CN116539655B - Method for evaluating water sensitivity of tight sandstone reservoir based on nuclear magnetic resonance technology - Google Patents
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Abstract
The invention relates to a method for evaluating water sensitivity of a tight sandstone reservoir, in particular to a method for evaluating water sensitivity of the tight sandstone reservoir based on nuclear magnetic resonance technology. Comprises the preparation of compact sandstone core; testing a core saturated water state T2 spectrogram by nuclear magnetic resonance; calculating a water sensitivity experiment and a water sensitivity index; establishing a relationship chart of a nuclear magnetic resonance T2 geometric mean and a water sensitivity index; testing a T2 spectrogram of the core after water sensitivity by nuclear magnetic resonance; analyzing a water-sensitive injury mechanism; and (5) analyzing water sensitivity of different production layers of the target block. The beneficial effects are that: the method solves the problems that the experiment period in the prior art is long, the core of the reservoir is damaged, and the inherent mechanism of the water-sensitive damage of the reservoir cannot be analyzed; by means of nuclear magnetic resonance technology, the water sensitivity of different layers of the tight sandstone reservoir can be rapidly and nondestructively evaluated, the testing efficiency is improved, the pore-throat injury mechanism of the water sensitivity can be analyzed, and the method has important significance for the tight sandstone reservoir water injection development technology.
Description
Technical Field
The invention relates to a method for evaluating water sensitivity of a tight sandstone reservoir, in particular to a method for evaluating water sensitivity of the tight sandstone reservoir based on nuclear magnetic resonance technology.
Background
In the petroleum industry, water-sensitive damage refers to the phenomenon that an external fluid has poor compatibility with a reservoir, causing hydration, swelling and dispersion of clay minerals in an oil and gas reservoir, resulting in release and migration of clay particles and clastic particles cemented by clay, resulting in a decrease in permeability. Especially for compact sandstone reservoirs, the permeability is low, pore throats are small, pore structures are complex, and water-sensitive injuries are more serious in the processes of well drilling and completion, reservoir transformation and water injection development, so that the development difficulty is greatly increased.
At present, water sensitivity evaluation is usually tested by referring to an industry standard of reservoir sensitivity flow experiment evaluation method (SY/T5358-2010), the damage degree of a rock core is evaluated by measuring the change of permeability before and after sensitivity damage, and the qualitative analysis and the main control factor research on the mechanism generated by water sensitivity damage are carried out from the aspects of clay mineral components, rock mineralogy characteristics, pore structures and the like by combining means of a scanning electron microscope, X diffraction, mercury pressing technology and the like, and nuclear magnetic resonance is a rapid and nondestructive detection method, so that the nuclear magnetic resonance is less applied to the researches on the aspects of water sensitivity evaluation, damage mechanism and the like. The domestic part of literature reports that core T caused by fracturing fluid invasion or formation water with different mineralization degrees is tested by utilizing nuclear magnetic resonance technology 2 Spectrum change, water sensitivity injury degree is calculated through nuclear magnetic resonance permeability model, but for compact sandstone, nuclear magnetic resonance T before and after water sensitivity 2 The smaller the spectral variation amplitude, the larger the error of the water sensitivity injury degree calculated by the permeability model.
According to the nuclear magnetic resonance fast diffusion surface relaxation model, the fluid relaxation rate in the rock depends on the acting force of the solid surface on the fluid molecules, and the intrinsic mechanism of the acting force depends on the pore size in the rock, the properties of the solid surface in the rock and the type and properties of the saturated fluid in the rock.T 2 The longer the relaxation time, the larger the pore throat radius;T 2 the shorter the relaxation time, the smaller the pore throat radius, a certainT 2 The amplitude of the relaxation time spectrum represents the proportion of a certain pore throat radius. In addition, in the case of the optical fiber,T 2 the relaxation time is also affected by the clay mineral content and its kind, the higher the clay mineral content,T 2 the shorter the relaxation time, the lower the clay mineral content,T 2 the longer the relaxation time, and the different clay mineralsT 2 Relaxation times range from small to large: montmorillonite<Kaolinite<Illite. Thus, the first and second substrates are bonded together,T 2 the relaxation time spectrum not only reflects the microscopic pore structure parameters of the rock sample, but also can reflect the information of the clay mineral content of the rock sample, and is consistent with the water sensitivity main control factor of the rock sample. Commonly usedT 2 Characterization of geometric meanT 2 Distribution, thus establishing nuclear magnetic resonance for a certain target development blockT 2 A plot of geometric mean versus water sensitivity index is feasible for rapid assessment of water sensitivity of tight reservoirs using nuclear magnetic resonance.
Disclosure of Invention
The invention aims at solving the defects existing in the prior art, and provides a method for evaluating the water sensitivity of a tight sandstone reservoir based on a nuclear magnetic resonance technology, which is used for solving the problems that the experimental period is long, the core of the reservoir is damaged, and the inherent mechanism of the water sensitivity damage of the reservoir cannot be analyzed in the prior art. The invention also relates to a method for quantitatively analyzing water sensitivity of different production layers by using the nuclear magnetic resonance technology based on the core test data obtained from the exploratory well.
The invention relates to a method for evaluating water sensitivity of a tight sandstone reservoir based on nuclear magnetic resonance technology, which adopts the following technical scheme: the method comprises the following steps:
step 1, preparing a compact sandstone core;
drilling a core from the full-diameter core, washing oil of the core, drying the core, and testing the diameter, the length and the gas permeability of the core; placing the rock core in a vacuumizing saturation system, vacuumizing, placing simulated formation water, and continuously vacuumizing until the rock core is saturated; then pressurizing and saturating to enable simulated formation water to enter all pores of the rock core until the rock core is fully saturated;
step 2, testing the saturated water state T of the rock core by nuclear magnetic resonance 2 A spectrogram;
wiping water on the surface of the rock core, testing the liquid measurement porosity of the rock core, then opening a nuclear magnetic resonance rock core analyzer for preheating, and carrying out nuclear magnetic resonance test after the temperature of the temperature control system is stable; core is put intoPlacing into nuclear magnetic resonance analyzer, and testing nuclear magnetic resonance T under saturated water state 2 A spectrum;
step 3, water sensitivity experiment and water sensitivity index calculation;
using displacement physical simulation experiment device, using simulated formation water to test initial liquid permeability of rock coreK 0 The method comprises the steps of carrying out a first treatment on the surface of the Then, using brine to displace by 10-15 times of the pore volume of the core, stopping displacement, keeping the temperature and confining pressure unchanged, soaking for a period of time, and testing the liquid permeability of the core; then using 10-15 times of core pore volume distilled water to displace the core, and testing the core liquid permeability during the displacement of distilled waterK i The method comprises the steps of carrying out a first treatment on the surface of the Calculating core water sensitivity indexI w The calculation formula is as follows:I w =（K 0 -K i ）/K 0 ×100%；
step 4, establishing nuclear magnetic resonance T 2 A relationship chart of geometric mean and water sensitivity index;
calculating core nuclear magnetic resonance T 2 Geometric mean and the calculation formula isWherein:T 2g is the geometric mean, ms;T 2i relaxation time at each point, ms;A i corresponding magnitudes for relaxation times at each point;A T is the sum of the relaxation amplitudes of each point; by nuclear magnetic resonance T 2 Geometric mean is abscissa, water sensitivity indexI w Establishing nuclear magnetic resonance T as ordinate 2 A relationship chart of geometric mean and water sensitivity index;
step 5, testing T after water sensitivity of core by nuclear magnetic resonance 2 Spectrogram of the graph
Taking out the core with water sensitivity test from the core holder, wiping water on the surface of the core, placing the core into a nuclear magnetic resonance analyzer, and testing nuclear magnetic resonance T of the core after water sensitivity 2 A spectrum;
step 6, analyzing the mechanism of the water-sensitive injury
Nuclear magnetic resonance T of core 2 The distribution is converted into pore throat radius distribution, and the formula isWherein r is pore throat radius, mum; t (T) 2 Is the fluid relaxation time, ms; n and C are power rate and conversion coefficient; drawing core nuclear magnetic resonance pore-throat distribution before and after water sensitivity in the same coordinate system, evaluating the degree of water sensitivity damage to pore-throats of different scales of a tight sandstone reservoir according to curve change rules, and analyzing a water sensitivity damage mechanism;
step 7, water sensitivity analysis of different production layers of target block
Nuclear magnetic resonance T for testing rock cuttings obtained from different production layers 2 And (3) spectrum, calculating the geometric mean value of the spectrum, and determining the water sensitivity index of the test production horizon corresponding to the plate obtained in the step (4).
Preferably, the above-mentioned nuclear magnetic resonance core analyzer needs to set parameters for the tight sandstone core, the echo interval TE is set to 0.1ms, the waiting time Tw is set to 3000ms, the echo number is 1024 times, and the scan superposition number is 128 times.
Preferably, the water sensitivity experiment and the water sensitivity index calculation in the step 3 further include: and (3) placing the core into a core holder, adding confining pressure, performing liquid permeability measurement by using a constant flow rate mode, wherein the flow rate is smaller than the critical flow rate of the core, the confining pressure is required to be larger than the pressure at the inlet end of the core by 2MPa in the experimental process, and when the pressure difference of the core is kept unchanged for more than 10min, recording displacement differential pressure and flow rate, and calculating the liquid permeability measurement of the core by using a Darcy formula.
Preferably, the preparation of the compact sandstone core in the step 1 is specifically as follows:
drilling a rock core with the diameter of 2.5cm or 3.8cm from a full-diameter rock core, washing oil from an experimental rock core, drying, and testing the diameter and the length of the rock core; placing the rock core in a vacuumizing saturation system, vacuumizing for 48 hours, then placing simulated formation water, and continuously vacuumizing until the rock core is saturated; and then pressurizing for saturation for 24 hours under 20MPa, so that simulated formation water enters all pores of the rock core until the rock core is fully saturated.
Preferably, in step 2, the saturated water state T of the core is tested by nuclear magnetic resonance 2 The spectrogram is specifically as follows:
wiping water on the surface of the rock core, testing the liquid measurement porosity of the rock core, then opening a nuclear magnetic resonance rock core analyzer, preheating for 4 hours, and performing nuclear magnetic resonance test after the temperature of the temperature control system is stable; placing the core into a nuclear magnetic resonance analyzer, and testing nuclear magnetic resonance T under saturated water state 2 A spectrum.
Preferably, the water sensitivity experiment and the water sensitivity index calculation in the step 3 are specifically as follows:
testing initial permeability of rock core by using simulated formation water by using displacement physical simulation experiment deviceK 0 The method comprises the steps of carrying out a first treatment on the surface of the Then using 1/2 initial fluid mineralized brine to displace 10-15 times of core pore volume, stopping displacement, keeping the temperature and confining pressure unchanged, soaking for more than 12 hours, and testing the permeability of the core; then using distilled water with 10-15 times of core pore volume to displace the core, and testing core permeability during distilled water displacementK i The method comprises the steps of carrying out a first treatment on the surface of the Calculating core water sensitivity indexI w The calculation formula is as follows:I w =（K 0 -K i ）/K 0 ×100%。
compared with the prior art, the invention has the following beneficial effects:
(1) The invention combines nuclear magnetic resonance technology and displacement physical simulation experiment technology to establish nuclear magnetic resonance T 2 The relationship plate of the geometric mean and the water sensitivity index can be used for rapidly and nondestructively evaluating the water sensitivity of the rock core, so that the test time is greatly shortened, the specification limit on the rock core is less, the irregular rock core and logging rock scraps can be tested, the water sensitivity of different layers of the reservoir can be evaluated, and the research means of the water sensitivity of the tight reservoir are enriched; particularly, the water sensitivity characteristics of different layers of the target block can be defined by testing nuclear magnetic resonance data of rock fragments obtained from different layers on the basis of fully analyzing the core data of the obtained target block exploratory well, and effective support is provided for fine development of oil fields;
(2) The invention uses nuclear magnetic resonance T before and after water sensitivity 2 The spectral distribution is converted into pore-throat distribution, and the change of the pore-throat distribution curve of nuclear magnetic resonance is compared to evaluate the water sensitivity to compact sandstone storageThe pore-throat injury degree of different scales of the layer can clearly determine the water-sensitive injury mechanism of the tight sandstone reservoir, and provide theoretical guidance for effectively preventing the water-sensitive injury in the development process of the tight sandstone reservoir.
Drawings
FIG. 1 shows nuclear magnetic resonance of the present inventionT 2 A geometric mean and water sensitivity index relation graph;
FIG. 2 is a graph of nuclear magnetic resonance pore throat distribution of core No. 5 before and after water sensitivity;
FIG. 3 is a graph of distribution of nuclear magnetic resonance pore throats before and after water sensitivity of a core No. 8;
FIG. 4 is a nuclear magnetic resonance T2 spectrum of cuttings from the production horizon of target block A;
FIG. 5 is a nuclear magnetic resonance T2 spectrum of cuttings from the production horizon of target block B.
Detailed Description
The preferred embodiments of the present invention will be described below with reference to the accompanying drawings, it being understood that the preferred embodiments described herein are for illustration and explanation of the present invention only, and are not intended to limit the present invention.
Example 1 a method of evaluating the water sensitivity of a tight sandstone reservoir based on nuclear magnetic resonance techniques according to the present invention comprises the steps of:
step 1, preparing a compact sandstone core;
13 compact sandstone cores with the diameter of 2.5cm are drilled from a full-diameter core to serve as experimental cores, the experimental cores are washed with oil and dried, and the diameters, the lengths and the gas permeability of the cores are tested; placing the rock core in a vacuumizing saturation system, vacuumizing for 48 hours, then placing simulated formation water, and continuously vacuumizing until the rock core is saturated; and then pressurizing for saturation for 24 hours under 20MPa, so that simulated formation water enters all pores of the rock core until the rock core is fully saturated.
Step 2, testing the saturated water state T of the rock core by nuclear magnetic resonance 2 A spectrogram;
wiping water on the surface of the core, testing the liquid measurement porosity of 13 cores by using a weighing method, as shown in table 1, then opening a nuclear magnetic resonance core analyzer and preheating for 4 hours, and performing nuclear magnetic resonance test after the temperature of the temperature control system is stable; rock is put intoPlacing the heart into a nuclear magnetic resonance analyzer to test nuclear magnetic resonance T under saturated water state 2 A spectrum.
Step 3, water sensitivity experiment and water sensitivity index calculation;
using displacement physical simulation experiment device, using simulated formation water to test initial liquid permeability of rock coreK 0 The method comprises the steps of carrying out a first treatment on the surface of the Then 1/2 of initial fluid mineralized brine is used for displacement for 10-15 times of core pore volume, displacement is stopped, the temperature and confining pressure are kept unchanged, soaking is carried out for more than 12 hours, and the liquid permeability of the core is tested; then using 10-15 times of core pore volume distilled water to displace the core, and testing the core liquid permeability during the displacement of distilled waterK i The method comprises the steps of carrying out a first treatment on the surface of the Calculating core water sensitivity indexI w The calculation formula is as follows:I w =（K 0 -K i ）/K 0 100% and the calculation results are shown in Table 1.
Step 4, establishing nuclear magnetic resonance T 2 Relationship between geometric mean and water sensitivity index;
calculating core nuclear magnetic resonance T 2 Geometric mean and the calculation formula isWherein:T 2g is the geometric mean, ms;T 2i relaxation time at each point, ms;A i corresponding magnitudes for relaxation times at each point;A T the calculation results are shown in table 1 for the sum of the relaxation amplitudes of each point; by nuclear magnetic resonance T 2 Geometric mean is abscissa, water sensitivity indexI w Establishing nuclear magnetic resonance T as ordinate 2 A graph of geometric mean versus water sensitivity index is shown in fig. 1.
Step 5, testing T after water sensitivity of core by nuclear magnetic resonance 2 Spectrogram of the graph
Taking out the core with water sensitivity test from the core holder, wiping water on the surface of the core, placing the core into a nuclear magnetic resonance analyzer, and testing nuclear magnetic resonance T of the core after water sensitivity 2 A spectrum.
Step 6, analyzing the mechanism of the water-sensitive injury
Nuclear magnetic resonance T of cores No. 5 and 8 2 The distribution is converted into pore throat radius distribution, and the formula isWherein r is pore throat radius, mum; t (T) 2 Is the fluid relaxation time, ms; n and C are power rate and conversion coefficient. The nuclear magnetic resonance pore throat distribution of the core before and after the water sensitivity is drawn in the same coordinate system, as shown in fig. 2 and 3, the pore throat space of the core with the size of more than 2 mu m after the water sensitivity of the core with the size of 5 is obviously reduced, the reduction amplitude is 28.02%, the pore throat space of 0.01-2 mu m is obviously increased, the increase amplitude is 11.36%, the water sensitivity index of the core is 43.02%, and the water sensitivity is moderately weak. The pore throat space of the core No. 8 with the water sensitivity of more than 0.7 mu m is reduced by 28.63%, the pore throat space of 0.06-0.7 mu m is increased by 22.62%, the pore throat space of 0.006-0.06 mu m is reduced by 11.48%, the pore throat curve distribution of more than 0.06 mu m is shifted left, the water sensitivity index is 56.20%, and the water sensitivity is moderately strong. After the water sensitivity happens, the movable fluid of the core No. 5 is reduced to 41.47% from 45.21%, the movable fluid of the core No. 8 is reduced to 30.58% from 37.63%, the water sensitivity not only reduces the permeability of the reservoir, but also changes part of movable pores in the reservoir into immovable pores, and the movable fluid is obviously reduced.
Table 1 results of the water sensitivity test of the tight sandstone cores
Step 7, water sensitivity analysis of different production layers of target block
(1) Nuclear magnetic resonance T of rock debris obtained by testing production horizon of target block A 2 Spectrum (FIG. 4) and calculate its geometric mean to be 10.26, corresponding to the nuclear magnetic resonance T described above 2 And (3) a relation chart of the geometric mean and the water sensitivity index (figure 1), wherein the water sensitivity index of the production horizon is 51.10 percent, and the water sensitivity is moderately strong. (2) Nuclear magnetic resonance T of rock debris obtained by producing horizon in test target block B 2 Spectrum (FIG. 5) and calculated to have a geometric mean of 6.37 corresponding to the above-mentioned nuclear magnetic resonance T 2 A graph of the relationship between the geometric mean and the water sensitivity index (figure 1), the water sensitivity index of the production horizon is 61.46%, the middleEqual bias strong water sensitivity. The method can obtain the water sensitivity indexes of different production horizons of the target block with high efficiency and high accuracy.
The above description is only a few preferred embodiments of the present invention, and any person skilled in the art may make modifications to the above described embodiments or make modifications to the same. Accordingly, the corresponding simple modifications or equivalent changes according to the technical scheme of the present invention fall within the scope of the claimed invention.
Claims (4)
1. A method for evaluating water sensitivity of a tight sandstone reservoir based on nuclear magnetic resonance technology is characterized by comprising the following steps: the method comprises the following steps:
step 1, preparing a compact sandstone core;
drilling a core from the full-diameter core, washing oil of the core, drying the core, and testing the diameter and the length of the core; placing the rock core in a vacuumizing saturation system, vacuumizing, placing simulated formation water, and continuously vacuumizing until the rock core is saturated; then pressurizing and saturating to enable simulated formation water to enter all pores of the rock core until the rock core is fully saturated;
step 2, testing the saturated water state T of the rock core by nuclear magnetic resonance 2 A spectrogram;
wiping water on the surface of the rock core, testing the liquid measurement porosity of the rock core, then opening a nuclear magnetic resonance rock core analyzer for preheating, and carrying out nuclear magnetic resonance test after the temperature of the temperature control system is stable; placing the core into a nuclear magnetic resonance analyzer, and testing nuclear magnetic resonance T under saturated water state 2 A spectrum;
step 3, water sensitivity experiment and water sensitivity index calculation;
testing initial permeability of rock core by using simulated formation water by using displacement physical simulation experiment deviceK 0 The method comprises the steps of carrying out a first treatment on the surface of the Then, using brine to displace by 10-15 times of the pore volume of the core, stopping displacement, keeping the temperature and confining pressure unchanged, soaking for a period of time, and testing the permeability of the core; then using distilled water with 10-15 times of core pore volume to displace the core, and testing core permeability during distilled water displacementK i The method comprises the steps of carrying out a first treatment on the surface of the Calculating core water sensitivity indexI w The calculation formula is as follows:I w =（K 0 -K i ）/K 0 ×100%；
step 4, establishing nuclear magnetic resonance T 2 A relationship chart of geometric mean and water sensitivity index;
calculating core nuclear magnetic resonance T 2 Geometric mean and the calculation formula isWherein:T 2g is the geometric mean, ms;T 2i relaxation time at each point, ms;A i corresponding magnitudes for relaxation times at each point;A T is the sum of the relaxation amplitudes of each point; by nuclear magnetic resonance T 2 Geometric mean is abscissa, water sensitivity indexI w Establishing nuclear magnetic resonance T as ordinate 2 A relationship chart of geometric mean and water sensitivity index;
step 5, testing T after water sensitivity of core by nuclear magnetic resonance 2 Spectrogram of the graph
Taking out the core with water sensitivity test from the core holder, wiping water on the surface of the core, placing the core into a nuclear magnetic resonance analyzer, and testing nuclear magnetic resonance T of the core after water sensitivity 2 A spectrum;
step 6, analyzing the mechanism of the water-sensitive injury
Nuclear magnetic resonance T of core 2 The distribution is converted into pore throat radius distribution, and the formula isWherein r is pore throat radius, mum; t (T) 2 Is the fluid relaxation time, ms; n and C are power rate and conversion coefficient; drawing core nuclear magnetic resonance pore-throat distribution before and after water sensitivity in the same coordinate system, evaluating the degree of water sensitivity damage to pore-throats of different scales of a tight sandstone reservoir according to curve change rules, and analyzing a water sensitivity damage mechanism;
step 7, water sensitivity analysis of different production layers of target block
Nuclear magnetic resonance T for testing rock cuttings obtained from different production layers 2 Spectrum and meterCalculating the geometric mean value of the water-sensitive index, corresponding to the plate obtained in the step 4, and determining the water-sensitive index of the test production horizon;
the nuclear magnetic resonance core analyzer needs to set parameters for a compact sandstone core, the echo interval TE is set to be 0.1ms, the waiting time Tw is set to be 3000ms, the echo times are set to be 1024 times, and the scanning superposition times are set to be 128 times;
the preparation of the compact sandstone core in the step 1 comprises the following steps:
drilling a rock core with the diameter of 2.5cm or 3.8cm from a full-diameter rock core, washing oil from an experimental rock core, drying, and testing the diameter and the length of the rock core; placing the rock core in a vacuumizing saturation system, vacuumizing for 48 hours, then placing simulated formation water, and continuously vacuumizing until the rock core is saturated; and then pressurizing for saturation for 24 hours under 20MPa, so that simulated formation water enters all pores of the rock core until the rock core is fully saturated.
2. The method for evaluating the water sensitivity of a tight sandstone reservoir based on nuclear magnetic resonance technology according to claim 1, wherein: the water sensitivity experiment and water sensitivity index calculation in the step 3 further comprises: and (3) placing the core into a core holder, adding confining pressure, performing liquid permeability measurement by using a constant flow rate mode, wherein the flow rate is smaller than the critical flow rate of the core, the confining pressure is required to be larger than the pressure at the inlet end of the core by 2MPa in the experimental process, and when the pressure difference of the core is kept unchanged for more than 10min, recording displacement differential pressure and flow rate, and calculating the liquid permeability measurement of the core by using a Darcy formula.
3. The method for evaluating the water sensitivity of a tight sandstone reservoir based on nuclear magnetic resonance technology according to claim 2, wherein: testing the saturated water state T of the rock core by nuclear magnetic resonance in step 2 2 The spectrogram is specifically as follows:
wiping water on the surface of the rock core, testing the liquid measurement porosity of the rock core, then opening a nuclear magnetic resonance rock core analyzer, preheating for 4 hours, and performing nuclear magnetic resonance test after the temperature of the temperature control system is stable; placing the core into a nuclear magnetic resonance analyzer, and testing nuclear magnetic resonance T under saturated water state 2 A spectrum.
4. A method for evaluating the water sensitivity of a tight sandstone reservoir based on nuclear magnetic resonance techniques as claimed in claim 3, wherein: the water sensitivity experiment and water sensitivity index calculation in the step 3 are specifically as follows:
testing initial permeability of rock core by using simulated formation water by using displacement physical simulation experiment deviceK 0 The method comprises the steps of carrying out a first treatment on the surface of the Then using 1/2 initial fluid mineralized brine to displace 10-15 times of core pore volume, stopping displacement, keeping the temperature and confining pressure unchanged, soaking for more than 12 hours, and testing the permeability of the core; then using distilled water with 10-15 times of core pore volume to displace the core, and testing core permeability during distilled water displacementK i The method comprises the steps of carrying out a first treatment on the surface of the Calculating core water sensitivity indexI w The calculation formula is as follows:I w =（K 0 -K i ）/K 0 ×100%。
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