section 102 and the lower conical section 103 is 10°-20°, which is a small-angle taper, and the model obtained by pressing is basically not different from a cylinder, and the taper has no effect on the seepage process during the displacement experiment, because the seepage is usually concentrated around the center line of the core sample, and the edge is the weakest.

[0104] Further, the pressure resistance of the barrel body 1 is not less than 150 MPa, and the inner wall of the barrel body 1 is smooth, and the roughness is less than 1.6 μm.

[0105] Further, as shown in the drawings, Figure 8, Figure 9 , Figure 10 As shown, both the upper end cap 2 and the lower end cap 3 include a cap body 15 and a plug 16. The cap body 15 has a stepped hole, which includes a large hole 151 and a small hole 152. The diameter of the large hole 151 is larger than the diameter of the small hole 152. The plug 16 includes a large-diameter section 161 and a small-diameter section 162. The outer diameter of the large-diameter section 161 is larger than the outer diameter of the small-diameter section 162. The outer diameter of the large-diameter section 161 is smaller than the diameter of the large hole 151 but larger than the diameter of the small hole 152. The outer diameter of the small-diameter section 162 is smaller than the diameter of the small hole 152. The large-diameter section 161 is located inside the large hole 151, and the small-diameter section 162 passes through the small hole 152. An annular insertion hole 153 is formed between the outer wall of section 161 and the inner wall of the large hole 151, which can mate with the side wall of the cylinder 1. The inner wall of the large hole 151 is provided with internal threads, and the outer wall of the large diameter section 161 is provided with an O-ring seal 39. The outer walls of both ends of the cylinder 1 are provided with external threads. When the end cap is installed on the cylinder 1, the side wall of the cylinder 1 is screwed into the annular insertion hole 153. Therefore, the cylinder 1 is threadedly connected to the inner wall of the large hole 151, and the cylinder 1 is sealed to the outer wall of the large diameter section 161, thereby realizing the detachable connection and overall sealing between the cylinder 1 and the end cap. The sealing effect is good, the pressure bearing capacity is strong, and the disassembly and assembly are convenient.

[0106] Furthermore, such as Figure 5 , Figure 6 , Figure 11 As shown, the upper connecting pipe 11, lower connecting pipe 12, injection extension section 140, and outlet extension section 150 are all pressure-resistant steel pipes. The plug 16 has a sealing through-hole 163 through which these pressure-resistant steel pipes pass. An O-ring seals the pressure-resistant steel pipes and the inner wall of the sealing through-hole 163. The upper piston 4 has multiple piston through-holes 401 through which the upper connecting pipe 11 and injection extension section 140 pass. The lower piston 5 has multiple piston through-holes 501 through which the lower connecting pipe 12 and outlet extension section 150 pass. For example, there are five piston through-holes 401 and five piston through-holes 501. The upper connecting pipe 11, lower connecting pipe 12, injection extension section 140, and outlet extension section 150 communicate with the pistons. The inner walls of the holes are also sealed by O-rings 39. The upper connecting pipe 11, the lower connecting pipe 12, the liquid injection extension section 140, the liquid outlet extension section 150, and the piston through hole are all parallel to the central axis of the cylinder 1 to facilitate the piston's up and down sliding. The inner wall of the piston through hole is smooth, for example, its roughness is less than 1.6μm. For example, the length of the straight section of each pressure-resistant steel pipe is not less than 20cm. The outer diameter of the pressure-resistant steel pipe is 3mm and the inner diameter is 1mm. The outer wall of the pressure-resistant steel pipe is smooth, for example, its roughness is less than 1.6μm. The plug 16 is also provided with an injection through hole 164. The pressurizing pipe is threaded to the injection through hole 164. The pressurizing liquid is injected into the pressurizing space from the pressurizing pipe through the injection through hole 164.

[0107] Further, the upper piston 4 and the lower piston 5 are made of stainless steel, the end faces are flat, the inner end faces facing the pressing cavity 6 are ground, the surface roughness is in the range of 100-200 μm, and the outer side faces are treated conventionally; the outer side faces of the upper piston 4 and the lower piston 5 are sealed and engaged with the inner wall of the cylinder 1 by O-shaped sealing rings 39; to ensure reliable sealing, double O-shaped ring grooves can be provided on the outer side wall of the piston, and the O-shaped sealing rings 39 installed in the O-shaped ring grooves can play the role of sealing and guiding smooth movement; similarly, to ensure reliable sealing between the pressure-resistant steel pipe and the through hole of the piston, double O-shaped ring grooves can also be provided on the inner side wall of the through hole of the piston, and the O-shaped sealing rings installed in the O-shaped ring grooves can play the role of sealing and keeping the piston in linear motion when moving.

[0108] Further, as shown in Figure 5 , the upper pressurizing pipe 9 is provided with a first on-off valve 17, the lower pressurizing pipe 10 is provided with a second on-off valve 18, the upper communication pipe 11 is provided with a third on-off valve 19, and the lower communication pipe 12 is provided with a fourth on-off valve 20, so as to control the opening and closing of the pipeline and facilitate experimental operation.

[0109] Further, the number of the upper communication pipes 11 is two and they are arranged at intervals, and the number of the lower communication pipes 12 is two and they are arranged at intervals, so as to provide sufficient outflow channels for the oil and sufficient injection channels for the subsequent injection of displacement fluid, to make the displacement fluid injected from multiple positions into the core sample and ensure the displacement effect.

[0110] In an embodiment of the present application, as shown in Figure 5 , the preparation device further comprises a displacement container 21 for containing displacement fluid, the displacement container 21 is connected with the upper communication pipe 11 or the lower communication pipe 12, the displacement container 21 is connected with the pressurizing pump 14, and the pressurizing pump 14 can pump the displacement fluid in the displacement container 21 into the pressing cavity 6, for example, the displacement fluid is gas or water, to simulate gas displacement oil experiment or water displacement oil experiment.

[0111] The preparation device of the present embodiment has the functions of preparing saturated oil shale core samples and conducting displacement experiments, and after the preparation of the saturated oil shale core samples is completed, the displacement experiments can be continuously carried out, so that the continuous operation of core preparation, saturation of oil and displacement experiment is realized.

[0112] Further, as shown in Figure 5 , the preparation device further comprises a back pressure controller 22, the back pressure controller 22 is connected with the upper communication pipe 11 and the lower communication pipe 12, and the back pressure controller 22 is arranged to facilitate pressure control and realize the preparation of saturated oil shale core samples and the displacement experiments under isobaric conditions.

[0113] Further, as shown in Figure 5As shown, the preparation device further comprises a fluid metering device 23 connected with the upper communication pipe 11 and the lower communication pipe 12 for metering the oil liquid discharged from the upper communication pipe 11 and the lower communication pipe 12.

[0114] Further, as shown, Figure 5 the preparation device further comprises a first multi-way valve 24, a second multi-way valve 25 and a third multi-way valve 26, the upper pressurizing pipe 9 and the lower pressurizing pipe 10 are connected with the pressurizing container 13 through the first multi-way valve 24, the upper communication pipe 11 is connected with the fluid metering device 23, the displacement container 21 and the back pressure controller 22 through the second multi-way valve 25, and the lower communication pipe 12 is connected with the fluid metering device 23, the displacement container 21 and the back pressure controller 22 through the third multi-way valve 26, which reduces the number of pipelines and simplifies the structure of the device, and is convenient for experimental control.

[0115] Further, as shown, Figure 5 the first multi-way valve 24 is connected with the pressurizing container 13 and the displacement container 21 through an inlet pipeline 27, and the second multi-way valve 25 and the third multi-way valve 26 are connected with the displacement container 21 through the first multi-way valve 24 and the inlet pipeline 27 respectively, which further reduces the number of pipelines and simplifies the structure of the device. For example, the inlet pipeline 27 is provided with a connection point M for connecting the liquid injection extension section 140.

[0116] Further, as shown, Figure 5 the first multi-way valve 24 is connected with a gas guide main pipe 28, the gas guide main pipe 28 is connected with the second multi-way valve 25 through a first gas guide branch pipe 29, the gas guide main pipe 28 is connected with the third multi-way valve 26 through a second gas guide branch pipe 30, the gas guide main pipe 28 is provided with a fifth switch valve 31, the first gas guide branch pipe 29 is provided with a sixth switch valve 32, and the second gas guide branch pipe 30 is provided with a seventh switch valve 33, so that the fluid in the displacement container 21 can flow into the core sample in the pressurized space through the inlet pipeline 27, the first multi-way valve 24, the gas guide main pipe 28, the first gas guide branch pipe 29, the second multi-way valve 25 and the upper communication pipe 11 in sequence, or flow into the core sample in the pressurized space through the inlet pipeline 27, the first multi-way valve 24, the gas guide main pipe 28, the second gas guide branch pipe 30, the third multi-way valve 26 and the lower communication pipe 12 in sequence, and one of the flow paths is selected for injecting the displacement fluid during the experiment, that is, one end of the pressurized cylinder is used as the injection end, and the other end is used as the production end.

[0117] Further, as shown, Figure 5As shown, the second multi-way valve 25 is connected with a first liquid guide pipe 34, the third multi-way valve 26 is connected with a second liquid guide pipe 35, the eighth switch valve 36 is arranged on the first liquid guide pipe 34, the ninth switch valve 37 is arranged on the second liquid guide pipe 35, the second multi-way valve 25 is connected with the fluid metering device 23 and the back pressure controller 22 through the first liquid guide pipe 34, and the third multi-way valve 26 is connected with the fluid metering device 23 and the back pressure controller 22 through the second liquid guide pipe 35, so that the upper oil in the pressing cavity 6 flows into the fluid metering device 23 through the upper communication pipe 11, the second multi-way valve 25, the first liquid guide pipe 34 in sequence during the pressing process, and the upper oil flows into the fluid metering device 23 through the lower communication pipe 12, the third multi-way valve 26, the second liquid guide pipe 35 in sequence.

[0118] Specifically, the first liquid guide pipe 34, the second liquid guide pipe 35, the fluid metering device 23 and the back pressure controller 22 are connected and communicated through two three-ways 40. For example, a connecting point N is arranged on the connecting pipeline between the two three-ways 40, which is used for connecting the liquid outlet extension section 150.

[0119] In an embodiment of the present application, as shown in Figure 5 A tenth switch valve 41 is arranged on the liquid injection extension section 140 of the horizontal fracture mold 100' and the liquid injection extension section 140 of the vertical fracture mold 100", and an eleventh switch valve 42 is arranged on the liquid outlet extension section 150 of the horizontal fracture mold 100' and the liquid outlet extension section 150 of the vertical fracture mold 100".

[0120] Specifically, for example, as shown in Figure 5 The liquid injection extension section 140 is detachably connected with the connecting point M of the inlet pipeline 27, so that the water in the pressurizing container 13 flows into the pipe body 110 through the inlet pipeline 27 and the liquid injection extension section 140 under the driving of the pressurizing pump 14; the liquid outlet extension section 150 is detachably connected with the connecting point N of the back pressure controller 22, so that the water flows from the liquid outlet extension section 150 to the fluid metering device 23 after flowing through the pipe body 110.

[0121] In an embodiment of the present application, as shown in Figure 5 The preparation device further comprises a rotating support 38 for supporting the pressing cylinder, and the cylinder body 1 is rotationally connected with the rotating support 38. When the saturated oil shale core sample is prepared, the pressing cylinder is rotated to the vertical state, and when the horizontal oil displacement experiment or the CO2 huff and puff experiment is performed, the pressing cylinder is rotated to the horizontal state.

[0122] The saturated oil shale core sample containing fractures (including horizontal fractures and vertical fractures) is prepared by using the preparation device of the present application, and the specific operation is as follows:

[0123] ① Preparation before pressing

[0124] Put the pressing cylinder horizontally, open the upper end cover 2 and the lower end cover 3, and take out the upper piston 4 and the lower piston 5, install the horizontal fracture mold and the vertical fracture mold which have been made on one end of the same piston (for example, the lower piston 5), adjust the position of the core in the fracture mold, and then install the lower piston 5 on one side of the cylinder body 1;

[0125] Adjust the cylinder to a vertical state, tighten the lower end cover 3, connect the lower communication pipe 12 and the lower pressurizing pipe 10 and other pipelines, and then inject water into the lower pressurizing cavity 8 through the lower pressurizing pipe 10, and the lower piston slowly rises during the water injection process, and the injection is stopped when it reaches the preset position;

[0126] Add oil liquid into the cylinder 1 from the top of the cylinder 1, and the volume of the oil liquid is recorded as Voil, and then add the fully mixed raw material to be pressed, and the volume of the raw material is recorded as Vso, Vso is the net volume of the raw material to be pressed, wherein the volume of the sand particles can be measured by the drainage method and then dried, the volume of the solid phase cementing material can be calculated by the drainage method of the particles with the same mass, and the volume of the cementing agent solution is liquid and can be accurately measured by a measuring cylinder, Voil>1.5Vso, that is, the oil liquid completely soaks the raw material to be pressed.

[0127] ②Vacuumizing

[0128] After the oil liquid completely soaks the raw material to be pressed, check whether the inner wall of the cylinder 1, especially the inner wall of the upper cylindrical segment of the cylinder 1, has solid phase particles adhered, and after confirming that the wall surface is smooth, install the upper end cover 2;

[0129] Open the third switch valve 19 on the upper communication pipe 11, and vacuumize from the vent valve of the second multi-way valve 25, and under the condition of -0.1 MPa, the vacuumizing time is not less than three hours, and the oil phase is completely contacted with the solid phase particles through vacuumizing.

[0130] ③Installing the upper piston 4 and the upper end cover 2

[0131] After vacuumizing, open the upper end cover 2, and after confirming that the inner wall surface of the cylinder 1 is smooth, put in the upper piston 4;

[0132] Open the third switch valve 19 on the upper communication pipe 11, and slowly push down the lower piston 5 with the hand, and stop when the oil phase flows out from the vent valve of the second multi-way valve 25, install the upper end cover 2, and connect the upper communication pipe 11 and the upper pressurizing pipe 9 and other pipelines;

[0133] Close the tenth switch valve 41 on the liquid injection extension segment 140 of the horizontal fracture mold 100' and the vertical fracture mold 100", and the eleventh switch valve 42 on the liquid outlet extension segment 150 of the horizontal fracture mold 100' and the vertical fracture mold 100".

[0134] ④Pressing and forming of the core sample

[0135] Open the first switch valve 17 on the upper pressurizing pipe 9, and slowly inject water in the upper pressurizing cavity 7 by the high-pressure plunger pump, stop the pump when the pressure has a rising trend;

[0136] Open the first switch valve 17 on the upper pressurizing pipe 9 and the second switch valve 18 on the lower pressurizing pipe 10 to inject water into the upper pressurizing cavity 7 and the lower pressurizing cavity 8 at the same time;

[0137] Open the third switch valve 19 on the upper communication pipe 11 and the fourth switch valve 20 on the lower communication pipe 12, open the corresponding valve of the second multi-way valve 25 and the third multi-way valve 26, close the fifth switch valve 31, the sixth switch valve 32 and the seventh switch valve 33, adjust the back pressure controller, and set the pressure to 1 MPa;

[0138] Start the high-pressure plunger pump to slowly inject water into the upper pressurizing cavity 7 and the lower pressurizing cavity 8, then the water pushes the upper piston 4 and the lower piston 5 to move to the middle of the cylinder 1, and squeezes the filled raw material to be pressed, during the squeezing process, part of the oil in the pressing cavity 6 flows out from the upper communication pipe 11 and the lower communication pipe 12, and the volume is accurately measured by the fluid metering device 23, and the measured volume is recorded as Voou;

[0139] When no oil flows out, set the pressure of the back pressure controller 22 to more than twice the displacement experiment working pressure, for example, the working pressure is 40 MPa, and the preset pressure is not less than 80 MPa, continue to inject water to squeeze the upper piston 4 and the lower piston 5, and when no oil flows out, stand by for the epoxy resin and the solid-phase cementing material to cement, consolidate and harden, and the time is not less than 72 hours; due to the slight expansion and subsequent shrinkage effect during the cementing process of the solid-phase particles, the pressure will have a small fluctuation, which is a normal phenomenon;

[0140] After standing, the saturated oil shale core sample is completed;

[0141] Close the first switch valve 17 on the upper pressurizing pipe 9 and the second switch valve 18 on the lower pressurizing pipe 10, and the pressure in the upper pressurizing cavity 7 and the lower pressurizing cavity 8 is maintained at the preset pressure of 80 MPa;

[0142] Then adjust the pressure of the back pressure controller 22 to the displacement experiment working pressure (i.e. 40 MPa), and the final value of the outflowing oil volume Voou is determined, then the total volume of the saturated oil in the core sample Vsat is Voil-Voou.

[0143] ⑤Manufacture cracks in the shale core sample

[0144] Adjust the pressing cylinder to a horizontal state, see Figure 6 and Figure 7 ;

[0145] The steps of manufacturing the shale fracture effect are as follows: before the pressure maintaining of the pressing cylinder, all the multi-way valves are closed, then the liquid injection extension section 140 of the horizontal fracture mold 100' is connected with the connection point M of the inlet pipeline 27, the liquid outlet extension section 150 of the horizontal fracture mold 100' is connected with the connection point N of the back pressure controller, the tenth switch valve 41 and the eleventh switch valve 42 on the liquid injection extension section 140 and the liquid outlet extension section 150 of the horizontal fracture mold 100' are opened, then the high-pressure plunger pump is started, and the water is slowly injected, so that the injected water flushes the sodium sulfate coating layer near the through hole 112 at the mold core of the horizontal fracture mold 100', and the water is produced from the outlet end of the back pressure controller, when the oil production is observed at the outlet end, the tenth switch valve 41 and the eleventh switch valve 42 are closed, and the injection is stopped. At this time, it is considered that the sodium sulfate in the horizontal fracture mold 100' has been completely dissolved, and a space in the shape of the mold is formed in the shale, simulating the shape of the horizontal fracture.

[0146] By the same steps, the shape of the vertical fracture is simulated.

[0147] After the saturated oil shale core sample containing fractures is prepared by the preparation device, the displacement experiment can be carried out, for example, the gas displacement oil experiment is taken as an example to simulate the horizontal displacement oil experiment, the gas is injected from the upper communication pipe 11 (referred to as the injection end), and the oil is produced from the lower communication pipe 12 (referred to as the production end), the working pressure of the production end is set as 40 MPa, and the specific experimental process is as follows:

[0148] ① Experimental preparation

[0149] The pressing cylinder is adjusted to be in a horizontal state, the fifth switch valve 31 and the sixth switch valve 32 are opened, the seventh switch valve 33 is closed, the third switch valve 19 on the upper communication pipe 11 and the fourth switch valve 20 on the lower communication pipe 12 are opened, the valve door of the corresponding third multi-way valve 26 is opened, the ninth switch valve 37 is opened, the eighth switch valve 36 is closed, and all the tenth switch valve 41 and the eleventh switch valve 42 are closed.

[0150] ② Gas injection displacement

[0151] The gas pressure in the displacement container 21 is adjusted to be 40 MPa in advance, the high-pressure plunger pump is started, the displacement is carried out at a speed of 0.05 mL / min, the gas gradually enters the pores of the core sample to displace, until a large amount of gas is produced at the production end and no oil is produced, and then the displacement process is ended.

[0152] ③ Device arrangement

[0153] After the experiment, the pressure in the pressing cylinder is released, then the upper end cap 2 and the lower end cap 3 are opened, the upper piston 4 and the lower piston 5 are taken out, and then the core sample in the cylinder body is destroyed and taken out by using a steel chisel, which can be used for analyzing the pore structure characteristics, etc. After a few days, the particles adhering to the inner wall of the core sample are removed by gently knocking, and then the inner surface of the core sample is cleaned for next use.

[0154] Embodiment Four

[0155] As shown in Figure 5 The present application also provides an experimental device for carbon dioxide huff and puff exploitation of shale oil, which comprises the preparation device for the saturated oil shale core sample with fractures according to the third embodiment, and the two ends of the fracture mold 100 are injection end and production end respectively, for example, the liquid injection extension section 140 is the injection end, and the liquid outlet extension section 150 is the production end, the liquid injection extension section 140 is connected with the carbon dioxide gas supply source, and after the fracture is manufactured, the CO2 gas is injected into the injection end to simulate the carbon dioxide huff and puff process.

[0156] Further, the liquid outlet extension section 150 is connected with the back pressure controller 22 and the fluid metering device 23 through the three-way joint 40.

[0157] In an embodiment of the present application, the experimental device further comprises two conventional well simulation tubes 43, one of which passes through the upper end cap 2 and the upper piston 4 and extends into the pressing cavity 6, and the other of which passes through the lower end cap 3 and the lower piston 5 and extends into the pressing cavity 6, the two conventional well simulation tubes 43 are separated from each other in the pressing cavity 6, and the two conventional well simulation tubes 43 can be respectively connected with the carbon dioxide gas supply source, the conventional well simulation tube 43 is not surrounded by fractures, and therefore the conventional carbon dioxide huff and puff experiment can be simulated through the conventional well simulation tube 43. The conventional oil displacement experiment is usually one end injection and the other end production, and by setting two conventional well simulation tubes 43 as two simulation wells, the flexibility of experimental design and implementation is facilitated.

[0158] After the saturated oil shale core sample with fractures (including horizontal fractures and vertical fractures) is prepared by using the experimental device of the present application, the carbon dioxide huff and puff exploitation experiment can be carried out, and the specific experimental process is as follows:

[0159] Taking the research content of comparing the influence of fractures as an example, the CO2 huff and puff oil displacement experiment is simulated, the conventional well simulation tube 43 (simulating a conventional well) is not surrounded by fractures, and is used for CO2 huff and puff without fractures, and is injected and produced from the same end; the pipe body 110 of the horizontal fracture mold 100' (simulating a horizontal fracture well) and the vertical fracture mold 100” (simulating a vertical fracture well) is surrounded by fractures, and is used for CO2 huff and puff with fractures, and can realize the functions of one end injection and the other end production. The working pressure of the production end is set to 40 MPa.

[0160] ① CO2 intake and output without cracks

[0161] like Figure 7 As shown, one end of a conventional well simulation pipe 43 (hereinafter referred to as the first end of the first conventional well simulation pipe 43) is connected to the connection point M of the inlet pipeline 27. A high-pressure plunger pump is started to inject CO2 gas. Since the initial saturated oil pressure in the core sample is 40 MPa, the maximum injection pressure is set to 60 MPa. When the plunger pump reaches 60 MPa, CO2 injection is stopped, and the well is left to stand (steam) for 4 hours. Then, the first end of the first conventional well simulation pipe 43 is connected to the back pressure controller 22, producing gas at a pressure difference of 0.1 MPa / hour. The final produced oil volume (Vpoc) and produced gas volume (Vpgc) are measured. The single recovery rate is then ηc1 = Vpoc / Vsat, completing one CO2 huff and puff cycle.

[0162] Then, the next injection is carried out, and the above steps are repeated. The recovery degree each time is ηc2···ηcn, until no more oil is produced. Then the final recovery degree of CO2 huff and puff in a conventional well is ηc=ηc1+ηc2+···+ηcn. Figure 7 Region E in the diagram represents the area affected by conventional CO2 throughput.

[0163] ② CO2 intake and output with cracks

[0164] like Figure 7 As shown, taking a horizontal fracture as an example, the injection extension section 140 of the horizontal fracture mold 100' is connected to the connection point M of the inlet pipeline 27, and the outlet extension section 150 of the horizontal fracture mold 100' is connected to the connection point N at the back pressure controller 22. Its tenth switch valve 41 is opened, and its eleventh switch valve 42 is closed, injecting CO2 to 60MPa through the injection extension section 140. Afterwards, it is left to stand (well-steaming) for 4 hours, then its tenth switch valve 41 is closed, and its eleventh switch valve 42 is opened, producing at a pressure difference of 0.1MPa / hour. The final produced oil volume (Vpol) and produced gas volume (Vpgl) are measured. The single production rate is then ηl1 = Vpol / Vsat, completing one CO2 huff and puff cycle.

[0165] Then, the next injection is carried out, and the above steps are repeated. The recovery degree each time is ηl2···ηln, until no more oil is produced. Then the final recovery degree of CO2 huff and puff in the horizontal fractured well is ηl=ηl1+ηl2+···+ηln. Figure 7 Region F in the diagram represents the horizontal fracturing influence zone.

[0166] Similarly, the final recovery rate of CO2 huff and puff in a vertically fractured well is ηv = ηv1 + ηv2 + ... + ηvn. Figure 7 Region G in the diagram represents the vertical fracturing influence zone.

[0167] Comparing the ultimate recovery degree of different ways will help to provide reliable guidance for field production.

[0168] ③ Device arrangement

[0169] After the experiment, the pressure of the pressing cylinder is released, then the upper end cover 2 and the lower end cover 3 are opened, the upper piston 4 and the lower piston 5 are taken out, then the core sample in the cylinder body is destroyed and taken out by using a steel chisel, which can be used for analyzing the pore structure characteristics, etc., after a few days, the particles adhering to the inner wall of the core sample are removed by gently knocking, and then the inner surface of the core sample is cleaned for next use.

[0170] The present application has the following characteristics and advantages:

[0171] 1. The present application provides a method for making a crack mold by inorganic salt melting method, which creates a realization path for the standardized design of cracks, and the crack mold completely matches different crack shapes, crack widths, crack lengths and other parameter designs, laying an experimental foundation for quantitative research;

[0172] 2. The present application provides a method for quickly dissolving a crack simulation layer, which solves the disadvantage of the influence of fillers on the seepage process, and when forming a crack by pressure in the laboratory, a crack forming tool needs to be set, and in the limited model space, the volume and shape of the tool will affect the seepage state, and the present application avoids these problems by dissolving the crack simulation layer;

[0173] 3. The present application provides an experimental device and an experimental process suitable for carbon dioxide huff and puff, the conventional CO2 huff and puff method is injection and production in different time periods in the same well, so there is a phenomenon that part of the fluid is driven into the rock pore again after entering the wellbore, which has been ignored, and the experimental process of the present application can realize the huff and puff mode of one side injection and one side production, which completely avoids the above phenomenon.

[0174] The above merely illustrates the specific implementation of the present application, and is not used to limit the scope of the present application. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principle of the present application shall fall within the scope of the present application. Moreover, it should be noted that the components of the present application are not limited to the above overall application, and the technical features described in the specification of the present application can be selected alone or combined with multiple to be used, therefore, the present application naturally covers other combinations and specific applications related to the present application.

Claims

1. A method of preparing a fractured saturated oil shale core sample, characterized by, The preparation method comprises: mixing sand particles and solid-phase cementing material with water absorption to obtain a solid-phase raw material, wherein the particle size of the solid-phase cementing material is smaller than that of the sand particles; diluting the cementing agent with water to obtain a cementing agent solution; spraying the cementing agent solution on the solid-phase raw material and mixing uniformly to obtain a to-be-pressed raw material; putting a crack mold into a pressing cavity of a pressing mold, wherein the crack mold comprises a pipe body and a crack simulation layer wrapping the outer sidewall of the pipe body, the crack simulation layer is made of a dissolvable material, the inside of the pipe body forms a flow passage, a plurality of through holes are arranged in the sidewall of the pipe body and penetrate the outer sidewall to the inner sidewall of the pipe body and communicate with the flow passage; filling the pressing cavity with oil; adding the to-be-pressed raw material into the pressing cavity; pressing the to-be-pressed raw material in the pressing cavity to obtain a saturated oil shale core sample containing the crack mold; passing a solvent for dissolving the crack simulation layer into the flow passage of the crack mold, and the space left after the crack simulation layer is dissolved is a crack to obtain a saturated oil shale core sample containing the crack.

2. The method of preparing a fractured saturated oil shale core sample of claim 1, wherein, The solid-phase cementing material comprises the following components in percentage by weight: aqueous calcium carbonate: 80% to 90%; clay: 10% to 15%; gypsum: 5% to 10%.

3. The method of preparing a fractured saturated oil shale core sample of claim 1, wherein, The content of the sand particles accounts for 85% to 90% of the total weight of the solid-phase raw material, and the content of the solid-phase cementing material accounts for 10% to 15% of the total weight of the solid-phase raw material.

4. The method of preparing a fractured saturated oil shale core sample of claim 1, wherein, The particle size of the sand particles is less than 100 μm, and the particle size of the solid-phase cementing material is 15 μm to 25 μm.

5. The method of preparing a fractured saturated oil shale core sample of claim 1, wherein, The cementing agent is aqueous epoxy resin.

6. The method of preparing a fractured saturated oil shale core sample of claim 1, wherein, The preparation method further comprises a method for preparing the crack mold, and the method for preparing the crack mold comprises: processing through holes on the pipe body and fixing steel needles at the through holes of the pipe body to obtain a crack mold core; making a forming mold with a containing cavity for containing the crack mold core; putting sodium sulfate powder and the crack mold core into the containing cavity to wrap the crack mold core with the sodium sulfate powder; putting the forming mold into a heating furnace and heating the forming mold at a temperature at which the sodium sulfate powder can be melted, so that the sodium sulfate powder melts and wraps the crack mold core to obtain the crack mold.

7. The method of preparing a fractured saturated oil shale core sample of claim 1 wherein, The crack simulation layer is made of sodium sulfate, and the crack simulation layer is formed by melting sodium sulfate powder.

8. The method of preparing a fractured saturated oil shale core sample of claim 1 wherein, The crack mold further comprises a plurality of steel needles fixed on the outer sidewall of the pipe body, the steel needles are perpendicular to the axial direction of the pipe body, and the crack simulation layer wraps the steel needles.

9. The method of preparing a fractured saturated oil shale core sample of claim 8, wherein, The plurality of steel needles are respectively fixed at the plurality of through holes.

10. The method of preparing a fractured saturated oil shale core sample of claim 1 wherein, The plurality of through holes are arranged along the axial direction and the circumferential direction of the pipe body.

11. The method of preparing a fractured saturated oil shale core sample of claim 1 wherein, The pipe body is a steel pipe.

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