A method for determining the resistance increase rate based on natural potential difference value

Abstract

The present application belongs to the technical field of oilfield testing and analysis, and particularly relates to a method for determining the resistance increase rate based on the natural potential difference. The method for determining the resistance increase rate based on the natural potential difference comprises the following steps: determining the natural potential baseline of the target layer according to the single-well natural potential logging curve; determining the difference between the measured natural potential SP and SP B ; obtaining the apparent formation water resistivity relationship formula based on the natural potential SP by regression according to the single-well formation water analysis data; determining the formation mixed solution resistivity; and determining the resistance increase rate based on the natural potential difference ΔSP. The present application uses the continuous natural potential logging curve SP which is commonly present in oilfields to obtain the resistance increase rate Iw based on the natural potential difference ΔSP, solves the problem that the formation resistivity of the formation saturated with formation water is difficult to determine, and the calculation process is simple and convenient, and the calculation result is accurate.

Description

Technical Field

[0001] This invention belongs to the field of oilfield testing and analysis technology, and specifically relates to a method for determining the resistance increase rate based on the natural potential difference. Background Technology

[0002] As oilfield exploration and development deepens, the focus has shifted from simple, high-amplitude structural oil and gas reservoirs to concealed oil and gas reservoirs primarily characterized by lithological traps. Low-resistivity reservoirs are a crucial type of relatively complex and concealed oil and gas reservoir. (Resistivity increase rate...) ( ) is an effective method for identifying low-resistivity oil layers.

[0003] Currently, there are no patents on calculating the resistivity increase rate using dual formation water, but there are two papers on this topic: 1. In the paper "Application of Apparent Resistivity Increase Rate in Oil, Gas and Water Research of Nanbaxian Oil and Gas Field" (Well Logging Technology, 2006, 30(5): 442-444), Han Qianfeng et al. defined the ratio of the formation resistivity after subdividing the layers to the resistivity of the typical water layer in the same layer as the apparent resistivity increase rate. Then, on two cross-plots of apparent resistivity increase rate and sonic transit time and apparent resistivity increase rate - compensation density, the oil, gas and water conclusions of all layers in the oil, gas and water tests and production tests were marked, and a statistical experience judgment standard for comprehensive interpretation of reservoir evaluation was established. 2. In her article "Research on Experimental Technology for Measuring Resistance Increase Rate Using New Methods" (Science and Technology Forum, No. 9, 2010, Part 2), Li Guoying pointed out that currently, the laboratory uses methods such as gas drive, oil drive, and centrifugation to gradually decrease the water saturation of the core from 100% before measuring the resistance increase rate; well logging calculations of resistance increase rate mainly rely on the measured original formation resistivity (…). ) and formation resistivity saturated with formation water ( The ratio is determined as follows: The existing technologies represented by the above papers employ two methods: one is to calculate the resistivity increase rate using well logging resistivity, and the other is to calculate the resistivity increase rate using laboratory simulations of formation conditions. The key to both lies in accurately determining the formation resistivity saturated with formation water. However, due to rapid lateral changes in strata and the influence of various factors such as changes in rock composition and water type, accurate determination is difficult. This presents a significant challenge. Especially after water injection, the formation water properties will change substantially, and the logging curves will also change accordingly. Therefore, relying solely on the previous methods is not feasible. The calculation results will have a large deviation. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this invention is to provide a method for determining the resistance increase rate based on the spontaneous potential difference. This method utilizes the continuous spontaneous potential logging curves (SP) commonly found in oilfields to determine the resistance increase rate based on the spontaneous potential difference. resistance increase rate Solving the problem of formation resistivity saturated with formation water For problems that are difficult to determine, the calculation process is simple and convenient, and the calculation results are accurate.

[0005] The technical solution of this invention is: a method for determining the resistance increase rate based on the natural potential difference, comprising the following steps: S1: Based on measured data from the oilfield, combined with the average surface temperature and geothermal gradient of the study area, determine the formation temperature T of the target layer: In the formula, D is the geothermal gradient, and H is the depth of the target layer. The average surface temperature; S2: Wells with formation water sampling and analysis data in the target layer of the study area are used as data wells. The formation water salinity is obtained from the analysis of the data wells. The following formula is used: Calculate the apparent formation water resistivity of the target layer in each data well. In the formula, T is the formation temperature of the target layer; S3: Based on the single-well logging data, calculate the apparent formation water resistivity for each step in S2. SP logging data for the same depth section of the well; and selecting stable pure mudstone sections at adjacent depths to determine the SP baseline of the target layer for each data well. ; and then determine the measured spontaneous potential (SP) and baseline of each data well. The difference: ; S4: Based on the calculation results of steps S2 and S3, regression is used to obtain the data wells. and The relationship will be based on the natural potential difference. Formation water resistivity Equivalent to and in step S3 Substituting into the formula, we obtain the apparent formation water resistivity based on the natural potential SP of the data well. Relationship; S5: Calculate the resistivity of the mixed solution in the target layer of the well data. : In the formula, φ is the original formation resistivity, φ is the effective porosity calculated from well logging, m is the cementation index, and a is the lithology coefficient related to the rock. S6: Based on the calculation results of steps S4 and S5, determine the value based on the natural potential difference. resistance increase rate formula; S7: Using the well to be measured as the target well, determine the resistivity Rt and porosity of the target layer in the target well. The spontaneous potential (SP) of the target layer was determined by selecting a stable pure mudstone section at an adjacent depth. ; S8: Calculate the value based on the natural potential difference according to the formula in step S6. resistance increase rate To determine the properties of reservoir fluids.

[0006] The specific process of single-well formation water analysis in step S2 is as follows: Based on the actual production dynamic analysis of the study area, water samples are taken from wells with stable production and where the influence of fracturing fluid has been eliminated. The total positive and negative ions in the water samples are analyzed to obtain the total mineralization of the formation water, thereby determining the apparent formation water resistivity.

[0007] In steps S3 and S7, the baseline of the natural potential of the target layer is determined. The specific process is as follows: Based on the measured spontaneous potential (SP) of the single-well spontaneous potential logging curve, select a stable mudstone layer that has not shown curve drift, read the average SP value, and determine it as the baseline of the spontaneous potential of the target layer. .

[0008] In step S5, the cementation index m and lithology coefficient a are determined according to the standard procedure of "Laboratory Measurement and Calculation Method of Rock Resistivity Parameters SY / T 5385-2007" and the measurement results are based on the relationship between formation factors and porosity. During the experiment, the experimental temperature and pressure are set according to the temperature and pressure environment of the core layer. The experimental temperature parameter is calculated according to the formula in step S1, and the pressure is calculated according to the requirements of "Original Formation Pressure and Pressure System Determination Method of Oil and Gas Reservoirs SY / T 6365-1998".

[0009] In step S4, the natural potential difference value of the data well is obtained. Apparent formation water resistivity Relationship: (1) Based on natural potential difference For the formation water resistivity Equivalent to and in step S3 Substituting into the formula, we obtain the apparent formation water resistivity based on the spontaneous potential SP of the study area. Relationship: (2) In the formula: k and c are fitting coefficients.

[0010] In step S6, the natural potential difference is used. resistance increase rate : (3) In steps S4 and S5 , Substituting the formula, we obtain the value based on the natural potential difference. resistance increase rate The calculation formula is as follows: (4) The technical effects of this invention are as follows: 1. This invention is based on existing spontaneous potential (SP) logging curves in oilfields, providing a broad data base. It does not require additional logging costs; it only adjusts the focus of logging analysis and parameter calculation, thus solving the problem of formation resistivity in formations saturated with formation water. A problem that is difficult to determine.

[0011] 2. This invention can quickly establish a standardized parameter calculation model, and then establish a block-based quantitative interpretation standard. The calculation results can be directly applied to the judgment of reservoir fluid properties, realize factory-style operation, effectively reduce costs, and play a significant role in the logging interpretation of new wells in low-resistivity oil reservoirs and the review of old wells, thus rapidly advancing the exploration and development process.

[0012] The following will provide further explanation in conjunction with the accompanying drawings. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating an embodiment of the present invention of a method for determining the resistance increase rate based on the natural potential difference.

[0014] Figure 2 It is a cross-plot of the natural potential difference and formation water resistivity in the study area.

[0015] Figure 3 This is a graph showing the Iw calculation results of well A, which is a test site with oil and water in the same layer, provided in an embodiment of the present invention.

[0016] Figure 4 This is a graph showing the calculation results of Iw in well B, which is a water layer, provided in an embodiment of the present invention.

[0017] Figure 5 This is a graph showing the calculation results of Iw in well C, which is a water layer, provided in an embodiment of the present invention. Detailed Implementation

[0018] Example 1 like Figure 1 As shown, a method for determining the resistance increase rate based on the natural potential difference includes the following steps: S1: Based on measured data from the oilfield, combined with the average surface temperature and geothermal gradient of the study area, determine the formation temperature T of the target layer: In the formula, D is the geothermal gradient, and H is the depth of the target layer. The average surface temperature; S2: Wells with formation water sampling and analysis data in the target layer of the study area are used as data wells. The formation water salinity is obtained from the analysis of the data wells. The following formula is used: Calculate the apparent formation water resistivity of the target layer in each data well. In the formula, T is the formation temperature of the target layer; S3: Based on the single-well logging data, calculate the apparent formation water resistivity for each step in S2. SP logging data for the same depth section of the well; and selecting stable pure mudstone sections at adjacent depths to determine the SP baseline of the target layer for each data well. ; and then determine the measured spontaneous potential (SP) and baseline of each data well. The difference: ; S4: Based on the calculation results of steps S2 and S3, regression is used to obtain the data wells. and The relationship will be based on the natural potential difference. Formation water resistivity Equivalent to and in step S3 Substituting into the formula, we obtain the apparent formation water resistivity based on the natural potential SP of the data well. Relationship; S5: Calculate the resistivity of the mixed solution in the target layer of the well data. : In the formula, φ is the original formation resistivity, φ is the effective porosity calculated from well logging, m is the cementation index, and a is the lithology coefficient related to the rock. S6: Based on the calculation results of steps S4 and S5, determine the value based on the natural potential difference. resistance increase rate formula; S7: Using the well to be measured as the target well, determine the resistivity Rt and porosity of the target layer in the target well. The spontaneous potential (SP) of the target layer was determined by selecting a stable pure mudstone section at an adjacent depth. ; S8: Calculate the value based on the natural potential difference according to the formula in step S6. resistance increase rate To determine the properties of reservoir fluids.

[0019] The specific process of single-well formation water analysis in step S2 is as follows: Based on the actual production dynamic analysis of the study area, water samples are taken from wells with stable production and where the influence of fracturing fluid has been eliminated. The total positive and negative ions in the water samples are analyzed to obtain the total mineralization of the formation water, thereby determining the apparent formation water resistivity.

[0020] In steps S3 and S7, the baseline of the natural potential of the target layer is determined. The specific process is as follows: Based on the measured spontaneous potential (SP) of the single-well spontaneous potential logging curve, select a stable mudstone layer that has not shown curve drift, read the average SP value, and determine it as the baseline of the spontaneous potential of the target layer. .

[0021] In step S5, the cementation index m and lithology coefficient a are determined according to the standard procedure of "Laboratory Measurement and Calculation Method of Rock Resistivity Parameters SY / T 5385-2007" and the measurement results are based on the relationship between formation factors and porosity. During the experiment, the experimental temperature and pressure are set according to the temperature and pressure environment of the core layer. The experimental temperature parameter is calculated according to the formula in step S1, and the pressure is calculated according to the requirements of "Original Formation Pressure and Pressure System Determination Method of Oil and Gas Reservoirs SY / T 6365-1998".

[0022] In step S4, the natural potential difference value of the data well is obtained. Apparent formation water resistivity Relationship: (1) Based on natural potential difference For the formation water resistivity Equivalent to and in step S3 Substituting into the formula, we obtain the apparent formation water resistivity based on the spontaneous potential SP of the study area. Relationship: (2) In the formula: k and c are fitting coefficients.

[0023] In step S6, the natural potential difference is used. resistance increase rate : (3) In steps S4 and S5 , Substituting the formula, we obtain the value based on the natural potential difference. resistance increase rate The calculation formula is as follows: (4).

[0024] Example 2 This embodiment takes the Jurassic reservoir in the Yanwu Highland of the western Huanqing Block in the Ordos Basin as an example to obtain the value based on the spontaneous potential difference. resistance increase rate Determine the properties of reservoir fluids.

[0025] like Figure 1 As shown, a method for determining the resistance increase rate based on the natural potential difference is performed according to the following steps: Step 101: Based on the measured data from the oilfield, combined with the average surface temperature of the study area... Given a geothermal gradient D = 2.4℃ / 100m, determine the formation temperature T of the target layer: In the formula, H is the depth of the target layer, in meters; Step 102: Using wells with formation water sampling and analysis data in the target layer of the study area as data wells, analyze the formation water salinity obtained from the data wells. The following formula is used: Calculate the apparent formation water resistivity of the target layer in each data well. The calculation results are shown in Table 1. In the formula, T is the formation temperature of the target layer determined by the formula in step 101 or the measured formation temperature, in °C. Step 103: Based on the single-well logging data, calculate the formation water resistivity of each formation from Step 102. SP logging data for the same depth section of the well; and selecting stable pure mudstone sections at adjacent depths to determine the SP baseline of the target layer for each data well. ; and then determine the measured spontaneous potential (SP) and baseline of each data well. The difference: The calculation results are shown in Table 1; Table 1. Formation water analysis and statistical calculation data of spontaneous potential logging curves.

[0026] Step 104: Based on the calculation results of Steps 102 and 103, the regression coefficients of determination k = 0.0009 and c = 0.0869 are obtained, yielding the data wells. and Relationship: Based on the natural potential difference For the formation water resistivity Equivalent to and in step 103 Substituting into the formula, we obtain the apparent formation water resistivity based on the natural potential SP of the data well. Relationship: ; Step 105: Based on the rock electrical test results, determine the rock electrical parameters m=1.376 and a=2.269, and calculate the resistivity of the mixed solution of the target layer in the data well. : In the formula, φ represents the original formation resistivity in Ω·m; φ represents the effective porosity calculated from well logging, in decimal form; m represents the cementation index; and a represents the lithology coefficient related to the rock. Step 106: Based on the calculation results of steps 104 and 105, determine the value based on the natural potential difference. resistance increase rate formula; Step 107: Using the well to be measured as the target well, determine the resistivity Rt and porosity of the target layer in the target well. The spontaneous potential (SP) of the target layer was determined by selecting a stable pure mudstone section at an adjacent depth. ; Step 108: According to the formula in step 106 Calculation based on natural potential difference resistance increase rate To determine the properties of reservoir fluids.

[0027] Figure 3 To calculate the results of an appraisal well in the Jurassic Yan 8 reservoir of the Huanqing block using an embodiment of the present invention, the calculation is based on the spontaneous potential difference. resistance increase rate And compared with the original resistivity at the corresponding depth using actual measurements. With formation resistivity saturated with formation water The resistivity increase rate I determined by the ratio is compared. The effect diagram shown in the figure is divided into 10 channels. The first channel is the formation channel; the second channel is the array inductive resistivity logging curve AT10-AT90; the third channel is the porosity curve, including sonic transit time DT, lithological density DEN, and compensated neutron CNL logging curves; the fourth channel is the depth; the fifth channel is the logging interpretation conclusion; the sixth channel is the perforation depth; the seventh channel is the lithology channel, including natural gamma ray GR, spontaneous potential SP, and caliper CAL curves; the eighth channel is the apparent formation water resistivity based on SP calculated by logging. resistivity of mixed solution with formation The ninth step is the resistivity increase rate I (original) determined using the ratio of measured resistivity Rt to the resistivity Ro of formations saturated with formation water; the tenth step is the value based on the natural potential difference obtained using the calculation method provided in the embodiments of the present invention. resistance increase rate The well's 2490.4-2492.4 meter section tested daily, producing 4.8 tons of oil and 3.7 cubic meters of water, concluding that the oil and water layers are in the same formation. As shown in the figure, using the original method to calculate the resistivity increase rate I (original), the 2490.4-2499.6 meter section of this well was determined to be a water layer, and the overall logging interpretation is an oil-bearing water layer; using the method calculated based on the spontaneous potential difference of this invention... resistance increase rate Analysis showed that the upper part of the layer (2490.4-2494.8 meters) was an oil-water co-layer, and the lower part (2494.8-2499.6 meters) was a water layer, consistent with the test results. This fully demonstrates the reliability of the method shown in the embodiments of the present invention.

[0028] Example 3 This embodiment takes the western Hudong structure of the western Huanqing block in the western Ordos Basin as an example to obtain the value based on the natural potential difference. resistance increase rate Determine the properties of reservoir fluids.

[0029] A method for calculating the resistance increase rate based on the natural potential difference is performed according to the following steps: Step 101: Based on the measured data from the oilfield, combined with the average surface temperature of the study area... Given a geothermal gradient D = 2.4℃ / 100m, determine the formation temperature T of the target layer: In the formula, H is the depth of the target layer, in meters; Step 102: Using wells with formation water sampling and analysis data in the target layer of the study area as data wells, analyze the formation water salinity obtained from the data wells. The following formula is used: Calculate the apparent formation water resistivity of the target layer in each data well. Both this embodiment and Embodiment 2 are located in the Huanqing Block in the western Ordos Basin. The calculation results are shown in Table 1. In the formula, T is the formation temperature of the target layer determined by the formula in step 101 or the measured formation temperature, in °C. Step 103: Based on the single-well logging data, calculate the formation water resistivity of each formation from Step 102. SP logging data for the same depth section of the well; and selecting stable pure mudstone sections at adjacent depths to determine the SP baseline of the target layer for each data well. ; and then determine the measured spontaneous potential (SP) and baseline of each data well. The difference: The calculation results are shown in Table 1; Step 104: Based on the calculation results of Steps 102 and 103, the regression coefficients of determination k = 0.0009 and c = 0.0869 are obtained, yielding the data wells. and Relationship: Based on the natural potential difference For the formation water resistivity Equivalent to and in step 103 Substituting into the formula, we obtain the apparent formation water resistivity based on the natural potential SP of the data well. Relationship: ; Step 105: Based on the rock electrical test results, determine the rock electrical parameters m=1.376 and a=2.269, and calculate the resistivity of the mixed solution of the target layer in the data well. : In the formula, φ represents the original formation resistivity in Ω·m; φ represents the effective porosity calculated from well logging, in decimal form; m represents the cementation index; and a represents the lithology coefficient related to the rock. Step 106: Based on the calculation results of steps 104 and 105, determine the value based on the natural potential difference. resistance increase rate formula; Step 107: Using the well to be measured as the target well, determine the resistivity Rt and porosity of the target layer in the target well. The spontaneous potential (SP) of the target layer was determined by selecting a stable pure mudstone section at an adjacent depth. ; Step 108: According to the formula in step 106 Calculation based on natural potential difference resistance increase rate To determine the properties of reservoir fluids.

[0030] Figure 4 This invention is used to calculate the results of an appraisal well in the western part of the Hudong structure of the Huanqing Block, specifically the westward extension of the Chang 8 oil reservoir. The calculations are based on the spontaneous potential difference. resistance increase rate and the original resistivity at the corresponding depth With formation resistivity saturated with formation water The resistance increase rate I determined by the ratio was compared. The effect diagram shown in the figure is divided into 10 lines, and the labeling is the same as that shown in Example 2. The well section from 2490.4 to 2492.4 meters produced 4.8 tons of oil and 3.7 cubic meters of water per day, and the test conclusion was that the oil and water layers were in the same layer. The well section from 2811.3 to 2813.8 meters produced 15.0 cubic meters of water per day, without oil, and the test conclusion was that it was a water layer. As can be seen from the figure, using the original method to calculate the resistance increase rate I (original), it was determined that the 2811.2-2814.3 meters, 2815.2-2817.2 meters, and 2818.1-2821 meters of this well were all oil layers; using the method of this invention, the resistance increase rate I was calculated based on the natural potential difference. resistance increase rate Analysis showed that all three reservoirs in this section were water-bearing layers, consistent with the test results. This fully demonstrates the reliability of the method shown in the embodiments of the present invention.

[0031] Example 4 This embodiment takes the northward extension of the Chang 8 oil reservoir in the western Hudong structure of the western Huanqing block in the Ordos Basin as an example to obtain the value based on the natural potential difference. resistance increase rate Determine the properties of reservoir fluids.

[0032] A method for calculating the resistance increase rate based on the natural potential difference is performed according to the following steps: Step 101: Based on the measured data from the oilfield, combined with the average surface temperature of the study area... Given a geothermal gradient D = 2.4℃ / 100m, determine the formation temperature T of the target layer: In the formula, H is the depth of the target layer, in meters; Step 102: Select wells with formation water sampling and analysis data in the target layer of the study area as data wells. Analyze the formation water salinity obtained from the data wells. The following formula is used: Calculate the apparent formation water resistivity of the target layer in each data well. Both this embodiment and Embodiment 2 are located in the Huanqing Block in the western Ordos Basin. The calculation results are shown in Table 1. In the formula, T is the formation temperature of the target layer determined by the formula in step 101 or the measured formation temperature, in °C. Step 103: Based on the single-well logging data, calculate the formation water resistivity of each formation from Step 102. SP logging data for the same depth section of the well; and selecting stable pure mudstone sections at adjacent depths to determine the SP baseline of the target layer for each data well. ; and then determine the measured spontaneous potential (SP) and baseline of each data well. The difference: The calculation results are shown in Table 1; Step 104: Based on the calculation results of Steps 102 and 103, the regression coefficients of determination k = 0.0009 and c = 0.0869 are obtained, yielding the data wells. and Relationship: Based on the natural potential difference For the formation water resistivity Equivalent to and in step 103 Substituting into the formula, we obtain the apparent formation water resistivity based on the natural potential SP of the data well. Relationship: ; Step 105: Based on the rock electrical test results, determine the rock electrical parameters m=1.376 and a=2.269, and calculate the resistivity of the mixed solution of the target layer in the data well. : In the formula, φ represents the original formation resistivity in Ω·m; φ represents the effective porosity calculated from well logging, in decimal form; m represents the cementation index; and a represents the lithology coefficient related to the rock. Step 106: Based on the calculation results of steps 104 and 105, determine the value based on the natural potential difference. resistance increase rate formula; Step 107: Using the well to be measured as the target well, determine the resistivity Rt and porosity of the target layer in the target well. The spontaneous potential (SP) of the target layer was determined by selecting a stable pure mudstone section at an adjacent depth. ; Step 108: According to the formula in step 106 Calculation based on natural potential difference resistance increase rate To determine the properties of reservoir fluids.

[0033] Figure 5 This invention is used to calculate the results of an appraisal well in the western Hudong structure of the Huanqing Block, specifically the northward extension of the Chang 8 oil reservoir. The calculations are based on the spontaneous potential difference. resistance increase rate And compared with the original resistivity at the corresponding depth using actual measurements. With formation resistivity saturated with formation water The resistance increase rate I determined by the ratio was compared. The effect diagram shown in the figure is divided into 10 lines, and the labeling is the same as that shown in Example 2. The well section of 2772.0-2775.0 meters produced 26.4 cubic meters of water per day, without oil, and the test conclusion was that it was a water layer. As can be seen from the figure, using the original method to calculate the resistance increase rate I (original), it was determined that the 2772.0-2773.0 meters and 2773.6-2778.6 meters of this well were both poor oil layers; using the method of this invention, the resistance increase rate I is calculated based on the difference in natural potential. resistance increase rate Analysis showed that all four reservoirs in this section were water-bearing layers, consistent with the test results. This fully demonstrates the reliability of the method shown in the embodiments of the present invention.

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the rate of increase in resistance based on the natural potential difference, characterized in that: Includes the following steps: S1: Based on measured data from the oilfield, combined with the average surface temperature and geothermal gradient of the study area, determine the formation temperature T of the target layer: In the formula, D is the geothermal gradient, and H is the depth of the target layer. The average surface temperature; S2: Wells with formation water sampling and analysis data in the target layer of the study area are used as data wells. The formation water salinity is obtained from the analysis of the data wells. The following formula is used: Calculate the apparent formation water resistivity of the target layer in each data well. In the formula, T is the formation temperature of the target layer; S3: Based on the single-well logging data, calculate the apparent formation water resistivity for each step in S2. SP logging data for the same depth section of the well; and selecting stable pure mudstone sections at adjacent depths to determine the SP baseline of the target layer for each data well. ; and then determine the measured spontaneous potential (SP) and the baseline spontaneous potential (SP) of each data well. B The difference: ; S4: Based on the calculation results of steps S2 and S3, regression is used to obtain the data wells. and The relationship will be based on the natural potential difference. Formation water resistivity Equivalent to and in step S3 Substituting into the formula, we obtain the apparent formation water resistivity based on the natural potential SP of the data well. The relationship is as follows: In step S4, the natural potential difference value of the data well is obtained. Apparent formation water resistivity Relationship: （1） Based on natural potential difference For the formation water resistivity Equivalent to and in step S3 Substituting into the formula, we obtain the apparent formation water resistivity based on the spontaneous potential SP of the study area. Relationship: （2） In the formula: k and c are fitting coefficients; S5: Calculate the resistivity of the mixed solution in the target layer of the well data. : In the formula, φ is the original formation resistivity, φ is the effective porosity calculated from well logging, m is the cementation index, and a is the lithology coefficient related to the rock. S6: Based on the calculation results of steps S4 and S5, determine the value based on the natural potential difference. resistance increase rate Formula; the step S6 based on the natural potential difference value resistance increase rate : （3） In steps S4 and S5 , Substituting the formula, we obtain the value based on the natural potential difference. resistance increase rate The calculation formula is as follows: （4） S7: Using the well to be measured as the target well, determine the resistivity Rt and porosity of the target layer in the target well. The spontaneous potential (SP) of the target layer was determined by selecting a stable pure mudstone section at an adjacent depth. ; S8: Calculate the value based on the natural potential difference according to the formula in step S6. resistance increase rate To determine the properties of reservoir fluids.

2. The method for determining the resistance increase rate based on the natural potential difference according to claim 1, characterized in that: The specific process of single-well formation water analysis in step S2 is as follows: Based on the actual production dynamic analysis of the study area, water samples are taken from wells with stable production and where the influence of fracturing fluid has been eliminated. The total positive and negative ions in the water samples are analyzed to obtain the total mineralization of the formation water, thereby determining the apparent formation water resistivity.

3. The method for determining the resistance increase rate based on the natural potential difference according to claim 1, characterized in that: In steps S3 and S7, the baseline of the natural potential of the target layer is determined. The specific process is as follows: Based on the measured spontaneous potential (SP) of the single-well spontaneous potential logging curve, select a stable mudstone layer that has not shown curve drift, read the average SP value, and determine it as the baseline of the spontaneous potential of the target layer. .

4. The method for determining the resistance increase rate based on the natural potential difference according to claim 1, characterized in that: In step S5, the cementation index m and lithology coefficient a are determined according to the standard procedure of "Laboratory Measurement and Calculation Method of Rock Resistivity Parameters SY / T5385-2007" based on the measurement results of the relationship between formation factors and porosity. During the experiment, the experimental temperature and pressure are set according to the temperature and pressure environment of the core layer. The experimental temperature parameter is calculated according to the formula in step S1, and the pressure is calculated according to the requirements of "Original Formation Pressure and Pressure System Determination Method of Oil and Gas Reservoirs SY / T 6365-1998".

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