Active isolation type reservoir depletion type development microfluidic simulation device and recovery ratio quantitative calculation method

Abstract

The invention discloses an active isolation type reservoir depletion type development microfluidic simulation device and a recovery ratio quantitative calculation method, the device comprises a chip integrated with an active isolation micro valve and a double-branch outlet system, and the chip and the double-branch outlet system are used for establishing a physical isolation boundary and controlling rollback pressure reduction; the method comprises the following steps: selecting oil-soluble fluorescent particles, compounding single-phase gas-containing fluorescent crude oil according to a mine field production gas-oil ratio, closing a micro valve after a model is saturated so as to construct a constant-volume closed system, blocking a dead volume of a pipeline, simulating exhaustion by utilizing high-pressure pump rollback, and accurately calculating the recovery ratio based on a linear response relationship between a fluorescence intensity integral value and oil saturation. According to the invention, the interference of fluid backflow in a dead volume on fluid flow characteristics in a microfluidic model is eliminated, the problem of inaccurate measurement of the saturation degree of crude oil is overcome, and high-precision simulation of depletion type development under a real stratum condition is realized.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development experimental evaluation technology, specifically involving the application of microfluidic chip technology in the study of oil and gas phase characteristics and enhanced oil recovery, and particularly involving a microfluidic device and experimental method that can eliminate dead volume interference and realize quantitative calculation of crude oil recovery. Background Technology

[0002] Microfluidics, due to its advantages such as high visualization, low reagent consumption, and rapid mass transfer equilibrium, is widely used in the study of seepage mechanisms at the pore scale of oil reservoirs. In simulating the depletion-type development of oil reservoirs, it is necessary to control the pressure within the model to gradually decrease in order to observe the phase transitions and transport patterns of fluids within the confined space of porous media.

[0003] However, existing microfluidic depletion experiments mainly suffer from the following technical problems: First, dead volume interference leads to distortion of pressure and phase characteristics. Existing devices typically consist of depletion development simulation and quantitative calculation, pipelines, intermediate containers, and microfluidic chips. Dead volume exists at the chip interface and the connection point with external devices. During depressurization during depletion, the fluid expansion and backflow within the dead volume interferes with the observation of the true phase characteristics within the model. Second, microscopic measurement in crude oil systems is difficult. Crude oil is typically dark brown and opaque. In microfluidic experiments, conventional binarization methods based on optical microscopic images are difficult to accurately reflect changes in oil film thickness at the micrometer scale, making it difficult to accurately count the change in crude oil volume caused by pressure reduction, thus affecting the accuracy of depletion-based recovery calculations. Therefore, an experimental device and method are needed that can both physically block dead volume interference and achieve quantitative calculations in crude oil systems. Summary of the Invention

[0004] The purpose of this invention is to provide an active isolation microfluidic simulation device for reservoir depletion development and a method for quantitatively calculating oil recovery. This invention aims to eliminate dead volume effects by integrating active control valves and a dual-branch outlet design at the boundary of the microfluidic model. Simultaneously, it introduces oil-soluble fluorescent particles and strictly blends gas-bearing crude oil according to the production gas-oil ratio, utilizing the response relationship between fluorescence intensity and oil saturation to solve the problem of microscopic volume measurement in the crude oil system, thereby improving the quantitative calculation accuracy of reservoir depletion simulation experiments.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: an active isolation reservoir depletion microfluidic simulation device, mainly comprising a microfluidic chip body, a fluid injection system connected to external pipelines, an outlet pressure control system, a fluorescence microscopy imaging acquisition system, and an active isolation unit. The microfluidic chip body has a porous media model region etched inside to simulate the pore structure of the formation; the active isolation unit is a microvalve disposed on the flow channel between the porous media model region and the external interface, preferably a chip-integrated pneumatic microvalve. This microvalve is located at the fluid inlet end of the porous media model region. The outlet pressure control system adopts a dual-branch parallel structure, connected to the first branch and the second branch respectively through switching valves. The first branch is connected in series with a back pressure valve and a gas-liquid separation metering device; the second branch is connected to a depletion development simulation and quantitative calculation system, used to control the system pressure during the depletion stage and control the pressure reduction through piston retraction.

[0006] Based on the above-mentioned device, the present invention also provides a method for quantitative calculation of oil recovery rate, comprising the following steps: S1, fluid preparation and pretreatment: selecting oil-soluble fluorescent particles with a density matching that of degassed crude oil, and compounding degassed crude oil, component gas and fluorescent particles according to the gas-oil ratio of the oilfield and the temperature and pressure conditions of the target reservoir to obtain single-phase gas-bearing fluorescent crude oil; S2, model saturation and benchmark establishment: injecting single-phase gas-bearing fluorescent crude oil into the model, establishing initial conditions and acquiring benchmark fluorescence images; S3, fluid isolation and switching: switching to the second branch, closing the active isolation unit, and blocking the dead volume of the external pipeline; S4, exhaustion development simulation and quantitative calculation: using exhaustion development simulation and quantitative calculation to reduce pressure, and calculating the oil recovery rate based on the integral difference of fluorescence intensity.

[0007] Beneficial effects of the invention The beneficial effects of the method provided by this invention are mainly reflected in the following three aspects: 1) Reproducing the true fluid phase characteristics. Existing experiments often neglect the influence of crude oil gas content on the depletion process, or struggle to smoothly switch between continuous flow and closed depletion. This invention prepares single-phase gas-containing fluorescent crude oil based on the gas-oil ratio produced in the field, ensuring that the fluid can reproduce the true dissolved gas precipitation and nucleation mechanism during depressurization. Simultaneously, with a dual-branch parallel outlet design, the first branch is responsible for pressure stabilization and saturation, while the second branch is responsible for pressure reduction and backflow, achieving a pressure-fluid-free switch from dynamic displacement to static closed depletion, ensuring the stability of the initial formation pressure state.

[0008] 2) Eliminating Dead Volume Interference. Existing microfluidic experimental setups typically connect the pump and chip directly via external pipelines. During depressurization, the dead volume fluid at the pipelines and interfaces expands and flows back into the chip, interfering with the phase characteristics within the model. This invention integrates an active isolation microvalve at the inlet of the microfluidic model, physically cutting off the fluid channel between the external injection pipeline and the porous media model region at the start of the decay experiment. This structural design transforms the model region into an independent, constant-volume closed system, physically blocking the mass exchange of external fluids and thus eliminating the interference of pipeline fluid expansion and backflow on experimental data.

[0009] 3) Corrected the calculation bias of oil recovery rate. Traditional microfluidic image processing uses optical binarization, which can only count the projected area of ​​crude oil in a two-dimensional plane and cannot identify the changes in oil film thickness in the vertical direction of opaque crude oil, resulting in a fundamental deviation in the calculation of volume changes during the decay process. This invention introduces oil-soluble fluorescent particles that match the density of crude oil and utilizes the linear response relationship between the integral value of fluorescence intensity and oil saturation to transform the measurement of three-dimensional volume change into the integral calculation of two-dimensional fluorescence signal intensity. This method overcomes the technical deficiency of transmitted light imaging in characterizing oil film thickness and corrects the volume deviation that is not included due to oil film thinning. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the overall system structure of the device of the present invention.

[0011] Figure 2 This is a flowchart illustrating the experimental method of the present invention.

[0012] Figure 3 This is a schematic diagram of the structure when the active isolation micro-valve is opened.

[0013] Figure 4 This is a schematic diagram of the structure when the active isolation micro-valve is closed.

[0014] Figure 5 This is a microscopic image of a depleted microflow obtained based on the experimental method of this invention.

[0015] Figure 6 This is a graph showing the change in oil recovery rate with pressure within the model during the exhaustion simulation process. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solution of this invention will be clearly and completely described below in conjunction with a preferred embodiment. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0017] Example: Volatile Oil Depletion Simulation and Recovery Calculation Based on Active Isolation and Fluorescent Quantitative Analysis. This example constructs a high-pressure resistant microfluidic device, with a core glass-silicon-glass chip, capable of withstanding pressures above 30 MPa, and integrating pneumatically controlled microvalves. The chip is placed on a high-resolution fluorescence microscope stage with a filter assembly. The inlet is connected to the depletion-induced development simulation and quantitative calculation, and the outlet is connected via a tee to both the backpressure valve branch (the first branch) and the depletion-induced development simulation and quantitative calculation backflow branch (the second branch). The specific steps of the quantitative calculation method based on this device are as follows: Step S1: Fluid Preparation and Apparatus Pretreatment. First, the experimental fluid is prepared. Degassed crude oil from the target block is selected, and oil-soluble fluorescent particles with a density matching that of the degassed crude oil (density difference < 0.05 g / cm³) are screened to ensure good suspension stability and flow following properties of the particles in the crude oil. The fluorescent particles are added to the degassed crude oil and ultrasonically dispersed evenly. The key is to restore the gas-bearing characteristics of the crude oil: the required amount of component gas is calculated based on the actual gas-oil ratio at the wellhead in the oilfield. The degassed crude oil containing fluorescent particles and a fixed amount of component gas are transferred into a high-temperature, high-pressure sampler. Under the temperature and pressure conditions of the target reservoir, a rotating device is used to accelerate mixing, while a high-pressure metering pump in constant pressure mode is connected to the bottom of the sampler. The volume reading of the high-pressure metering pump is monitored in real time. When the volume inside the pump remains constant within a preset time period, it is determined that the oil and gas have reached phase equilibrium, and the sample preparation is complete. Subsequently, the prepared single-phase gas-bearing fluorescent crude oil is filtered through a high-pressure filter for later use.

[0018] Step S2: Model Saturation and Baseline Establishment. With the microvalve open, inject the prepared single-phase gas-containing fluorescent crude oil into the model to establish an initial pressure of 30 MPa. During this process, monitor the outlet gas-oil ratio in real time through the first branch. When the outlet gas-oil ratio stabilizes and matches the sample value, the fluid saturation within the model is considered complete. At this point, use a fluorescence microscopy system to acquire a full-field image and calculate the sum of fluorescence intensities of all pixels within the model area, recording this as the initial total fluorescence intensity value. S initial This corresponds to an initial oil saturation of 100%.

[0019] Step S3: Fluid Isolation and Switching. Adjust the pressure of the second branch in the depletion-type development simulation and quantitative calculation to achieve equilibrium at 30 MPa. Then, switch the outlet three-way valve to open the second branch and close the first branch. Next, start the high-pressure gas source and apply 35 MPa pressure to the control gas channel layer of the inlet microvalve, driving the elastic diaphragm to deform and close, thereby physically blocking the fluid communication between the dead volume of the injection pipeline and the model region, establishing a closed experimental system.

[0020] Step S4: Exhaustion-based development simulation and quantitative calculation.

[0021] With the inlet microvalve closed, the second branch's exhaustion-type development simulation and quantitative calculation enters a retraction mode, causing the pump piston to retract at a constant rate, controlling the model pressure to decrease at a rate of 0.2 MPa per minute. Images are acquired using a fluorescence microscope after each pressure reduction. The acquired images are imported into analysis software for background denoising. The porous media model region is selected as the region of interest, and all pixels within the region are traversed to calculate the current total fluorescence intensity integral value. S i Based on the linear relationship between fluorescence intensity and oil saturation, the depletion pressure is calculated using the following formula. P i Oil recovery rate at that time η i :

[0022] This formula can calculate the changes in oil recovery rate during depletion development, which are caused by pressure reduction leading to crude oil expansion, dissolved gas precipitation and discharge.

[0023] Experimental results show that this method not only clearly captures the microbubble nucleation phenomenon at 22.5 MPa, but also accurately calculates the crude oil recovery rate at each pressure drop using the aforementioned fluorescence quantitative formula. Compared with the traditional method that relies solely on visual observation of crude oil area ratio, this method corrects the volume estimation bias caused by changes in oil film thickness, and exhibits good data repeatability.

Claims

1. An actively isolated reservoir depletion microfluidic simulation device, comprising: The microfluidic chip body is internally etched with a porous medium model area, and a positive isolation unit is further integrated on the microfluidic chip body, which is arranged on a flow channel between the porous medium model area and an external pipeline interface, and is used to close the flow channel under external driving to block the fluid communication between the external pipeline and the porous medium model area.

2. The active isolated reservoir depletion microfluidic mimic of claim 1, wherein, The positive isolation unit is a pneumatic micro valve, which adopts a multi-layer structure, including a control air channel layer, a fluid passage layer, and an elastic membrane between the two layers; the cross section of the fluid passage at the micro valve is semicircular, and the elastic membrane is used to deform and fit the fluid passage wall under the action of the pressure of the control air channel layer to close the micro valve.

3. A method for microfluidic simulation of recovery factor quantification of oil reservoir depletion using the apparatus of claim 1, wherein, The method comprises the following steps: S1, fluid preparation and pretreatment: selecting oil-soluble fluorescent particles matching the density of degassed crude oil, according to the gas-oil ratio of the production site and the temperature and pressure conditions of the target oil reservoir, compounding the degassed crude oil, component gas and fluorescent particles to make the gas completely dissolved in the crude oil, and obtaining single-phase gas-containing fluorescent crude oil; S2, model saturation and benchmark establishment: injecting the single-phase gas-containing fluorescent crude oil into the porous medium model area, establishing an initial oil reservoir pressure system, and collecting the fluorescent image under the initial state as a calculation benchmark; S3, fluid isolation and switching: switching the outlet pressure control system to the second branch, and driving the positive isolation unit to close, to establish a fluid isolation boundary; S4, depletion development simulation and quantitative calculation: controlling the depletion development simulation and quantitative calculation of the second branch to retreat and depressurize, acquiring images at different pressure moments by using the fluorescent microscopic imaging acquisition system, and calculating the oil recovery based on the correlation between the fluorescent intensity and the oil saturation.

4. The method of claim 3, wherein, The process of fluid preparation in step S1 specifically comprises: connecting a high-pressure metering pump in constant pressure mode at the bottom of the sample preparation device, stirring and mixing the sample preparation device by using a rotating device, monitoring the volume reading of the high-pressure metering pump in real time, and determining that the oil and gas reach phase equilibrium when the volume reading remains constant within a preset time period.

5. The method of claim 3, wherein, The density difference between the oil-soluble fluorescent particles and the degassed crude oil is less than 5%.

6. The method of claim 3, wherein, The quantitative calculation in the step S4 specifically comprises: selecting a porous medium model region as a region of interest, calculating the sum of the fluorescence intensities of all pixel points in the region to obtain a total integral value of the fluorescence intensity; based on the total integral value of the fluorescence intensity under the initial saturated state S initial and the total integral value of the fluorescence intensity under the current depletion pressure S i , calculating the oil recovery ratio by using the following formula The density difference between the oil-soluble fluorescent particles and the degassed crude oil is less than 5%. : ； wherein In step S3, the positive isolation unit is arranged at the inlet end of the microfluidic chip body; in step S4, only the volume expansion of the depletion development simulation and quantitative calculation connected through the outlet end is used for depressurization. is the oil recovery factor, S initial is the total integral value of the fluorescence intensity in the initial saturated state, S i is the total integral value of the fluorescence intensity measured at the current pressure.

7. The method of claim 3, wherein, ​

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