Method for testing and evaluating the plugging removal and oil displacement capacity of a biosourced complex system

Abstract

The present application belongs to the technical field of petroleum engineering, and particularly relates to a method for testing and evaluating the plugging removal and oil displacement capacity of a biological source composite system, comprising: injecting the biological source composite system into an optimized offshore oilfield core for plugging removal and oil displacement experiments; testing T2 spectrum and micron core CT scanning of the crude oil saturated core, formation water contaminated core, core after the biological source composite system is injected for plugging removal and oil displacement, and core after secondary water flooding; taking the relaxation time as the horizontal coordinate and the nuclear magnetic resonance signal intensity as the vertical coordinate, drawing a point-line graph of the T2 spectrum test results, obtaining the integral area and peak signal intensity of the T2 spectrum; according to the results of the micron core CT scanning, calculating characteristic parameters, defining the occurrence state of residual oil through the characteristic parameters, and obtaining the imaging results. The present application verifies the plugging removal and oil displacement effect of the biological source composite system from multiple dimensions, the evaluation indexes are specific and quantifiable, and the present application has the characteristics of being intuitive, simple, high resolution, and strong pertinence.

Description

Technical Field

[0001] This invention belongs to the field of petroleum engineering technology, specifically relating to a test and evaluation method for the oil displacement and unblocking capability of a bio-based composite system. Background Technology

[0002] With the continued growth of global energy demand, oil, as an important traditional energy source, plays a crucial role in economic development through its extraction and utilization. However, oil extraction faces numerous technical challenges, among which well blockage and low crude oil recovery rates are two key issues restricting the development of the oil industry. To effectively address these challenges, researchers are constantly exploring and developing new technologies aimed at improving well production efficiency, reducing extraction costs, and minimizing negative environmental impacts.

[0003] In recent years, the application of biotechnology in the petroleum industry has gradually attracted attention. Biotechnology utilizes microorganisms and their metabolites to improve the physicochemical properties of oil reservoirs, offering advantages such as environmental friendliness, low cost, and long-lasting effects. Against this backdrop, unblocking and oil displacement agents based on bio-derived composite systems have emerged and are gradually becoming a research hotspot. Bio-derived composite systems improve the physicochemical properties of reservoirs by screening and cultivating specific microorganisms and utilizing their metabolites, such as biosurfactants and biopolymers, thereby achieving the purpose of unblocking and oil displacement. Through systematic testing and evaluation of the unblocking and oil displacement capabilities of bio-derived composite systems, this technology can be further optimized, improving its application effect in actual oilfields and providing new technical support for improving oilfield recovery and promoting the sustainable development of the petroleum industry.

[0004] Therefore, scientifically and systematically testing and evaluating the unblocking and oil displacement performance of bio-based composite systems, enabling their effective application in oilfield production, is crucial for stabilizing and increasing oil production. However, conventional evaluations of unblocking and oil displacement technologies are based on core displacement experiments in the laboratory, yielding technical indicators such as unblocking rate, damage coefficient, crude oil recovery rate, and water cut. These evaluation indicators are singular and lack observation of changes in reservoir cores and crude oil within the reservoir. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a testing and evaluation method for the oil displacement and unblocking capabilities of a bio-based composite system.

[0006] Specifically, the present invention is achieved through the following technical solutions:

[0007] A method for testing and evaluating the oil displacement and unblocking capabilities of a bio-based composite system, comprising:

[0008] S1 After drying the offshore oilfield core, it is displaced with crude oil until saturation to obtain crude oil saturated core. The crude oil saturated core is subjected to T2 spectrum test and micron core CT scan to determine the initial permeability k0 and the integral area A0 of the T2 curve.

[0009] S2 uses formation water to reverse displace the crude oil-saturated core, causing core blockage and obtaining a formation water-contaminated core. The formation water-contaminated core is subjected to T2 spectrum testing and micron core CT scanning to determine the permeability k1 and the integral area A1 of the T2 curve during blockage.

[0010] S3 injects a bio-based composite system into the formation water contaminated core to conduct an oil displacement and unblocking experiment, obtaining the core after the bio-based composite system is injected to unblock and displace oil. The core after the bio-based composite system is injected to unblock and displace oil is subjected to T2 spectrum testing and micron core CT scanning; the permeability k2 and the integral area A2 of the T2 curve after unblocking are measured.

[0011] S4 calculates the damage coefficient and unblocking rate during and after core blockage based on the formulas for unblocking rate and damage coefficient;

[0012] S5 injects formation water into the core after unblocking and oil displacement in the bio-source composite system to a water cut of over 98%, obtaining a core after secondary waterflooding. The core after secondary waterflooding is then subjected to T2 spectrum testing and micron core CT scanning.

[0013] S6 plots a dotted-line graph of the T2 spectrum test results with relaxation time as the x-axis and nuclear magnetic resonance signal intensity as the y-axis to obtain the integral area and peak signal intensity of the T2 spectrum.

[0014] S7 calculates characteristic parameters based on the results of micron core CT scans, defines the occurrence state of residual oil through these characteristic parameters, and obtains image-based results.

[0015] The above-mentioned method for testing and evaluating the oil displacement capacity of the bio-based composite system includes formation water containing 2.8-3.5 mg / L oil, 0.2-0.5 mg / L iron ions, and 20-25 num / mL sulfate-reducing bacteria.

[0016] In the above-mentioned method for testing and evaluating the oil displacement and unblocking capabilities of the bio-based composite system, step S2, the criteria for judging core blockage are: the water content at the core inlet reaches 98% or more, and the injection pressure increases significantly.

[0017] The above-mentioned method for testing and evaluating the unblocking and oil displacement capabilities of the bio-based composite system is described in the case of a compound of bio-acid, rhamnolipid surfactant, and lipopeptide surfactant, with a slug ratio of 1:1:2 to 2:1:1 and a concentration of 500-2000 mg / L.

[0018] The above-mentioned method for testing and evaluating the oil displacement and unblocking capabilities of the bio-based composite system involves using a nuclear magnetic resonance spectrometer for T2 spectrum testing and a micron-sized core CT scan using a micro-nano dual-ray tube core CT scanning system.

[0019] The above-mentioned method for testing and evaluating the oil displacement and unblocking capabilities of the bio-based composite system uses the following parameters for the nuclear magnetic resonance spectrometer: CPMG sequence is used, echo time TE is 0.1-0.5ms, waiting time TW is 4000-12000ms, and the number of echoes is 100-5000.

[0020] The aforementioned method for testing and evaluating the oil displacement and unblocking capabilities of the bio-based composite system includes the following characteristic parameters: area coefficient, overlap ratio, and Euler number.

[0021] The above-mentioned method for testing and evaluating the oil displacement and unblocking capabilities of the bio-based composite system includes the following storage states: clustered, sieve-like, droplet-like, columnar, and sheet-like.

[0022] The above-mentioned method for testing and evaluating the oil displacement and unblocking capabilities of the bio-derived composite system uses a micron core CT scan with a resolution of 4 μm and a sample diameter of 10 mm.

[0023] The above-mentioned method for testing and evaluating the oil displacement capacity of the bio-based composite system refers to the offshore oilfield core, which is one of the following: low-permeability core, medium-permeability core, and high-permeability core; wherein, the permeability of the low-permeability core is less than 10 mD, the permeability of the medium-permeability core is 10-100 mD, and the permeability of the high-permeability core is greater than 100 mD.

[0024] The technical solution of the present invention has the following advantages over the prior art:

[0025] (1) The test and evaluation method of the unblocking and oil displacement capacity of the bio-derived composite system of the present invention is mainly aimed at the bio-derived composite system. It verifies the unblocking and oil displacement effect of the system from multiple dimensions. The evaluation indicators are specific and quantifiable. It has the characteristics of being intuitive, simple, high resolution and highly targeted. It can be used as an important reference for evaluating the adaptability of the agent and improving the efficiency of oilfield development and exploitation.

[0026] (2) The test and evaluation method of the bio-based composite system for unblocking and oil displacement of the present invention, when testing the unblocking and oil displacement effect of the one-dimensional model of the bio-based composite system, can intuitively reflect the oil displacement effect of the bio-based composite system on the core and its mechanism of action by testing the T2 spectrum of the marine oilfield core through nuclear magnetic resonance. It has the characteristics of non-destructive testing, convenient and efficient process, and quantifiable evaluation indicators.

[0027] (3) The method for testing and evaluating the oil displacement capacity of the bio-based composite system of the present invention evaluates the oil displacement effect of the bio-based composite system by using a three-dimensional model. It has the characteristics of high resolution, rich data information, accurate fluid characteristics and intuitive model. Attached Figure Description

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.

[0029] Figure 1 The flowchart shows the testing and evaluation method for the oil displacement and unblocking capability of the bio-based composite system of the present invention.

[0030] Figure 2 The T2 spectrum of the crude oil saturated core from Example 1;

[0031] Figure 3 The T2 spectrum of the formation water contaminated core from Example 1;

[0032] Figure 4 T2 spectra of core samples after unblocking and oil displacement using the bio-based composite system injected in Example 1;

[0033] Figure 5 The T2 spectrum of the core sample after secondary waterflooding in Example 1;

[0034] Figure 6 The curves showing the changes in injection pressure and recovery rate with the injection dosage in Example 1 are shown.

[0035] Figure 7 Example 1 shows the T2 spectra of core samples measured at different times after injection into the bio-based composite system;

[0036] Figure 8 The image shows the results of a micron-CT scan of the core sample used in the oil displacement experiment of the bio-based composite system in Example 1.

[0037] Figure 9 This is a columnar section of residual oil distribution in the core after an oil displacement experiment was conducted on the bio-based composite system of Example 1.

[0038] Figure 10 This is the T2 spectrum of a medium-permeability core after injecting a bio-based composite system, as shown in Example 2.

[0039] Figure 11 The image shows the results of a micron-CT scan of the core sample from the bio-based composite system used in the oil displacement experiment of Example 2.

[0040] Figure 12 This is a bar chart showing the distribution of residual oil in the core after an oil displacement experiment was conducted on the bio-based composite system in Example 2. Detailed Implementation

[0041] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided to illustrate the invention in detail. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0042] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0043] The inventive concept and principle of this invention are as follows: On the one hand, nuclear magnetic resonance (NMR) technology can quantitatively describe the distribution of the relative content of residual oil in pores with varying pore size. This information, reflected in charts, allows for a simple assessment of pore blockage and reservoir distribution, thereby evaluating the unblocking and oil displacement capabilities of the bio-based composite system. On the other hand, X-CT scanning technology can accurately describe and construct the pore distribution within reservoir cores, as well as the fluid flow characteristics within the core. By rotating and scanning water-driven oil cores at different displacement ratios at different angles, the microscopic pore structure and fluid saturation distribution of the reservoir core are obtained. Combined with computer-aided fault image processing, slice reconstruction interpolation, and pore structure construction techniques, the reservoir core is converted into a three-dimensional data volume model. The necessary pore and oil-water distribution information within the core are reconstructed and extracted, enabling a spatial display of the three-dimensional morphology of residual oil in the reservoir's microscopic core. This data is then used to evaluate the enhanced oil recovery capabilities of the bio-based composite system, ensuring targeted enhanced oil recovery measures for the reservoir.

[0044] Specifically, such as Figure 1 As shown, the method for testing and evaluating the oil displacement and unblocking capabilities of the bio-based composite system of the present invention includes:

[0045] S1 After drying the offshore oilfield core, it is displaced with crude oil until saturation to obtain crude oil saturated core. The crude oil saturated core is subjected to T2 spectrum test and micron core CT scan to determine the initial permeability k0 and the integral area A0 of the T2 curve.

[0046] S2 uses formation water to reverse displace the crude oil-saturated core, causing core blockage and obtaining a formation water-contaminated core. The formation water-contaminated core is subjected to T2 spectrum testing and micron core CT scanning to determine the permeability k1 and the integral area A1 of the T2 curve during blockage.

[0047] S3 injects a bio-based composite system into the formation water contaminated core to conduct an oil displacement and unblocking experiment, obtaining the core after the bio-based composite system is injected to unblock and displace oil. The core after the bio-based composite system is injected to unblock and displace oil is subjected to T2 spectrum testing and micron core CT scanning; the permeability k2 and the integral area A2 of the T2 curve after unblocking are measured.

[0048] S4 calculates the damage coefficient and unblocking rate during and after core blockage based on the formulas for unblocking rate and damage coefficient;

[0049] S5 injects formation water into the core after unblocking and oil displacement in the bio-source composite system to a water cut of over 98%, obtaining a core after secondary waterflooding. The core after secondary waterflooding is then subjected to T2 spectrum testing and micron core CT scanning.

[0050] S6 plots a dotted-line graph of the T2 spectrum test results with relaxation time as the x-axis and nuclear magnetic resonance signal intensity as the y-axis to obtain the integral area and peak signal intensity of the T2 spectrum.

[0051] S7 calculates characteristic parameters based on the results of micron core CT scans, defines the occurrence state of residual oil through these characteristic parameters, and obtains image-based results.

[0052] The present invention provides a testing and evaluation method for the unblocking and oil displacement capacity of a bio-based composite system, which mainly includes a one-dimensional model evaluation technique and a three-dimensional model evaluation technique. The one-dimensional model evaluation technique primarily relies on T2 spectra provided by a nuclear magnetic resonance (NMR) spectrometer, which reflects the distribution of residual oil with varying core pore sizes. The three-dimensional model evaluation technique primarily relies on data such as core pore conditions, fluid flow dynamics, and residual oil distribution provided by a micron-sized core CT scanning system. Through data analysis and model construction, a three-dimensional dynamic visualization image of the relative content and occurrence state of residual oil in the core can be established.

[0053] The formula for calculating the unblocking rate is as follows:

[0054]

[0055] In the formula, k0 is the initial permeability of the crude oil saturated core, mD;

[0056] A0 is the integral area of ​​the T2 curve of the crude oil saturated core, which is dimensionless;

[0057] k1 is the permeability of the core sample contaminated with formation water, in mD;

[0058] A1 is the integral area of ​​the T2 curve of the core sample contaminated with formation water, which is dimensionless;

[0059] k2 represents the permeability of the core sample after unblocking and oil displacement by injecting the bio-based composite system, in mD;

[0060] A2 is the integral area of ​​curve T2, which is dimensionless;

[0061] t is a correction factor, the value of which depends on the core condition and the unblocking situation.

[0062] The formula for calculating the damage coefficient is as follows:

[0063]

[0064] In the formula, k takes the values ​​k1 and k2 respectively to calculate the damage coefficients when the core is blocked and after unblocking.

[0065] The unblocking rate and damage coefficient are used to quantitatively analyze the damage to core samples and are dimensionless variables. When calculating the unblocking rate, the changes in core permeability and the influence of the integral area of ​​the T2 spectrum are fully considered. The calculation process combines these two factors and introduces a correction factor to ensure the rationality of the formula. The damage coefficient reflects the permeability recovery during the rock unblocking process; the higher the degree of permeability recovery, the smaller the damage coefficient.

[0066] The large amounts of metallic inorganic salt ions, light organic matter, and abundant microorganisms contained in the formation water of offshore oil fields are important factors causing core blockage.

[0067] In some preferred embodiments, the offshore oilfield formation water used in this invention contains 2.8-3.5 mg / L of oil, 0.2-0.5 mg / L of iron ions, and 20-25 num / mL of sulfate-reducing bacteria.

[0068] In some preferred embodiments, the temperature of the unblocking and oil displacement experiment is 20-100℃, the pH of the formation water is 1-10, and the formation water salinity is 3000-15000 mg / L.

[0069] In some preferred embodiments, the criteria for judging core blockage are as follows: when formation water is used to displace the core from the outlet end of the core column in reverse, and the water content at the inlet end reaches more than 98% and the core injection pressure increases significantly, the core is considered to be blocked by formation water contamination.

[0070] In some preferred embodiments, the bio-derived composite system is a mixture of bio-acid, rhamnolipid surfactant, and lipopeptide surfactant, with a succinate-to-sulfate ratio of 1:1:2 to 2:1:1 and a concentration of 500-2000 mg / L.

[0071] The types and ratios of bio-acids, rhamnolipid surfactants, and lipopeptide surfactants in the bio-derived composite system can be selected according to actual needs, and this invention does not impose specific limitations on them.

[0072] In this invention, the T2 spectrum test is performed using a nuclear magnetic resonance (NMR) spectrometer. The NMR T2 spectrum is essentially a signal showing the change in the transverse magnetization component of protons as a function of relaxation time in a magnetic field. Since the polarization process of protons in the core solid is slow, the T2 relaxation time is difficult to capture and can be ignored. Therefore, the spectrum only represents the magnetization component signal of the fluid in the core pores. The fluid relaxation time is negatively correlated with the specific surface area and relaxation rate of the core pores; the longer the relaxation time, the smaller the specific surface area of ​​the core pores, which can be approximated as a larger core pore size.

[0073] Therefore, this invention proposes that the integrated area of ​​the T2 spectrum can, to a certain extent, reflect the relative content of remaining oil reservoirs in the core, the overall pore condition, and the degree of crude oil displacement. The peak signal intensity of the T2 spectrum can, to a certain extent, reflect the relative content of remaining oil reservoirs in the core distributed across different pore sizes.

[0074] In some preferred embodiments, the nuclear magnetic resonance spectrometer is configured with the following parameters: CPMG sequence, echo time (TE) of 0.1-0.5 ms, wait time (TW) of 4000-12000 ms, and approximately 100-5000 echoes.

[0075] Among them, relaxation time reflects the size of core pores to a certain extent. As relaxation time increases, nuclear magnetic resonance signals from small pores to large pores in the core are detected sequentially.

[0076] In some preferred embodiments, the relaxation time ranges from 0.001 to 10000 ms.

[0077] In this invention, the micron core CT scan is performed using a micro-nano dual-ray tube core CT scanning system.

[0078] In some preferred embodiments, the resolution of the micron core CT scan is 4 μm and the sample diameter is 10 mm.

[0079] In some preferred embodiments, the characteristic parameters include area index (S), overlap (C), and Euler number (E).

[0080] Where, area coefficient = surface area 3 / (36π × volume) 2 ), overlap = contact area between oil and rock / surface area of ​​oil, Euler number = 1 - connected volume + closed loop.

[0081] In some preferred embodiments, the occurrence state includes clusters, sieves, drops, columns, and flakes.

[0082] In some preferred embodiments, the occurrence state is defined by the area factor, the degree of overlap and the Euler number, as shown in Table 2.

[0083] In this invention, the permeability of the offshore oilfield core is one of three types: low-permeability core, medium-permeability core, and high-permeability core. Specifically, the permeability of the low-permeability core is less than 10 mD, the permeability of the medium-permeability core is 10-100 mD, and the permeability of the high-permeability core is greater than 100 mD.

[0084] The present invention provides a testing and evaluation method for the unblocking and oil displacement capabilities of a bio-based composite system. This method is mainly designed for bio-based composite systems and verifies the unblocking and oil displacement effects of the system from multiple dimensions. The evaluation indicators are specific and quantifiable, and the method is characterized by being intuitive, simple, high-resolution, and highly targeted. It can serve as an important reference for evaluating the suitability of reagents and improving the efficiency of oilfield development and exploitation.

[0085] Example

[0086] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, were performed according to conventional methods and conditions. The raw materials used in the following embodiments were all commercially available.

[0087] Example 1

[0088] S1 involves completely drying offshore oilfield cores with a permeability of 800-1000 mD, injecting crude oil into the cores until the core oil saturation reaches the initial oil saturation of the formation, simulating a real formation core. Then, T2 spectrometry and micron-level core CT scanning are performed on the crude oil-saturated cores to determine the initial permeability k0, and the integrated area of ​​the T2 curve is A0 (results are shown in Table 1). The nuclear magnetic resonance (NMR) instrument settings are as follows: CPMG sequence, echo time (TE) of 0.3 ms, wait time (TW) of 6000 ms, and approximately 300 echoes; the micron-level core CT scan resolution is 4 μm, and the sample diameter is 10 mm.

[0089] In step S2, formation water with a salinity of 8000 mg / L and a pH of 6.5 was used to reverse-displace the core from the outlet end of the core column at 30℃. When the water cut at the inlet end reached over 98% and the core injection pressure increased significantly, the core was considered to be contaminated by formation water, thus obtaining a formation water contaminated core. Then, T2 spectrometry and micron-sized core CT scanning were performed on the formation water contaminated core to determine the permeability k1 when the core was contaminated. The integral area of ​​the T2 curve was A1 (results are shown in Table 1). The parameter settings for the T2 spectrometry and micron-sized core CT scanning were the same as in step S1.

[0090] In step S3, a bio-based composite system was injected forward into a core sample contaminated with formation water until the water cut at the core outlet reached 98%, yielding a core sample after unblocking and oil displacement using the injected bio-based composite system. Then, T2 chromatography and micron-level core CT scanning were performed on the unblocked core sample to determine the permeability k2, and the area of ​​the T2 curve integral was A2 (results are shown in Table 1). The bio-based composite system consisted of bio-acids, rhamnolipid surfactants, and lipopeptide surfactants, with a slub-to-block ratio of 1:1:1 and a concentration of 1500 mg / L. The parameter settings for T2 chromatography and micron-level core CT scanning were the same as in step S1.

[0091] S4 calculates the damage coefficient and unblocking rate of the core sample before and after blockage, based on the formulas for unblocking rate and damage coefficient. The calculation results are shown in Table 1. The calculation formulas are as follows:

[0092] Congestion relief rate Where t is a correction factor, and in this embodiment, t takes the value of 3.

[0093] Damage coefficient

[0094] In step S5, formation water is injected again into the core after unblocking and oil displacement using the bio-based composite system until the water cut reaches over 98%, resulting in a core after secondary waterflooding. The core after secondary waterflooding is then subjected to T2 mapping and micron-level core CT scanning. The parameter settings for T2 mapping and micron-level core CT scanning are the same as in step S1.

[0095] S6 plots a dotted-line graph of the T2 spectrum test results with relaxation time as the x-axis and nuclear magnetic resonance signal intensity as the y-axis, obtaining the integral area and peak signal intensity of the T2 spectrum.

[0096] Based on the results of micron core CT scans, the characteristic parameters area coefficient (S), overlap (C), and Euler number (E) were calculated, and the results are shown in Table 2. The occurrence state of residual oil was defined by the aforementioned characteristic parameters, and the imaged results were obtained.

[0097] Table 1

[0098]

[0099] Among them, the T2 spectrum of crude oil saturated cores, such as Figure 2 As shown; T2 spectrum of formation water contaminated core, as follows. Figure 3 As shown; T2 spectra of core samples after unblocking and oil displacement via injection of a bio-based composite system, as shown. Figure 4 As shown; the T2 spectrum of the core after secondary waterflooding, as follows. Figure 5 As shown.

[0100] Figure 2The peak value of the unblocked core was around 300ms, indicating a large number of large pores, and the area of ​​the T2 spectrum was 167068.2. Figure 3 After the blockage, two peak values ​​appeared in the core sample. The left peak value was around 1 ms, indicating a significant increase in the number of small pores; the right peak value was around 100 ms, which is consistent with... Figure 2 Compared to the original core, the right peak value shifts significantly towards the direction of decreasing relaxation time, and the T2 spectrum area is 110416.7. Compared to... Figure 3 Compared to the core images after blockage, Figure 4 The left and right peaks still exist, but both the left and right peaks have shifted towards the direction of increasing relaxation time, indicating that the number of macropores has increased and the diameter of micropores has increased. The integral area of ​​the T2 spectrum is 146995.1. Figure 5 The right peak shifts slightly in the direction of increasing relaxation time, and the integral area of ​​the T2 spectrum is 153089.6, which is consistent with... Figure 4 There was no significant difference, but with Figure 3 The significant differences demonstrate that the bio-based composite system has a good unblocking effect. The above test results indicate that the unblocking ability of the bio-based composite system is consistent with the changes in the core T2 spectra during the unblocking experiment. Therefore, the one-dimensional effect evaluation model of the bio-based composite system based on nuclear magnetic resonance T2 spectra can serve as an important basis for analyzing reservoir conditions and blockage status, and evaluating the system's unblocking ability.

[0101] Figure 6 The pressure and recovery curves during the displacement process are shown. After the injection of the bio-based composite system, the displacement pressure decreased significantly, macroscopically verifying the unblocking effect of the bio-based composite system on the blocked core. The degree of crude oil recovery is given by the recovery curve. After the displacement by the bio-based composite system, the recovery rate increased from 60% at the end of waterflooding to 78.42%.

[0102] Figure 7 The images show the T2 spectra of core samples measured at different times after injection into the bio-based composite system. It can be seen that within 24 hours of injection, the signal intensity of the pore fluid decreases significantly, and the peak relaxation time shortens, demonstrating the good unclogging and oil-washing effect of the bio-based composite system. From 24 to 96 hours after injection, the integrated area of ​​the T2 spectra continues to decrease, indicating that the bio-based composite system has a sustained effect.

[0103] The calculation results of the characteristic parameters are shown in Table 2; micron-CT scans were performed on the core samples from the 1500 mg / L bio-based composite system used in the oil displacement experiment, and the results are as follows. Figure 8 As shown in the bar chart, this illustrates the distribution of residual oil in the core after the displacement experiment. Figure 9 As shown.

[0104] Table 2

[0105] flakes 8％ 2.9 0.35 0.15 droplets 2％ 1.3 0 0.3 columnar 6％ 2.1 0.48 0.05 sieve 18％ 2.4 0.47 -0.5 clustered 65％ 2.2 0.43 -2.2

[0106] When the concentration of the bio-based composite system is 1500 mg / L, the residual oil distribution morphology of waterflooding is divided into clustered residual oil, sieve residual oil, columnar residual oil, droplet residual oil, and flake residual oil. As waterflooding ends and the system is converted to bio-based composite system for oil displacement, the proportion of clustered continuous phase decreases continuously from 75% to 65%, which increases the recovery rate by 13.3% compared to waterflooding.

[0107] Example 2

[0108] Example 2 was identical to Example 1 in terms of displacement experiment, T2 spectrum test, and CT scan process. The difference was that the high permeability core of 800-1000mD was replaced with a medium permeability core of 50-100mD, and the bio-derived composite system was changed from 1500mg / L to 2000mg / L.

[0109] The T2 spectrum test results are as follows: Figure 10 As shown, the bio-based composite system has the ability to reduce injection pressure and improve oil recovery. The occurrence state of crude oil in pores can affect the response of pores at different relaxation times. In low-permeability cores, the integrated area of ​​the T2 spectrum of the bio-nano-displacement agent system in the small pore distribution region decreases, indicating that the residual oil from waterflooding in low-permeability reservoirs is mainly distributed in small pores, and the bio-based composite system can displace this portion of crude oil. In medium-permeability cores, crude oil is mainly stored in the large pore space of the reservoir; after injecting the bio-based composite system, the integrated area of ​​the T2 spectrum decreases, and the core recovery rate increases by 20.06%. The above test results show that the ability of the bio-based composite system to improve oil recovery is consistent with the changes in the core T2 spectrum in the oil displacement experiment. Therefore, the one-dimensional effect evaluation model of the bio-based composite system based on the nuclear magnetic resonance T2 spectrum can serve as an important basis for analyzing reservoir conditions and evaluating the oil displacement capacity of the system.

[0110] The definition of crude oil occurrence state based on characteristic parameters is shown in Table 3. Micron-CT scanning was performed on core samples from a 2000 mg / L bio-based composite system used in oil displacement experiments. The results are as follows: Figure 11 As shown in the bar chart, this illustrates the distribution of residual oil in the core after the displacement experiment. Figure 12 As shown.

[0111] Table 3

[0112] flakes 6％ 2.8 0.3 0.2 droplets 4％ 1.2 0 0.1 columnar 9％ 2.1 0.48 0.05 sieve 28％ 2.5 0.45 -0.5 clustered 49％ 2.2 0.46 -2.5

[0113] When the concentration of the bio-based composite system was 2000 mg / L, the residual oil distribution morphology after waterflooding included clustered residual oil, sieve-like residual oil, columnar residual oil, droplet-like residual oil, and flake-like residual oil. As waterflooding transitioned to the bio-based composite system, the proportion of clustered continuous phase decreased continuously from 71% to 49%. The bio-based composite system exhibited good emulsifying and dispersing ability for crude oil. At a concentration of 2000 mg / L, the residual oil saturation after displacement was 39.8%, representing a 10.5% increase in oil recovery compared to waterflooding.

[0114] The above test results demonstrate that micron-based core CT results can quantitatively analyze the relative content and distribution morphology of residual oil in reservoirs, which helps in the targeted analysis and formulation of oil production technology schemes to improve crude oil recovery. After the bio-based composite system is injected into the core, it alters the wettability of the rock surface and reduces the structural separation pressure between the rock and crude oil. The reservoir modification effect corresponds to the change in the distribution morphology of residual oil, and the improvement in crude oil recovery corresponds to the reduction in the relative content of residual oil in different morphologies. Therefore, the three-dimensional effect evaluation model of the bio-based composite system based on micron-based core CT scanning technology can serve as an important basis for studying reservoir geological characteristics and fluid seepage characteristics, analyzing and simulating reservoir distribution morphology, and evaluating the oil displacement capacity of the bio-based composite system.

[0115] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are merely illustrative of the invention and should not be construed as limiting its scope. It should be noted that any variations and substitutions equivalent to these embodiments should be considered to be covered within the scope of the claims. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for testing and evaluating the oil displacement and unblocking capabilities of a bio-based composite system, characterized in that, include: S1 After drying the offshore oilfield core, it is displaced with crude oil until saturation to obtain crude oil saturated core. The crude oil saturated core is subjected to T2 spectrum test and micron core CT scan to determine the initial permeability k0 and the integral area A0 of the T2 curve. S2 uses formation water to reverse displace the crude oil-saturated core, causing core blockage and obtaining a formation water-contaminated core. The formation water-contaminated core is subjected to T2 spectrum testing and micron core CT scanning to determine the permeability k1 and the integral area A1 of the T2 curve during blockage. S3 injects a bio-based composite system into the formation water contaminated core to conduct an oil displacement and unblocking experiment, obtaining the core after the bio-based composite system is injected to unblock and displace oil. The core after the bio-based composite system is injected to unblock and displace oil is subjected to T2 spectrum testing and micron core CT scanning; the permeability k2 and the integral area A2 of the T2 curve after unblocking are measured. S4 calculates the damage coefficient and unblocking rate during and after core blockage based on the formulas for unblocking rate and damage coefficient; S5 injects formation water into the core after unblocking and oil displacement in the bio-source composite system to a water cut of over 98%, obtaining a core after secondary waterflooding. The core after secondary waterflooding is then subjected to T2 spectrum testing and micron core CT scanning. S6 plots a dotted-line graph of the T2 spectrum test results with relaxation time as the x-axis and nuclear magnetic resonance signal intensity as the y-axis to obtain the integral area and peak signal intensity of the T2 spectrum. S7 calculates characteristic parameters based on the results of micron core CT scans, defines the occurrence state of residual oil through these characteristic parameters, and obtains image-based results.

2. The testing and evaluation method according to claim 1, characterized in that, The formation water contains 2.8-3.5 mg / L of oil, 0.2-0.5 mg / L of iron ions, and 20-25 num / mL of sulfate-reducing bacteria.

3. The testing and evaluation method according to claim 1, characterized in that, In step S2, the criteria for judging core blockage are: the water content at the core inlet reaches 98% or more, and the injection pressure increases significantly.

4. The testing and evaluation method according to claim 1, characterized in that, The bio-derived composite system is a compound of bio-acids, rhamnolipid surfactants, and lipopeptide surfactants, with a slub-to-butane ratio of 1:1:2 to 2:1:1 and a concentration of 500-2000 mg / L.

5. The testing and evaluation method according to claim 1, characterized in that, The T2 spectrum test was performed using a nuclear magnetic resonance spectrometer, and the micron core CT scan was performed using a micro-nano dual-ray tube core CT scanning system.

6. The testing and evaluation method according to claim 5, characterized in that, The settings parameters of the nuclear magnetic resonance spectrometer are as follows: CPMG sequence is used, echo time TE is 0.1-0.5ms, waiting time TW is 4000-12000ms, and the number of echoes is 100-5000.

7. The testing and evaluation method according to claim 1, characterized in that, The characteristic parameters include area coefficient, overlap, and Euler number.

8. The testing and evaluation method according to claim 1, characterized in that, The occurrence states include clustered, sieve-like, droplet-like, columnar, and sheet-like.

9. The testing and evaluation method according to claim 1, characterized in that, The resolution of the micron core CT scan is 4 μm, and the sample diameter is 10 mm.

10. The testing and evaluation method according to claim 1, characterized in that, The offshore oilfield core is one of three types: low-permeability core, medium-permeability core, and high-permeability core; wherein the permeability of the low-permeability core is less than 10 mD, the permeability of the medium-permeability core is 10-100 mD, and the permeability of the high-permeability core is greater than 100 mD.

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