Injection process of high-efficiency microemulsion oil-displacing agent suitable for low-permeability reservoir

Abstract

The invention relates to the technical field of chemical oil displacement control, in particular to an injection process of an efficient microemulsion oil displacement agent suitable for a low-permeability reservoir. The method comprises the following steps: firstly, monitoring data in a preset injection disturbance mode, carrying out time domain alignment, and then obtaining a corrected pressure sequence and a corrected flow sequence after a background trend line is removed; a dynamic fluctuation resistance ratio is further obtained according to the fluctuation difference between the corrected pressure sequence and the corrected flow sequence, and the fluid state is judged; when it is judged that the fluid is in the high-resistance response state, phase-space reconstruction is conducted on the standardized correction pressure sequence, and a fluctuation regularity index is calculated; comparing the fluctuation regularity index with a preset reference fluctuation regularity, and setting a fluid state flag bit; and finally, the injection of the efficient microemulsion oil displacement agent is regulated and controlled based on the fluid state flag bit, so that the fluid state is accurately distinguished under the high-pressure working condition, and the oil displacement economic benefit is optimized.

Description

Technical Field

[0001] This invention relates to the field of chemical flooding control technology, specifically to an injection process for a highly efficient microemulsion flooding agent suitable for low-permeability reservoirs. Background Technology

[0002] In the development of low-permeability reservoirs, due to the complex and highly heterogeneous pore structure of the reservoir, conventional waterflooding is difficult to establish an effective driving pressure differential. Therefore, microemulsion flooding technology is often used to improve the degree of matrix mobilization.

[0003] However, the reservoir fluid flow state is highly uncertain during microemulsion injection. Existing monitoring methods mainly rely on surface pressure and flow data to calculate injection resistance. While this linear index can identify low-resistance fracture leakage, it cannot distinguish between ineffective pore inlet blockage and effective pore seepage under high-pressure conditions. Both exhibit high macroscopic resistance values, making it difficult to determine on-site whether to take deblocking measures or maintain normal injection, often resulting in ineffective consumption of chemical agents or loss of well productivity. Summary of the Invention

[0004] To address the technical problem of accurately distinguishing fluid states and precisely controlling the injection of efficient microemulsion flooding agents under high-pressure injection conditions during microemulsion flooding in low-permeability reservoirs, this invention aims to provide an injection process for efficient microemulsion flooding agents suitable for low-permeability reservoirs. The specific technical solution adopted is as follows: Under the preset injection perturbation mode, the flow data and pressure data in the current data buffer are time-domain aligned based on cross-correlation analysis. The background trend lines of the aligned pressure data and flow data are extracted respectively, and the corrected pressure sequence and corrected flow sequence are obtained after removing the background trend lines. Based on the fluctuation difference between the modified pressure sequence and the modified flow sequence, the dynamic fluctuation resistance ratio is obtained, and combined with a preset leakage threshold, the fluid state is determined. When the fluid is determined to be in a high-resistance response state, the phase space of the standardized modified pressure sequence is reconstructed, a recursive graph matrix is ​​constructed, and the fluctuation regularity index is calculated. The fluctuation regularity index is compared with a preset benchmark fluctuation regularity, and a fluid state flag is set. When the fluid is determined not to be in a high-resistance response state, the fluid state flag is set to a preset first state. The injection of highly efficient microemulsion oil displacement agents is regulated based on the fluid state flag.

[0005] Furthermore, the method for obtaining the volatility regularity index includes: From the standardized modified pressure sequence, state vectors are extracted according to a preset embedding dimension and delay time; a recursive graph matrix is ​​constructed based on the state vectors; the length distribution of line segments parallel to the main diagonal in the recursive graph matrix is ​​statistically analyzed, and a deterministic index is calculated as the volatility regularity index.

[0006] Furthermore, when the fluctuation regularity index is not less than the preset benchmark fluctuation regularity, the fluid state flag is set to a preset second state; when the fluctuation regularity index is less than the preset benchmark fluctuation regularity, the fluid state flag is set to a preset third state.

[0007] Furthermore, the method for regulating the injection of the high-efficiency microemulsion oil displacement agent based on the fluid state flag bit includes: A graded control strategy is executed based on the current fluid state: when the preset first state is in effect, the injection rate is increased by a preset testing ratio within a preset testing window. If the maximum dynamic fluctuation resistance ratio calculated within the preset testing window is less than a preset leakage threshold, and the increase rate of the maximum dynamic fluctuation resistance relative to the dynamic fluctuation resistance before the preset testing window is less than a preset rise threshold, then the channel plugging agent injection pump is started to mix a preset graded high-viscosity gel plug into the injection pipeline. When in the preset second state, the injection concentration of the surfactant is increased by a preset concentration step. When in the preset third state, the injection pump speed remains constant.

[0008] Furthermore, after injecting high-viscosity gel or increasing the injection concentration of interfacial activity modifier, the inhibition phase begins. Once the cumulative injection volume reaches the wellbore tubing volume, the inhibition phase ends.

[0009] Furthermore, the method for obtaining the background trend line includes: Linear fitting is performed on the aligned pressure data and flow data respectively, and the fitted lines are used as their respective background trend lines.

[0010] Furthermore, the method for obtaining the dynamic fluctuation resistance ratio includes: The dynamic fluctuation resistance ratio is obtained based on the difference between the standard deviation of the modified pressure sequence and the standard deviation of the modified flow sequence.

[0011] Furthermore, the method for determining the fluid state includes: When the dynamic fluctuation resistance ratio is less than the preset leakage threshold, the fluid is determined not to be in a high-resistance response state; when the dynamic fluctuation resistance ratio is greater than or equal to the preset leakage threshold, the fluid is determined to be in a high-resistance response state.

[0012] Furthermore, the method for obtaining the preset benchmark fluctuation regularity includes: When the formation connectivity is known to be good or the water injection stage has just been established, the fluctuation regularity index is calculated based on the flow and pressure data in the data buffer, and the fluctuation regularity index of the preset proportion is used as the preset benchmark fluctuation regularity.

[0013] Furthermore, the preset injection disturbance mode is: a preset sinusoidal flow disturbance signal is superimposed on the preset constant current injection.

[0014] The present invention has the following beneficial effects: This invention first monitors data under a preset injection disturbance mode to obtain dynamic response data reflecting formation porosity characteristics, and performs time-domain alignment to avoid phase misalignment in analysis. Then, it obtains the corrected pressure sequence and corrected flow sequence after removing the background trend line, improving the sensitivity to capture weak signals under high-pressure conditions. Furthermore, based on the fluctuation difference between the corrected pressure sequence and the corrected flow sequence, it obtains the dynamic fluctuation resistance ratio, which characterizes the macroscopic impedance response intensity of the formation system to the injection flow fluctuation. Based on the macroscopic fluctuation characteristics, it quickly screens the fluid response state. When the fluid is determined to be in a high-resistivity response state, it reconstructs the phase space of the standardized corrected pressure sequence and calculates the fluctuation regularity index as a data mapping index reflecting the abnormal flow characteristics, used to distinguish between two working conditions with similar macroscopic resistance but different waveform shapes. Then, it compares the fluctuation regularity index with the preset benchmark fluctuation regularity to set a fluid state flag. Finally, it regulates the injection of high-efficiency microemulsion oil displacement agent based on the fluid state flag. This invention utilizes disturbance monitoring, time-domain alignment, and detrending processing to perform preliminary screening using dynamic fluctuation resistance ratio. It combines phase space reconstruction and fluctuation regularity index to decouple the blockage and seepage states under high pressure, thereby regulating injection and accurately distinguishing fluid states under high pressure conditions to optimize oil displacement economic benefits. Attached Figure Description

[0015] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A flowchart illustrating an injection process for a highly efficient microemulsion flooding agent suitable for low-permeability reservoirs, provided as an embodiment of the present invention; Figure 2 This is a flowchart illustrating the regulation of injection of a highly efficient microemulsion oil displacement agent, as provided in one embodiment of the present invention. Detailed Implementation

[0017] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of an injection process for a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0019] The following describes in detail, with reference to the accompanying drawings, a specific scheme for the injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs provided by the present invention.

[0020] Please see Figure 1 The document illustrates a flowchart of an injection process for a highly efficient microemulsion flooding agent suitable for low-permeability reservoirs, provided by an embodiment of the present invention. The process specifically includes: Step S1: Monitor data under the preset injection perturbation mode, align the flow data and pressure data in the current data buffer in the time domain based on cross-correlation analysis, extract the background trend lines of the aligned pressure data and flow data respectively, and obtain the corrected pressure sequence and corrected flow sequence after removing the background trend lines.

[0021] To obtain dynamic response data reflecting formation porosity characteristics, a small active disturbance needs to be superimposed on conventional constant-flow injection. Therefore, data is monitored under a preset injection disturbance mode. In one embodiment of the present invention, the injection pump is started and an initialization procedure is executed. The basic injection displacement is set. As a preset constant current injection, for example, it is set according to the reservoir injection requirements. Based on the preset constant current injection, a preset sinusoidal flow disturbance signal is superimposed, and the superposition frequency of the variable frequency pump is controlled to be [value missing]. , amplitude The sinusoidal flow disturbance signal.

[0022] Among them, for the perturbation frequency If the frequency is too high (e.g.) Pressure waves are completely attenuated by the wellbore storage effect (analogous capacitance filtering) during long-distance wellbore transmission, resulting in no signal at the bottom of the well; if the frequency is too low (e.g. If the test cycle is too long, it cannot meet the real-time control requirements. This embodiment is preferred. The range is (corresponding period) (seconds). Within this frequency range, although wellbore effects still exist, pressure waves retain a detectable residual amplitude (typically the wellhead amplitude) upon reaching the bottom of the well. This is sufficient to elicit an impedance response in the formation pores.

[0023] Disturbance amplitude The selection of [specific parameter] needs to ensure a good signal-to-noise ratio without affecting normal water injection operations; it is generally set to [specific value]. of .

[0024] As an example, Take the corresponding 5%, disturbance frequency Take 0.05Hz.

[0025] It should be noted that the basic injection displacement is set according to the reservoir injection requirements, and the sinusoidal flow disturbance signal can be adjusted according to the actual needs of the scenario, which will not be elaborated further.

[0026] The system synchronously collects inlet flow rate and wellhead pressure data using a high-frequency sensor at the wellhead and stores them in a circular data buffer in chronological order. The data buffer employs a first-in, first-out (FIFO) sliding window mechanism. In one embodiment of the invention, the length of the data buffer is... Set to Override Each disturbance period corresponds to the number of data points. During the regular injection process, discretization analysis is performed at intervals based on the perturbation period, and a low-frequency analysis strategy is executed. When a probe operation is performed, the high-frequency analysis strategy is switched within a preset probe window, such as setting the analysis interval to 5 sampling points.

[0027] The disturbance period is determined by the disturbance frequency. OK, M is set to 3. Set the sampling interval. At that time, it is necessary to meet the requirements of The requirement for waveform reconstruction of a signal under certain conditions (based on the Nyquist sampling theorem). Take 0.1 seconds.

[0028] It should be noted that if the data buffer is not full, the data support is deemed insufficient and no analysis is performed. The installation and setup of the sensor are well-known technologies. In other embodiments of the present invention, the implementer may adjust the settings of M and the analysis interval as needed, which will not be described in detail here.

[0029] Because the propagation speed of pressure waves in fluid media is limited (approximately...), For oil wells thousands of meters deep, there is a signal transmission delay of seconds between the wellhead pressure response and the wellhead flow excitation. Without correction, subsequent analysis will result in phase misalignment. Therefore, we first perform time-domain alignment of the flow and pressure data in the current data buffer based on cross-correlation analysis.

[0030] In one embodiment of the invention, the number of hysteresis sampling points is limited during cross-correlation analysis. The range is 0 to , This represents the total number of sampling points within a single disturbance period. traversal Calculate the cross-correlation function and take the maximum value of the cross-correlation function. The corresponding physical time is used as the signal transmission delay time. ,use The pressure data sequence is reversed and time-shifted for alignment. For data points missing at the end due to translation, linear interpolation is used to complete them.

[0031] Wherein, due to the lag in pressure data, the cross-correlation function is: .

[0032] It should be noted that the operation of aligning two signals in the time domain using cross-correlation analysis is a well-known technique in the art, and will only be briefly described here.

[0033] Because the absolute value of formation pressure (e.g., 20 MPa) is affected by reservoir depth and static pressure, and a slow background drift (trend term) occurs during water injection due to energy accumulation, these low-frequency background values ​​mask the high-frequency fluctuation components reflecting pore characteristics and must be removed. Therefore, background trend lines are extracted from the aligned pressure and flow data respectively, and corrected pressure and flow sequences are obtained after removing the background trend lines. This eliminates the modulation effect of long-period background noise on short-period fluctuation signals, allowing subsequent algorithms to focus on analyzing the relative morphological characteristics of fluctuations rather than their absolute magnitude, thus improving the sensitivity of capturing weak signals under high-pressure conditions.

[0034] Preferably, in one embodiment of the present invention, linear fitting is performed on the aligned pressure data and flow data respectively, and the fitted straight line is used as the respective background trend line.

[0035] As an example, the least squares method is used to perform linear fitting on the aligned pressure data to obtain a background trend line. The pressure data at each sampling point is then subtracted from the corresponding time value on the background trend line to obtain the pure fluctuation component, which serves as the corrected pressure sequence. Similarly, by processing the flow data, the pure fluctuation component of the flow data is obtained, which serves as the corrected flow sequence. .

[0036] It should be noted that the least squares method for fitting straight lines is a well-known technique and will not be elaborated further.

[0037] Step S2: Based on the fluctuation difference between the modified pressure sequence and the modified flow sequence, obtain the dynamic fluctuation resistance ratio, and determine the fluid state by combining it with the preset leakage threshold; when the fluid is determined to be in a high resistance response state, reconstruct the phase space of the standardized modified pressure sequence, construct the recursive graph matrix and calculate the fluctuation regularity index; compare the fluctuation regularity index with the preset benchmark fluctuation regularity and set the fluid state flag bit; when the fluid is determined not to be in a high resistance response state, set the fluid state flag bit to the preset first state.

[0038] Considering that when low-permeability reservoirs experience fracture leakage, the fluid rapidly flows out along high-permeability channels, resulting in a weak pressure response, while the formation can establish a significant pressure difference under normal displacement or blocking conditions, the dynamic fluctuation resistance ratio is obtained based on the fluctuation difference between the modified pressure sequence and the modified flow rate sequence. This characterizes the macroscopic impedance response strength of the formation system to the injection flow rate fluctuation. Then, combined with a preset leakage threshold, the fluid state is determined, and the fluid response state is quickly screened based on the macroscopic fluctuation characteristics. When the fluid is determined to be in a high-resistivity response state, it indicates that the injected fluid has established an effective pressure field in the deep formation. However, the macroscopic resistance value alone cannot distinguish whether the high pressure is caused by ineffective elastic blockage of the pore inlet or effective nonlinear seepage of the matrix. Further analysis is required. Since the standardization process eliminates the interference of differences in well depth, static pressure and absolute dimensions on waveform morphology analysis, the data focuses on pure wave characteristics. The phase space reconstruction technology can map a one-dimensional time series into a multi-dimensional spatial trajectory. The determinism and repeatability of the trajectory are quantified through the recursive graph matrix to reveal the inherent dynamic degrees of freedom of the system. Therefore, it is necessary to perform phase space reconstruction on the standardized corrected pressure series, construct the recursive graph matrix and calculate the wave regularity index as a data mapping index reflecting the abnormal flow characteristics, which is used to distinguish two working conditions with similar macroscopic resistance but different waveform morphologies. By comparing the fluctuation regularity index with the preset benchmark fluctuation regularity, setting fluid state flags, accurately decoupling the state ambiguity under high pressure conditions, and accurately distinguishing fluid states based on microdynamic characteristics, a basis for differentiated regulation is provided. When it is determined that the fluid is not in a high-resistivity response state, it indicates that the fluid mainly flows out along large fractures or high-permeability strips and fails to form an effective pressure differential to drive the matrix crude oil. The fluid state flag is set to the preset first state to provide a basis for subsequent regulation.

[0039] Preferably, in one embodiment of the present invention, considering that the standard deviation can directly quantify the dispersion of the time series from the mean, and that the corrected pressure and flow series have eliminated background trend interference, the ratio of their standard deviations physically corresponds strictly to the system's pressure response sensitivity to unit flow disturbances. Therefore, the standard deviation is used to measure the fluctuation characteristics of the corrected data series. Based on the difference between the standard deviation of the corrected pressure series and the standard deviation of the corrected flow series, the dynamic fluctuation resistance ratio is obtained, which characterizes the macroscopic impedance strength and energy transfer efficiency of the formation system.

[0040] As an example, the standard deviation of the corrected pressure sequence corresponding to the current data buffer is used as the numerator, and the sum of the standard deviation of the corrected flow sequence and the preset positive parameter divided by zero is used as the denominator. The ratio of these fractions is used as the current dynamic fluctuation resistance ratio. ; Among them, the preset division by zero positive parameter is taken as follows: To prevent the denominator from being zero; k is the index at the current time, which also corresponds to the index of the data buffer. The dynamic fluctuation drag ratio characterizes the magnitude of the pressure fluctuation response generated when the formation is excited by a unit flow fluctuation.

[0041] like If the value is very small, it indicates that large fluctuations in flow rate have almost no impact on pressure. This usually means that the fluid has leaked directly into large fractures or high-permeability channels, failing to establish an effective displacement pressure differential. Therefore, when the dynamic fluctuation resistance ratio is less than the preset leakage threshold, the fluid is determined not to be in a high-resistance response state, i.e., the fluid is determined to be in a low-resistance channel leakage state. At this time, the fluid status flag is set to the preset first state. Specifically, the settings are... 1 represents the preset first state; when the dynamic fluctuation resistance ratio is greater than or equal to the preset leakage threshold, the fluid is determined to be in a high resistance response state.

[0042] The preset leakage threshold is obtained through benchmark testing or historical statistics. For example, it is measured in well sections where fracture leakage is known to exist. The average value is used as a reference lower limit (typical value, for example). ).

[0043] Preferably, in one embodiment of the present invention, the standardized corrected pressure sequence is analyzed, specifically: First, define the reconstruction parameters: the embedding dimension *d* determines the dimension of the reconstruction space. For formation seepage systems, based on Takens' embedding theorem and experience, it is usually taken as... This contains the main dynamic information of the system; here, we take 5. Delay time. The extent to which the reconstructed trajectory unfolds is determined, and here the period of the perturbation is taken. The corresponding number of sampling points (i.e., a phase difference of 90 degrees) is used to maximize the trajectory's opening.

[0044] Then, from the standardized modified pressure sequence, the state vector is extracted according to the preset embedding dimension and delay time; For the normalized pressure fluctuation sequence within the current window From the first Starting from a data point, at intervals... take out These points form a multidimensional state vector: ; Each vector This represents the state of the system at a certain moment. As time progresses ( (Increase), these vectors connect to form a trajectory in multidimensional space. The shape of this trajectory (whether it is a regular circle or a messy tangled ball) directly reflects the essence of the system's dynamics; The length is N, and it is traversed starting from m=1 data points until... This forms a series of multidimensional state vectors.

[0045] Next, a recursive graph matrix is ​​constructed based on the state vectors: the Euclidean distance between vectors within all vector pairs is calculated to form a distance matrix. The smaller the element value in the distance matrix, the more similar the two corresponding moments are, indicating that the system exhibits repetition or periodicity.

[0046] The distance threshold is set to 10% of the standard deviation of all element values ​​in the distance matrix. The standard deviation is used to dynamically characterize the characteristic divergence radius of the phase space trajectory. By selecting 10% of it as the adaptive truncation threshold, it is mathematically ensured that the neighborhood judgment range is always in the optimal signal-to-noise ratio range between the "upper limit of noise error" and the "lower limit of trajectory structure scale".

[0047] When the calculated distance threshold is 0 (which usually occurs in extreme cases where the signal is extremely stable or the sensor malfunction causes the standard deviation of the distance matrix to be zero), to prevent the recursive graph matrix from becoming completely white (without recursive points) due to the failure of the judgment conditions, which would lead to the collapse or zeroing of the fluctuation regularity index calculation, its value is forcibly set to a preset minimum value, such as 0.001.

[0048] Then, the distance matrix is ​​binarized, setting the element values ​​at positions less than the distance threshold to 1 and the element values ​​at positions greater than or equal to the distance threshold to 0, thus obtaining the recursive graph matrix.

[0049] In a recursive graph, a line segment parallel to the main diagonal represents a system trajectory that completely overlaps with another time period, indicating that the system is undergoing regular periodic motion.

[0050] Finally, the length distribution of line segments parallel to the main diagonal in the statistical recursion graph matrix is ​​calculated, and the deterministic index is used as the volatility regularity index D.

[0051] As an example, ;in The minimum line segment length to eliminate noise interference (usually taken as 2), when When the value is 0, it means that there are no repeating points in the recursive graph matrix, and the system is in a completely irregular state. The fluctuation regularity index is directly set to 0. The larger the D value, the more regular and periodic the system trajectory is. The smaller the D value (closer to 0), the more random and chaotic the system trajectory is.

[0052] Next, a fluid state flag is set. When the fluctuation regularity index is not less than the preset benchmark fluctuation regularity, it indicates that the dynamic response of the current formation system exhibits high orderliness and determinism. The pressure fluctuation trajectory forms a regular closed or quasi-closed structure in the phase space, characterizing the system response as exhibiting highly regular elastic oscillation characteristics. In engineering experience, this corresponds to a pore inlet blockage state, i.e., an ineffective pore inlet blockage state. The fluid state flag is then set to the preset second state, i.e., set... Let 2 represent the preset second state; When the fluctuation regularity index is less than the preset baseline fluctuation regularity, it indicates that the dynamic response of the current formation system has undergone a significant chaotic evolution compared to the baseline state. The determinism of the pressure fluctuation trajectory is greatly reduced and exhibits highly irregular divergent characteristics, indicating that the determinism of the current pressure fluctuation sequence is significantly reduced. In engineering experience, this corresponds to the matrix seepage state (i.e., the non-blocking state). The fluid state flag is set to the preset third state, i.e., set... , where 3 represents the preset third state.

[0053] It should be noted that Recurrence Plot Analysis (RPA) and the calculation of the Determinism (DET) index are well-established and classic algorithms in the field of nonlinear dynamics; in other embodiments of this invention, the implementer may set other... The rules for marking fluid state flags will not be elaborated further.

[0054] Preferably, in one embodiment of the present invention, in the initial stage of water injection (when the formation connectivity is known to be good or in the newly established water injection stage), the system maintains a preset injection disturbance mode for a period of time, such as 3 disturbance cycles, collects flow rate data and pressure data and stores them in the data buffer, and executes the process of calculating the fluctuation regularity index described in steps S1 to S2. Starting from time domain alignment, the background trend line is removed, and the small step of determining the fluid state (obtaining the dynamic fluctuation resistance ratio and combining it with the preset leakage threshold to determine the fluid state) is skipped. The system directly constructs a recursive graph matrix, calculates the fluctuation regularity index, and uses the fluctuation regularity index of the preset proportion as the preset benchmark fluctuation regularity. .

[0055] The preset ratio is 90%~95%, and 90% is chosen here because as water injection proceeds, even in an effective seepage state, the regularity index may naturally decrease slightly due to the gradual manifestation of formation heterogeneity or minor disturbances. Therefore, a 10% safety margin is left for actual operation.

[0056] It should be noted that in other embodiments of the present invention, the implementer may adjust the value of the preset ratio at his own discretion, which will not be elaborated further.

[0057] Step S3: The injection of the high-efficiency microemulsion oil displacement agent is controlled based on the fluid state flag.

[0058] The fluid state flag contains the decoupled identification results of the fluid state. Therefore, the injection of high-efficiency microemulsion oil displacement agent is finally controlled based on the fluid state flag. The fluid state is accurately identified in terms of physical mechanism, which reduces the risk of irreversible formation damage caused by misjudgment and optimizes the matrix mobilization efficiency and oil displacement economic benefits of microemulsion in low-permeability reservoirs.

[0059] Preferably, in one embodiment of the present invention, a graded control strategy is executed according to the current fluid state. (See also...) Figure 2 The diagram illustrates a flowchart of a method for regulating the injection of a highly efficient microemulsion oil displacement agent according to an embodiment of the present invention, specifically including: Step S301: When in the preset first state, the injection volume is increased by a preset testing ratio within the preset testing window. If the maximum dynamic fluctuation resistance ratio calculated within the preset testing window is less than the preset leakage threshold, and the increase rate of the maximum dynamic fluctuation resistance relative to the dynamic fluctuation resistance before the preset testing window is less than the preset rise threshold, then the channel sealing agent injection pump is started to mix a preset graded high-viscosity gel plug into the injection pipeline.

[0060] When the preset first state is in the low-resistance channel leakage state, it needs to be blocked in time. However, due to the high risk of blocking operation, the blocking is not carried out immediately. Instead, a trial phase is entered. The dynamic resistance ratio is observed by increasing the injection volume in the short term, and the effectiveness of the preset first state identification is determined for the second time to reduce the risk.

[0061] Specifically, starting from the current time point, a preset testing window is established, such as one with a length of 15 minutes, and a preset testing ratio is used as the base injection volume. 10% of the data is switched to a high-frequency analysis strategy within a preset trial window. For example, if the analysis interval is set to 5 sampling points, multiple dynamic fluctuation resistances are calculated based on the real-time updated data buffer. The dynamic fluctuation resistance ratio before the preset trial window (when the preset first state is currently set) is used as the benchmark fluctuation resistance ratio. If the calculated maximum dynamic fluctuation resistance ratio is less than the preset leakage threshold, it indicates that leakage continues during the trial period. The difference between the calculated maximum dynamic fluctuation resistance within the preset trial window and the baseline fluctuation resistance ratio is used as the numerator, and the baseline fluctuation resistance ratio is used as the denominator. The ratio of the fractions is used as the increase rate. If the maximum dynamic fluctuation resistance during the trial is still small, it indicates that the increase in flow rate has not caused a significant increase in pressure. Therefore, when the increase rate is less than the preset increase threshold, leakage is confirmed to exist, and the preset first state is effective. At this time, the sealing mode is executed, the channel sealing agent injection pump is started, and a preset graded high-viscosity gel septum is mixed into the injection pipeline.

[0062] When the calculated maximum dynamic fluctuation resistance ratio is greater than or equal to the preset leakage threshold, or the increase rate is greater than the preset rise threshold, it indicates that the pressure response is sensitive. The preset first state is a misjudgment of interference. The original displacement (before the preset trial window) is restored, the monitoring state is returned, and the strategy is converted to low frequency analysis.

[0063] In this example, the preset rise threshold is preferably set to 5%~10% (e.g., 8%), and the preset gradation is pre-configured based on the average fracture pore size range statistically analyzed from the geological exploration data or historical logging data of the reservoir (e.g., selecting 1 / 3 to 1 / 2 of the statistical width as the main particle size). Gel slugs are used instead of permanent solid particles because gel has a certain deformability and degradability (which can be removed later with a breaker), greatly reducing the risk of accidental plugging. The volume of the injected high-viscosity gel slug is typically 1.2 to 1.5 times the wellbore volume, determined by wellbore structural parameters (such as casing depth and diameter) and the estimated formation fracture volume. Implementers can adjust this according to the specific implementation scenario, which will not be elaborated further.

[0064] It should be noted that if the benchmark volatility resistance ratio is extremely small, such as less than... If the leakage is extremely obvious, there is no need to test, so the preset first state is determined to be effective and a high-viscosity gel plug is injected.

[0065] Step S302: When in the preset second state, increase the injection concentration of the surfactant by a preset concentration step.

[0066] When the microemulsion is in the preset second state, it indicates that the pore inlet is blocked. It is necessary to reduce the interfacial tension and viscosity of the microemulsion to make it easier to pass through the narrow pore throat. The injection concentration of the surfactant should be increased in preset concentration steps. Since adding surfactant is a reversible operation (it can be diluted with water afterward), this type of adjustment has low risk and can be performed directly.

[0067] As an example, the preset concentration step size is... The initial injection concentration of the interfacial activity modifier is determined by the optimal baseline concentration based on the reservoir geological characteristics, microemulsion basic formulation design, and indoor core displacement experiments, and is not limited here; in other embodiments of the present invention, the implementer can adjust the preset concentration step according to actual needs.

[0068] Step S303: When in the preset third state, keep the injection pump speed constant.

[0069] When the preset third state is in, it indicates that the current matrix seepage state is effective and stable. The superposition state of the basic injection discharge and the preset sinusoidal flow disturbance signal remains unchanged, and the current working condition is maintained for continuous monitoring.

[0070] It should be noted that due to the transmission delay in the physical flow of the chemical agent from the wellhead injection point to the deep formation and the resulting pressure response, a suppression phase begins after the injection of high-viscosity gel or an increase in the injection concentration of the interfacial activity modifier. During this suppression phase, the system continuously monitors data but does not perform fluid state discrimination or update the fluid state flag, nor does it output new control commands. The suppression phase ends and the system returns to monitoring mode once the cumulative injected volume reaches the wellbore string volume. The wellbore string volume is determined by the actual scenario and will not be specified here.

[0071] It should be noted that, considering the complexity of on-site working conditions, the system has multiple built-in exception handling logics to ensure operational safety: Sensor fault detection: If the collected data is continuous for a period of time (e.g. Maintain a constant value (no fluctuation) or exceed the physical range (such as pressure). If a sensor malfunction is detected, the system will automatically disconnect the closed-loop control, maintain the current injection parameters, and trigger an audible and visual alarm to prompt manual inspection.

[0072] Surfactant concentration limit and ineffective protection: If the system continuously executes multiple control actions to increase the surfactant concentration, and if the status flag does not change after three consecutive increases in surfactant concentration, or if the current surfactant injection concentration has reached the preset safe upper limit concentration (this upper limit is determined based on indoor compatibility experiments to prevent emulsion demulsification or formation emulsion blockage, and is no longer limited), it indicates that the chemical agent adjustment capability has been exceeded. At this time, chemical agent injection is stopped, the system switches to pure water cleaning mode, and a manual intervention request signal is output.

[0073] During the injection and testing of the gel slug, the wellhead pressure is continuously monitored. If the pressure value instantaneously exceeds the safety threshold (such as the tubing string pressure limit), the wellhead pressure will be monitored. If the injection fails, immediately terminate the trial or gel plug injection and restore the original flow rate.

[0074] In summary, to address the technical problem of inaccurate fluid state differentiation and precise control of efficient microemulsion displacement agent injection under high-pressure injection conditions during microemulsion flooding in low-permeability reservoirs, this invention provides an injection process for efficient microemulsion displacement agents suitable for low-permeability reservoirs. This invention first monitors data under a preset injection disturbance mode and performs time-domain alignment. Then, it obtains the corrected pressure sequence and corrected flow sequence after removing the background trend line. Further, based on the fluctuation difference between the corrected pressure sequence and the corrected flow sequence, it obtains the dynamic fluctuation resistance ratio to determine the fluid state. When the fluid is determined to be in a high-resistance response state, it performs phase space reconstruction on the standardized corrected pressure sequence and calculates the fluctuation regularity index. Then, it compares the fluctuation regularity index with a preset benchmark fluctuation regularity to set a fluid state flag. Finally, it controls the injection of the efficient microemulsion displacement agent based on the fluid state flag. This invention utilizes disturbance monitoring, time-domain alignment, and detrending processing to perform preliminary screening using dynamic fluctuation resistance ratio. It combines phase space reconstruction and fluctuation regularity index to decouple the blockage and seepage states under high pressure, thereby regulating injection and accurately distinguishing fluid states under high pressure conditions to optimize oil displacement economic benefits.

[0075] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0076] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. An injection process for a highly efficient microemulsion oil displacement agent suitable for low-permeability reservoirs, characterized in that, The injection process includes: Under the preset injection perturbation mode, the flow data and pressure data in the current data buffer are time-domain aligned based on cross-correlation analysis. The background trend lines of the aligned pressure data and flow data are extracted respectively, and the corrected pressure sequence and corrected flow sequence are obtained after removing the background trend lines. Based on the fluctuation difference between the modified pressure sequence and the modified flow sequence, the dynamic fluctuation resistance ratio is obtained, and combined with a preset leakage threshold, the fluid state is determined. When the fluid is determined to be in a high-resistance response state, the phase space of the standardized modified pressure sequence is reconstructed, a recursive graph matrix is ​​constructed, and the fluctuation regularity index is calculated. The fluctuation regularity index is compared with a preset benchmark fluctuation regularity, and a fluid state flag is set. When the fluid is determined not to be in a high-resistance response state, the fluid state flag is set to a preset first state. The injection of highly efficient microemulsion oil displacement agents is regulated based on the fluid state flag.

2. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 1, characterized in that, The method for obtaining the volatility regularity index includes: From the standardized modified pressure sequence, state vectors are extracted according to a preset embedding dimension and delay time; a recursive graph matrix is ​​constructed based on the state vectors; the length distribution of line segments parallel to the main diagonal in the recursive graph matrix is ​​statistically analyzed, and a deterministic index is calculated as the volatility regularity index.

3. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 1, characterized in that, When the fluctuation regularity index is not less than the preset benchmark fluctuation regularity, the fluid state flag is set to the preset second state. When the fluctuation regularity index is less than the preset benchmark fluctuation regularity, the fluid state flag is set to the preset third state.

4. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 3, characterized in that, The method for regulating the injection of high-efficiency microemulsion oil displacement agent based on the fluid state flag includes: A graded control strategy is executed based on the current fluid state: when the preset first state is in effect, the injection rate is increased by a preset testing ratio within a preset testing window. If the maximum dynamic fluctuation resistance ratio calculated within the preset testing window is less than a preset leakage threshold, and the increase rate of the maximum dynamic fluctuation resistance relative to the dynamic fluctuation resistance before the preset testing window is less than a preset rise threshold, then the channel plugging agent injection pump is started to mix a preset graded high-viscosity gel plug into the injection pipeline. When in the preset second state, the injection concentration of the surfactant is increased by a preset concentration step. When in the preset third state, the injection pump speed remains constant.

5. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 4, characterized in that, After injecting high-viscosity gel or increasing the injection concentration of interfacial activity modifier, the inhibition phase begins. Once the cumulative injection volume reaches the wellbore tubing volume, the inhibition phase ends.

6. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 1, characterized in that, The method for obtaining the background trend line includes: Linear fitting is performed on the aligned pressure data and flow data respectively, and the fitted lines are used as their respective background trend lines.

7. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 1, characterized in that, The method for obtaining the dynamic fluctuation resistance ratio includes: The dynamic fluctuation resistance ratio is obtained based on the difference between the standard deviation of the modified pressure sequence and the standard deviation of the modified flow sequence.

8. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 1, characterized in that, The method for determining the fluid state includes: When the dynamic fluctuation resistance ratio is less than the preset leakage threshold, the fluid is determined not to be in a high-resistance response state; when the dynamic fluctuation resistance ratio is greater than or equal to the preset leakage threshold, the fluid is determined to be in a high-resistance response state.

9. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 1, characterized in that, The method for obtaining the preset benchmark fluctuation regularity includes: When the formation connectivity is known to be good or the water injection stage has just been established, the fluctuation regularity index is calculated based on the flow and pressure data in the data buffer, and the fluctuation regularity index of the preset proportion is used as the preset benchmark fluctuation regularity.

10. The injection process of a high-efficiency microemulsion oil displacement agent suitable for low-permeability reservoirs according to claim 1, characterized in that, The preset injection disturbance mode is: a preset sinusoidal flow disturbance signal is superimposed on the preset constant current injection.

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