A method for evaluating core imbibition response of low-permeability oil reservoirs based on time-series incremental representation

Abstract

The application relates to the field of petroleum and natural gas engineering, in particular to a low-permeability oil reservoir core imbibition response evaluation method based on time sequence increment representation, which comprises the following steps: obtaining a target low-permeability oil reservoir core, obtaining the exposed area and weight of the target low-permeability oil reservoir core, and performing an imbibition experiment on the target low-permeability oil reservoir core, recording imbibition weight data at different times, and using the imbibition weight data to represent the imbibition response characteristics of the low-permeability oil reservoir core under the action of water phase; based on the weight change of the target low-permeability oil reservoir core, calculating the change trend of the imbibition amount, combining the time weight, and representing the imbibition importance at different time points; calculating an imbibition response speed factor, and representing the imbibition capacity of the target low-permeability oil reservoir core. The application can more effectively distinguish the imbibition dynamic characteristics of different types of cores, and is favorable for improving the pertinence and accuracy of early imbibition capacity identification of the low-permeability oil reservoir core.

Description

Technical Field

[0001] This invention relates to the field of oil and gas engineering, and in particular to a method for evaluating the core permeability response of low-permeability reservoirs based on time-series incremental characterization during exploration and development. Background Technology

[0002] Low-permeability reservoirs typically exhibit characteristics such as small pore throats, low permeability, strong reservoir heterogeneity, and high fluid migration resistance. Under conventional displacement conditions, the extent of crude oil mobilization is limited, and development often faces challenges such as high start-up pressure, slow water injection effectiveness, and low recovery rates. For these reservoirs, percolation is one of the important mechanisms affecting oil-water replacement and the mobilization of remaining oil, especially in fracture-matrix systems. The process by which the aqueous phase enters the matrix pores under capillary force and displaces crude oil often has a significant impact on development outcomes. Therefore, how to objectively, quantitatively, and comparablely evaluate the strength of percolation in low-permeability reservoirs at the core scale has always been a key technical issue in the research and development of low-permeability reservoirs.

[0003] (1) Chinese Patent CN110082272A, entitled "A Device and Method for Evaluating Spontaneous Core Immersion under Formation Conditions," discloses a device and method capable of simulating and measuring the spontaneous core immersion oil removal rate and displacement capacity under high temperature and high pressure conditions. This type of technology can simulate formation conditions well and is highly targeted for core immersion experiments. However, the focus of this patent is on the simulation of experimental conditions and the construction of the testing device, mainly addressing the problem of "how to measure the immersion phenomenon." It involves relatively little on how to establish a unified, concise, and easily comparable strength evaluation index system based on the data of the entire immersion process.

[0004] (2) Chinese Patent CN106872507B, entitled "A Method for Evaluating the Self-Water Displacement Effect and Displacement Time of Shale Oil Reservoirs," uses nuclear magnetic resonance T2 spectrum changes to evaluate the self-water displacement effect of shale oil reservoirs and determine the optimal displacement time accordingly. This method can analyze the self-water displacement effect from the perspective of experimental response and has certain practical value in evaluating displacement time. However, this method focuses more on analyzing the displacement effect and optimal time point using nuclear magnetic resonance testing. Its evaluation results rely on specialized testing equipment and mainly reflect the displacement performance under specific experimental conditions. It is still not direct enough for a unified quantitative characterization of the early response speed, later sustainability, and dynamic changes of the core permeation process.

[0005] (3) Chinese Patent CN121366679A, entitled "Optimization Method for Clay Stabilizer Dosage in Low-Permeability Tight Reservoirs," discloses a method that involves permeation between rock samples and clay stabilizer solutions of different concentration gradients, obtaining the peak area of ​​nuclear magnetic resonance signals at different permeation times, and then calculating the rate of change of injection volume, the rate of change of permeability, and comprehensive decision-making indicators to determine the optimal clay stabilizer concentration. This type of technology can optimize the clay stabilizer dosage through dynamic permeation and nuclear magnetic resonance monitoring, and has certain practical value in reservoir protection and reagent selection. However, the focus of this patent is on the optimization of clay stabilizer concentration and reservoir damage control, mainly solving the problem of "how to determine the optimal dosage concentration"; its evaluation object is the comprehensive decision-making result under the action of different concentrations of working fluid, rather than a direct characterization of the strength of permeation of the core itself. Meanwhile, this method relies on a parameter system including the peak area of ​​the nuclear magnetic resonance signal, the rate of change of permeability, and threshold constraints. The calculation process is closely related to the reagent concentration gradient. It provides relatively little information on how to conduct a concise and unified quantitative evaluation of the early response characteristics and dynamic strength of the core permeation process based solely on mass-time data from core permeation experiments.

[0006] (4) Chinese Patent CN115808380A, entitled "A Method for Characterizing Immersion Capacity in Aqueous Phase Immersion Experiments of Shale Gas Reservoir Cores," discloses a method for characterizing the shale core's immersion capacity by drying the core, measuring its cross-sectional area and weight, setting a non-immersion surface, conducting aqueous phase immersion experiments, processing the time data, and combining the immersion end area and core mass. This method can normalize the sample size and shape based on the core immersion experiment data, and is highly targeted in characterizing the overall immersion capacity of shale samples. However, the focus of this patent is on constructing a normalized characterization relationship between the immersion amount per unit mass and the cross-sectional area, and using time raised to the power of 0.5 to characterize the immersion capacity and maximum immersion capacity, which reflects more the overall immersion level of the core. The characterization of the distribution differences of the incremental permeation in adjacent time periods, the speed of the early response, and the dynamic contribution characteristics of different stages in the whole process of core permeation is still not direct enough. In particular, for different types of cores, such as those with a fast early response and a slowing later response, or those with a moderate early response and a continuous increase later response, it is difficult to highlight the temporal response differences in the permeation process when relying solely on the overall normalized curve.

[0007] In summary, while existing technologies have been extensively studied in areas such as core permeability testing, oil displacement effect evaluation, permeabilizer screening, and recovery prediction, some shortcomings remain: First, some methods focus on the construction of experimental apparatus or testing methods, capable of measuring permeability phenomena but lacking a concise and unified evaluation index for permeability intensity; second, some methods emphasize oil displacement effect, agent effect, or recovery prediction, rather than evaluating the permeability intensity of the core itself; third, existing technologies rarely directly utilize core mass change data over time to characterize the dynamic distribution characteristics of permeability increment from a full-process time-series perspective, and quantitatively characterize the core permeability response rate by combining time weights. Therefore, it is necessary to propose a method for evaluating the core permeability response of low-permeability reservoirs based on time-series incremental characterization. This method uses mass change data during core permeability experiments as a foundation to construct quantitative relationships between permeability change trends, normalized permeability increase, time weights, and permeability response rate factors, thereby achieving an objective evaluation and comparison of the permeability capacity of different core samples. Summary of the Invention

[0008] To address the aforementioned issues, this invention provides a method for evaluating the permeation response of low-permeability reservoir cores based on time-incremental characterization, which can highlight the differences in temporal response during the permeation process.

[0009] This invention discloses a method for evaluating the permeability response of core samples from low-permeability oil reservoirs based on time-series incremental characterization, comprising the following steps: Step 1) Obtain the core of the target low-permeability reservoir, obtain the exposed area and weight of the core, and conduct a permeation test on it to record the permeation weight data at different times, which is used to characterize the permeation response characteristics of the low-permeability reservoir core under the action of water phase. Step 2) Based on the weight change of the core of the target low-permeability reservoir, calculate the trend of the permeation rate and normalize the permeation rate at different times to more intuitively represent the permeation rate change at different times. Combined with time weight, the importance of permeation at different time points is represented. Step 3) Calculate the permeation response rate factor to characterize the permeation capacity of the target low-permeability reservoir core. The faster the response rate, the stronger the permeation capacity, thereby achieving the purpose of quantitative evaluation.

[0010] Preferably, the calculation method for permeation in step 2) is as follows: place the core of the target low-permeability reservoir in the permeation test device, conduct the permeation test, and record the trend of the weight of the core of the target low-permeability reservoir changing with time to obtain the core weight curve at multiple time points. Calculation of osmosis: Different recording time points correspond to different osmosis amounts. The calculation formula is as follows: Formula (1) Formula (2) Formula (3) Where: m i Let g be the core mass at time i. m0 is the initial core mass, in grams; A represents the exposed area of ​​the core sample, in cm². 2 ; ρ w The density of the aqueous phase is g / cm³. 3 ; q i Let be the amount of osmosis at time i, in cm. 3 / cm 2 ; Q n The total permeate volume of the core, in cm 3 / cm 2 ; s i The normalized increase in osmotic pressure is dimensionless. ∆q i The increase in osmosis at adjacent time points, in cm 3 / cm 2 .

[0011] Preferably, in step 2), the time weight is calculated by combining the seepage data at different times to represent the degree of seepage influence at different time points. The calculation formula is as follows: Formula (4) Formula (5) In the formula: t i Let h be the time at time i. T represents the total time, in hours. t j Let h be the time at time j. n represents the total number of time points; w i Let be the time weight at time i, which is dimensionless; f i h is the median value between adjacent time points.

[0012] Preferably, in step (3), the osmosis response rate factor is calculated by combining time weight and normalized osmosis increase, and the calculation formula is as follows: Formula (6) In the formula: E is the rate factor for osmosis response, which is dimensionless.

[0013] This invention does not merely provide a general characterization of the final permeability or overall permeability capacity of the core. Instead, it uses data on the change in mass over time during the core permeability experiment as a basis, dividing the entire permeability process into multiple adjacent time periods. It extracts the increase in permeability in each time period and constructs a permeability response rate factor E by combining the normalized increase in permeability with a time weight. This allows for a more prominent characterization of the core's response speed in the initial stage of permeability. Compared to existing methods that focus on overall permeability characterization, this invention can more effectively distinguish the permeability dynamic characteristics of different types of cores, such as those with "rapid initial response followed by a slower pace" and "moderate initial response followed by a gradual increase." It avoids the problem of insufficient characterization of sensitive early-stage information when evaluating solely based on cumulative permeability or overall curve morphology, thus improving the targeting and accuracy of identifying the early permeability capacity of cores in low-permeability reservoirs.

[0014] This invention directly calculates based on readily available parameters such as time, core mass, exposed area, and fluid density from conventional percolation experiments. It does not rely on specialized testing equipment such as nuclear magnetic resonance, nor does it require the introduction of too many complex physical property parameters or empirical fitting processes. It has the advantages of fewer parameters, easy acquisition, clear calculation process, low implementation cost, and strong engineering operability.

[0015] This invention can be used for lateral comparison of the permeation response rate between different core samples, as well as for reservoir sample screening, analysis of the effects of fracturing fluids or working fluids, and rapid evaluation of permeation potential during the development of low-permeability reservoirs. The evaluation results are intuitive and clear, and have good applicability and promotion value.

[0016] Because this invention adopts the evaluation approach of "time-period incremental contribution + time weight", it transforms the permeation process from a simple result representation to a quantitative characterization of the dynamic response process. Therefore, it can better reflect the stage differences and early main control characteristics in the permeation process of low-permeability reservoirs, and provide a more practical evaluation basis for the analysis of permeation mechanism of low-permeability reservoir cores, reservoir classification evaluation and development effect judgment. Attached Figure Description

[0017] Figure 1 This is a graph showing the changes in core mass in the example.

[0018] Figure 2 This is a graph showing the change in cumulative absorption per unit area in the example.

[0019] Figure 3 This is a graph showing the increase in percolation at different time periods in the example.

[0020] Figure 4 This is a normalized percolation increment graph for each time period in the example.

[0021] Figure 5 This is a comparison chart of the time weights and normalized increase in permeation at different time periods in core A in the example.

[0022] Figure 6 This is a comparison chart of the time weights and normalized increase in permeation at different time periods in core B in the example. Detailed Implementation

[0023] The present invention will be described below with reference to the accompanying drawings.

[0024] This invention provides a method for evaluating the core permeability response of low-permeability oil reservoirs based on time-series incremental characterization, as detailed below:

[0025] This paper selects typical low-permeability oil reservoir rock samples from western China as examples. Taking downhole rock samples from the main development sections of two vertical wells as examples, the paper uses the present invention to quantitatively characterize the intensity of permeation and adsorption, and demonstrates the practicality of the method.

[0026] Step 1) Obtain the target core, obtain its various physical parameters, and conduct a permeation experiment to record the permeation weight data at different times. This data is used to characterize the permeation response of low-permeability reservoir cores under aqueous phase conditions. The specific details are as follows: Step 1) Obtain physical parameters: The exposed area of ​​the low-permeability reservoir core is 5.15 cm². 2 Core A weighed 57.8g, and core B weighed 58.2g.

[0027] Step 2) Permeation test: Place the core in the experimental apparatus and record the trend of its weight change over time to obtain core weight curves at multiple time points, such as... Figure 1 As shown.

[0028] Based on the changes in core weight, the trend of permeation is calculated, and the permeation at different times is normalized to more intuitively represent the changes in permeation at different times. Then, time weights are given to represent the degree of permeation influence at different time points. The specific content is as follows: (1) Calculation of permeation: The water phase density of the two core samples obtained was 1.0 g / cm³. 3 The increase in permeate and the normalized increase in permeate for core A and core B are shown in Table 1. The changes in core quality are as follows: Figure 1 As shown, the permeation rate per unit area is as follows Figure 2 As shown, the increase in osmosis at each time period is as follows: Figure 3 As shown, the normalized osmotic increments for each time period are as follows: Figure 4 As shown, taking the 0-0.5 segment of core A as an example, we can... Figure 1 The weight at 0.5h is 58.3g. Substituting the initial weight, the weight at 0.5h, and the exposure area of ​​5.15 into formula (1), we get the following result: The calculated increase in osmosis at this point was 0.097 cm. 3 / cm 2The same calculation was performed at other times, and the total increase in osmosis was calculated to be 0.563 cm. 3 / cm 2 Therefore, substituting into formula (3), we can obtain the normalized increase in osmosis at time 0-0.5h as 0.172, and the same calculation is performed at other times; Table 1. Immersion Increment Table ; (2) Calculate the time weight: Combine the infiltration data at different times for calculation, such as Figure 5 As shown, the calculation process is as follows: The time point is: ; The formula for calculating the median value for each time period is shown in formula (4), and the result is: ; The total experimental time is T=120h; Therefore, the denominator of formula (5) can be calculated. ; Therefore, taking the 0-0.5h period as an example, we can calculate its time weight as 0.123645 by substituting it into formula (5). The calculation for other time periods is the same.

[0029] Step 3) Calculate the seepage response rate factor. The seepage response rate factor represents the response rate of seepage in the core. The faster the response rate, the stronger the seepage capacity, thus achieving the purpose of quantitative evaluation. The specific content is as follows: Immersion response rate factor: Calculated by combining time weight and normalized increase in immersion. The calculated immersion response rate factor for core A is 0.6869, and for core B it is 0.3715. Taking core A as an example, the calculation process is as follows: Calculate formula (6) in two parts: First half: ; The second half ; Therefore, they sought to obtain... ; Similarly, the permeation response rate factor of core B was found to be 0.3715; It can be seen that the permeation capacity of core A is stronger than that of core B.

Claims

1. A method for evaluating the permeability response of low-permeability oil reservoir cores based on time-series incremental characterization, characterized in that, Includes the following steps: Step 1) Obtain the core of the target low-permeability reservoir, obtain the exposed area and weight of the core, and conduct a permeation test on it to record the permeation weight data at different times, which is used to characterize the permeation response characteristics of the low-permeability reservoir core under the action of water phase. Step 2) Based on the weight change of the core of the target low-permeability reservoir, calculate the trend of the permeation rate and normalize the permeation rate at different times to more intuitively represent the permeation rate change at different times. Combined with time weight, the importance of permeation at different time points is represented. Step 3) Calculate the permeation response rate factor to characterize the permeation capacity of the target low-permeability reservoir core. The faster the response rate, the stronger the permeation capacity, thereby achieving the purpose of quantitative evaluation.

2. The method for evaluating the core permeability response of low-permeability oil reservoirs based on time-series incremental characterization as described in claim 1, characterized in that, The calculation method for permeation in step 2) is as follows: Place the core of the target low-permeability reservoir in the permeation test device, conduct the permeation test, and record the trend of the weight of the core of the target low-permeability reservoir changing with time to obtain the core weight curve at multiple time points. Calculation of osmosis: Different recording time points correspond to different osmosis amounts. The calculation formula is as follows: Official (1) Official (2) Official (3) Where: m i Let g be the core mass at time i. m0 is the initial core mass, in grams; A represents the exposed area of ​​the core sample, in cm². 2 ; ρ w The density of the aqueous phase is g / cm³. 3 ; q i Let be the amount of osmosis at time i, in cm. 3 / cm 2 ; Q n The total permeate volume of the core, in cm 3 / cm 2 ; s i The normalized increase in osmotic pressure is dimensionless. ∆q i The increase in osmosis at adjacent time points, in cm 3 / cm 2 .

3. The method for evaluating the core permeability response of low-permeability oil reservoirs based on time-series incremental characterization as described in claim 2, characterized in that, In step 2), the time weight is calculated by combining the seepage data at different times to represent the degree of seepage influence at different time points. The calculation formula is as follows: Official (4) Official (5) In the formula: t i Let h be the time at time i. T represents the total time, in hours. t j Let h be the time at time j. n represents the total number of time points; w i Let be the time weight at time i, which is dimensionless; f i h is the median value between adjacent time points.

4. The method for evaluating the core permeability response of low-permeability oil reservoirs based on time-series incremental characterization as described in claim 3, characterized in that, In step (3), the osmotic response rate factor is calculated by combining time weight and normalized osmotic increase, and the calculation formula is as follows: Official (6) In the formula: E is the rate factor for osmosis response, which is dimensionless.

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