Saturation correction method based on oil-water loss equivalent

Abstract

A saturation correction method based on oil-water loss equivalent belongs to the technical field of petroleum and natural gas exploration and development and comprises the following steps: step 1, acquiring a core sample of a research area under the same conditions of pressure, temperature and coring process of a coring well section, and performing an oil-water saturation experiment on the core sample to obtain a core sample; obtaining the oil-water saturation of the experimental measurement rock core sample, and dotting the actually measured oil-water saturation value into the cross plot; and 2, correcting the actually measured oil-water saturation based on the oil-water loss equivalent of the research area to obtain an underground actual oil-water saturation value. Compared with the conventional method for correcting the oil saturation by singly utilizing a projection method, the method has the advantages that the oil saturation is corrected by considering the influence of different oil-water volatilization loss amounts, and the method is not limited to closed coring data and is simple to operate and good in correction effect.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas exploration and development, and particularly relates to a saturation correction method based on oil-water loss equivalent. Background Art

[0002] In the field of oil and gas development technology, reservoir fluid saturation is one of the important parameters for evaluating oil reservoir reserves, and is also an indispensable and important data for the quantitative evaluation of reservoir sweet spots in the later stage.

[0003] Conventional calculations of reservoir fluid saturation typically employ Archie's formula or a multivariate regression model. Model coefficients are calibrated based on core test results to produce a saturation calculation model for the study area. However, due to technical and environmental factors, the oil and water saturations measured in the laboratory often fall below the actual oil and water saturations at underground pressures. Therefore, when calibrating model coefficients using core test data, the oil and water saturations measured must first be corrected to the actual oil and water saturations at underground pressures. Currently, there are numerous methods for correcting oil saturation, primarily targeting closed coring data. However, saturation data obtained through core analysis and testing is often based on conventional coring data. Summary of the Invention

[0004] In order to solve the above problems, the present invention proposes a method for saturation correction based on oil-water loss equivalent, comprising the following steps:

[0005] Step 1: Obtain core samples from the study area under the same conditions of pressure, temperature, and coring process in the coring section, conduct oil-water saturation experiments on the core samples, obtain the experimentally measured oil-water saturation of the core samples, and plot the measured oil-water saturation values ​​on the crossplot;

[0006] Step 2: Correct the measured oil-water saturation based on the oil-water loss equivalent in the study area to obtain the actual underground oil-water saturation value.

[0007] Furthermore, according to the oil-water saturation crossplot in step 1, correction is performed using the following method based on the relationship between oil saturation and water saturation:

[0008] When the oil and water losses are equal, and there is no free gas in the formation but only oil and water phases, the relationship between oil and water saturation satisfies the following physical formula:

[0009] S w +S o =100 (1)

[0010] Where: S o is the original oil saturation of the formation (%); S w is the initial water saturation of the formation (%).

[0011] Furthermore, for the same well, under various external influence conditions, under the same coring section pressure, temperature, coring process, and saturation process, from coring to the final core analysis data, if the interval analysis is performed according to the oil plus water saturation, the crude oil loss rate is a constant. Based on this, the crude oil loss rate is set as a constant η1, and the water loss rate is η2. Substituting them into formula (1) yields:

[0012] S o 1 / η1+S w 1 / η2=100 (2)

[0013] Where: S o 1 is the oil saturation of core analysis (%); S w 1 Water saturation (%) for core analysis.

[0014] Furthermore, there is a linear relationship between the oil and water saturations in the core, S o 1 and S w 1 The linear relationship between them is clear, and its general expression is: S w 1 =A+B×S o 1 (3)

[0015] Where: A and B are constants,

[0016] After transforming (2), we can get S w 1 =100×η2-η2 / η1×S o 1 (4)

[0017] Since Equation (3) and Equation (4) represent the same physical meaning, that is, S of a certain core sample w 1 With S o 1 There is a definite correlation law, so: η1=-0.01×A / Bη2=0.01×A

[0018] The constant values ​​of A and B can be directly read from the linear regression relationship. The saturation correction amount is obtained through η1 and η2. The saturation after correction is set as Sw' and So', then So'=S o 1 / η1.

[0019] Furthermore, during the coring analysis, since the oil saturation and water saturation are measured twice independently, the corrected data are used as the basis for further normalization so that the sum of the final corrected oil and water saturations is 100. The total oil and water loss is ΔV, ΔV = 100-S W 1 -S O 1 The ratio of oil saturation loss to total loss is y = (So'-S O 1 ) / (So'+Sw'-S O 1 -S w 1 ), then: So=S O 1 +ΔV×y, Sw=Sw'+ΔV×(1-y), thereby correcting the coring data.

[0020] Furthermore, when the water loss is greater than the oil, the loss during the coring process is considered to be water.

[0021] Furthermore, during the coring process, the saturation correction method is as follows: the original point of the fitting line is moved along S o The axis is translated to the pure reservoir point with oil saturation of 100%, and the translation correction ΔS o The results are obtained through fitting formulas, and it is shown that cores with certain oil and water loss have the same translation correction amount.

[0022] Furthermore, after translation correction, only the oil saturation value changes. This is based on the premise that the water saturation remains basically unchanged. The error caused by the change in water saturation is eliminated by the rotation correction. Since the sum of the oil and water phase fluids should meet 100%, the fitting line after translation correction is rotated to a 45° diagonal line with the "pure reservoir point" as the center. The oil and water saturations of the core analysis are added with a certain rotation correction on the basis of equal translation. That is, the original formation oil and water saturations are obtained through normalization processing:

[0023] The correction formula is as follows:

[0024]

[0025] S oc =100-S wc

[0026] Where S o is the oil saturation of core analysis (%); S w is the water saturation of core analysis (%); ΔS o is the translation correction amount (%); S ocis the corrected oil saturation (%); S wc is the corrected water saturation (%).

[0027] The beneficial effects of the present invention are as follows: compared with the previous single projection method for oil saturation correction, the present invention takes into account the different effects of oil and water volatilization losses to perform oil saturation correction, and the present invention is not limited to closed coring data, is simple to operate, and has a good correction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the saturation relationship diagram of the core analysis;

[0029] Figure 2 is the saturation correction chart;

[0030] Figure 3 Comparison of measured oil saturation and resistivity curves of core samples from conventional coring wells and comparison of corrected oil saturation and resistivity curves. DETAILED DESCRIPTION

[0031] To make the technical means and objectives of the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments. A method for saturation correction based on oil-water loss equivalent specifically comprises the following steps:

[0032] Step 1: Obtain core samples from the study area under the same pressure, temperature, and coring process conditions as those in the coring section, conduct an oil-water saturation experiment on the core samples, obtain the experimentally measured oil-water saturation of the core samples, and plot the measured oil-water saturation values ​​on the crossplot;

[0033] Step 2: Correct the measured oil-water saturation based on the oil-water loss equivalent in the study area to obtain the actual underground oil-water saturation value.

[0034] Based on the oil-water saturation crossplot obtained in step 1, different correction methods are used according to the relationship between oil saturation and water saturation. They can be roughly divided into the following two methods:

[0035] Method 1: When the oil and water losses are equal, and there is no free gas in the formation but only oil and water phases, the relationship between oil and water saturation satisfies the following physical formula:

[0036] S w +S o =100 (1)

[0037] Where: S o is the original oil saturation of the formation (%); S w is the initial water saturation of the formation (%).

[0038] For the same well, under basically the same external influencing conditions, such as pressure, temperature, coring process, and saturation process, from coring to the final core analysis data, if the interval analysis is performed according to oil and water saturation, the crude oil loss rate is a constant. Based on this, the crude oil loss rate is set as a constant η1 and the water loss rate as η2. Substituting them into formula (1) yields:

[0039] S o 1 / η1+S w 1 / η2=100 (2)

[0040] Where: S o 1 is the oil saturation of core analysis (%); S w 1 Water saturation (%) for core analysis.

[0041] Statistics show that there is a certain linear relationship between the oil and water saturation in core sampling. o 1 and S w 1 The linear relationship between them is clear, and its general expression is: S w 1 =A+B×S o 1 (3)

[0042] Where: A and B are constants.

[0043] After transforming (2), we can get S w 1 =100×η2-η2 / η1×S o 1 (4)

[0044] Since Equation (3) and Equation (4) represent the same physical meaning, that is, S of a certain core sample w 1 With S o 1 There is a definite correlation law, so: η1=-0.01×A / Bη2=0.01×A

[0045] The constant values ​​of A and B can be directly read from the linear regression relationship. In this way, the saturation correction value can be obtained through η1 and η2. The saturation after correction is set as Sw' and So', then So'=S o 1 / η1.

[0046] During the coring analysis process, since the oil saturation and water saturation are measured twice independently, the sum of the oil and water saturations obtained after correction is not necessarily 100, and there is often a small fluctuation. Therefore, it is necessary to further normalize the corrected data so that the final sum of the corrected oil and water saturations is 100.

[0047] Assume that the total loss of oil and water is ΔV (ΔV = 100-S W 1 -S O 1 ), the ratio of oil saturation loss to total loss is y = (So'-S O 1 ) / (So'+Sw'-S O 1 -Sw 1 ), then: So=S O 1 +ΔV×y, Sw=Sw'+ΔV×(1-y).

[0048] Method 2: When water loss is greater than oil loss, it is assumed that the main loss during the coring process is water.

[0049] In the coring process, in addition to the effect of pressure reduction and degassing, the drilling fluid invades, resulting in a relatively large loss of oil and water. The following method is used to correct the saturation. The original point of the fitting line is moved along S o The axis is translated to the pure reservoir point with oil saturation of 100%, and the translation correction ΔS o The fitting formula also shows that cores with a constant amount of oil and water loss have the same translation correction. Of course, after translation correction, only the oil saturation value changes, assuming that the water saturation remains essentially unchanged. Errors caused by changes in water saturation can be eliminated by rotation correction. Since the sum of the oil and water phases should be 100%, the translation-corrected fitting line is rotated 45° around the "pure reservoir point" to obtain the oil and water saturations from the core analysis, adding a certain rotation correction to the equivalent translation. This normalization process yields the original formation oil and water saturations.

[0050] The correction formula is as follows:

[0051]

[0052] S oc =100-S wc

[0053] Where S o is the oil saturation of core analysis (%); S wis the water saturation of core analysis (%); ΔS o is the translation correction amount (%); S oc is the corrected oil saturation (%); S wc is the corrected water saturation (%).

[0054] Unless otherwise specified, the methods used in the following examples are all conventional methods.

[0055] Specific implementation method: Using the core analysis data of Mu E2-17 in Jilin exploration area to perform saturation correction of oil-water loss equivalent, the following steps are included:

[0056] Step 1: If Figure 1 As shown in the figure, for the coring data of Mu E2-17, the saturation relationship is analyzed based on the coring, and the relationship between oil saturation and water saturation is determined. The HG line shows that the water loss is greater than the oil, and it is believed that the main loss during the coring process is water.

[0057] Step 2: Since this well loses more water than oil, it is assumed that the primary loss during coring is water. The original point of the fitted line is translated along the axis to the pure reservoir point with 100% oil saturation. The translation correction is calculated using the fitting formula, demonstrating that cores with a given amount of oil and water loss have the same translation correction. After translation correction, only the oil saturation changes, assuming that the water saturation remains essentially unchanged. Errors caused by changes in water saturation can be eliminated by applying a rotation correction. Since the sum of the oil and water phases should be 100%, the translated fitted line is rotated 45° around the "pure reservoir point" to a diagonal line. This allows the oil and water saturations from the core analysis to be translated equally and then corrected by a certain rotation correction. This normalization process yields the original formation oil and water saturations.

[0058] Step 3: If Figure 2 As shown in FIG, the results of saturation correction for Well E2-17 are shown. After saturation correction by the method proposed in the present invention, the oil saturation is improved. The corrected oil saturation is consistent with the empirical value of the region and is in good agreement with the resistivity curve. Figure 3 As shown, it shows that the method proposed in the present invention is not limited to closed coring data, is simple to operate, and has good correction effect.

[0059] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed in the present invention, who makes equivalent replacements or changes based on the technical solutions and concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for saturation correction based on oil-water loss equivalent, characterized in that: The steps include: Step 1: Obtain core samples from the study area under the same conditions of pressure, temperature, and coring process in the coring section, conduct oil-water saturation experiments on the core samples, obtain the experimentally measured oil-water saturation of the core samples, and plot the measured oil-water saturation values ​​on the crossplot; Step 2: Correct the measured oil-water saturation based on the oil-water loss equivalent in the study area to obtain the actual underground oil-water saturation value.

2. The method for saturation correction based on oil-water loss equivalent according to claim 1, characterized in that: According to the oil-water saturation crossplot in step 1, the following method is used to perform correction based on the relationship between oil saturation and water saturation: When the oil and water losses are equal, and there is no free gas in the formation but only oil and water phases, the relationship between oil and water saturation satisfies the following physical formula: S w +S o =100 (1) Where: S o is the original oil saturation of the formation (%); S w is the initial water saturation of the formation (%).

3. The method for saturation correction based on oil-water loss equivalent according to claim 2, characterized in that: For the same well, under various external influence conditions, under the same coring section pressure, temperature, coring process, and saturation process, from coring to the final core analysis data, if the interval analysis is performed according to the oil plus water saturation, the crude oil loss rate is a constant. Based on this, the crude oil loss rate is set as a constant η1 and the water loss rate as η2. Substituting them into formula (1) gives: S o 1 / η1+S w 1 / η 2 =100 (2) Where: S o 1 is the oil saturation of core analysis (%); S w 1 Water saturation (%) for core analysis.

4. The method for saturation correction based on oil-water loss equivalent according to claim 3, characterized in that: There is a linear relationship between the oil and water saturation in core sampling, S o 1 and S w 1 The linear relationship between them is clear, and its general expression is: S w 1 =A+B×S o 1 (3) Where: A and B are constants, After transforming (2), we can get S w 1 =100×η 2 -η 2 / η 1 ×S o 1 (4) Since Equation (3) and Equation (4) represent the same physical meaning, that is, S of a certain core sample w 1 With S o 1 There is a definite correlation law, so: η1=-0.01×A / Bη2=0.01×A The constant values ​​of A and B can be directly read from the linear regression relationship. The saturation correction amount is obtained through η1 and η2. The saturation after correction is set as Sw' and So', then So'=S o 1 / η1.

5. The method for saturation correction based on oil-water loss equivalent according to claim 4, characterized in that: During the coring analysis, since the oil saturation and water saturation are measured twice independently, the corrected data are used as the basis for further normalization so that the sum of the final corrected oil and water saturations is 100. The total oil and water loss is ΔV, ΔV = 100-S W 1 -S O 1 The ratio of oil saturation loss to total loss is y = (So'-S O 1 ) / (So'+Sw'-S O 1 -S w 1 ), then: So=S O 1 +ΔV×y, Sw=Sw'+ΔV×(1-y), thereby correcting the coring data.

6. The method for saturation correction based on oil-water loss equivalent according to claim 1, characterized in that: When water loss is greater than oil, the loss during coring is considered to be water.

7. The method for saturation correction based on oil-water loss equivalent according to claim 1, characterized in that: During the coring process, the saturation correction method is as follows: move the original point of the fitting line along S o The axis is translated to the pure reservoir point with oil saturation of 100%, and the translation correction ΔS o The results are obtained through fitting formulas, and it is shown that cores with certain oil and water loss have the same translation correction amount.

8. The method for saturation correction based on oil-water loss equivalent according to claim 7, characterized in that: After translation correction, only the oil saturation value changes. This is based on the premise that the water saturation remains basically unchanged. The error caused by the change in water saturation is eliminated by the rotation correction. Since the sum of the oil and water phase fluids should meet 100%, the fitted line after translation correction is rotated to a 45° diagonal line with the "pure reservoir point" as the center. The oil and water saturations of the core analysis are then subjected to equal translation and then the rotation correction is added. That is, the original formation oil and water saturations are obtained through normalization processing: The correction formula is as follows: S oc =100-S wc Where S o is the oil saturation of core analysis (%); S w is the water saturation of core analysis (%); ΔS o is the translation correction amount (%); S oc is the corrected oil saturation (%); S wc is the corrected water saturation (%).

Images