Design and use of artificial fracture devices for gel assessment

Abstract

Systems and methods for testing a preformed particulate gel in an artificial fracture system (100) may include introducing a suspension comprising a preformed particulate gel into a testing device, the testing device including an artificial fracture device (103, 200) having a plurality of fracture model units. The system may be configured to first inject a preformed particulate gel into an accumulator (102, 300) having a magnetic stirrer (109) and then into a series of fracture model units configured to receive a fluid through the flow channel and alter the flow channel in a transverse direction relative to a fluid flow direction.

Description

Background Art

[0001] Hydrocarbon resources (including oil and natural gas) are generally located in underground porous rock formations below the surface. In order to obtain these resources, drilling is required to extract hydrocarbon fluids from the reservoir. Fracturing is a common technique for increasing reservoir production and obtaining hydrocarbons in the formation. Enhanced oil recovery (EOR) methods can be used to extract oil from reservoirs, while oil may not be extracted from fractured reservoirs using traditional primary recovery methods. EOR operations can generally include injecting fluids (e.g., gases, polymer mixtures, foams, or liquids) down an injection well to change downhole formation pressure and / or improve oil displacement or fluid flow in the reservoir. The main challenge of enhanced oil recovery (EOR) is to ensure contact between the injected fluid and the hydrocarbons retained in the reservoir.

[0002] In fractured reservoirs, the permeability of hydrocarbon-bearing rocks may vary, and the injected fluids tend to pass through or through high permeability layers and, therefore, do not reach low permeability layers, although the amount of hydrocarbons in these rock formations may not change. This is called the consistency problem. Due to this consistency problem, the displaceable oil in the unswept areas of the rock formation may not be fully recovered. In order to overcome the consistency problem, various techniques are used to allow the remaining hydrocarbons in different areas of the reservoir to circulate to more appropriate consistency conditions. One of these techniques is the use of plugging agents. Plugging agents are widely used to increase hydrocarbon production in fractured reservoirs. By injecting plugging agents into the fractures, high permeability areas can be sealed; this technology increases the redistribution of injected fluids to lower permeability areas, thereby reducing water content and increasing well productivity overall. Gels (including in situ gels and preformed particle gels (PPGs)) are often used as plugging agents to solve consistency control problems.

[0003] Preformed particle gel (PPG) treatments are used in EOR applications to effectively control consistency issues, water shut-off, and ensure fluid transfer in heterogeneous fractured reservoirs. When injected into fractured reservoirs, PPG can form gel packs that block high permeability areas within the fractures, which helps to divert fluids to flow to adjacent matrix, such as to low permeability areas, and recover trapped oil in the formation. This helps to maximize oil recovery and well productivity. Summary of the invention

[0004] This summary is intended to introduce a series of concepts that are further described in the detailed description below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0005] In one aspect, embodiments disclosed herein relate to a system for testing gels for consistency control of artificial fracture devices. The system may include a pump, an accumulator, and an artificial fracture device, all of which are connected in series. The system may also include a pressure measurement system for measuring the pressure at various points in the system. The gel suspension may be introduced into the accumulator, which has a magnetic stirrer inside to ensure continuous mixing of the suspension. The pump may include a hydraulic fluid that may pressurize the suspension contained in the accumulator so that it flows through an outlet. The artificial fracture device is configured to receive a suspension flowing out of the accumulator through a flow channel. The pressure measurement system may include a pressure sensor connected to the artificial fracture device to measure the pressure of various regions in the artificial fracture device.

[0006] In another aspect, the embodiments disclosed herein relate to a method for testing gel for consistency control in an artificial fracture device. The method may include first preparing a gel suspension containing at least a gel-type plugging agent. Next, the suspension may be introduced into an accumulator having a magnetic stirrer that ensures continuous mixing. In addition, a pump with a hydraulic fluid may be used to pressurize the suspension in the accumulator to cause it to flow, and the suspension may be injected from the accumulator into the artificial fracture device. Gel particles may get stuck in the cracks of the artificial fracture device and restrict flow. This may cause an increase in pressure within the cracks. The pressure measurement system may include a pressure sensor connected to the cracks in the artificial fracture device, which may monitor pressure changes within the cracks due to restricted flow, and may provide real-time pressure data during testing.

[0007] Other aspects and advantages of the claimed subject matter will be apparent from the following description and appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Now will be described in detail with reference to the accompanying drawings the specific embodiments of the disclosed technology. For consistency, the same elements in the various figures are represented by the same reference numerals.

[0009] Figure 1 is a schematic diagram of an artificial fracture device for gel evaluation according to an embodiment of the present invention.

[0010] Figure 2 is a schematic diagram of a fracture model unit from a useful artificial fracture apparatus used in embodiments of the present disclosure, showing the shape and size of a stainless steel plate equipped with an O-ring.

[0011] Figure 3 is a schematic diagram of a piston accumulator system used in embodiments of the present disclosure.

[0012] Figure 4is a flow chart illustrating steps involved in a method of ensuring uniformity of gel in an accumulator, injecting fluid in a fracture, and measuring pressure at various points in a designed system according to one or more embodiments.

[0013] Figure 5 is a graph showing pressure during PPG injection in an artificial fracture, illustrating an example according to one or more embodiments. DETAILED DESCRIPTION

[0014] In the following detailed description of the embodiments of the present disclosure, many specific details are set forth to provide a more comprehensive understanding of the present disclosure. However, it will be appreciated by those skilled in the art that the present disclosure may be implemented without these specific details. In other cases, well-known features are not described in detail to avoid unnecessarily complicating the description.

[0015] Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as adjectives of elements (i.e., any noun in the application). The use of ordinal numbers does not imply or create any particular ordering of the elements, nor does it limit any element to only a single element, unless explicitly disclosed, such as using the terms "before," "after," "single," and other such terms. Instead, the use of ordinal numbers is to distinguish elements. For example, a first element is different from a second element, and a first element may include more than one element and be located after (or before) a second element in the ordering of elements.

[0016] The term "uniformity" refers to a measure of the uniformity of the displacement front of an injected drive fluid as it propagates through an oil reservoir during an oil recovery flooding operation.

[0017] The term "compliance control" refers to any action taken to improve the injection or production profile of a hydrocarbon well. This may refer to procedures to increase recovery efficiency, improve wellbore / casing integrity, and meet environmental regulations.

[0018] The term "simulated fracture" used in one or more embodiments of the present disclosure should be understood as the space between two plates of the artificial fracture device as shown in one or more embodiments.

[0019] The term "plugging agent" or "blocking agent" refers to a chemical or composition used to plug or block selected permeable zones of a subterranean formation.

[0020] The term "suspension" refers to a heterogeneous mixture in which the solute particles are not dissolved but suspended in a bulk solvent, floating freely in the medium. The internal phase is dispersed throughout the external phase, either as a stable dispersion or by mechanical agitation, and in some embodiments, using certain excipients or suspending agents.

[0021] The term "gel" refers to a soft solid or solid-like material composed of two or more components, one of which is a liquid present in large quantities. Gels are widely used as plugging agents and can be used in different forms, including preformed particle gels (PPGs) and in situ gels, where a polymer solution and a cross-linking agent are injected into the reservoir to form a three-dimensional (3D) gel network at the bottom of the well.

[0022] The term "preformed particulate gel (PPG)" refers to a particulate superabsorbent polymer system, particulate gel or composite system. A polymer system refers to a gel network comprising a polymer cross-linked with other metals or organic chemicals. A particulate gel refers to a network of aggregated colloidal particles with soft solid-like mechanical properties. A composite gel refers to a gel network composed of oil bodies with at least one cross-linked inorganic or organic chemical. PPG can swell up to 200 times its original size in brine. PPG is commonly used as a blocking agent or chemical that can be used to stimulate the area to be treated to ensure uniform injection to create fractures. When injected into the reservoir, PPG enters the fracture with the carrier water and forms a gel pack, thereby blocking the fracture and diverting flow to the adjacent matrix. Preformed particulate gel (PPG) is larger than other commercially available blocking / plugging agents and preferentially penetrates high permeability areas without damaging low permeability areas. PPG can divert flow by creating a temporary blocking effect that can be safely removed after another conventional cleaning treatment, thereby increasing the production capacity of the entire treatment interval.

[0023] In one or more embodiments, the terms "gel," "PPG," "blocking agent," and "occluding agent" may be used interchangeably.

[0024] In one aspect, embodiments disclosed herein relate to artificial fracture systems and methods of gel evaluation using the artificial fracture systems. Embodiments herein relate to methods and systems that can be used to estimate the properties of any given PPG, which are physically simulated in the laboratory. Embodiments herein also relate to performing simulation tests while ensuring the uniformity of the PPG.

[0025] Figure 1 The design of an artificial fracture system 100 for evaluating the blocking effect of preformed particle gel (PPG) on fractures is shown. The system includes a pump 101, an accumulator 102, an artificial fracture device 103, and a pressure measurement system 104. Generally, the pump 101 is used to displace the PPG suspension from the accumulator 102 into the artificial fracture device 103, and the pressure measurement system 104 measures the pressure of the fluid in various parts of the fracture model to evaluate the effectiveness of the PPG in blocking the fracture.

[0026] The pump 101 can be, for example, a positive displacement pump or a piston pump, and can be used to provide a constant flow rate of hydraulic fluid or a constant pressure to the accumulator through a flow line connecting the pump outlet 110 and the accumulator hydraulic fluid inlet 111. The hydraulic fluid can be understood to mean any liquid that can be used in a piston pump, and can include any number of compounds that can be readily available liquids, gases, or supercritical fluids, and can provide the desired pressure or flow rate control of the accumulator. Incompressible fluids such as water, brine, light hydrocarbons or mixtures of various hydrocarbons, or other fluids commonly used as hydraulic media can be used. Water is the preferred hydraulic fluid for driving the accumulator piston in the pump 101, but other fluids can also be used when the pump 101 and / or the accumulator 102 are to be used in a high temperature environment. The pump 101 can be used to inject hydraulic fluid into the accumulator through the injection port of the accumulator and generate enough pressure to move the piston from the top to the bottom and displace the test fluid in the accumulator.

[0027] The accumulator 102 may have a cylindrical shape with an internal chamber for containing a certain volume of fluid to be tested. The fluid may be understood to represent any mixture that can be tested as a plugging agent in an artificial fracture device. Examples of such plugging agents may be microspheres, such as a gel suspension in a carrier liquid. Within the accumulator is a floating piston that can be moved axially in either direction in a cylinder chamber by a pressure difference applied on both sides of the piston. Typically, the pressure difference is caused by injecting or extracting a hydraulic fluid using a pump 101. Injecting hydraulic fluid from the pump 101 into the accumulator 102 may cause the test plugging agent to flow from the accumulator to the artificial fracture device 103. If hydraulic fluid is extracted from the accumulator 102 by the pump 101, this may cause the piston to retract. Although the shape and material of the chamber are not limited, the accumulator 102 may be a piston container containing a test fluid, an example of which may be a gel suspension in a carrier liquid. The gel may be formed by crosslinking a polymer, such as a preformed particle gel (PPG), and the carrier fluid may be any fluid used for fracturing applications, an example of which may be water. In some embodiments of the present disclosure, the accumulator may be fluidically connected to a fluid circuit system (not shown) for supplying a fluid (which may be, for example, a plugging agent or a suspension containing a plugging agent) to the accumulator chamber via a fluid inlet and discharging the fluid from the accumulator chamber via a fluid outlet.

[0028] A stirrer can be set in the accumulator, and the stirrer is set on the side of the floating piston where the test fluid is placed. The stirrer can be a mechanical stirrer, which is connected to the motor through the head of the accumulator. In other embodiments, a magnetic stirrer 109 can be set at the bottom of the accumulator 102 to stir the test fluid. Stirring can avoid the precipitation of suspended solids (such as PPG suspension in water) in the test fluid, and the test fluid can be tested using an artificial fracture system. The magnetic stirrer 109 can have different shapes, sizes, and the construction material can also change, and the example of this magnetic stirrer 109 can have a rod-like shape. The magnetic stirrer 109 can be placed inside the accumulator 102 before any fluid is injected into the accumulator 102, and during and after the fluid is inserted into the accumulator 102, the magnetic stirrer 109 can be used to ensure the uniform mixing of the fluid, keeping the particles fully suspended. The magnetic stirrer 109 can rotate clockwise or counterclockwise, or clockwise and counterclockwise. By stirring alternately clockwise and counterclockwise, the magnetic stirrer 109 can keep any particles present in the fluid uniformly suspended in the accumulator 102 .

[0029] During testing, hydraulic fluid may be pumped into the accumulator 102 by the pump 101. Thus, the test fluid may be pushed from the accumulator 102 through the accumulator outlet 112 by the piston 116 and supplied to the fracture model of the artificial fracture device 103 through the artificial fracture device inlet 113 through the flow line 114 for testing. A valve 115 may be provided between the accumulator 102 and the artificial fracture device 103 to control the flow rate of the test fluid in the flow line 114. One or more valves may be provided to allow or restrict flow from the accumulator 102, for example, between test intervals for cleaning the artificial fracture device.

[0030] The artificial fracture device 103 described further below can be used to simulate a series of formation fractures. The artificial fracture device can simulate dynamic conditions within the formation fracture, and one such example can be to simulate the flow path, mode and dynamics of the plugging agent in one or more formation fractures. The plugging agent together with the carrier fluid can be introduced into the artificial fracture device through the accumulator inlet 111, as described above, by the pump 101 to push the hydraulic fluid to the piston 116 in the accumulator 102. This can generate enough pressure to push the test fluid from the accumulator 102 through the accumulator outlet 112 and into the artificial fracture device inlet 113 of the artificial fracture device 103 at a constant flow rate or constant pressure. Inside the artificial fracture device 103, the gel plugging agent (e.g., PPG in water) can form a gel plug in the fracture. When the plugging agent forms a plug in the fracture, the carrier fluid may leak through the filling gel or solid bed established by the accumulation of the plugging gel. This may result in an increase in pressure inside the artificial fracture model at the fracture segments including the first model fracture segment 117, the second model fracture segment 118, and the third model fracture segment 119, and eventually the permeability of the gel plug may become so low that the carrier fluid cannot pass through. In one or more embodiments, the artificial fracture system can be used to evaluate PPG or other plugging agents, including bulk gels, resins, and cements.

[0031] The effectiveness of the plugging agent can be monitored by one or more pressure sensors. For example, the pressure measurement system 104 can be used to measure the pressure of the artificial fracture device inlet 113, and the pressure of the test fluid in the three fracture model fracture segments (including the first model fracture segment 117, the second model fracture segment 118 and the third model fracture segment 119) inside the artificial fracture device 103. In some embodiments, the pressure measurement system 104 may include one or more pressure sensors, a data collection unit and a data processing unit. The pressure measurement system 104 can be connected to the artificial fracture device 103 so as to measure the pressure in the three fracture model fracture segments during the test operation. For example, the pressure measurement system 104 can include three pressure sensors, wherein the first pressure sensor 105 can be connected to the fluid inlet of the first model fracture segment 117, the second pressure sensor 106 can be connected to the fluid inlet of the second model fracture segment 118, and the third pressure sensor 107 can be connected to the fluid inlet of the third model fracture segment 119. Other positions of the pressure sensor can also be used. These pressure sensors can send signals to the data collection and processing system 108. Pressure sensors including the first pressure sensor 105, the second pressure sensor 106, and the third pressure sensor 107 can be placed along the artificial fracture device to monitor the injection pressure of each section along the fracture, and the data collection and processing system 108 can record real-time pressure data for analysis. When PPG is used as a plugging agent, the pressure sensors can record pressure data to estimate the PPG blocking efficiency in the artificial fracture model section.

[0032] In one or more embodiments, the system can include one or more temperature sensors. The one or more temperature sensors can be connected to the accumulator chamber, to the flow lines from the pump to the accumulator and from the accumulator to the fracture model unit, or within the fracture device itself.

[0033] In one or more embodiments, the system may include a heating system for emulating or simulating similar pressures and temperatures that may be encountered downhole, thereby providing a simulation of the plugging agent under downhole conditions. To this end, the heating unit may be connected to the artificial fracture device 103, and the artificial fracture system 100 may include a water bath or an oil bath or a heat trace, and may be used to provide heating of the artificial fracture device 103 to test the performance of the plugging agent (e.g., PPG) under simulated downhole conditions (T, P).

[0034] In one or more embodiments, the pump, accumulator, artificial fracture device and pressure measurement unit can all be controlled by an automated computer system. In addition, each of the accumulator and fracture model can be configured to be disassembled for cleaning and reassembled to test additional plugging agents or test fluids.

[0035] According to embodiments herein, an artificial fracture device may include a housing having a series of connected volumes or channels of decreasing thickness and / or width, simulating fractures emanating from a wellbore. Figure 2 As shown, the artificial fracture device 200 can be a cuboid block 201, having a first void region 202 of the largest size inside, a second void region 203 of a medium size, and a third void region 204 of the smallest size, which can be used to simulate fractures in a downhole formation. Although three void regions are shown, fewer or more number of size reductions can be used in other embodiments.

[0036] To facilitate cleaning between tests, a multi-piece construction can be used to form an artificial fracture device. In some embodiments, for example, the fracture device can be formed using an upper portion 207 and a lower portion 208 that are separated along the middle of each void region 209. Although illustrated as having mirrored void regions in the upper and lower portions 208, other multi-piece constructions of fracture models can be used. For example, in one or more embodiments, the top or bottom piece of the artificial fracture model unit can have a constant inner surface height, while the other of the top or bottom can be stepped in the void region to achieve a desired artificial fracture model.

[0037] The artificial fracture device may have an inlet or fluid injection port 205 for receiving a test fluid flow from the accumulator. A fluid outlet or production port 206 may also be provided to simulate flow further into the formation, and the fluid outlet or production port 206 may be used to monitor or measure flow through the fracture model.

[0038] The artificial fracture device 200 has two rectangular parallelepiped halves. Three connected notches of different depths are made on each half. The assembly of the two halves can form a fracture model with a fracture of decreasing size (three fracture segments in series). Although the metal-to-metal seal between the rectangular parallelepiped halves may be sufficient, O-rings or other sealing rings can be used between the two halves to seal the fracture and prevent undesirable flow or leakage from the fracture model during the test. The fracture is designed to have a decreasing height to simulate a 3D shrinkage fracture in the reservoir. A fluid injection port 205 and a production port 206 can be drilled at an obtuse angle on one of the halves to allow the test fluid to flow into and out of the fracture. The outlet of the accumulator is connected to the fluid injection port 205 of the artificial fracture device by a flow line with a sufficient inner diameter so that particles suspended in the test fluid will not block the flow line.

[0039] In one or more embodiments, the length and width of the simulated fracture can vary. For example, a fracture model used during testing can have a first void region with a height of 0.5 cm, a second void region with a height of 0.2 cm, and a third void region with a height of 0.1 cm. A second fracture model can have first, second, and / or third void regions of different heights to simulate other fracture sizes that may be encountered downhole. Although illustrated as having a step change in height, the fracture model can have a gradual or inclined void region. The void regions of the artificial fracture model may not have uniform sizes, but may have sizes that suddenly shrink or expand.

[0040] In one or more embodiments, the artificial fracture device can have a shape that can mimic or simulate three-dimensional flow in real formation fractures. Although real fractures may have jagged or winding flow paths, it has been found that rectangular void areas (e.g. Figure 1 and 2 Those shown in ) are sufficient to simulate cracks and facilitate cleaning between tests.

[0041] In one or more embodiments, the artificial fracture device can have a cylindrical void shape, which can mimic or simulate three-dimensional flow in a real formation fracture.

[0042] Figure 1 and 2An artificial fracture device with three void regions as three model fracture segments is shown. In one or more embodiments, four or more volumes of different three-dimensional shapes may be connected in series to form an artificial fracture device.

[0043] In one or more embodiments, the order of the different volumes may vary. In one or more embodiments, there may also be two or more different sub-volumes connected in parallel inside one of the volumes.

[0044] In one or more embodiments, the artificial fracture device can be made of high stress resistance materials (including stainless steel), which can be used under high temperature and high pressure conditions. If necessary, a viewing window can also be provided to visually observe the test fluid in the fracture model.

[0045] Figure 3The accumulator 300 that can be used in embodiments of the present invention is illustrated. The accumulator 300 can include an accumulator cylinder 301, which can provide a housing for a test fluid 313, in which a floating piston 304 is provided; and a magnetic stirrer 306, which can be used to keep the microsphere particle gel 305 suspended in the carrier liquid of the test fluid 313. The accumulator cylinder 301 can be located on legs 311 and a base 312. The top of the accumulator 300 can have a seal 308. The floating piston 304 within the chamber of the accumulator cylinder 301 can move vertically freely inside the accumulator cylinder 301 and can separate the hydraulic fluid 302 and the test fluid 313. The hydraulic fluid 302 can be gaseous or liquid. When the hydraulic fluid 302 is injected into the accumulator cylinder 301, this can create pressure on the floating piston 304, which can then cause the test fluid 313 to be pushed through the outlet 307 of the accumulator. The magnetic stirrer 306 can be used to continuously mix the microsphere particle gel 305 present in the test fluid 313. The outlet 307 of the accumulator can be located at the lowest position to help the microsphere particle gel 305 and the test fluid 313 flow out. The clockwise and counterclockwise alternating stirring function of the magnetic stirrer 306 can avoid vortexes in one direction and make it easy for particles to enter the outlet 307. The accumulator cylinder 301 can have a charging port 309 on the side, for example, for connection with a second container or accumulator when needed; and a connection port 310 at the top of the accumulator cylinder 301 for connection with the pump 101. The charging port 309 can be used to introduce a plugging agent (such as a PPG suspension) into the accumulator for testing by injection or other means. The charging port 309 can be located at the lower part of the accumulator cylinder 301, below the lowest level of the floating piston 304, so that the PPG suspension can be loaded into the accumulator, pushing the piston upward and filling the lower chamber of the accumulator. The connection port 310 can be used as a hydraulic fluid (gas / liquid) inlet connected to the pump 101, wherein a volume of hydraulic fluid 302 displaced by the pump 101 displaces a similar volume of test fluid 313 (e.g., a suspension of PPG in water) from the reservoir into the flow line and thus into the artificial fracture device 200.

[0046] In one or more embodiments, the accumulator can be made of stainless steel, which can be used under high temperature and high pressure conditions.

[0047] Figure 4400, which illustrates the steps included in the method of ensuring the uniformity of the plugging agent in the accumulator, injecting the test fluid containing the plugging agent into the fracture device, and measuring the pressure at different points of the design system according to one or more embodiments. As a first step 401, a test fluid sample is prepared. For example, a PPG suspension is prepared by first mixing with a brine solution and then mixing with a polymer powder. In step 402, the suspension is then introduced into the accumulator using a pump, wherein the accumulator has a piston and a magnetic stirrer inside. In step 403, an artificial fracture device with one or more artificial fracture model units is assembled and connected to the accumulator using a flow line, which has a sufficient inner diameter to avoid being blocked by the suspension. In the next step 404, one or more pressure sensors are connected to the artificial fracture model unit to record the pressure changes of the entire artificial fracture device. After assembling the fracture model including the sensor, the accumulator and the artificial fracture device are fluidly connected. If necessary, the artificial fracture device can be heated using an external heating device to simulate the fractures in a real hydrocarbon reservoir. Then assemble and operate the artificial fracture system. The hydraulic fluid in the pump is pushed to move the accumulator piston, thereby pushing the test fluid toward the outlet of the accumulator and injecting the test fluid into the fracture device. During the test, the pressure, temperature or any other parameters (if necessary) are monitored to determine the effectiveness and other characteristics of the plugging agent. In step 405, once the test run is completed, the artificial fracture device is disassembled to evaluate any plug formation in the fracture. Based on the pressure recorded within the artificial fracture model unit and the plug formation of the artificial fracture model unit, in step 406, the efficacy of the plugging agent can be determined.

[0048] In one or more embodiments, the inner diameter of the pipeline used for fluid communication throughout the system can be in the range of 4 to 10 mm. In other embodiments, the inner diameter of the pipeline can be at least 3 times, at least 5 times, or at least 10 times the expected diameter of the expanded particles to be suspended in the test fluid. In one or more embodiments, multiple artificial fracture model units can be tested using the artificial fracture device for gel evaluation.

[0049] Example

[0050] The following examples are illustrative only and should not be construed as limiting the scope of the present disclosure.

[0051] Example

[0052] Experiments were conducted in a laboratory setting to demonstrate the testing procedure and efficacy of preformed particle gels in an artificial fracture setup as described above.

[0053] according to Figure 1 The design shown builds a prototype of the artificial fracture system. Figure 3A schematic cross-section of a piston accumulator with a magnetic stirrer at the bottom is shown.

[0054] Polymer (M w =14 million g / mol) was obtained from Anhui Tianrun Chemical Industry Company, China with a purity of 89%. PPG was purchased from HOPECOil Company, China with a purity of 99%.

[0055] First, the PPG sample was prepared in a laboratory environment, and then the PPG sample was introduced into the artificial fracture model by injection using a pump, accumulator and pipeline assembly as a prototype. The average diameter of the PPG was 0.43mm and the water content was less than 1%. The PPG was then immersed in a saline solution with a salinity of 2425mg / L. After swelling in the saline solution for 2 hours, the diameter increased to 2.4mm. The test procedure is listed below.

[0056] First, to prepare the PPG sample, 90 grams of dry PPG was mixed in 0.5L of saline solution using a stirrer at room temperature. The NaCl concentration of the saline solution was 2425 mg / L. After mixing for 60 minutes, the PPG in the saline mixture or suspension was then allowed to fully stand overnight. This caused the PPG to swell.

[0057] Next, the polymer powder is added to the PPG in the brine suspension and the polymer-PPG-brine mixture is stirred at a rate of 800r / min until fully dispersed. The PPG dispersed in the brine suspension is not soluble, but rather swellable and / or shrinkable. PPG as swollen particles tends to sink during flow in pipelines and fractures. The polymer can increase the viscosity of the water phase and improve the suspendability of the PPG. Water-soluble polymers can be used for this application. Non-limiting examples of such polymers can be polyacrylamide and xanthan gum].

[0058] The polymer-PPG-brine suspension is then introduced into the accumulator. There is magnetic stirring at the bottom of the accumulator to ensure adequate mixing inside the accumulator. An artificial fracture device including three fracture model units is assembled, each of which is attached with a pressure sensor. Next, the accumulator is connected to the artificial fracture device and the pressure measurement model unit using a pipeline with an inner diameter of 4 mm. The pipeline is composed of a metal tube, such as stainless steel, Hastelloy or titanium alloy used as a construction material. The inner diameter of the pipeline is 4 mm to allow particles to pass through the pipeline. For high pressure, the thickness of the pipeline or pipe wall is about 1 mm or greater. The test polymer-PPG-brine mixture sample is continuously stirred with clockwise and counterclockwise rotations alternately at intervals of 1 minute to ensure uniform mixing.

[0059] The polymer-PPG-saline suspension was injected into the artificial fracture device at a flow rate of 5 ml / min for 1 hour. The pressure along the fracture was recorded using an attached pressure sensor and a pressure monitoring system.

[0060] After running the above test for 1 hour, the fracture apparatus was disassembled and the gel pack formed in the fracture was evaluated.

[0061] Figure 5 Figure 2 is a graph showing the pressure buildup profile measured in three fractures. The pressure difference in the first fracture is first established, indicating that particles enter the fracture and produce a blockage. The pressure increase is not linear, but is accompanied by pressure fluctuations. A small amount of PPG particles can be observed at the outlet. When the absolute pressure value is above a certain threshold, the pressure is suddenly released to a very low value. A large amount of PPG sample is observed from the outlet. At the same time, the pressure in the second fracture begins to build up. Compared with the pressure increase rate in the first fracture, the pressure increase rate in the second fracture is faster and the maximum value is higher. After the second fracture breaks through, the pressure in the third fracture begins to increase. But the maximum value is not very high and is released very quickly. After that, although the PPG injection was not stopped, the pressure in the three fractures became very low. No effective pressure buildup was observed until the end of the test. The results show that the PPG particles were successfully injected into the fracture by design.

[0062] In one or more embodiments, the effectiveness of the plugging agent can be measured and evaluated in a test environment that simulates the dynamic geometry of a real-world fracturing operation, particularly a real downhole fracture transfer operation. Figure 5 As can be seen in Figure 1, the number of plugs in an artificial fracture can vary, much like the plugs in a real formation fracture can vary (either along the length of a complex geometry or due to changes in downhole conditions). Therefore, the effectiveness of the plugging agent can be measured, specifically the way pressure is generated due to plug formation and restriction of fluid flow in the formation fracture.

[0063] Embodiments of the present disclosure may provide at least one of the following advantages. In conventional methods, there is no design to stably suspend PPG in water. In order to be successfully applied to real situations, any laboratory test needs to mimic real situations. Using conventional testing methods, chemical blockers tend to precipitate quickly in the accumulator, making it difficult to inject chemical blockers into the fractures. The three-dimensional structure of the fractures in the reservoir brings complexity to the use of traditional tube methods. Therefore, traditional tube methods cannot fully mimic the flow in real fractures. The system of the present invention is designed to overcome this challenge by ensuring more controllable particle gel flow. The device can be cleaned and reused. It can also be used to test different materials such as block gels, resins, and cements.

[0064] Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications may be made in the exemplary embodiments without substantially departing from the invention. Therefore, all such modifications are intended to be included within the scope of the present disclosure defined in the following claims.

[0065] Unless defined otherwise, all technical and scientific terms used have the same meaning as commonly understood by one of ordinary skill in the art to which these systems, apparatuses, methods, processes, and compositions belong.

[0066] The singular forms "a," "an," and "the" include plural referents unless the context dictates otherwise.

[0067] As used herein and in the appended claims, the words "comprising," "having," and "including" and all grammatical variations thereof are intended to have an open, non-limiting meaning that does not exclude additional elements or steps.

[0068] "Optionally" means that the subsequently described event or circumstance may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not.

[0069] When the word "about" or "approximately" is used, the term may mean that the value may vary by up to ±10%, up to 5%, up to 2%, up to 1%, up to 0.5%, up to 0.1%, or up to 0.01%.

[0070] The term "substantially" when used refers to a majority or majority, such as at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

[0071] Ranges can be expressed as from about one particular value to about another particular value (including both particular values). When such a range is expressed, it should be understood that another embodiment is from the one particular value to the other particular value, and all particular values ​​and combinations thereof within the range.

[0072] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications in the example embodiments are possible without materially departing from the invention. All such modifications are therefore intended to be included within the scope of the present disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover structures described herein that perform the described function, not only structural equivalents, but also equivalent structures. Thus, while nails and screws may not be structural equivalents because nails employ cylindrical surfaces to secure wood parts together and screws employ helical surfaces, nails and screws may be equivalent structures in the context of fastening wood parts. Applicant expressly disclaims any limitation of any claim herein by invoking 35 U.S.C. §112(f), except for those claims that expressly use the term "means for..." and the associated function.

[0073] While one or more embodiments of the present disclosure have been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be designed without departing from the scope of the present disclosure. Accordingly, the scope of the present disclosure shall be limited only by the appended claims.

Claims

1. A system for evaluating or estimating the performance of a plugging agent in a fracture of an oil-bearing reservoir, the system comprising a pump, an accumulator, an artificial fracture device and a pressure measurement system, in: The accumulator includes a floating piston separating an upper accumulator chamber and a lower accumulator chamber; the pump being fluidly connected to the upper accumulator chamber; A magnetic stirrer is disposed in the lower accumulator chamber, and the lower accumulator chamber is fluidically connected to the artificial fracture device; The artificial fracture device includes a plurality of fracture model units, the plurality of fracture model units including void areas configured to simulate formation fractures; and The pressure measurement system is configured to measure pressure at one or more locations within the artificial fracture device.

2. The system of claim 1 , wherein the accumulator further comprises an outlet proximate a lowest point of the lower accumulator chamber; and An injection port is disposed between the outlet and the floating piston.

3. The system according to claim 2, The outlet of the accumulator is fluidly connected to the injection port of the artificial fracture device through a flow pipeline.

4. The system of claim 3, wherein the flow line connecting the outlet fluid to the injection port has an inner diameter that is at least 3 times the diameter of particles contained in the test fluid located within the lower accumulator chamber.

5. The system according to claim 1, Wherein the magnetic stirrer is configured to rotate clockwise and counterclockwise.

6. The system according to claim 1, The pressure measurement system include: a plurality of pressure sensors, wherein the plurality of pressure sensors are configured to measure pressure at locations along the plurality of fracture model elements; as well as Data collection system.

7. The system according to claim 1, The artificial crack device include: Two stainless steel cuboid halves, the two stainless steel cuboid halves comprising an upper half and a lower half; as well as A void region within each of the upper half and the lower half, wherein the void region of the upper half and the void region of the lower half are similar and are configured such that when the upper half and the lower half are assembled, a plurality of artificial fracture model units having different cross-sectional areas are formed.

8. The system according to claim 7, The artificial fracture device comprises an inlet fluidically connected to the accumulator, wherein the inlet is at an obtuse angle relative to the plurality of artificial fracture model units.

9. A gel evaluation method using an artificial crack system, the method include: Assembling a pump, an accumulator, a pressure measurement system, and an artificial fracture device having a plurality of artificial fracture model units connected in series, wherein the plurality of artificial fracture model units simulate fractures in a hydrocarbon reservoir; injecting a plugging agent from the accumulator into the artificial fracture device through a connecting pipeline; measuring the pressure in the artificial fracture device while injecting the plugging agent; disassembling the artificial crack device; as well as The plugging effect of the plugging agent is measured based on the pressure data and the gel formation formed in the artificial fracture device.

10. The method according to claim 9, The plugging agent is any one of the following: Polymer systems; Particle gels with diameters ranging from 0.01 to 10 mm; and The diameters of the composite gels range from 100 to 10000 nm.

11. The method according to claim 9, in, The method includes one or more of the following: preparing a suspension comprising a preformed particulate gel as the plugging agent and a carrier fluid, and then introducing the suspension into the accumulator; Using at least one valve to monitor the flow rate of the suspension from the outlet of the accumulator; Using one or more temperature sensors to monitor the temperature of the suspension in the accumulator, the connecting pipeline and the plurality of artificial fracture model units; as well as The artificial fracture device is heated using an external heating unit.

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