Water logging identification method based on pulse neutron deceleration and diffusion double-physical process

Abstract

The invention discloses a water logging identification method based on pulse neutron deceleration and diffusion double physical processes, belongs to the technical field of geophysical logging and oilfield development, and adopts a pulse neutron detection system composed of a D-T controllable neutron tube source and a double-spacing thermal neutron detector. According to the method, on the basis of the interaction process of inelastic scattering, elastic scattering, radiation capture and the like of neutrons and formation element nuclei, the close correlation between the deceleration process of the neutrons and the hydrogen content in the formation is utilized, and the water logging evaluation of the reservoir is achieved. And the diffusion process is mainly influenced by the formation capture capability, new parameters are constructed by integrating the two physical processes, and the response degree to reservoir flooding is remarkably improved. The method has high interpretation coincidence rate, can eliminate the influence of formation water mineralization degree and porosity on water flooded layer evaluation, and can provide theoretical basis and technical support for rapid and accurate identification of reservoir flooding conditions in pulsed neutron lifetime logging.

Description

Technical Field

[0001] The invention belongs to the technical field of geophysical well logging and oilfield development, and in particular relates to a flooding identification method based on the dual physical processes of pulse neutron deceleration and diffusion. Background Art

[0002] The exploration and development of oil and gas resources is a key factor in promoting national economic growth and maintaining energy security. Its oil and gas saturation parameters are key parameters for reserve estimation and development plan formulation. With the continuous deepening of exploration and development, most of the main domestic oil reservoirs have entered the middle and late stages of development. After years of water injection development, the lithology, physical properties, oil content, electrical and acoustic characteristics of the oil and gas layers have undergone significant changes. The distribution of underground remaining oil is complex, the reservoir flooding area is large, and the distribution of high and low water content areas is uneven. How to optimize the oil field development plan, control the water content, stabilize the oil production and tap the potential of old wells has become a key issue that needs to be solved in oil field development.

[0003] Pulsed neutron logging technology is a conventional means of monitoring the remaining oil saturation through casing, laying the foundation for oilfield water drive, gas drive and other adjustment plans. The oil and gas saturation is determined by measuring the gamma rays and thermal neutron information released by the 14MeV high-energy fast neutrons generated by the DT controllable neutron source penetrating the instrument casing, well fluid, steel casing and cement ring and other media, and directly interacting with the element nuclei in the formation and pore fluid through inelastic scattering, radiation capture and other interactions. Carbon-oxygen ratio logging, neutron lifetime logging, fast neutron cross-section gas content and chlorine spectrum logging are important methods for measuring oil saturation through casing and evaluating water-flooded layers. The difference in wellbore and annulus fluids will significantly affect these methods to determine the final oil saturation of the formation, resulting in difficulty in accurately identifying water flooding in low-porosity and tight reservoirs.

[0004] In recent years, pulsed neutron-neutron logging technology has been widely used to determine the remaining oil saturation in medium and high mineralization formations. This technology accurately evaluates the saturation of the reservoir by measuring the macroscopic capture cross section of the formation and combining it with the rock volume physical model, and has achieved remarkable application results. This method not only improves the accuracy of residual oil identification, but also provides more reliable data support in complex formation conditions, providing important technical guarantees for oilfield development and optimization. However, the traditional method of using neutron lifetime to qualitatively identify water-flooded layers is to identify water-flooded layers by overlapping the capture cross section with the resistivity logging curve. When the porosity and formation water mineralization change, its application effect is not ideal. Therefore, there is an urgent need for a new method that can overcome the limitations of existing technologies. Summary of the invention

[0005] In view of the above problems existing in the prior art, the present invention proposes a flooding identification method based on the dual physical processes of pulse neutron deceleration and diffusion, which has a reasonable design, solves the shortcomings of the prior art and has good effects.

[0006] A water flooding identification method based on the dual physical processes of pulsed neutron deceleration and diffusion is adopted. A dual-detector pulsed neutron detection system consisting of a DT controllable neutron tube source and a dual-source distance thermal neutron detector is used to extract the thermal neutron count ratio and macroscopic capture cross section to quickly realize reservoir water flooding evaluation. The method specifically includes the following steps: Step 1: Based on the existing detection system consisting of DT controllable neutron tube source and dual-source distance thermal neutron detector, the Monte Carlo method is used to carry out numerical simulation of formations with different oil saturation, porosity and salinity, record the time spectrum information of near and far source distance thermal neutron detectors, and extract the thermal neutron counting ratio and macro capture cross section information; Step 2: Based on the measured responses of thermal neutron count ratio and macroscopic capture cross section in formations with different porosities, different salinities and different oil saturations, the relationship between the combined parameters of the dual physical processes of neutron deceleration and diffusion under theoretical conditions and the formation porosity is obtained, forming a theoretical chart for identifying the flooding level by combining thermal neutron count ratio and macroscopic capture cross section; Step 3: Preprocess the spectral data of the actually detected thermal neutron time spectrum, use a filtering algorithm to reduce the error caused by low statistical data, improve the accuracy of the data, and use an adaptive single exponential fitting algorithm to avoid the influence of the wellbore to accurately extract the true capture cross section of the formation and calculate the near and far thermal neutron count ratios; Step 4: Select the water layer section with purer lithology and lower mud content through the conventional curve, calculate the regression formula of the water line, and combine the theoretical chart to obtain the actual oil line regression formula under the corresponding formation mineralization conditions; Step 5: Establish a qualitative identification chart for flooding, display the combined parameter values ​​of the reservoir calculated in step 3 on the qualitative identification chart, and quickly identify the flooding situation of the reservoir.

[0007] Furthermore, in step 1, the thermal neutron count expression is: (1); in, T 1 , T 2 are the neutron lifetimes of thermal neutrons in the wellbore and in the formation, respectively; N 1 and N 2 are the initial neutron numbers in the borehole and formation attenuation processes, respectively; According to formula (1), the near thermal neutron count and far thermal neutron count are calculated respectively, and the thermal neutron count ratio isRatio is the ratio of near thermal neutron counts to far thermal neutron counts; Macroscopic capture cross section of formation Σ The relationship with thermal neutron lifetime is as follows: (3).

[0008] Further, in step 2, the formation mineralization includes five types: 0 ppm, 20000 ppm, 50000 ppm, 100000 ppm and 150000 ppm, the porosity includes eight types: 1%, 3%, 5%, 8%, 10%, 12%, 15% and 20%, and the oil saturation includes five types: 0%, 25%, 50%, 75% and 100%; Combined parameters of the dual physical processes of neutron deceleration and diffusion DRS It is expressed as: (4); Among them, a and b are constant coefficients, Sigma is the macroscopic capture cross section of the formation, L e is the fast neutron deceleration length, Ratio is the thermal neutron count ratio; Establishing the combined parameters under theoretical conditions DRS With the regression formula of formation porosity, mineralization and oil saturation, a theoretical chart is formed to identify the flooding level by combining the combined parameters of the dual physical processes of neutron deceleration and diffusion.

[0009] Furthermore, in step 3, the measured thermal neutron time spectrum is first subjected to combined filtering in the depth domain and the time domain to reduce the error caused by low statistical data; then the constraints of formula (5) and formula (6) are applied to the actual time spectrum, so as to adaptively select the formation region for calculating the macro capture cross section; (5); (6); in, k ( t )for t The curvature of the thermal neutron time spectrum at time , t n , t n+1 are two adjacent moments, starting from moment 0 and iterating, setting the threshold ε 1 To control the fluctuation of the tail end not to exceed ε 1 , while ensuring that the thermal neutron count at the tail end is greater than ε 2 ; The capture cross section and thermal neutron count ratio were calculated using a single exponential fitting algorithm.

[0010] Furthermore, in step 4, the water layer section with relatively pure lithology and low mud content is determined by comprehensive analysis of conventionally measured natural gamma, natural potential, resistivity and three-porosity curves; Combined with the water analysis data of the area to be identified, determine the mineralization of the water layer segment and calculate the waterline combination parameters DRS The expression of porosity changes, and the oil line combination parameters under the corresponding formation water salinity conditions are determined according to the theoretical chart. DRS Expressions that vary with porosity; The formation oil saturation is given by the following formula: (7); in, S o is the formation oil saturation, DRS is the ratio of the formation macroscopic capture cross section to the thermal neutron count ratio under a certain porosity condition, DRS oil , DRS water It is the ratio of the macroscopic capture cross section of the oil layer and water layer to the thermal neutron count ratio under the corresponding porosity conditions.

[0011] Furthermore, the combined parameters of the oil line and water line in the measured well established in step 4 are DRS Expression and formula (7) are used to obtain the corresponding oil saturation under different formation conditions. DRS The regression formula that changes with porosity is combined with the evaluation standard of water-flooded layers in oilfield blocks to establish a qualitative identification chart for water-flooding; the combined parameters of the reservoir calculated in step 3 are DRS Placed in the qualitative identification plate for display, DRS The interpretation conclusion corresponding to the numerical value will indicate the degree of water flooding in the reservoir and can intuitively display the water flooding situation of the formation.

[0012] Beneficial technical effects brought by the present invention: The present invention can eliminate the influence of formation water salinity and porosity on the evaluation of water-flooded layers, and provide a new theoretical method for pulse neutron lifetime logging to quickly and accurately identify formation water-flooding conditions. In practical applications, the interpretation conformity rate is as high as 90%, providing important technical support for oilfield development and optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of the dual-detector pulse neutron detection system in the present invention.

[0014] Figure 2 Thermal neutron time spectra of sandstone formations with different formation water salinity and oil saturation under the condition of 10% porosity.

[0015] Figure 3 Under different mineralization conditions DRS Relationship diagram with formation porosity.

[0016] Figure 4 Under the condition of formation water salinity of 20000ppm and different oil saturation formation conditions DRS Relationship diagram with formation porosity.

[0017] Figure 5 This is the effect diagram of the actual well map application.

[0018] Among them, 1-DT controllable neutron source; 2-first composite material shielding body; 3-near-source thermal neutron detector; 4-second composite material shielding body; 5-far-source thermal neutron detector; 6-instrument housing; 7-wellbore environment; 8-casing; 9-formation. DETAILED DESCRIPTION

[0019] The specific implementation of the present invention is further described below in conjunction with specific embodiments: A flooding identification method based on the dual physical process of pulsed neutron deceleration and diffusion, based on the inelastic scattering, elastic scattering and radiation capture process between neutrons and the nuclei of formation elements, adopts a dual-detector pulsed neutron detection system consisting of a DT controllable neutron tube source and a dual-source distance thermal neutron detector, such as Figure 1 As shown, the inside of the instrument housing 6 is sequentially arranged from bottom to top to consist of a DT controllable neutron source 1, a first composite material shielding body 2, a near-source thermal neutron detector 3, a second composite material shielding body 4, and a far-source thermal neutron detector 5. The first composite material shielding body 2 is filled between the DT controllable neutron source 1 and the near-source thermal neutron detector 3, and the length is set to 4-6 cm, and the diameter of the first composite material shielding body 2 is set to 40 mm; the diameter of the near-source thermal neutron detector 3 is set to 12 mm, the length is set to 80 mm, the distance between the near-source thermal neutron detector 3 and the DT controllable neutron source 1 is set to 42 cm, and the inside is filled with He-3 gas at 4 atmospheres; the second composite material shielding body 4 is filled between the near-source thermal neutron detector 3 and the far-source thermal neutron detector 5, the length of the second composite material shielding body 4 is set to 5-7 cm, and the diameter of the second composite material shielding body 4 is set to 100 mm; the diameter of the far-source thermal neutron detector 5 is set to 12 mm, the length is set to 100 mm, the distance between the far-source thermal neutron detector 5 and the DT controllable neutron source 1 is set to 72 cm, and the inside is filled with He-3 gas at 6 atmospheres. The dual-detector pulsed neutron detection system is arranged in a measurement environment consisting of a borehole environment 7, a casing 8 and a formation 9 for detection.

[0020] A flooding identification method based on the dual physical process of pulsed neutron deceleration and diffusion, using the dual-detector pulsed neutron detection system as described above, recording the thermal neutron time spectra of near and far thermal neutron detectors, extracting macroscopic capture cross sections and thermal neutron count ratio information based on the inelastic scattering, elastic scattering and radiation capture process between neutrons and formation element nuclei, realizing the evaluation of formation saturation and the elimination of environmental influences such as mineralization and porosity, and being able to quickly identify the flooding of the reservoir, specifically comprising the following steps: Step 1: Based on the existing DT controllable neutron tube source and dual-source thermal neutron detector, the Monte Carlo method is used to carry out numerical simulation of formations with different oil saturation, porosity and salinity, record the thermal neutron time spectrum information of near and far detectors, and extract the thermal neutron counting ratio and macro capture cross section information; Step 2: Based on the measured responses of thermal neutron count ratio and macroscopic capture cross section in formations with different porosities, different salinities and different oil saturations, the regression formula of the combined parameters of the dual physical processes of neutron deceleration and diffusion under theoretical conditions as the formation porosity changes is obtained, forming a theoretical chart for identifying the flooding level by combining thermal neutron count ratio and macroscopic capture cross section; Step 3: Preprocess the spectral data of the actually detected thermal neutron time spectrum, use a suitable filtering algorithm to reduce the error caused by low statistical data, improve the accuracy of the data, avoid the influence of the wellbore through the adaptive single exponential fitting algorithm to accurately extract the true capture cross section of the formation, and calculate the near and far thermal neutron count ratio; Step 4: Select the water layer section with purer lithology and lower mud content through the conventional curve, calculate the regression formula of the water line, and combine the theoretical chart to obtain the actual oil line fitting formula under the corresponding formation mineralization conditions; Step 5: Introduce the calculation results of open hole well porosity and combine them with regional water analysis data to analyze and study the reservoir section; establish a qualitative identification plate for water flooding, and display the combined parameter values ​​of the reservoir calculated in step 3 on the qualitative identification plate to quickly identify the reservoir flooding situation.

[0021] In step 1, the instrument releases 14MeV high-energy fast neutrons when working. The fast neutrons interact with the nuclei of formation elements by inelastic scattering and elastic scattering, and are decelerated to thermal neutrons that are captured by the nuclei of formation elements and disappear. The macroscopic capture ability of the formation is reflected by recording the change of thermal neutrons over time, the ratio of near and far detector counts reflects the hydrogen content of the formation, and the macroscopic capture cross section of the formation is extracted using the time spectrum information of near-detected thermal neutrons to calculate the thermal neutron count ratio.

[0022] Using the Monte Carlo method, the formation model was established, in which the formation mineralization included five types: 0ppm, 20000ppm, 50000ppm, 100000ppm and 150000ppm, the porosity included eight types: 1%, 3%, 5%, 8%, 10%, 12%, 15% and 20%, and the oil saturation included five types: 0%, 25%, 50%, 75% and 100%. The thermal neutron time spectrum of the pulsed neutron lifetime logging instrument in formations with different oil saturation, porosity and mineralization was simulated, and the near-detection thermal neutron time spectrum was recorded. Figure 2 As shown, according to Figure 2 The recorded thermal neutron time spectrum is used to extract the formation macroscopic capture cross section and the thermal neutron count ratio information of near and far detectors using a single exponential fitting algorithm.

[0023] Thermal neutron counting N ( t ) is expressed as: (1); in, T 1 , T 2 are the neutron lifetimes of thermal neutrons in the wellbore and in the formation, respectively; N 1 and N 2 are the initial neutron numbers in the borehole and formation attenuation processes, respectively; The thermal neutron distribution of near and far detectors can be expressed as: (2); In the formula, D is the thermal neutron diffusion coefficient, L e is the fast neutron deceleration length, L t The near-far thermal neutron count ratio reflects the formation's ability to decelerate fast neutrons, and the formation's ability to capture and absorb thermal neutrons is combined to evaluate the formation's flooding.

[0024] Macroscopic capture cross section of formation Σ The relationship with thermal neutron lifetime is as follows: (3).

[0025] In step 2, the combined parameters of the dual physical processes of neutron deceleration and diffusion are DRS It is expressed as: (4); Among them, a and b are constant coefficients, Sigma is the macroscopic capture cross section of the formation, L eis the fast neutron deceleration length, Ratio is the thermal neutron count ratio; Establish theoretical conditions for the combination of parameters under different salinities and different oil saturations DRS The regression formula that changes with the formation porosity is as follows: Figure 3 and Figure 4 It indicates that a theoretical diagram for identifying flooding levels is formed by combining the parameters of the dual physical processes of neutron deceleration and diffusion.

[0026] In step 3, the thermal neutron count in the thermal neutron time spectrum of pulse neutron lifetime logging is low and the statistical fluctuation is large. First, the measured thermal neutron time spectrum is subjected to combined filtering in the depth domain and time domain to reduce the error caused by low statistical data. The filtered time spectrum will have differences in the transition section from the borehole area to the formation area under different formation conditions. In order to accurately extract the formation macroscopic capture cross section, the time period for selecting the single exponential fitting should be strictly screened; (5); middle, k ( t )for t The curvature of the thermal neutron time spectrum at time , t n , t n+1 They are two adjacent moments, and the iteration starts from moment 0; As shown in formula (5), the transition section is roughly found by using the curvature change of the thermal neutron time spectrum, and the transition time from the borehole area to the formation area is precisely determined by using the Newton iteration algorithm. From this moment onward, single exponential fitting can minimize the influence of the wellbore environment on the extraction of the formation macroscopic capture cross section, and achieve the effect of accurately extracting the formation macroscopic capture cross section. At the same time, the statistical fluctuations at the tail end of the thermal neutron time spectrum also need to be constrained by certain restrictions, otherwise the error caused by low thermal neutron counts will cause errors in parameter extraction.

[0027] (6); Set the threshold ε 1 To control the fluctuation of the tail end not to exceed ε 1 , while ensuring that the thermal neutron count at the tail end is greater than ε 2 ; By imposing constraints of formula (5) and formula (6) on the actual time spectrum, the formation area for calculating the macro capture cross section can be adaptively selected; this method not only avoids the statistical fluctuation caused by low counts at the tail end, but also effectively avoids the wellbore area, thereby accurately obtaining the true capture cross section of the formation.

[0028] The capture cross section is calculated using a single exponential fitting algorithm, and the near and far thermal neutron counts are obtained from the dual-source distance thermal neutron detector, thereby calculating the thermal neutron count ratio.

[0029] In step 4, the water layer section with relatively pure lithology and low mud content is determined by comprehensive analysis of natural gamma, natural potential, resistivity and three-porosity curves measured by conventional methods; Combined with the water analysis data of the area to be identified, determine the salinity of the water layer, calculate the expression of the water line combination parameters changing with porosity, and determine the expression of the oil line combination parameters changing with porosity under the corresponding formation water salinity conditions according to the theoretical chart; The formation oil saturation is given by the following formula: (7); in, S o is the formation oil saturation, DRS is the ratio of the formation macroscopic capture cross section to the thermal neutron count ratio under a certain porosity condition, DRS oil , DRS water It is the ratio of the macroscopic capture cross section of the oil layer and water layer to the thermal neutron count ratio under the corresponding porosity conditions.

[0030] The combined parameters of the measured well oil line and water line established in step 4 DRS Expression and formula (7) are used to obtain the corresponding oil saturation under different formation conditions. DRS The regression formula that changes with porosity is combined with the evaluation standard of water-flooded layers in oilfield blocks to establish a qualitative identification chart for water-flooding; the combined parameters of the reservoir calculated in step 3 are DRS Placed in the qualitative identification plate for display, DRS The interpretation conclusion corresponding to the numerical value will indicate the degree of water flooding in the reservoir and can intuitively display the water flooding situation of the formation.

[0031] If the ground is flooded, it will show DRS On the contrary, if the stratum has not been mined, DRS The value is smaller and closer to the oil line. Figure 5 The chart application effect diagram obtained by using the pulsed neutron logging data parameter combination under the conditions of formation water salinity of 150g / L and medium formation porosity is shown. Practice has proved that the actual point interpretation results of the chart are consistent with perforation production at a rate of up to 90%, which can quickly and accurately evaluate the water-flooded layer.

[0032] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A flooding identification method based on the dual physical processes of pulsed neutron deceleration and diffusion, characterized in that: A dual-detector pulsed neutron detection system consisting of a DT controllable neutron tube source and a dual-source distance thermal neutron detector is used to extract the thermal neutron count ratio and macroscopic capture cross section to quickly evaluate reservoir flooding. The specific steps include: Step 1: Based on the existing detection system consisting of DT controllable neutron tube source and dual-source distance thermal neutron detector, the Monte Carlo method is used to carry out numerical simulation of formations with different oil saturation, porosity and salinity, record the time spectrum information of near and far source distance thermal neutron detectors, and extract the thermal neutron counting ratio and macro capture cross section information; Step 2: Based on the measured responses of thermal neutron count ratio and macroscopic capture cross section in formations with different porosities, different salinities and different oil saturations, the relationship between the combined parameters of the dual physical processes of neutron deceleration and diffusion under theoretical conditions and the formation porosity is obtained, forming a theoretical chart for identifying the flooding level by combining thermal neutron count ratio and macroscopic capture cross section; Step 3: Preprocess the spectral data of the actually detected thermal neutron time spectrum, use a filtering algorithm to reduce the error caused by low statistical data, improve the accuracy of the data, and use an adaptive single exponential fitting algorithm to avoid the influence of the wellbore to accurately extract the true capture cross section of the formation and calculate the near and far thermal neutron count ratios; Step 4: Select the water layer section with purer lithology and lower mud content through the conventional curve, calculate the regression formula of the water line, and combine the theoretical chart to obtain the actual oil line regression formula under the corresponding formation mineralization conditions; Step 5: Establish a qualitative identification chart for flooding, display the combined parameter values ​​of the reservoir calculated in step 3 on the qualitative identification chart, and quickly identify the flooding situation of the reservoir.

2. The flooding identification method based on the dual physical process of pulsed neutron deceleration and diffusion according to claim 1 is characterized in that: In step 1, the thermal neutron count expression is: (1)； in, T 1. T 2 are the neutron lifetimes of thermal neutrons in the wellbore and in the formation, respectively; N 1 and N 2 represent the initial neutron numbers in the borehole and formation attenuation process, respectively; According to formula (1), the near thermal neutron count and far thermal neutron count are calculated respectively, and the thermal neutron count ratio is Ratio is the ratio of near thermal neutron counts to far thermal neutron counts; Macroscopic capture cross section of formation Σ The relationship with thermal neutron lifetime is as follows: (3)。 3. The flooding identification method based on the dual physical process of pulse neutron deceleration and diffusion according to claim 2 is characterized in that: In step 2, the formation mineralization includes five types: 0 ppm, 20000 ppm, 50000 ppm, 100000 ppm and 150000 ppm; the porosity includes eight types: 1%, 3%, 5%, 8%, 10%, 12%, 15% and 20%; and the oil saturation includes five types: 0%, 25%, 50%, 75% and 100%; Combined parameters of the dual physical processes of neutron deceleration and diffusion DRS It is expressed as: (4)； Among them, a and b are constant coefficients, Sigma is the macroscopic capture cross section of the formation, L e is the fast neutron deceleration length, Ratio is the thermal neutron count ratio; Establishing the combined parameters under theoretical conditions DRS With the regression formula of formation porosity, mineralization and oil saturation, a theoretical chart is formed to identify the flooding level by combining the combined parameters of the dual physical processes of neutron deceleration and diffusion.

4. The flooding identification method based on the dual physical process of pulsed neutron deceleration and diffusion according to claim 3 is characterized in that: In step 3, the measured thermal neutron time spectrum is first subjected to combined filtering in the depth domain and the time domain to reduce the error caused by low statistical data; then the constraints of formula (5) and formula (6) are applied to the actual time spectrum, so as to adaptively select the formation region for calculating the macro capture cross section; (5)； (6)； in, k ( t )for t The curvature of the thermal neutron time spectrum at time , t n , t n+1 For two adjacent moments, iterate from moment 0 and set the threshold ε1 to control the fluctuation of the tail end not to exceed ε1, while ensuring that the thermal neutron count at the tail end is greater than ε2; The capture cross section and thermal neutron count ratio were calculated using a single exponential fitting algorithm.

5. The flooding identification method based on the dual physical process of pulsed neutron deceleration and diffusion according to claim 4 is characterized in that: In step 4, the water layer section with relatively pure lithology and low shale content is determined by comprehensive analysis of conventionally measured natural gamma, natural potential, resistivity and three-porosity curves; Combined with the water analysis data of the area to be identified, determine the mineralization of the water layer segment and calculate the waterline combination parameters DRS The expression of porosity changes, and the oil line combination parameters under the corresponding formation water salinity conditions are determined according to the theoretical chart. DRS Expressions that vary with porosity; The formation oil saturation is given by the following formula: (7)； in, S o is the formation oil saturation, DRS is the ratio of the formation macroscopic capture cross section to the thermal neutron count ratio under a certain porosity condition, DRS oil , DRS water It is the ratio of the macroscopic capture cross section of the oil layer and water layer to the thermal neutron count ratio under the corresponding porosity conditions.

6. The flooding identification method based on the dual physical process of pulsed neutron deceleration and diffusion according to claim 5 is characterized in that: The combined parameters of the oil line and water line in the measured well established in step 4 DRS Expression and formula (7) are used to obtain the corresponding oil saturation under different formation conditions. DRS The regression formula that changes with porosity is combined with the evaluation criteria for water-flooded layers in oilfield blocks to establish a qualitative identification chart for water-flooding; The combined parameters of the reservoir calculated in step 3 DRS Placed in the qualitative identification chart for display, DRS The interpretation conclusion corresponding to the numerical value will indicate the degree of water flooding in the reservoir and can intuitively display the water flooding situation of the formation.

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