A capillary number-energy loss relationship analysis system and method

Abstract

This invention provides a system and method for analyzing the relationship between capillary number and energy loss. It relates to the field of reservoir development experimental technology. The system includes: a confining pressure and core holding module, comprising at least two core holders connected in series, and pressure monitoring units located at the inlet and outlet of each core holder; each core holder holds a core sample containing pre-fabricated fractures filled with proppant, and the core samples are arranged sequentially along the displacement direction in descending order of proppant density; an injection module for injecting displacement fluid into the confining pressure and core holding module; a backpressure module for acquiring the backpressure of the outflowing displacement fluid from the confining pressure and core holding module; and a data acquisition and processing module, connected to the pressure monitoring unit and the backpressure module, for acquiring differential pressure data at the inlet and outlet of each core holder and velocity data of the outflowing displacement fluid, and obtaining the energy loss and capillary number corresponding to each core holder based on the differential pressure data and velocity data; and establishing a capillary number-energy loss chart.

Description

Technical Field

[0001] This invention relates to the field of reservoir development experimental technology, and in particular to a capillary number-energy loss relationship analysis system and method. Background Technology

[0002] In the development of fractured reservoirs and tight oil and gas reservoirs after fracturing, the proppant concentration directly determines the fracture conductivity and fluid seepage energy consumption. Establishing a chart showing the relationship between capillary number and energy loss can quantify the microscopic flow resistance and macroscopic energy cost under different proppant structures, providing experimental basis for fracturing scheme optimization, injection-production energy consumption prediction, and fracture life-cycle management. Existing methods for determining the relationship between capillary number and energy loss mainly employ the single-core batch testing method, which involves preparing core samples with different proppant concentrations, conducting independent displacement experiments, recording the pressure difference data of each core, calculating the capillary number and energy loss, and then plotting the relationship.

[0003] However, the propped fractures in real reservoirs are spatially complex and heterogeneous. Single core tests can only obtain local energy consumption characteristics of isolated concentration points, which is difficult to reflect the energy dissipation law and the superposition effect of flow resistance at the overall scale of the fracture network system. This results in a systematic deviation between the drawn capillary number-energy loss chart and the actual reservoir flow behavior, and cannot provide a high-precision basis for the optimization of fracturing schemes. Summary of the Invention

[0004] Based on this, it is necessary to provide a capillary number-energy loss relationship analysis system and method to address the above-mentioned technical problems, so as to solve the defect in the existing technology that cannot quantify the overall energy dissipation of non-homogeneous mesh, realize the accurate simulation of the cumulative effect of energy loss along the process, and construct a high-precision capillary number-energy loss chart.

[0005] The following technical solution is adopted in this specification: This specification provides a capillary number-energy loss relationship analysis system, including: The confining pressure and core holding module includes at least two core holders connected in series, and a pressure monitoring unit set at the inlet and outlet of each core holder; wherein, each core holder holds a core sample containing a pre-fabricated fracture, the pre-fabricated fracture is filled with proppant, and the core samples are arranged in sequence along the displacement direction and according to the decreasing sequence of proppant density. The injection module is used to inject displacement fluid into the confining pressure and core clamping module; The back pressure module is used to obtain the confining pressure and the outflow displacement fluid from the core clamping module; The data acquisition and processing module is connected to the pressure monitoring unit and the back pressure module, respectively. It is used to acquire the pressure difference data at the inlet and outlet of each core holder and the flow velocity data of the outflowing displacement fluid. It is used to acquire the energy loss and capillary number of each core holder based on the pressure difference data and flow velocity data. It is also used to establish a capillary number-energy loss chart.

[0006] Furthermore, the number of capillaries is determined based on the aqueous permeability of the core sample, the pressure gradient along the flow path, and the interfacial tension of the displacing fluid; wherein, Water phase permeability is positively correlated with capillary number. Water phase permeability is determined by the aperture characteristics of precast cracks. The larger the aperture, the higher the crack permeability. The friction pressure gradient is positively correlated with the number of capillaries. The friction pressure gradient is determined by the ratio of the pressure difference data at the inlet and outlet of the core holder to the length of the precast crack. The interfacial tension of the displacing fluid is negatively correlated with the capillary number and is determined by the interfacial tension between the phases in the displacing fluid.

[0007] Furthermore, the energy loss is determined by the product of the pressure difference data at the inlet and outlet of each core holder and the outflowing displacing fluid.

[0008] Furthermore, the establishment of the capillary number-energy loss chart specifically includes: A two-dimensional coordinate system is established with the number of capillaries as the horizontal axis and energy loss as the vertical axis. The number of capillaries and energy loss of each core holder under different displacement pressure conditions are marked in a two-dimensional coordinate system to form a data point set. Data points are categorized according to pressure differential. Then, data points on capillary count and energy loss corresponding to different proppant densities under the same pressure differential are fitted along the increasing trend of capillary count to obtain a chart containing multiple curves showing the variation of energy loss along the pressure gradient. This chart is used to characterize: The relationship between capillary number and energy loss under the same proppant density conditions; The relationship between proppant density and energy loss under the same capillary number condition; The relationship between pressure difference and energy loss under the same capillary number and proppant density conditions; Based on the aforementioned diagram, the optimal proppant density under the constraints of target capillary number and energy loss is determined to guide the optimization design of proppant density.

[0009] Furthermore, the injection module includes: Multiple intermediate containers are used to isolate and store different types of displacing fluids. Multiple ISCO pumps are connected one-to-one to the inlet of multiple intermediate containers to independently control the injection flow rate and pressure of each displacing fluid, thereby enabling separate or coordinated injection of the displacing fluid.

[0010] Furthermore, the injection module includes: The vacuum pump is connected to the inlets of multiple intermediate containers and the confining pressure and core clamping modules via multi-port valves. It is used to remove air and residual gas from the intermediate containers, confining pressure and core clamping modules.

[0011] Furthermore, the confining pressure and core clamping module includes a confining pressure pump, which is used to provide confining pressure simulating formation conditions to the core clamp.

[0012] Furthermore, the back pressure module includes: The back pressure valve is connected to the outlet of the confining pressure and core clamping module to maintain the pressure stability at the outlet of the core clamp. The back pressure pump, connected to the back pressure valve, is used to provide back pressure to the back pressure valve and works in conjunction with the confining pressure pump to simulate the pressure environment of the formation conditions.

[0013] Furthermore, the back pressure module includes: A gas-liquid separator, connected to a back pressure valve, is used to separate the gas phase and liquid phase in the displacing fluid. A gas-liquid metering device, connected to a gas-liquid separator, is used to measure the volume of the separated liquid phase.

[0014] This specification provides a method for analyzing the relationship between capillary number and energy loss, including: Different densities of proppant are filled into the prefabricated fractures of multiple core samples, and the multiple core samples are placed in each core holder in order of decreasing proppant density along the displacement direction. Pressure simulating formation conditions is applied to the core holder using a confining pressure pump, a back pressure valve, and a back pressure pump. Displacement fluid is injected into the confining pressure and core clamping module through the injection module, and the pressure data of the displacement fluid at the inlet and outlet of each core clamp is obtained through the pressure monitoring unit. The gas and liquid phases in the confining pressure and the displacing fluid flowing out of the core clamping module are separated by a gas-liquid separator, and the volume of the separated liquid phase is measured by a gas-liquid metering device. The pressure data and liquid volume are processed by the data acquisition and processing module to obtain the pressure difference data at the inlet and outlet of each core holder and the flow velocity data of the outflowing displacement fluid. Based on the pressure difference data and flow velocity data, the energy loss and capillary number corresponding to each core holder are calculated to establish a capillary number-energy loss chart.

[0015] The above-mentioned technical solutions adopted in this specification can achieve the following beneficial effects: This invention places core samples with different proppant densities sequentially along the displacement path, constructing a continuous heterogeneous flow channel. This allows the fluid to pass through sections with different proppant concentrations sequentially, reproducing the true law of energy loss accumulation along the path of fluid crossing the fracture network in the reservoir. Simultaneously, relying on pressure monitoring units set at the inlet and outlet of each core holder to obtain pressure difference data for each section, segmental decoupling of energy loss in each concentration region is achieved. Moreover, since the pressure and velocity data of all concentration points are collected synchronously in the same closed flow loop, the comparison error caused by boundary condition fluctuations in batch experiments is fundamentally eliminated, making the energy loss under different proppant concentrations strictly comparable and significantly improving the accuracy of the capillary number-energy loss chart. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0017] Figure 1 This is a schematic diagram of a capillary number-energy loss relationship system provided in this specification; Figure 2 This document provides a flowchart illustrating a method for understanding the relationship between capillary number and energy loss. Figure 3 This manual provides a schematic diagram of the pressure change profile at each pressure measurement point during real-time testing. Figure 4 This specification provides a schematic diagram illustrating the change in the number of capillaries in a series shale core under conditions of simultaneous injection of CH4 and formation water (gas-liquid ratio of 5). Figure 5 A CH provided in this specification 4- Schematic diagram showing the effect of salt water ratio and fracture filler concentration on the number of two-phase flow capillaries in artificial fracture cores. Figure 6 This is a schematic diagram illustrating the effect of pressure differential and fracture proppant concentration on the number of capillary tubes in the two-phase flow of methane and formation water in a fracture core, as provided in this specification. Figure 7 This is a schematic diagram illustrating the relationship between capillary number and energy loss, provided in this specification. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this specification clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments in this specification without creative effort are within the scope of protection of this application.

[0019] The technical solution provided by this invention can be applied to the development of shale gas reservoirs and fractured reservoirs. When fluids migrate through heterogeneous media such as the matrix and fractures, significant energy loss is usually associated with them. Propionage, as a core method of fracturing, directly determines the fluid's transport capacity through its concentration and structure. However, existing technologies mostly remain at the level of qualitative comparisons of macroscopic permeability or pressure differential, lacking systematic quantitative research on the coupling relationship between proppant concentration, capillary number, and energy dissipation.

[0020] Traditional single-core linear displacement experiments, while capable of characterizing porosity and permeability under specific conditions, struggle to accurately reflect the cumulative energy loss behavior of fluids traversing complex propagation fracture networks from the far end of the formation to near the wellbore. Furthermore, existing methods for estimating energy consumption through pressure differentials generally lack the interconnected analysis of changes in microcapillary structures. This fails to reveal how capillary control mechanisms affect energy transfer efficiency and lacks a graphical and parameterized chart construction methodology to intuitively represent the microdynamic characteristics of the displacement process.

[0021] Based on this, the present invention aims to provide a method for constructing a capillary number-energy loss relationship chart based on core displacement experiments. This method, through the rational design of experimental equipment, acquires a large amount of seepage data under different proppant concentrations, injection pressures, and fluid properties, establishes a coupled model between pressure difference, capillary number, and energy loss, and draws a standardized relationship chart. This chart can accurately quantify the impact of different proppant-filled structures on displacement energy efficiency, solving the problem of inaccurate traditional energy consumption estimation methods. The method provided in this embodiment has strong repeatability and wide applicability. The relationship chart constructed can be directly applied to engineering practices such as fracture conductivity assessment, proppant concentration optimization, and injection-production energy consumption management in unconventional oil and gas reservoirs, providing scientific and visualized experimental basis for the development of complex reservoirs.

[0022] The capillary number-energy loss relationship system of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] Figure 1 This specification provides a structural diagram of a capillary number-energy loss relationship system, as shown below. Figure 1 As shown, the system includes the following: The confining pressure and core holding module includes at least two core holders connected in series, and pressure monitoring units set at the inlet and outlet of each core holder; wherein, each core holder holds a core sample containing a pre-fabricated fracture, the pre-fabricated fracture is filled with proppant, and the core samples are arranged sequentially along the displacement direction according to the proppant density decreasing sequence.

[0024] For example, the confining pressure and core holding module includes a confining pressure pump, at least two core holders connected in series, and pressure monitoring units located at the inlet and outlet of each core holder. Each core holder contains a core sample with pre-fabricated fractures filled with proppant. The core samples are arranged sequentially along the displacement direction in descending order of proppant density. The confining pressure pump provides confining pressure simulating formation conditions to the core holders, placing the core under realistic stress conditions. This prevents core fracturing or fluid flow along the annulus during displacement, ensuring the test results are consistent with formation conditions. Core holders (1-4) are connected in series to hold core samples, enabling displacement of long or multi-segment cores. This simulates the long-distance seepage and displacement process of fluids in actual oil reservoirs, while providing a sealed environment for the core to isolate confining pressure from the displacing fluid. Pressure measuring points (1-5) monitor the inlet / outlet pressure at different locations on the core in real time, acquiring pressure distribution data along the flow path. This data is used to calculate core permeability, pressure gradient, and displacement front advancement, providing fundamental data support for subsequent analysis of the relationship between capillary number and energy loss. The sensor module collects parameters such as temperature and resistivity at different locations on the core. Combined with pressure monitoring data, it allows for real-time analysis of fluid distribution and displacement efficiency changes, providing multi-dimensional data for seepage mechanism research.

[0025] The injection module is used to inject displacement fluid into the confining pressure and core clamping module.

[0026] For example, the injection module includes multiple intermediate containers arranged in parallel for isolating and storing different types of displacement fluids; multiple ISCO pumps, each connected to the inlet of one of the intermediate containers, for independently controlling the injection flow rate and pressure of each displacement fluid, enabling separate or coordinated injection of the displacement fluids; and a vacuum pump, connected via a multi-port valve to the top of the intermediate containers and the inlet of the confining pressure and core clamping module, for evacuating the intermediate containers, core, and piping system to remove air and residual gases, ensuring that the core is saturated with fluid without interference and guaranteeing the accuracy of the initial experimental state.

[0027] The back pressure module is used to obtain the confining pressure and the outflow displacement fluid from the core clamping module.

[0028] For example, the backpressure module includes a backpressure valve, a backpressure pump, a gas-liquid separator, and a gas-liquid metering device. The backpressure valve is connected to the outlet of the confining pressure and core clamping module to simulate formation outlet pressure, maintain stable pressure at the core clamping device outlet, and prevent pressure fluctuations from interfering with the displacement process. The backpressure pump is connected to the backpressure valve to provide stable back pressure, precisely control the outlet pressure, and work with the confining pressure pump to simulate the formation pressure environment. The gas-liquid separator is connected to the backpressure valve to separate the gas and liquid phases in the displacing fluid, facilitating separate metering of gas and liquid production and avoiding the impact of gas-liquid mixing on metering accuracy. The gas-liquid metering device is connected to the gas-liquid separator to accurately meter the separated gas and liquid volumes, used to calculate key indicators such as displacement efficiency, gas-oil ratio, and recovery rate.

[0029] The data acquisition and processing module is connected to the pressure monitoring unit and the back pressure module, respectively. It is used to acquire the pressure difference data at the inlet and outlet of each core holder and the flow velocity data of the outflowing displacement fluid. It is used to acquire the energy loss and capillary number of each core holder based on the pressure difference data and flow velocity data. It is also used to establish a capillary number-energy loss chart.

[0030] For example, the data acquisition and processing module is connected to the pressure monitoring unit and the back pressure module, respectively, to acquire the pressure difference data at the inlet and outlet of each core holder and the flow velocity data of the displacing fluid. Based on the pressure difference and flow velocity data, it calculates the energy loss and capillary number corresponding to each core holder and establishes a capillary number-energy loss chart. For instance, this module collects parameters such as temperature and resistivity at different locations in the core using sensors, and combines this with pressure data to analyze the fluid distribution and displacement efficiency changes in real time, providing multi-dimensional data for mechanism research. Simultaneously, the computer collects and stores data from all sensors, pressure measuring points, and metering devices, enabling real-time monitoring of the experimental process and subsequent data processing, analysis, and visualization, ensuring the accuracy and efficiency of data processing.

[0031] The core of this invention lies in establishing a functional relationship between "pressure difference and energy loss" and a correlation model between "pressure difference and capillary number" through pressure difference experiments, and then drawing a "capillary number-energy loss" chart. By introducing different proppant concentration variables, multi-parameter response evaluation can be achieved. This chart can be used to derive the energy consumption demand or seepage capacity under arbitrary pressure difference and proppant conditions, thereby guiding the optimal selection of proppant concentration in actual gas reservoir fracturing design.

[0032] To achieve the aforementioned core objectives, the experimental procedure is divided into three main stages: preparation, displacement, and production. In the preparation stage, after vacuuming with a vacuum pump, the ISCO pump saturates the core with oil or water through an intermediate container. Simultaneously, a confining pressure pump applies confining pressure, and a backpressure pump sets the outlet pressure to simulate the formation environment. In the displacement stage, the ISCO pump injects displacement fluid, which flows sequentially through four core holders connected in series. Pressure measuring points and sensors collect data along the flow path in real time. In the production stage, the fluid enters a gas-liquid separator after passing through a backpressure valve. The separated gas and liquid phases are measured separately by a metering device. Finally, a computer integrates all the data to complete the experimental analysis, achieving a quantitative characterization from microscopic capillary structure parameters to macroscopic injection and production energy consumption. Figure 2 This is a flowchart illustrating a capillary number-energy loss relationship method provided in this specification. The specific experimental procedure includes:

[0033] Step 1: Collect representative core samples from the target reservoir and measure basic physical properties such as porosity and permeability of the collected core samples to assess their representativeness and applicability.

[0034] Representative core samples from the target reservoir were collected. First, the length and diameter of the cores were precisely measured using vernier calipers. Then, representative core samples from the target block, approximately 25 mm in diameter and 50 mm in length, were selected. After drying, cutting, and end-face treatment, their basic physical properties, such as porosity and permeability, were measured. The basic physical property tests of the core samples were completed using a core porosity and permeability measuring instrument software system. The representativeness of the core samples was evaluated based on the measured porosity and permeability parameters, clarifying their applicability in the experiment.

[0035] Step 2: Test the ion concentration of formation water samples from the experimental block, and prepare artificial formation water with chemical properties consistent with the formation water of the target block based on the test results; according to experimental requirements, obtain the required gases such as methane through market procurement and use them as experimental working fluids.

[0036] First, the ion composition and concentration of formation water samples collected from the experimental block were analyzed. Based on the test results, laboratory-simulated formation water with chemical characteristics consistent with that of the target block's formation water was prepared. Simultaneously, according to experimental requirements, 99.99% pure methane gas was procured commercially as the experimental gas medium. The displacement medium used in the experiment was high-purity methane gas (purity ≥ 99.99%), and the saturated fluid was the aforementioned commercially procured artificial formation water prepared according to the ion concentration ratio of the target block's water samples.

[0037] After the core was evacuated and saturated, a secondary saturation method was used to ensure full saturation. The core saturation experiment ended when the displacement pressure reached 10 MPa. Subsequently, methane gas (99% methane in the reservoir natural gas composition) was injected into the core through the gas-filling intermediate container to perform secondary saturation and pressurize it to the simulated formation pressure of 30 MPa. Simultaneously, an experimental confining pressure of 35 MPa was applied to the core using a confining pressure pump, and this state was maintained until the pressure in the high-pressure intermediate containers at the core inlet and outlet no longer decreased. At this point, the shale gas was basically in its original formation storage state. The relevant valves were closed and the high-pressure gas source was removed, completing the preliminary preparations for the experiment, and the shale gas well full life cycle development simulation experiment was ready to be carried out.

[0038] Step 3: Pre-fabricate fractures in the rock sample using the Brazilian splitting method; then, according to the requirements of the field conditions, mix quartz sand and ceramsite with different mass fractions to form a proppant, and fill the fractures with proppant material of different volumes to complete the preparation of the fracture-supported rock core.

[0039] First, artificial fractures with a width of 0.3–0.5 mm were prefabricated in the rock samples using the Brazilian splitting method. Then, according to the requirements of the field conditions, proppant mixtures of quartz sand and ceramsite with different mass ratios were prepared, and three sets of proppant concentrations were set, corresponding to mass ratios of quartz sand and ceramsite mixtures of 20%, 35%, and 50%, respectively. The proppant mixtures with different proportions were filled into the prefabricated fractures, and the filling length and density of each proppant mixture were controlled to be consistent. After the preparation of the fracture-supported rock core was completed, the rock core was sealed and stored for later use.

[0040] Step 4: Arrange the four core holders in series, connect pressure gauges to the inlet and outlet of each holder, and install necessary supporting equipment such as back pressure valves, back pressure pumps, and confining pressure pumps; place the pre-fractured and sand-filled core samples into each holder to construct a series experimental system simulating the flow of crude oil from the far end of the reservoir to the vicinity of the wellbore during the depletion development process.

[0041] First, the core equipment of the experimental system was installed and connected: four high-pressure core holders were selected and installed in series. Each core holder had a high-precision pressure sensor with an accuracy of 0.01 MPa installed at both ends to monitor the inlet and outlet pressures in real time. A backpressure valve and a backpressure pump were connected at the end of the series system to maintain a constant outlet pressure (e.g., 1.5 MPa). Simultaneously, a confining pressure pump was installed outside each holder to provide a constant confining pressure (e.g., 10 MPa) to simulate the formation stress environment. Next, the supplementary equipment was installed: pressure gauges were connected to the inlet and outlet of each core holder to further assist in monitoring pressure data. At the same time, all necessary supporting equipment, such as the backpressure valve, backpressure pump, and confining pressure pump, were ensured to be installed in place and securely connected to guarantee the stability of the system operation and the accuracy of data monitoring. Finally, core samples were loaded and the system was assembled: core samples with pre-fabricated fractures and proppant were placed in each high-pressure core holder. The core samples were loaded in the order of "low concentration - medium concentration - high concentration - control blank". Stainless steel pipes were used to seal and connect each holder. Finally, a series experimental system was constructed to simulate the flow of crude oil from the reservoir to the vicinity of the wellbore during the entire life cycle of depletion development, and the assembly of the entire experimental system was completed.

[0042] Step 5: Using a computer-controlled data acquisition system, monitor and record the pressure at the front and rear ends of each clamp in real time during the experiment; calculate the energy loss value and corresponding capillary number at each stage based on the pressure difference-energy loss formula and the pressure difference-capillary number calculation model, and draw a capillary number-energy loss chart to analyze the relationship between microscopic seepage characteristics and displacement efficiency.

[0043] For example, during the experimental data processing phase, the data acquisition and processing module is used to monitor and record the pressure at the front and rear ends of each gripper in real time during the experiment; for each core segment, the energy loss per unit volume is calculated based on the acquired data using the pressure difference-energy loss formula: ; in, Indicates energy loss, J; This represents differential pressure data; Indicates the volume of the displacing fluid; The coefficient of friction is a dimensionless coefficient used to describe the frictional losses of fluid flowing in a pipe. L represents the length of the pipe (m); D represents the diameter of the pipe (m). The density of the fluid is expressed in kg / m³. This indicates the flow velocity of the fluid, in m / s.

[0044] Simultaneously, the corresponding capillary count is calculated based on the capillary count calculation model: ; in, This represents the water phase permeability in shale fractures, characterized by... Characterization (where h represents crack thickness), m 2 ; It is the pressure difference across the tested fractured shale core, in kPa; It is the length of the fracture, equivalent to the length of the shale core sample tested for the fracture, in meters (m). It is the interfacial tension between the gas and liquid systems, in mN / m.

[0045] Based on the above calculation results, a "capillary number-energy loss" chart was created to analyze the relationship between microscopic flow characteristics and displacement efficiency. Analysis of the chart shows that under the same injection pressure differential, higher proppant concentration results in lower unit energy loss, indicating that proppant helps reduce capillary confinement. Simultaneously, a threshold effect exists for the number of capillary units at different pressure differentials; exceeding a certain capillary number range significantly increases unit energy consumption. This chart is ultimately used as a reference template to identify the microscopic flow capacity and energy consumption trends under different injection conditions and proppant concentrations, predicting energy consumption under specific pressure gradients or proppant structures. This provides data support and decision-making basis for proppant selection and fracture support structure optimization design in gas reservoirs.

[0046] This application provides experimental results obtained based on the above experimental steps, such as... Figures 3-7 As shown: Figure 3 This is a schematic diagram of the pressure change profile at various pressure measurement points during real-time testing, provided in this manual. Figure 3 It intuitively reflects the dynamic evolution of pressure at different pressure measurement locations of the series core system during the experiment, as well as the time / injection conditions. It can clearly show the distribution characteristics of pressure loss along the flow path, providing an intuitive basis for analyzing the pressure transmission and seepage resistance changes during the displacement process.

[0047] Figure 4 This specification provides a schematic diagram illustrating the variation of capillary number in a series shale core under conditions of simultaneous CH4-formation water injection (gas-liquid ratio of 5). Figure 4 This study demonstrates the changing trend of capillary number under specific gas-liquid ratio injection conditions, as the experiment progresses or the core location changes, revealing the seepage characteristics of gas and water phases in shale matrix and fractures and the law of capillary force action.

[0048] Figure 5 A CH provided in this specification 4- A schematic diagram illustrating the effects of brine ratio and fracture-filling proppant concentration on the number of capillary tubes in two-phase flow within an artificial fracture core reflects the response variation of capillary tube number under the combined effects of different gas-water ratios and different proppant concentrations, clarifying the quantitative relationship between two-phase flow state and key control parameters.

[0049] Figure 6 This specification provides a schematic diagram illustrating the influence of pressure differential and fracture-filling proppant concentration on the number of capillary tubes in the two-phase flow of methane and formation water in fractured cores. It demonstrates the individual and coupled effects of the two major variables, driving pressure differential and proppant concentration, on the number of capillary tubes, and quantitatively characterizes the regulatory effect of seepage dynamics and fracture filling state on the number of two-phase capillary tubes.

[0050] Figure 7 This specification provides a schematic diagram of the relationship between capillary number and energy loss, establishing a quantitative correspondence between capillary number and system energy loss, forming a standard diagram that can be directly used for engineering evaluation and mechanism analysis, and providing data support and judgment criteria for assessing the gas-water two-phase seepage resistance and predicting the displacement effect in fractured cores.

[0051] The procedure for the capillary number-energy loss relationship method provided in this specification may include: S1. Fill the prefabricated fractures of multiple core samples with proppant of different densities, and place the multiple core samples in each core holder in order of decreasing proppant density along the displacement direction.

[0052] S2. Apply pressure simulating formation conditions to the core holder using a confining pressure pump, a back pressure valve, and a back pressure pump. S3. Displacement fluid is injected into the confining pressure and core clamping module through the injection module, and the pressure data of the displacement fluid at the inlet and outlet of each core clamp is obtained through the pressure monitoring unit.

[0053] S4. The gas phase and liquid phase in the confining pressure and the displacement fluid flowing out of the core clamping module are separated by a gas-liquid separator, and the volume of the separated liquid phase is measured by a gas-liquid metering device.

[0054] S5. The pressure data and liquid volume are processed by the data acquisition and processing module to obtain the pressure difference data at the inlet and outlet of each core holder and the flow velocity data of the outflowing displacement fluid. Based on the pressure difference data and flow velocity data, the energy loss and capillary number of each core holder are calculated to establish a capillary number-energy loss chart.

[0055] For specific limitations on the capillary number-energy loss relationship method, please refer to the limitations of the capillary number-energy loss relationship system mentioned above, which will not be repeated here. Each module in the above capillary number-energy loss relationship system can be implemented entirely or partially through software, hardware, or a combination thereof.

[0056] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0057] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A capillary number-energy loss relationship analysis system, characterized in that, include: The confining pressure and core holding module includes at least two core holders connected in series, and a pressure monitoring unit set at the inlet and outlet of each core holder; wherein, each core holder holds a core sample containing a pre-fabricated fracture, the pre-fabricated fracture is filled with proppant, and the core samples are arranged in sequence along the displacement direction and according to the decreasing sequence of proppant density. The injection module is used to inject displacement fluid into the confining pressure and core clamping module; The back pressure module is used to obtain the confining pressure and the outflow displacement fluid from the core clamping module; The data acquisition and processing module is connected to the pressure monitoring unit and the back pressure module, respectively. It is used to acquire the pressure difference data at the inlet and outlet of each core holder and the flow velocity data of the outflowing displacement fluid. It is used to acquire the energy loss and capillary number of each core holder based on the pressure difference data and flow velocity data. It is also used to establish a capillary number-energy loss chart.

2. The capillary number-energy loss relationship analysis system as described in claim 1, characterized in that, The number of capillaries is determined based on the aqueous permeability of the core sample, the pressure gradient along the flow path, and the interfacial tension of the displacing fluid; among which... Water phase permeability is positively correlated with capillary number. Water phase permeability is determined by the aperture characteristics of precast cracks. The larger the aperture, the higher the crack permeability. The friction pressure gradient is positively correlated with the number of capillaries. The friction pressure gradient is determined by the ratio of the pressure difference data at the inlet and outlet of the core holder to the length of the precast crack. The interfacial tension of the displacing fluid is negatively correlated with the capillary number and is determined by the interfacial tension between the phases in the displacing fluid.

3. The capillary number-energy loss relationship analysis system as described in claim 1, characterized in that, The energy loss is determined by the product of the pressure difference data at the inlet and outlet of each core holder and the outflowing displacing fluid.

4. The capillary number-energy loss relationship analysis system as described in claim 1, characterized in that, The establishment of the capillary number-energy loss chart specifically includes: A two-dimensional coordinate system is established with the number of capillaries as the horizontal axis and energy loss as the vertical axis. The number of capillaries and energy loss of each core holder under different displacement pressure conditions are marked in a two-dimensional coordinate system to form a data point set. Data points are categorized according to pressure differential. Then, data points on capillary count and energy loss corresponding to different proppant densities under the same pressure differential are fitted along the increasing trend of capillary count to obtain a chart containing multiple curves showing the variation of energy loss along the pressure gradient. This chart is used to characterize: The relationship between capillary number and energy loss under the same proppant density conditions; The relationship between proppant density and energy loss under the same capillary number condition; The relationship between pressure difference and energy loss under the same capillary number and proppant density conditions; Based on the aforementioned diagram, the optimal proppant density under the constraints of target capillary number and energy loss is determined to guide the optimization design of proppant density.

5. The capillary number-energy loss relationship analysis system as described in claim 1, characterized in that, The injection module includes: Multiple intermediate containers are used to isolate and store different types of displacing fluids. Multiple ISCO pumps are connected one-to-one to the inlet of multiple intermediate containers to independently control the injection flow rate and pressure of each displacing fluid, thereby enabling separate or coordinated injection of the displacing fluid.

6. The capillary number-energy loss relationship analysis system as described in claim 5, characterized in that, The injection module includes: The vacuum pump is connected to the inlets of multiple intermediate containers and the confining pressure and core clamping modules via multi-port valves. It is used to remove air and residual gas from the intermediate containers, confining pressure and core clamping modules.

7. The capillary number-energy loss relationship analysis system as described in claim 1, characterized in that, The confining pressure and core clamping module includes a confining pressure pump, which is used to provide confining pressure simulating formation conditions to the core clamp.

8. The capillary number-energy loss relationship analysis system as described in claim 7, characterized in that, The back pressure module includes: The back pressure valve is connected to the outlet of the confining pressure and core clamping module to maintain the pressure stability at the outlet of the core clamp. The back pressure pump, connected to the back pressure valve, is used to provide back pressure to the back pressure valve and works in conjunction with the confining pressure pump to simulate the pressure environment of the formation conditions.

9. The capillary number-energy loss relationship analysis system as described in claim 8, characterized in that, The back pressure module includes: A gas-liquid separator, connected to a back pressure valve, is used to separate the gas phase and liquid phase in the displacing fluid. A gas-liquid metering device, connected to a gas-liquid separator, is used to measure the volume of the separated liquid phase.

10. A capillary number-energy loss relationship analysis method for a capillary number-energy loss relationship analysis system according to any one of claims 1-9, characterized in that, include: Different densities of proppant are filled into the prefabricated fractures of multiple core samples, and the multiple core samples are placed in each core holder in order of decreasing proppant density along the displacement direction. Pressure simulating formation conditions is applied to the core holder using a confining pressure pump, a back pressure valve, and a back pressure pump. Displacement fluid is injected into the confining pressure and core clamping module through the injection module, and the pressure data of the displacement fluid at the inlet and outlet of each core clamp is obtained through the pressure monitoring unit. The gas and liquid phases in the confining pressure and the displacing fluid flowing out of the core clamping module are separated by a gas-liquid separator, and the volume of the separated liquid phase is measured by a gas-liquid metering device. The pressure data and liquid volume are processed by the data acquisition and processing module to obtain the pressure difference data at the inlet and outlet of each core holder and the flow velocity data of the outflowing displacement fluid. Based on the pressure difference data and flow velocity data, the energy loss and capillary number corresponding to each core holder are calculated to establish a capillary number-energy loss chart.

Images