Method for determining fluid saturation profile after carbon dioxide flooding

Abstract

The application provides a method for determining fluid saturation profile after carbon dioxide flooding. The method comprises the following steps: obtaining the pulsed neutron logging data of each target position before and after boron injection after the completion of carbon dioxide flooding in the well section of the working area, so as to determine the formation macroscopic capture cross-section value of each target position before and after boron injection after the completion of carbon dioxide flooding in the well section of the working area; wherein the number of target positions is not less than 6; obtaining the porosity and shale content of each target position in the well section of the working area; based on the porosity, shale content and formation macroscopic capture cross-section value of each target position in the well section of the working area before and after boron injection after the completion of carbon dioxide flooding, determining the gas saturation, water saturation and oil saturation of each target position in the well section of the working area after the completion of carbon dioxide flooding, so as to realize the determination of the fluid saturation profile after carbon dioxide flooding in the well section of the working area.

Description

Technical Field

[0001] This invention relates to a method for determining the fluid saturation distribution profile after carbon dioxide flooding. Background Technology

[0002] As crude oil and natural gas are developed in oil and gas reservoirs, formation energy gradually decreases and becomes insufficient to support oil and gas production. Therefore, it is necessary to replenish formation energy through water injection or CO2 injection to achieve oil and gas production. During CO2 enhanced oil recovery, the interaction between CO2, water, and rock in the reservoir leads to some CO2 dissolving in formation water, some dissolving in oil, and some transforming into new secondary carbonates and mineralized precipitates. Due to differences in CO2 diffusion within reservoir pores, the characteristic parameters of formation water change over time, and mineral dissolution alters reservoir porosity and pore structure, resulting in complex changes in the electrical parameters of the rock. These complex changes make it difficult to quantitatively determine CO2 saturation using conventional logging data processing.

[0003] Based on energy dispersive spectroscopy (EDS) measurements, the C / O method was proposed. This method assesses remaining oil saturation by the count ratio of the carbon and oxygen windows through inelastic gamma interactions. Although C / O logging is not limited by salinity, porosity directly determines the accuracy of C / O interpretation. Because the inelastic gamma of carbon in natural gas is much smaller than that in oil, the carbon-oxygen ratio in natural gas exhibits significant statistical fluctuations. Therefore, C / O logging is generally not used for gas saturation measurement.

[0004] In pulsed neutron logging, the signal from the interaction between neutrons or gamma rays and formation materials is used to calculate gas saturation, thereby evaluating gas content. Multi-detector pulsed neutron technology has been proposed for the quantitative determination of formation gas saturation, offering significant advantages over traditional neutron capture methods in detecting and quantifying formation gas saturation. A key improvement in multi-detector pulsed neutron logging tools is the addition of an ultra-long-range detector to the existing dual-detector pulsed neutron instrument, enhancing gas sensitivity. The inelastic gamma ratio of the near-to-ultra-long-range detector and the capture gamma ratio of the near-to-ultra-long-range detector are used to determine gas saturation.

[0005] If a low-mineralized saline layer is injected with CO2 for sequestration, then the formation fluid consists of only two phases: gas and water. The gas saturation can be estimated using the macroscopic capture cross-section of thermal neutrons in CO2 and water.

[0006] The physicochemical processes involved in CO2 injection into reservoirs for oil displacement or storage include: multiphase flow migration, dissolution-desorption dynamics, solute migration, viscous fingering, and upward migration due to gravity overburden. Therefore, it is essential to understand the gas saturation profile distribution after CO2 injection to assess the oil displacement and storage effects. Summary of the Invention

[0007] The purpose of this invention is to provide a technical solution that can determine the gas saturation profile distribution after CO2 injection into the formation.

[0008] To achieve the above objectives, the present invention provides a method for determining the fluid saturation distribution profile after carbon dioxide flooding, the method comprising the following steps:

[0009] The pulsed neutron logging data of each target location before and after boron injection following the completion of carbon dioxide flooding in the work area are obtained, thereby determining the macroscopic capture section value of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area; wherein, the number of target locations is not less than 6;

[0010] Obtain the porosity and clay content at each target location in the work area;

[0011] Based on the porosity and clay content of each target location in the work area, as well as the macroscopic capture section values ​​of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area, the gas saturation, water saturation, and oil saturation at each target location after the completion of carbon dioxide flooding in the work area are determined, thereby realizing the determination of the fluid saturation distribution profile after carbon dioxide flooding in the work area.

[0012] Furthermore, the formation macroscopic capture section values ​​at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area can be determined using conventional methods based on pulsed neutron logging data at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area.

[0013] Furthermore, the porosity at each target location in the well section can be obtained using conventional acoustic, density, or neutron logging methods.

[0014] Furthermore, the mud content at each target location in the work area can be obtained through spontaneous potential logging, spontaneous gamma logging, neutron logging, or cross-plots such as neutron-density and neutron-sonic logging.

[0015] Furthermore, based on the porosity and clay content of each target location in the work area, as well as the macroscopic capture section values ​​of the formation at each target location before and after boron injection following carbon dioxide flooding, the gas saturation, water saturation, and oil saturation at each target location after carbon dioxide flooding are determined, thereby realizing the determination of the fluid saturation distribution profile after carbon dioxide flooding in the work area, including:

[0016] 1) Obtain the initial values ​​of the formation water capture section before and after boron injection following the completion of carbon dioxide flooding in the work area well section;

[0017] 2) Obtain the initial gas saturation values ​​at each target location in the work area well section;

[0018] 3) Based on the initial value of the formation water capture section before and after boron injection following the completion of carbon dioxide flooding in the work area, and combined with the porosity of each target location in the work area and the macroscopic capture section value of the formation before and after boron injection following the completion of carbon dioxide flooding in the work area, the initial value of water saturation at each target location in the work area is determined.

[0019] 4) Based on the porosity, clay content, initial water saturation, initial gas saturation, and macroscopic trapping section values ​​of the formation at each target location in the work area well section before and after boron injection following the completion of carbon dioxide flooding, determine the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before and after boron injection following the completion of carbon dioxide flooding in the work area well section.

[0020] 5) Based on the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding are determined in step 4), and combined with the initial values ​​of porosity, clay content, and water saturation at each target location in the work area, as well as the macroscopic trapping section values ​​of the formation at each target location before boron injection after carbon dioxide flooding, the gas saturation at each target location in the work area is re-determined.

[0021] 6) Based on the trapping section values ​​of formation water before and after boron injection following the completion of carbon dioxide flooding in the well section of the work area determined in step 4), and combined with the porosity of each target location in the well section of the work area and the macroscopic trapping section values ​​of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the well section of the work area, the water saturation of each target location in the well section of the work area is re-determined.

[0022] 7) Compare the gas saturation at each target location in the work area determined in step 5) with the initial water saturation value used in step 4) to determine the gas saturation at each target location in the work area:

[0023] If the error between the two is less than or equal to the error threshold, proceed to step 8);

[0024] If the error between the two is greater than the error threshold, then the gas saturation of each target location in the work area obtained in step 5) is taken as the initial value of the gas saturation of each target location in the work area, and the water saturation of each target location in the work area obtained in step 6) is taken as the initial value of the water saturation of each target location in the work area, and steps 4)-7) are repeated.

[0025] 8) Based on the gas saturation of each target location in the work area determined in step 5) and the water saturation of each target location in the work area determined in step 6), determine the oil saturation of each target location in the work area; based on the gas saturation of each target location in the work area determined in step 5), the water saturation of each target location in the work area determined in step 6), and the oil saturation of each target location in the work area, determine the fluid saturation distribution profile after carbon dioxide flooding in the work area.

[0026] Furthermore, in step 2), obtaining the initial values ​​of gas saturation at each target location in the work area includes:

[0027] Based on pulsed neutron logging data of each target location before boron injection after carbon dioxide flooding in the work area, the count rate ratio of each target location before boron injection after carbon dioxide flooding in the work area was determined.

[0028] Based on the count rate ratios of each target location after carbon dioxide flooding and before boron injection in the work area, combined with the count rate ratios of pure water layers and pure gas layers, the initial gas saturation values ​​of each target location in the work area are determined.

[0029] Furthermore, the gas saturation is determined using the following formula:

[0030]

[0031] In the formula, RLS is the count rate ratio at the target location, which is dimensionless; RLS w RLS is the count rate ratio of the pure water layer, dimensionless. g S is the count rate ratio of pure gas layers, dimensionless; g0 This represents the gas saturation level.

[0032] Furthermore, in steps 3) and 6), the water saturation is determined using the following formula:

[0033]

[0034] In the formula, S w φ is the water saturation, dimensionless; φ is the porosity, dimensionless; σ f The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m -1 ;σ′ f The macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 ;σ′ wThe value of the formation water capture section after boron injection following carbon dioxide flooding, in m -1 .

[0035] Further, in step 4), based on the porosity, clay content, initial water saturation, and initial gas saturation at each target location in the work area, as well as the macroscopic trapping cross-sectional values ​​of the formation at each target location before and after boron injection following carbon dioxide flooding in the work area, the trapping cross-sectional values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before and after boron injection following carbon dioxide flooding in the work area are determined, including:

[0036] Based on the porosity, clay content, initial water saturation, initial gas saturation, and macroscopic trapping section values ​​of the formation at each target location in the work area before boron injection after carbon dioxide flooding, the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding in the work area were determined.

[0037] Based on the capture section values ​​of the formation rock skeleton, pore gas, pore crude oil, and mudstone in the work area, combined with the macroscopic capture section values ​​of the formation at each target location after boron injection following carbon dioxide flooding in the work area, the capture section value of formation water after boron injection following carbon dioxide flooding was determined.

[0038] Furthermore, the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding in the work area are determined based on the following formulas:

[0039]

[0040] Wherein: S g,i Let φ be the gas saturation at target location i, dimensionless; i σ represents the porosity at target location i, which is dimensionless; f,i The macroscopic capture section value of the formation at target location i before boron injection after carbon dioxide flooding, m -1 ;σ fm The capture section value of the stratigraphic rock skeleton, m -1 ;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1 ;σ sh For the capture section of mudstone, m -1 ;σw The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w,i Let be the water saturation at target location i, dimensionless; i = 1, 2, 3...n.

[0041] Furthermore, the trapping section value of formation water after boron injection following carbon dioxide flooding is determined based on the following formula:

[0042] σ′ f =σ f,m (1-φ)(1-V sh )+σ gas φS g +σ oil φ(1-S g -S w )+σ′ w φS w +σ sh (1-φ)V sh

[0043] In the formula, S g φ represents gas saturation, dimensionless; φ represents porosity, dimensionless; σ′ f The macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ;σ f,m The capture section value of the stratigraphic rock skeleton, m -1 ;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1 ;σ sh For the capture section of mudstone, m -1 ;σ′ w The value of the formation water capture section after boron injection following carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w The value represents water saturation, which is dimensionless.

[0044] Further, in step 5), the gas saturation is determined using the following formula:

[0045]

[0046] In the formula, S g φ represents gas saturation, dimensionless; φ represents porosity, dimensionless; σ represents... f The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m-1 ;σ f,m The capture section value of the stratigraphic rock skeleton, m -1 ;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1 ;σ sh For the capture section of mudstone, m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w The value represents water saturation, which is dimensionless.

[0047] Further, in step 7), the error threshold is 10. -3 .

[0048] The technical solution provided by this invention can determine the water saturation and gas saturation after CO2 injection, thereby understanding the distribution of residual oil and the CO2 profile distribution after CO2 injection into the formation, so as to carry out the next step of enhanced oil recovery operation. Attached Figure Description

[0049] Figure 1 This is a cross-sectional view of the fluid saturation distribution obtained in Example 1. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below. Here, the illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0051] In the description of this specification, the terms "comprising," "including," "having," and "containing" are open-ended terms, meaning that they include but are not limited to. The terms "an embodiment," "a specific embodiment," "some embodiments," and "for example," etc., refer to specific features, structures, or characteristics described in connection with that embodiment or example that are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. The order of steps involved in the various embodiments is used to illustrate the implementation of this application, and the order of steps is not limited and can be adjusted appropriately as needed.

[0052] During CO2 enhanced oil recovery (EOR) or oil storage operations, CO2 injection alters the oil saturation, water saturation, and gas saturation of wellbore components. The CO2 injection process displaces oil and water, causing changes in water saturation before and after CO2 injection. Therefore, it is necessary to calculate the water and gas saturation after CO2 injection to obtain accurate formation parameters and understand the distribution of remaining oil and CO2 profiles after CO2 injection, in order to implement further EOR operations. Consequently, the inventors have dedicated themselves to researching and determining the fluid saturation distribution profile after CO2-driven oil recovery.

[0053] In formations, the macroscopic capture cross section is mainly related to formation water salinity and chlorine content. During well logging, a pulsed neutron source emits neutrons with an energy of 14 MeV into the formation, and the thermal neutrons or captured gamma rays that return to the wellbore after being slowed down by the formation are measured. Based on the decay of the count rate over time, the macroscopic capture cross section of the formation thermal neutrons is determined (the macroscopic capture cross section refers to the sum of the microscopic capture cross sections of all atomic nuclei in a unit volume of medium).

[0054] Rocks and minerals in the formation, such as quartz, calcite, dolomite, and shale, as well as fluids in the pores, such as water, crude oil, gas, and CO2, can all capture neutrons. The emitted neutron pulse undergoes inelastic scattering, emitting inelastically scattered gamma rays, which then undergo elastic scattering and are finally captured by the formation. The near-source detector has a source-to-source distance of 0.45 m, the mid-source detector has a source-to-source distance of 0.9 m, and the far-source detector has a source-to-source distance of 1.8 m. The longitudinal resolution of the RMT instrument is 24 in (0.6 m).

[0055] Water and crude oil have relatively similar neutron-modulating abilities, while CO2's neutron-modulating ability is significantly weaker. During CO2 injection into the reservoir, CO2 near the wellbore displaces water and crude oil, leading to a significant increase in CO2 gas saturation near the wellbore. This significant increase in CO2 gas saturation causes a change in the macroscopic neutron capture cross-section σ. f Reduced. In pulsed neutron logging technology, the signal of the interaction between neutrons or gamma rays and formation materials is used to determine gas saturation, thereby enabling the evaluation of gas content.

[0056] CO2 has a low thermal neutron macroscopic trapping cross section, therefore the distribution of gamma rays reflects significantly different CO2 environments in the count rate and recorded energy spectrum. This invention utilizes the signal of pulsed neutron interaction with formation material to determine CO2 saturation, thereby enabling the evaluation of gas content and oil saturation, and ultimately determining the fluid saturation distribution profile after carbon dioxide flooding.

[0057] A specific embodiment of the present invention provides a method for determining the fluid saturation distribution profile after carbon dioxide flooding, the method comprising the following steps:

[0058] Step 101: Obtain pulsed neutron logging data of each target location before and after boron injection following the completion of carbon dioxide flooding in the work area well section, thereby determining the formation macroscopic capture section value of each target location before and after boron injection following the completion of carbon dioxide flooding in the work area well section; wherein, the number of target locations is not less than 6.

[0059] Step 102: Obtain the porosity and clay content at each target location in the work area well section;

[0060] Step 103: Based on the porosity and clay content of each target location in the work area well section, as well as the macroscopic capture section values ​​of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area well section, determine the gas saturation, water saturation, and oil saturation at each target location after the completion of carbon dioxide flooding in the work area well section, thereby determining the fluid saturation distribution profile after carbon dioxide flooding in the work area well section.

[0061] In one embodiment, in step 101, the formation macroscopic capture section values ​​at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area can be determined using conventional methods based on pulsed neutron logging data at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area.

[0062] In one embodiment, in step 102, the porosity of each target location in the well section can be obtained by conventional acoustic, density, or neutron logging methods.

[0063] In one embodiment, in step 102, the mud content at each target location in the work area can be obtained through spontaneous potential logging, spontaneous gamma logging, neutron logging, or cross-plots such as neutron-density and neutron-acoustic.

[0064] In one embodiment, in step 103, based on the porosity and clay content of each target location in the work area, and the macroscopic capture section values ​​of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area, the gas saturation, water saturation, and oil saturation at each target location after the completion of carbon dioxide flooding in the work area are determined, thereby realizing the determination of the fluid saturation distribution profile after carbon dioxide flooding in the work area, including:

[0065] Step 1031: Obtain the initial value of the formation water capture section before and after boron injection following the completion of carbon dioxide flooding in the work area well section;

[0066] Step 1032: Obtain the initial gas saturation value at each target location in the work area well section;

[0067] Step 1033: Based on the initial value of the formation water capture section before and after boron injection following the completion of carbon dioxide flooding in the work area well section, and combined with the porosity of each target location in the work area well section and the macroscopic capture section value of the formation before and after boron injection following the completion of carbon dioxide flooding in the work area well section, determine the initial value of water saturation at each target location in the work area well section.

[0068] Step 1034: Based on the porosity, clay content, initial water saturation, and initial gas saturation of each target location in the work area, as well as the macroscopic trapping section values ​​of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area, determine the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before and after boron injection following the completion of carbon dioxide flooding in the work area.

[0069] Step 1035: Based on the trapping cross-sectional values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding, which were determined in Step 1034, the gas saturation of each target location in the work area is re-determined, taking into account the initial values ​​of porosity, clay content, and water saturation at each target location in the work area, as well as the macroscopic trapping cross-sectional values ​​of the formation at each target location before boron injection after carbon dioxide flooding in the work area.

[0070] Step 1036: Based on the trapping section values ​​of formation water before and after boron injection following the completion of carbon dioxide flooding in the work area well section determined in step 1034, and combined with the porosity of each target location in the work area well section and the macroscopic trapping section values ​​of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area well section, the water saturation of each target location in the work area well section is re-determined.

[0071] Step 1037: Compare the gas saturation at each target location in the work area determined in Step 1035 with the initial water saturation value used in Step 1034 to determine the gas saturation at each target location in the work area.

[0072] If the error between the two is less than or equal to the error threshold, proceed to step 1038;

[0073] If the error between the two is greater than the error threshold, the gas saturation of each target location in the work area obtained in step 1035 is taken as the initial value of the gas saturation of each target location in the work area, and the water saturation of each target location in the work area obtained in step 1036 is taken as the initial value of the water saturation of each target location in the work area, and steps 1034-1037 are repeated.

[0074] Step 1038: Determine the oil saturation at each target location in the work area based on the gas saturation at each target location in the work area determined in Step 1035 and the water saturation at each target location in the work area determined in Step 1036; Determine the fluid saturation distribution profile after carbon dioxide flooding in the work area based on the gas saturation at each target location in the work area determined in Step 1035, the water saturation at each target location in the work area determined in Step 1036, and the oil saturation at each target location in the work area.

[0075] In one embodiment, in step 1031, the initial value of the formation water capture section before and after boron injection following the completion of carbon dioxide flooding in the work area well section is determined by indoor experiments.

[0076] In one embodiment, step 1032, obtaining the initial gas saturation value at each target location in the work area well section includes:

[0077] Based on pulsed neutron logging data of each target location before boron injection after carbon dioxide flooding in the work area, the count rate ratio of each target location before boron injection after carbon dioxide flooding in the work area was determined.

[0078] Based on the count rate ratio of each target location after the completion of carbon dioxide flooding and before boron injection in the work area well section, combined with the count rate ratio of the pure water layer and the count rate ratio of the pure gas layer, the initial value of gas saturation at each target location in the work area well section is determined.

[0079] Furthermore, the gas saturation is determined using the following formula:

[0080]

[0081] In the formula, RLS is the count rate ratio at the target location, which is dimensionless; RLS w RLS is the count rate ratio of the pure water layer, dimensionless. g S is the count rate ratio of pure gas layers, dimensionless; g0 This represents the gas saturation level.

[0082] In one embodiment, in steps 1033 and 1036, the water saturation is determined using the following formula:

[0083]

[0084] In the formula, S w φ is the water saturation, dimensionless; φ is the porosity, dimensionless; σ f The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m -1 ;σ′ fThe macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 ;σ′ w The value of the formation water capture section after boron injection following carbon dioxide flooding, in m -1 .

[0085] In one embodiment, in step 1034, based on the porosity, clay content, initial water saturation, and initial gas saturation at each target location in the work area, and the macroscopic trapping cross-sectional values ​​of the formation at each target location before and after boron injection following carbon dioxide flooding in the work area, the trapping cross-sectional values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before and after boron injection following carbon dioxide flooding in the work area are determined, including:

[0086] Step 10341: Based on the porosity, clay content, initial water saturation, initial gas saturation, and macroscopic trapping section values ​​of the formation at each target location in the work area well section, and before boron injection after carbon dioxide flooding in the work area well section, determine the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding in the work area well section.

[0087] Step 10342: Based on the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, and mudstone in the work area well section, and combined with the macroscopic trapping section values ​​of the formation at each target location after boron injection following the completion of carbon dioxide flooding in the work area well section, determine the trapping section value of formation water after boron injection following the completion of carbon dioxide flooding.

[0088] Further, in step 10341, the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding are determined based on the following formulas:

[0089]

[0090] Wherein: S g,i Let φ be the gas saturation at target location i, dimensionless; i σ represents the porosity at target location i, which is dimensionless; f,i The macroscopic capture section value of the formation at target location i before boron injection after carbon dioxide flooding, m -1 ;σ fmThe capture section value of the stratigraphic rock skeleton, m -1 ;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1 ;σ sh For the capture section of mudstone, m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w,i Let be the water saturation at target location i, dimensionless; i = 1, 2, 3...n;

[0091] The above formulas are used to determine the trapping cross-sectional values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding in the work area. The formulas take into account the three-phase fluids of oil, gas and water in the pores, which can accurately characterize the formation fluid occurrence and more realistically simulate the changes in fluid saturation of the formation fluid during the CO2 enhanced oil recovery process.

[0092] In one specific embodiment, the determination of the trapping cross-sectional values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding in the work area and well section, based on the above formula, is carried out in the following manner:

[0093] The coefficient matrix A of the above formula is determined as follows:

[0094]

[0095] Transpose the coefficient matrix A to obtain the transpose matrix A′ of A:

[0096]

[0097] Multiplying both sides of the above formula by the transpose matrix A′, and letting m = A′A, we can see that m is a 5×5 matrix;

[0098]

[0099] Based on this, σ can be... f,m σ w σ sh σ oil ,σ gas The optimal values ​​for the 5 parameters were obtained;

[0100] Further, in step 10342, the trapping section value of formation water after boron injection following carbon dioxide flooding is determined based on the following formula:

[0101] σ′ f =σ f,m (1-φ)(1-V sh )+σ gas φS g +σ oil φ(1-S g -S w )+σ′ w φS w +σ sh (1-φ)V sh

[0102] In the formula, S g φ represents gas saturation, dimensionless; φ represents porosity, dimensionless; σ′ f The macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ;σ f,m The capture section value of the stratigraphic rock skeleton, m -1 ;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1 ;σ sh For the capture section of mudstone, m -1 ;σ′ w The value of the formation water capture section after boron injection following carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w The value represents water saturation, which is dimensionless.

[0103] In one embodiment, in step 1035, the gas saturation is determined using the following formula:

[0104]

[0105] In the formula, S g φ represents gas saturation, dimensionless; φ represents porosity, dimensionless; σ represents... f The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m -1 ;σ f,m The capture section value of the stratigraphic rock skeleton, m -1 ;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1;σ sh For the capture section of mudstone, m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w The value represents water saturation, which is dimensionless.

[0106] In one embodiment, in step 1037, the error threshold is 10. -3 .

[0107] In one embodiment, in step 1038, the oil saturation is determined using the following formula:

[0108] S o =1-S w -S g,n

[0109] In the formula, S o S represents oil saturation, dimensionless; g S represents gas saturation, dimensionless; w The value represents water saturation, which is dimensionless.

[0110] Example 1:

[0111] This embodiment provides a method for determining the fluid saturation distribution profile after carbon dioxide flooding. This method is used to determine the fluid saturation distribution profile after carbon dioxide flooding in well A, and specifically includes the following steps:

[0112] 1. Before boron injection after carbon dioxide flooding in well A, pulsed neutron logging was performed on the well section of the work area. The length of the well section was discretized, and a point was taken every 0.5m to determine the formation macroscopic capture section value of each target location in the well section of well A before boron injection after carbon dioxide flooding.

[0113] 2. Inject boron into the wellbore of Well A, and perform pulsed neutron logging on the well section of the work area again. Discretize the length of the well section of the work area, and take a point every 0.5m to determine the formation macroscopic capture section value of each target location after boron injection following the completion of carbon dioxide flooding in the well section of Well A.

[0114] 3. Obtain the porosity and clay content at each target location in the A well section;

[0115] Porosity was obtained through sonic logging, and clay content was obtained through natural gamma logging.

[0116] 4. The initial values ​​of the formation water capture section before and after boron injection following the completion of carbon dioxide flooding in the A well section were determined through indoor experiments.

[0117] 5. Based on pulsed neutron logging data from the A well section after CO2 flooding and before boron injection, determine the count rate ratios at each target location in the A well section before boron injection. Based on these count rate ratios, and combining them with the count rate ratios of pure water and pure gas layers, determine the initial gas saturation values ​​at each target location in the A well section using the following formula:

[0118]

[0119] In the formula, RLS is the count rate ratio at the target location, which is dimensionless; RLS w RLS is the count rate ratio of the pure water layer, dimensionless. g S is the count rate ratio of pure gas layers, dimensionless; g0 This represents the gas saturation level.

[0120] 6. Based on the initial values ​​of formation water capture sections before and after boron injection following carbon dioxide flooding in well section A, and combining the porosity at each target location in well section A with the macroscopic formation water capture sections before and after boron injection following carbon dioxide flooding in well section A, the initial values ​​of water saturation at each target location in well section A are determined using the following formula:

[0121]

[0122] In the formula, S w φ is the water saturation, dimensionless; φ is the porosity, dimensionless; σ f The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m -1 ;σ′ f The macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 ;σ′ w The value of the formation water capture section after boron injection following carbon dioxide flooding, in m -1 .

[0123] 7. Based on the porosity, clay content, initial water saturation, and initial gas saturation values ​​at each target location in the A well section, and the macroscopic trapping cross-section values ​​of the formation at each target location before boron injection after carbon dioxide flooding in the A well section, determine the trapping cross-section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding in the A well section based on the following formulas:

[0124]

[0125] Wherein: S g,i Let φ be the gas saturation at target location i, dimensionless; i σ represents the porosity at target location i, which is dimensionless; f,i The macroscopic capture section value of the formation at target location i before boron injection after carbon dioxide flooding, m -1 ;σ fm The capture section value of the stratigraphic rock skeleton, m -1 ;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1 ;σ sh For the capture section of mudstone, m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w,i Let be the water saturation at target location i, dimensionless; i = 1, 2, 3...n.

[0126] 8. Based on the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, and mudstone in the work area, combined with the macroscopic trapping section values ​​of the formation at each target location after boron injection following carbon dioxide flooding in the work area, the trapping section value of formation water after boron injection following carbon dioxide flooding is determined based on the following formula:

[0127] σ′ f =σ f,m (1-φ)(1-V sh )+σ gas φS g +σ oil φ(1-S g -S w )+σ′ w φS w +σ sh (1-φ)V sh

[0128] In the formula, S g φ represents gas saturation, dimensionless; φ represents porosity, dimensionless; σ′ f The macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ;σ f,m The capture section value of the stratigraphic rock skeleton, m -1;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1 ;σ sh For the capture section of mudstone, m -1 ;σ′ w The value of the formation water capture section after boron injection following carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w The value represents water saturation, which is dimensionless.

[0129] 9. Based on the trapping cross-sectional values ​​of the formation rock skeleton, pore gas, pore crude oil, and mudstone in the A well section determined in step 7, and the trapping cross-sectional value of formation water before boron injection after carbon dioxide flooding, combined with the initial values ​​of porosity, clay content, and water saturation at each target location in the A well section, and the macroscopic trapping cross-sectional values ​​of the formation at each target location before boron injection after carbon dioxide flooding in the A well section, the gas saturation at each target location in the A well section is re-determined based on the following formula:

[0130]

[0131] In the formula, S g φ represents gas saturation, dimensionless; φ represents porosity, dimensionless; σ represents... f The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m -1 ;σ f,m The capture section value of the stratigraphic rock skeleton, m -1 ;σ gas The trapping cross section for pore gas, m -1 ;σ oil The cross section for capturing crude oil in porous structures, m -1 ;σ sh For the capture section of mudstone, m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 V sh S represents the clay content, dimensionless; w The value represents water saturation, which is dimensionless.

[0132] 10. Based on the formation water capture section values ​​before and after boron injection following the completion of carbon dioxide flooding in well section A, as determined in steps 7 and 8, and combined with the porosity of each target location in well section A and the macroscopic formation water capture section values ​​before and after boron injection following the completion of carbon dioxide flooding, the water saturation at each target location in well section A is re-determined using the following formula:

[0133]

[0134] In the formula, S w φ is the water saturation, dimensionless; φ is the porosity, dimensionless; σ f The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m -1 ;σ′ f The macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ;σ w The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 ;σ′ w The value of the formation water capture section after boron injection following carbon dioxide flooding, in m -1 .

[0135] 11. Compare the gas saturation at each target location in well section A obtained in step 9 with the initial water saturation value used in step 9 to determine the gas saturation at each target location in well section A:

[0136] If |S g,n -S g,n-1 |≤=10 -3 Then proceed to step 1038; where S g,n The gas saturation at each target location in the A well section determined in step 9 is dimensionless; S g,n-1 The initial water saturation value used to determine the gas saturation at each target location in the A well section for step 9 is dimensionless;

[0137] Otherwise, the gas saturation of each target location in the A well section determined in step 9 shall be used as the initial value of the gas saturation of each target location in the A well section, and the water saturation of each target location in the A well section determined in step 10 shall be used as the initial value of the water saturation of each target location in the A well section, and steps 7-11 shall be repeated.

[0138] 12. Based on the gas saturation at each target location in the A well section determined in step 9 and the water saturation at each target location in the A well section determined in step 10, the oil saturation at each target location in the A well section is determined using the following formula:

[0139] S o =1-S w -S g,n

[0140] In the formula, S o S represents oil saturation, dimensionless; g S represents gas saturation, dimensionless; w The value represents water saturation, which is dimensionless.

[0141] 13. Based on the gas saturation at each target location in the A well section determined in step 9, the water saturation at each target location in the A well section determined in step 10, and the oil saturation at each target location in the A well section determined in step 12, the distribution profile of oil, gas, and water saturation after carbon dioxide flooding in the A well section is obtained. The results are as follows: Figure 1 As shown.

[0142] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the fluid saturation distribution profile after carbon dioxide flooding, the method comprising the following steps: The pulsed neutron logging data of each target location before and after boron injection following the completion of carbon dioxide flooding in the work area are obtained, thereby determining the macroscopic capture section value of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area; wherein, the number of target locations is not less than 6; Obtain the porosity and clay content at each target location in the work area; Based on the porosity and clay content of each target location in the work area, as well as the macroscopic capture section values ​​of the formation at each target location before and after boron injection following the completion of carbon dioxide flooding in the work area, the gas saturation, water saturation, and oil saturation at each target location after the completion of carbon dioxide flooding in the work area are determined, thereby realizing the determination of the fluid saturation distribution profile after carbon dioxide flooding in the work area. Specifically, based on the porosity and clay content of each target location in the work area, as well as the macroscopic capture section values ​​of the formation at each target location before and after boron injection following carbon dioxide flooding, the gas saturation, water saturation, and oil saturation at each target location in the work area after carbon dioxide flooding are determined, thereby realizing the determination of the fluid saturation distribution profile after carbon dioxide flooding in the work area. 1) Obtain the initial values ​​of the formation water capture section before and after boron injection following the completion of carbon dioxide flooding in the work area well section; 2) Obtain the initial gas saturation value at each target location in the work area well section; 3) Based on the initial value of the formation water capture section before and after boron injection following the completion of carbon dioxide flooding in the work area, and combined with the porosity of each target location in the work area and the macroscopic capture section value of the formation before and after boron injection following the completion of carbon dioxide flooding in the work area, the initial value of water saturation at each target location in the work area is determined. 4) Based on the porosity, clay content, initial water saturation, initial gas saturation, and macroscopic trapping section values ​​of the formation at each target location in the work area well section before and after boron injection following the completion of carbon dioxide flooding, determine the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before and after boron injection following the completion of carbon dioxide flooding in the work area well section. 5) Based on the trapping cross-sectional values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after completing carbon dioxide flooding, determined in step 4), and combined with the initial values ​​of porosity, clay content, and water saturation at each target location in the work area, as well as the macroscopic trapping cross-sectional values ​​of the formation at each target location before boron injection after completing carbon dioxide flooding, the gas saturation at each target location in the work area is re-determined. 6) Based on the trapping section values ​​of formation water before and after boron injection following the completion of carbon dioxide flooding in the well section of the work area determined in step 4), and combined with the porosity of each target location in the well section of the work area and the macroscopic trapping section values ​​of the formation before and after boron injection following the completion of carbon dioxide flooding in the well section of the work area, the water saturation of each target location in the well section of the work area is re-determined. 7) Compare the gas saturation at each target location in the work area determined in step 5) with the initial water saturation value used in step 4) to determine the gas saturation at each target location in the work area: If the error between the two is less than or equal to the error threshold, then proceed to step 8). If the error between the two is greater than the error threshold, then the gas saturation of each target location in the work area determined in step 5) is taken as the initial value of the gas saturation of each target location in the work area, and the water saturation of each target location in the work area determined in step 6) is taken as the initial value of the water saturation of each target location in the work area, and steps 4)-7) are repeated. 8) Based on the gas saturation of each target location in the work area determined in step 5) and the water saturation of each target location in the work area determined in step 6), determine the oil saturation of each target location in the work area; based on the gas saturation of each target location in the work area determined in step 5), the water saturation of each target location in the work area determined in step 6), and the oil saturation of each target location in the work area, determine the fluid saturation distribution profile after carbon dioxide flooding in the work area.

2. The method according to claim 1, wherein, In step 2), obtaining the initial gas saturation values ​​at each target location in the work area includes: Based on pulsed neutron logging data of each target location before boron injection after carbon dioxide flooding in the work area, the count rate ratio of each target location before boron injection after carbon dioxide flooding in the work area was determined. Based on the count rate ratios of each target location after carbon dioxide flooding and before boron injection in the work area, combined with the count rate ratios of pure water layers and pure gas layers, the initial gas saturation values ​​of each target location in the work area are determined.

3. The method according to claim 2, wherein, The gas saturation is determined using the following formula: In the formula, RLS is the count rate ratio at the target location, which is dimensionless; RLS w RLS is the count rate ratio of the pure water layer, dimensionless. g S is the count rate ratio of pure gas layers, dimensionless; g0 This represents the gas saturation level.

4. The method according to claim 1, wherein, In steps 3) and 6), the water saturation is determined using the following formula: In the formula, S w The water saturation level is dimensionless. Porosity is a dimensionless quantity. The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m -1 ; The macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ; The capture section value of formation water before boron injection after carbon dioxide flooding, in m -1 ; To determine the capture section value of formation water after boron injection following carbon dioxide flooding, m -1 .

5. The method according to claim 1, wherein, In step 4), based on the porosity, clay content, initial water saturation, and initial gas saturation at each target location in the work area, as well as the macroscopic trapping cross-sectional values ​​of the formation at each target location before and after boron injection following carbon dioxide flooding, the trapping cross-sectional values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before and after boron injection following carbon dioxide flooding are determined, including: Based on the porosity, clay content, initial water saturation, initial gas saturation, and macroscopic trapping section values ​​of the formation at each target location in the work area before boron injection after carbon dioxide flooding, the trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding in the work area were determined. Based on the capture section values ​​of the formation rock skeleton, pore gas, pore crude oil, and mudstone in the work area, combined with the macroscopic capture section values ​​of the formation at each target location after boron injection following carbon dioxide flooding in the work area, the capture section value of formation water after boron injection following carbon dioxide flooding was determined.

6. The method according to claim 5, wherein, The trapping section values ​​of the formation rock skeleton, pore gas, pore crude oil, mudstone, and formation water before boron injection after carbon dioxide flooding in the work area are determined based on the following formulas: Wherein: S g,i Let i be the gas saturation at target location i, which is dimensionless; Let be the porosity at target location i, dimensionless; The macroscopic capture section value of the formation at target location i before boron injection after carbon dioxide flooding, m -1 ; The capture section value of the stratigraphic rock skeleton, m -1 ; The trapping cross section for pore gas, m -1 ; The cross section for capturing crude oil in porous structures, m -1 ; For the capture section of mudstone, m -1 ; The capture section value of formation water before boron injection after carbon dioxide flooding, m -1 V sh S represents the clay content, dimensionless; w,i Let be the water saturation at target location i, dimensionless; i = 1, 2, 3...n.

7. The method according to claim 5, wherein, The trapping section value of formation water after boron injection following carbon dioxide flooding is determined based on the following formula: In the formula, S g The gas saturation is dimensionless. Porosity is a dimensionless quantity. The macroscopic capture section value of the formation at the target location after boron injection following carbon dioxide flooding, in m -1 ; The capture section value of the stratigraphic rock skeleton, m -1 ; The trapping cross section for pore gas, m -1 ; The cross section for capturing crude oil in porous structures, m -1 ; For the capture section of mudstone, m -1 ; To determine the capture section value of formation water after boron injection following carbon dioxide flooding, m -1 V sh S represents the clay content, dimensionless; w The value represents water saturation, which is dimensionless.

8. The method according to claim 1, wherein, In step 5), the gas saturation is determined using the following formula: In the formula, S g The gas saturation is dimensionless. Porosity is a dimensionless quantity. The macroscopic capture section value of the formation at the target location before boron injection after carbon dioxide flooding, in m -1 ; The capture section value of the stratigraphic rock skeleton, m -1 ; The trapping cross section for pore gas, m -1 ; The cross section for capturing crude oil in porous structures, m -1 ; For the capture section of mudstone, m -1 ; The capture section value of formation water before boron injection after carbon dioxide flooding, m -1 V sh S represents the clay content, dimensionless; w The value represents water saturation, which is dimensionless.

9. The method according to claim 1, wherein, In step 7), the error threshold is 10. -3 .

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