Oil-water saturation correction method

Abstract

The invention belongs to the technical field of oil and gas field exploration and development, and discloses an oil-water saturation correction method. The method comprises the following steps: firstly, acquiring a rock core sample of a research area, performing a pressure pore permeability experiment on the rock core sample, and calculating an average compaction coefficient of the research area; then carrying out an oil-water saturation experiment on the core sample to obtain the oil-water saturation of the core sample measured by the experiment, and dotting the actually measured oil-water saturation value into the cross plot; and finally, comprehensively correcting the actually measured oil-water saturation based on the compaction coefficient of the research area and a projection correction method to obtain an underground actual oil-water saturation value. And the oil-water saturation interpretation precision is improved. The method is not limited to closed coring data, operation is easy, and the correction effect is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field exploration and development, and relates to an oil-water saturation correction method, and in particular to a new oil-water saturation correction method. Background Art

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

[0003] Conventional calculations of reservoir fluid saturation generally use Archie's formula or establish a multivariate regression model, and calibrate the model coefficients based on the core test results to obtain the saturation calculation model for the study area. However, when the core is taken out from underground and transported to the laboratory, the oil and water saturation measured in the laboratory is often less than the actual oil and water saturation value under underground pressure due to technical conditions and environmental changes. Therefore, when using core experimental data to calibrate the model coefficients, the oil and water saturation values ​​measured in the core experiment must first be corrected to the actual oil and water saturation values ​​under underground pressure. Nowadays, there are many methods to correct oil saturation, such as experimental simulation correction, mathematical method correction, etc. However, the above methods are all for closed coring data, and the experimental simulation correction process is complicated, and the mathematical method correction does not take into account changes in the formation environment. Summary of the invention

[0004] The measured oil and water saturation after coring in low-porosity and low-permeability reservoirs has different degrees of volatilization, which leads to large errors in the core test results and cannot accurately calibrate the saturation calculation model. Therefore, before establishing the saturation interpretation model, the measured oil and water saturation values ​​of the core should be corrected first. The main reasons for the errors in the measured oil and water saturation of the core are the influence of drilling fluid invasion, the influence of degassing due to cooling and pressure reduction, the influence of oil and water volatilization during core transportation and experiments, the influence of pore volume expansion due to pressure reduction, and the influence of pore volume expansion due to liquid nitrogen freezing. In order to overcome the problems and shortcomings of the above-mentioned prior art, the present invention provides a new method for oil and water saturation correction, which is an oil and water saturation correction method based on average formation compaction coefficient correction and projection method correction to improve the accuracy of oil and water saturation interpretation. And the present invention is not limited to closed coring data, is simple to operate, and has a good correction effect.

[0005] The above object of the present invention is achieved through the following technical solutions:

[0006] A method for correcting oil and water saturation, firstly obtaining core samples of a study area, and conducting an overburden porosity test on the core samples to calculate the average compaction coefficient of the study area; then conducting an oil and water saturation test on the core samples to obtain the oil and water saturation of the experimentally measured core samples, and adding the measured oil and water saturation values ​​to a cross-plot; finally, based on the compaction coefficient of the study area and a projection correction method, the measured oil and water saturation is comprehensively corrected to obtain the actual underground oil and water saturation value.

[0007] A method for correcting oil-water saturation, the specific steps are as follows:

[0008] 1) First, obtain core samples from the study area, conduct overburden pressure porosity test on the core samples, and calculate the average compaction coefficient of the study area;

[0009] 2) Then, an oil-water saturation experiment is performed on the core sample to obtain the experimentally measured oil-water saturation of the core sample, and the measured oil-water saturation value is plotted on the intersection diagram;

[0010] 3) Finally, the measured oil-water saturation is corrected based on the compaction coefficient of the study area and the projection correction method to obtain the actual underground oil-water saturation value.

[0011] Furthermore, the calculation formula of the average compaction coefficient in step 1) is shown in the following formula 1:

[0012]

[0013] Among them C _ave is the average compaction coefficient of the study area, φ i_s is the ground porosity of the i-th core sample in the overburden porosity experiment, φ i_u is the underground porosity of the i-th core sample in the overburden pressure porosity experiment, and n is the total number of core samples obtained in the study area.

[0014] The principle of the oil-water saturation correction method is as follows: when there is only oil-water two-phase flow in the formation, the relationship between the actual oil saturation and the actual water saturation is shown in the following formula 2:

[0015] So+Sw=100 Formula 2

[0016] Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage.

[0017] Under the condition of surface pressure, the pressure change will cause the change of pore volume, thus causing the change of saturation. Therefore, the oil saturation So' and the surface water saturation Sw' of the core taken out from underground can be expressed as shown in the following formula 3 and formula 4:

[0018]

[0019]

[0020] Therefore, the relationship between So' and Sw' can be expressed as follows:

[0021] So′+Sw′=100 / C_ are Formula 5

[0022] Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage. So' is the oil saturation of the core taken from underground to the surface, in percentage; Sw' is the surface water saturation. ave is the average compaction coefficient of the study area.

[0023] In formula 5, So' and Sw' fall on the intersection diagram with a slope of "-1" and an intercept of "100 / C_ ave ". For the oil saturation So_m and water saturation Sw_m in the experimental measurement, due to the volatilization of oil and water during transportation and the experiment, they will fall below the straight line in the intersection diagram. Therefore, for light oil, considering that both oil and water volatilize, the measured data points should be projected vertically onto the straight line to correct them to So' and Sw', so as to obtain So and Sw; for heavy oil, considering that the volatilization of oil is much smaller than that of water, the measured data points should be projected onto the straight line parallel to the water saturation axis to correct them to So' and Sw', so as to obtain So and Sw.

[0024] For light oil, the oil-water correction is as shown in Formula 6 below:

[0025] (So′-So_m) / (Sw′-Sw_m)=1 Formula 6

[0026] Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage. So_m is the oil saturation during experimental measurement; Sw_m is the water saturation during experimental measurement.

[0027] Combined with the above formula 6, the corrected So and Sw can be obtained as follows:

[0028] So=(100 / C_ ave -Sw_m+So-m) / 2*C_ ave Formula 7

[0029] Sw=(100 / C_ ave -So-m+Sw-m) / 2*C_ ave Formula 8

[0030] Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage. So_m is the oil saturation during experimental measurement; Sw_m is the water saturation during experimental measurement. ave is the average compaction coefficient of the study area.

[0031] The beneficial effects of the present invention compared with the prior art are:

[0032] Compared with the previous single projection method for oil saturation correction, the present invention takes into account the influence of formation pressure and uses formation compaction coefficient and projection correction method to correct oil saturation. The present invention is not limited to closed coring data, is simple to operate, and has good correction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0034] Figure 1 It is a flow chart of the main operation process of the present invention;

[0035] Figure 2 It is a crossplot of the oil-water saturation actually measured in the closed coring sample of the present invention and a crossplot of the oil-water saturation after correction;

[0036] Figure 3 It is a crossplot of the measured oil-water saturation of conventional coring samples and a corrected crossplot of the oil-water saturation of conventional coring samples of the present invention;

[0037] Figure 4 It is a comparison chart of the measured oil saturation of the closed coring sample and the corrected oil saturation of the sample according to the present invention;

[0038] Figure 5 It is a comparison chart of the measured oil saturation of the conventional coring sample of the present invention and the corrected oil saturation;

[0039] Figure 6 The invention relates to the comparison between the actually measured oil saturation and the resistivity curve of the core sample in the closed coring well and the comparison between the corrected oil saturation and the resistivity curve.

[0040] Figure 7 The invention provides a comparison between the actually measured oil saturation and the resistivity curve of the core sample in the conventional coring well and a comparison between the corrected oil saturation and the resistivity curve. DETAILED DESCRIPTION

[0041] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0042] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0043] Example 1

[0044] like Figure 1 As shown in the figure, a method for oil-water saturation correction is provided. First, core samples of the study area are obtained, and overburden porosity test is performed on the core samples to calculate the average compaction coefficient of the study area. Then, an oil-water saturation experiment is performed on the core samples to obtain the oil-water saturation of the experimentally measured core samples, and the measured oil-water saturation values ​​are added to the intersection diagram. Finally, the measured oil-water saturation is comprehensively corrected based on the compaction coefficient of the study area and the projection correction method to obtain the actual underground oil-water saturation value.

[0045] A method for correcting oil-water saturation, the specific steps are as follows:

[0046] 4) First, obtain core samples from the study area, conduct overburden pressure porosity test on the core samples, and calculate the average compaction coefficient of the study area;

[0047] 5) Then, an oil-water saturation experiment is performed on the core sample to obtain the experimentally measured oil-water saturation of the core sample, and the measured oil-water saturation value is plotted on the intersection diagram;

[0048] 6) Finally, based on the compaction coefficient of the study area and the projection correction method, the measured oil and water saturation is corrected to obtain the actual underground oil and water saturation value.

[0049] Furthermore, the calculation formula of the average compaction coefficient in step 1) is shown in the following formula 1:

[0050]

[0051] Among them C _ave is the average compaction coefficient of the study area, φ i_s is the ground porosity of the i-th core sample in the overburden porosity experiment, φ i_u is the underground porosity of the i-th core sample in the overburden pressure porosity experiment, and n is the total number of core samples obtained in the study area.

[0052] The principle of the oil-water saturation correction method is as follows: when there is only oil-water two-phase flow in the formation, the relationship between the actual oil saturation and the actual water saturation is shown in the following formula 2:

[0053] So+Sw=100 Formula 2

[0054] Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage.

[0055] Under the condition of surface pressure, the pressure change will cause the change of pore volume, thus causing the change of saturation. Therefore, the oil saturation So' and the surface water saturation Sw' of the core taken out from underground can be expressed as shown in the following formula 3 and formula 4:

[0056]

[0057]

[0058] Therefore, the relationship between So' and Sw' can be expressed as follows:

[0059] So′+Sw′=100 / C_ ave From formula 5

[0060] Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage. So' is the oil saturation of the core taken from underground to the surface, in percentage; Sw' is the surface water saturation. ave is the average compaction coefficient of the study area.

[0061] In formula 5, So' and Sw' fall on the intersection diagram with a slope of "-1" and an intercept of "100 / C_ ave ". For the oil saturation So_m and water saturation Sw_m in the experimental measurement, due to the volatilization of oil and water during transportation and the experiment, they will fall below the straight line in the intersection diagram. Therefore, for light oil, considering that both oil and water volatilize, the measured data points should be projected vertically onto the straight line to correct them to So' and Sw', so as to obtain So and Sw; for heavy oil, considering that the volatilization of oil is much smaller than that of water, the measured data points should be projected onto the straight line parallel to the water saturation axis to correct them to So' and Sw', so as to obtain So and Sw.

[0062] For light oil, the oil-water correction is as shown in Formula 6 below:

[0063] (So′-So_m) / (Sw′-Sw_m)=1 Formula 6

[0064] Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage. So_m is the oil saturation during experimental measurement; Sw_m is the water saturation during experimental measurement.

[0065] Combined with the above formula 6, the corrected So and Sw can be obtained as follows:

[0066] So=(100 / C_ ave -Sw-m+So-m) / 2*C_ ave Formula 7

[0067] Sw=(100 / C_ ave -So-m+Sw-m) / 2*C_ ave Formula 8

[0068] The measured oil-water saturation cross-plot of the sealed coring sample of the present invention and the corrected oil-water saturation cross-plot are shown in FIG. Figure 2 The closed core oil-water saturation (Sw_m, So_m) (circles) measured in the laboratory are corrected to obtain the actual oil-water saturation (Sw, So) (squares), and So+Sw=100.

[0069] The measured oil-water saturation crossplot of conventional coring samples and the corrected oil-water saturation crossplot of the present invention are shown in FIG. Figure 3 The conventional coring oil-water saturation (Sw_m, So_m) (triangle) measured in the laboratory is corrected to obtain the actual oil-water saturation (Sw, So) (diamond), and So+Sw=100.

[0070] The comparison diagram of the measured oil saturation of the sealed coring sample of the present invention and the corrected oil saturation is as follows: Figure 4 As shown in FIG. 1 , the comparison diagram of the measured oil saturation of the conventional coring sample and the corrected oil saturation of the conventional coring sample of the present invention is shown in FIG. Figure 5 shown. Figure 4 , Figure 5 It shows that the corrected oil saturation is significantly higher than the experimentally measured oil saturation, and the correction amount of closed coring is smaller than that of conventional coring.

[0071] The comparison between the measured oil saturation and resistivity curve of the core sample in the closed coring well of the present invention and the comparison between the corrected oil saturation and resistivity curve are shown in FIG. Figure 6 As shown in FIG. 1 , the comparison between the measured oil saturation and resistivity curve of the core sample in the conventional coring well of the present invention and the comparison between the corrected oil saturation and resistivity curve are shown in FIG. Figure 7 As shown. Figure 6 , Figure 7It can be seen that, whether it is closed coring or conventional coring, the oil saturation is improved after saturation correction by the method proposed in the present invention, and the corrected oil saturation is consistent with the empirical value of the region and is well consistent with the resistivity curve. This shows that the method proposed in the present invention is not limited to closed coring data, is simple to operate, and has a good correction effect.

[0072] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for correcting oil-water saturation, characterized in that first Core samples from the study area were obtained, and overburden porosity tests were carried out on the core samples to calculate the average compaction coefficient of the study area. Then, an oil-water saturation experiment was carried out on the core samples to obtain the experimentally measured oil-water saturation of the core samples, and the measured oil-water saturation values ​​were added to the intersection diagram. Finally, the measured oil-water saturation was comprehensively corrected based on the compaction coefficient of the study area and the projection correction method to obtain the actual underground oil-water saturation value.

2. The oil-water saturation correction method according to claim 1, characterized in that: The specific steps are as follows: 1) First, obtain core samples from the study area, conduct overburden pressure porosity test on the core samples, and calculate the average compaction coefficient of the study area; 2) Then, an oil-water saturation experiment is performed on the core sample to obtain the experimentally measured oil-water saturation of the core sample, and the measured oil-water saturation value is plotted on the intersection diagram; 3) Finally, based on the compaction coefficient of the study area and the projection correction method, the measured oil and water saturation is corrected to obtain the actual underground oil and water saturation value.

3. The oil-water saturation correction method according to claim 2, characterized in that the step 1) The calculation formula of the average compaction coefficient is shown in the following formula 1: Among them C _ave is the average compaction coefficient of the study area, φ i_s is the ground porosity of the i-th core sample in the overburden porosity experiment, φ i_u is the underground porosity of the i-th core sample in the overburden pressure porosity experiment, and n is the total number of core samples obtained in the study area.

4. The oil-water saturation correction method according to claim 3, characterized in that the oil-water The principle of the saturation correction method is as follows: when there is only oil-water two-phase flow in the formation, the relationship between the actual oil saturation and the actual water saturation is shown in the following formula 2: So+Sw=100 Formula 2 Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage.

5. The oil-water saturation correction method according to claim 4, characterized in that: Under the condition of surface pressure, the pressure change will cause the change of pore volume, thus causing the change of saturation. Therefore, the oil saturation So' and the surface water saturation Sw' of the core taken out from underground can be expressed as shown in the following formula 3 and formula 4: Therefore, the relationship between So' and Sw' can be expressed as follows: So′+Sw′=100 / C _ave Formula 5 Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage; So' is the oil saturation of the core taken out from underground to the surface, in percentage; Sw' is the ground water saturation; C _ave is the average compaction coefficient of the study area.

6. The oil-water saturation correction method according to claim 5, characterized in that the formula In 5, So' and Sw' fall on the intersection plot with a slope of "-1" and an intercept of "100 / C _ave "; for the oil saturation So_m and water saturation Sw_m in the experimental measurement, due to the volatilization of oil and water during transportation and the experiment, they will fall below the straight line in the intersection diagram; for light oil, considering that both oil and water volatilize, the measured data points should be projected vertically onto the straight line to be corrected to So' and Sw', so as to obtain So and Sw; for heavy oil, considering that the volatilization of oil is much smaller than that of water, the measured data points should be projected parallel to the water saturation axis onto the straight line to be corrected to So' and Sw', so as to obtain So and Sw.

7. The oil-water saturation correction method according to claim 6, characterized in that: For light oil, the oil-water correction is as shown in Formula 6 below: So′So_m) / (Sw′-Sw_m)=1 Formula 6 Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage; So_m is the oil saturation during experimental measurement; Sw_m is the water saturation during experimental measurement.

8. The oil-water saturation correction method according to claim 7, characterized in that: Combined with formula 6, the corrected So and Sw can be obtained as follows: So=(100 / C _ave -Sw_m+So_m) / 2*C _ave Formula 7 Sw=(100 / c _ave -SO_m+Sw_m) / 2*C _ave Formula 8 Where So is the actual oil saturation, in percentage; Sw is the actual water saturation, in percentage; So_m is the oil saturation during experimental measurement; Sw_m is the water saturation during experimental measurement; C _ave is the average compaction coefficient of the study area.

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