A method for identifying pore types of dolomite gas layers

Abstract

The present invention relates to a method for identifying the pore type of a dolomite gas layer, and belongs to the technical field of oil and gas exploration and development. The method comprises the following steps: 1) obtaining the lithology density, compensated neutron and acoustic time difference curves of the well section to be identified in a single well, and performing standardization processing; 2) setting fixed scale intervals for the standardized curves, placing the standardized lithology density curve and the compensated neutron curve on the same curve track, and placing the standardized lithology density curve and the acoustic time difference curve on the same curve track; 3) when the standardized lithology density curve is on the left side of the standardized compensated neutron curve, and the standardized lithology density curve is on the left side of the standardized acoustic time difference curve, it is determined that the gas layer section is a reservoir section dominated by intragranular dissolved pores. The present invention can relatively accurately and reliably identify the reservoir section dominated by intragranular dissolved pores in the dolomite gas layer by comprehensively analyzing the above two positional relationships.

Description

Technical Field

[0001] The invention relates to a method for identifying pore types of dolomite gas layers, belonging to the technical field of oil and gas exploration and development. Background Art

[0002] The pore type of reservoir rock directly affects the storage and seepage characteristics of the rock. The pore types of carbonate oil and gas reservoirs are often complex and diverse, mainly including intercrystalline pores, intergranular pores, intragranular pores, dissolution pores, fractures and other types. Most reservoirs are dominated by secondary pores formed during the transformation process in the diagenetic and surface stages after deposition. Due to the great differences in secondary transformation effects, the secondary pore structure of carbonate reservoirs is more complex than that of clastic reservoirs. Therefore, studying the pore types of carbonate reservoir rocks can lay the foundation for studying the porosity and permeability of carbonate reservoirs.

[0003] There are many carbonate gas reservoirs in the Sichuan Basin of China, and dolomite reservoirs are the most common type of carbonate gas reservoirs. These dolomite gas layers are formed under the joint control of sedimentation, diagenesis and tectonic action, resulting in the existence of various types of pores in the dolomite gas layers, such as intercrystalline solution pores, intergranular solution pores, intragranular solution pores, matrix pores, etc., which leads to an extremely complex relationship between the porosity and permeability of the reservoir. Previous studies have also done a lot of research on dolomite gas layers with different pore types. These studies have shown that the matrix pores, intercrystalline solution pores or intergranular solution pores are the main gas layers. The porosity and permeability of reservoirs mostly show a similar positive correlation, that is, high porosity corresponds to relatively high permeability, and low porosity corresponds to relatively low permeability. However, due to the difference in the degree of dissolution, there are multiple relationships between the porosity and permeability of reservoirs dominated by intragranular dissolved pores. There may be multiple possibilities such as high porosity corresponding to relatively high permeability and high porosity corresponding to relatively low permeability. Therefore, it is necessary to use logging technology to identify reservoirs dominated by intragranular dissolved pores in the study of dolomite gas layers, laying a foundation for the permeability research and fine classification of dolomite gas layers.

[0004] Previous researchers have also conducted some research on using logging data to identify intragranular dissolved pores in dolomite gas layers as the main reservoir, mainly including the following three identification methods:

[0005] The first method is to use the ratio of acoustic time difference and density. For example, the article "Well Logging Identification of Pore Types and Porosity-Permeability Relationship of Carbonate Reservoirs in Puguang Area" in the journal "Well Logging Technology" with the journal number of 2016 Volume 41, Issue 12 discloses a method of identifying pore types using the ratio of acoustic time difference and density. This method is based on the characteristics that the acoustic time difference is larger and the lithology density is smaller in reservoirs dominated by intragranular dissolved pores than in reservoirs dominated by intergranular dissolved pores. The ratio of acoustic time difference and density is used to identify reservoirs dominated by intragranular dissolved pores. In actual applications, based on the propagation mechanism of sound waves in rocks, reservoirs with relatively low dissolution degree dominated by intergranular dissolved pores also show the characteristics of low acoustic time difference, and large-pore reservoirs dominated by intergranular dissolved pores also have the characteristics of low density. The ratio of acoustic time difference and density has certain uncertainty in reservoirs of various pore types, resulting in misjudgment when using this method to identify reservoirs dominated by intragranular dissolved pores in dolomite gas layers;

[0006] The second method is to use the ratio of deep and shallow lateral resistivity. For example, the journal "Well Logging Technology", the journal number is 2016 Volume 41 Issue 12, and the article titled "Well Logging Identification of Pore Types and Porosity-Permeability Relationship of Carbonate Reservoirs in Puguang Area" discloses a method of identifying pore types using the ratio of deep and shallow lateral resistivities. This method is based on the fact that the permeability of reservoirs dominated by intragranular dissolved pores is relatively poor, and they have the characteristics of high porosity and low permeability. It proposes a method of identifying reservoirs dominated by intragranular dissolved pores using the difference in the ratio of deep and shallow lateral resistivities. In actual applications, core sampling analysis data found that the porosity-permeability relationship of reservoirs dominated by intragranular dissolved pores is complex. There are not only sample points with high porosity and low permeability, but also sample points with high porosity and high permeability. In addition, the deep and shallow lateral resistivities often have large differences in the permeability of dolomite gas layers. The deep and shallow lateral resistivities have a certain relationship with the gas saturation of the gas reservoir, the mud ratio during drilling, etc., which leads to misjudgment when using this method to identify reservoirs dominated by intragranular dissolved pores in dolomite gas layers.

[0007] The third method is to use the ratio of the acoustic wave time difference and the density amplitude. For example, an article entitled “Study on the Lower Limit Standard of Gas Layers in Reef-Shoal Carbonate Gas Reservoirs” in the journal “Block Oil and Gas Fields”, with the journal number of 2010 Volume 17, Issue 5, and an article entitled “Characterization Method of Reef-Shoal Reservoirs in Puguang Gas Field” in the journal “Natural Gas Industry”, with the journal number of 2011 Volume 31, Issue 3, both disclose a method of identifying pore types by using the ratio of acoustic wave transit time and density amplitude. The proposed method has a similar mechanism to the first method mentioned above. By using the difference in the frequency distribution histogram of the density and acoustic wave transit time amplitude ratio of reservoirs with different pore types, it is determined that gas layers with a density and acoustic wave transit time amplitude ratio greater than 1.42 are identified as reservoirs dominated by intragranular dissolved pores. It can be seen from the frequency distribution histogram of the density and acoustic wave transit time amplitude ratio of reservoirs with different pore types that the density and acoustic wave transit time amplitude ratio of reservoirs dominated by intergranular dissolved pores and reservoirs dominated by intragranular dissolved pores are seriously overlapped, resulting in misjudgment when using this method to identify reservoirs dominated by intragranular dissolved pores in dolomite gas layers in actual use.

[0008] It can be seen that in the process of using existing logging methods to identify the pore types of dolomite gas layers, there are defects such as poor certainty, artificial qualitative identification, and easy misjudgment. It is difficult to accurately identify the intragranular dissolved pores in the dolomite gas layer as the main reservoir, which brings obstacles to the accurate characterization and precise classification of the permeability of the gas layer, affecting the rational and efficient development of the gas reservoir. Summary of the invention

[0009] The purpose of the present invention is to provide a method for identifying the pore type of dolomite gas layer, so as to solve the problem of low accuracy of the existing pore type identification methods.

[0010] To achieve the above object, the present invention proposes a method for identifying the pore type of dolomite gas layer, comprising the following steps:

[0011] 1) Obtaining the lithology density, compensated neutron and acoustic wave time difference curves of the well section to be identified in a single well, and performing standardization processing on the lithology density, compensated neutron and acoustic wave time difference curves of the well section to be identified in a single well;

[0012] 2) Set fixed scale intervals for the standardized lithology density, the standardized compensated neutron, and the standardized acoustic time difference curves, respectively, put the standardized lithology density curve and the standardized compensated neutron curve on the same curve track, and put the standardized lithology density curve and the standardized acoustic time difference curve on the same curve track;

[0013] 3) Comprehensively compare the positional relationship between the standardized lithology density curve and the standardized compensated neutron curve in a gas layer section, as well as the positional relationship between the standardized lithology density curve and the standardized acoustic wave time difference curve, and determine that the gas layer section is a reservoir section dominated by intragranular dissolved pores when the set conditions are met;

[0014] The setting condition is that the lithology density curve after the standardization process is on the left side of the compensated neutron curve after the standardization process, and the lithology density curve after the standardization process is on the left side of the acoustic time difference curve after the standardization process.

[0015] The beneficial effect is that the present invention identifies the intragranular dissolved pores in the dolomite gas layer as the main reservoir section by comprehensively analyzing the positional relationship between the standardized lithology density and the standardized compensated neutron curve in the target single well to be identified, as well as the positional relationship between the standardized lithology density and the standardized acoustic wave time difference curve in the gas layer section. The method for identifying the pore type of the dolomite gas layer can relatively accurately and reliably use conventional logging data to identify the intragranular dissolved pores in the dolomite gas layer as the main reservoir section, laying a foundation for accurate characterization and precise classification of the permeability of the gas layer, thereby supporting the rational and efficient development of the gas reservoir.

[0016] Furthermore, the cross plot method or the frequency histogram method is used to standardize the lithology density, compensated neutron and sonic time difference curves.

[0017] Further, the steps of standardizing the lithology density, compensated neutron and acoustic time difference curves by using the cross plot method include:

[0018] A. Comprehensively utilize the logging lithology description and the logging response characteristics of each logging curve to determine the pure anhydrite rock section or pure tight limestone section of a single well;

[0019] B. Make any two cross-plots of the compensated neutron and lithology density, the compensated neutron and acoustic wave time difference, and the lithology density and acoustic wave time difference in the pure anhydrite rock section or the pure tight limestone section;

[0020] C. Determine the standardized correction amount corresponding to the lithology density, compensated neutron and acoustic time difference curves by moving the sample point position of the pure anhydrite rock section or the pure dense limestone section in the intersection diagram to the corresponding pure anhydrite rock or pure dense limestone theoretical skeleton point;

[0021] D. Use the lithology density, compensated neutron and acoustic time difference curves and add the corresponding standardized correction amount to obtain the standardized lithology density curve, the standardized compensated neutron curve and the standardized acoustic time difference curve.

[0022] Further, the steps of standardizing the lithology density, compensated neutron and acoustic time difference curves by using the frequency histogram method include:

[0023] a. Comprehensively utilize the logging lithology description and the logging response characteristics of each logging curve to determine the pure anhydrite rock section or pure dense limestone section of a single well;

[0024] b. Make the frequency histogram of lithology density, compensated neutron and acoustic wave time difference in pure anhydrite rock section or pure dense limestone section respectively;

[0025] c. Determine the standardized correction amount corresponding to the lithology density, compensated neutron and acoustic time difference curve by moving the peak of each frequency histogram of the pure anhydrite rock section or the pure dense limestone section to the corresponding theoretical skeleton point of the pure anhydrite rock or the pure dense limestone;

[0026] d. Using the lithology density, compensated neutron and acoustic time difference curves and adding the corresponding standardized correction amount, a standardized lithology density curve, a standardized compensated neutron curve and a standardized acoustic time difference curve are obtained.

[0027] Furthermore, the fixed scale interval set for the standardized lithology density curve is 2.2-3.05 g / cm 3 The fixed scale interval set for the standardized compensated neutron curve is 30 to -20P.U, and the fixed scale interval set for the standardized acoustic time difference curve is 90 to 20μs / ft.

[0028] Furthermore, the gas layer section in the well section to be identified in the single well is the gas layer section in the well section to be identified in the single well interpreted by conventional logging data of the target single well. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of the method for identifying pore types of dolomite gas layers of the present invention;

[0030] Figure 2 The cross-plot of compensated neutron and lithology density of the pure anhydrite rock section and the dense limestone section of the A well of the P gas field before normalization in the method for identifying the pore type of the dolomite gas layer of Example 1 of the present invention;

[0031] Figure 3 The cross-plot of compensated neutron and acoustic time differences of the pure anhydrite rock section and the dense limestone section of the A well of the P gas field before normalization in the method for identifying the pore type of the dolomite gas layer in Example 1 of the present invention;

[0032] Figure 4 The cross-plot of compensated neutron and lithology density of the normalized curves of the pure anhydrite rock section and the dense limestone section of the A well of the P gas field in Example 1 of the method for identifying the pore type of the dolomite gas layer of the present invention;

[0033] Figure 5 The conventional logging combination result and the result diagram of the identification of the gas layer segment dominated by intragranular dissolved pores of the A well of the P gas field in Example 1 of the method for identifying the pore type of the dolomite gas layer of the present invention are shown;

[0034] Figure 6This is a cast thin section image of a core analysis at a depth of 5592.1 m in Well A of the P gas field in Example 1 of the method for identifying pore types of dolomite gas layers of the present invention;

[0035] Figure 7 This is a cast thin section image of a core analysis at a depth of 5601 m in Well A of the P gas field in Example 1 of the method for identifying pore types of dolomite gas layers of the present invention;

[0036] Figure 8 The cross-plot of compensated neutron and lithology density of the pure anhydrite rock section and the dense limestone section of the B well of the P gas field before normalization in the method for identifying the pore type of the dolomite gas layer of Example 2 of the present invention;

[0037] Fig. 9 The cross-plot of compensated neutron and acoustic time differences of the pure anhydrite rock section and the dense limestone section of the B well of the P gas field before normalization in the method for identifying the pore type of the dolomite gas layer in Example 2 of the present invention;

[0038] Fig.10 The cross-plot of compensated neutron and lithology density of the normalized curves of the pure anhydrite rock section and the dense limestone section of the B well of the P gas field in Example 2 of the method for identifying the pore type of the dolomite gas layer of the present invention;

[0039] Fig.11 The conventional logging combination result and the result diagram of the identification of the gas layer segment dominated by intragranular dissolved pores of the B well of the P gas field in Example 2 of the method for identifying the pore type of the dolomite gas layer of the present invention are shown;

[0040] Fig.12 This is a cast thin section image of a core analysis at a depth of 5362.8 m in Well B of the P gas field in Example 2 of the method for identifying pore types of dolomite gas layers of the present invention;

[0041] Fig.13 This is a cast thin section image of a core analysis at a depth of 5380.5 m in Well B of the P gas field in Example 2 of the method for identifying the pore type of dolomite gas layers of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below in conjunction with the dolomite reservoir of China's P gas field. Well A and Well B of the P gas field are oolitic beach phase reservoirs at the edge of the platform. The main lithology of the reservoir is dolomite. A large amount of core analysis data show that the pore types of the dolomite gas layer mainly include three types: intergranular solution pores as the main reservoir, intragranular solution pores as the main reservoir, and matrix pores as the main reservoir.

[0043] Example 1 of identification method of pore type of dolomite gas layer:

[0044] This embodiment takes Well A of the P gas field as an example to introduce a method for identifying the pore type of a dolomite gas layer, including the following steps: Figure 1As shown:

[0045] 1) The cross plot method is used to standardize the lithology density, compensated neutron, and acoustic time difference curves of the well section to be identified in a single well, and the standardized lithology density curve, the standardized compensated neutron curve, and the standardized acoustic time difference curve are obtained.

[0046] In carbonate oil and gas reservoirs, the crossplot method is the most commonly used method for standardization of logging lithology density, compensated neutron, and acoustic time difference curves. Its principle is based on the difference between the logging sample point value and the theoretical skeleton value of the lithology density, compensated neutron, and acoustic time difference curves in pure anhydrite rock sections or pure tight limestone sections as the standardized correction amount of each curve, and then the lithology density curve, compensated neutron curve, and acoustic time difference curve are added with the corresponding standardized correction amount to obtain the standardized lithology density curve, the standardized compensated neutron curve, and the standardized acoustic time difference curve;

[0047] In the pure anhydrite section or pure tight limestone section, any two cross-plots of the cross-plot of compensated neutron and lithology density, the cross-plot of compensated neutron and acoustic wave time difference, and the cross-plot of lithology density and acoustic wave time difference are made. For example, the cross-plot of the normalized curves of the pure anhydrite section and the pure tight limestone section of Well A in the P gas field is as follows: Figure 2 and Figure 3 As shown, from Figure 2 and Figure 3 It can be seen that there are differences between the lithologic density and theoretical skeleton values ​​of the pure anhydrite rock section and the pure dense limestone section of Well A, while the compensated neutron and acoustic wave time difference of the pure anhydrite rock section and the pure dense limestone section are consistent with the theoretical skeleton values. By moving the sample positions of the pure anhydrite rock section and the pure dense limestone section in the lithologic density and compensated neutron intersection diagram to the position of the theoretical skeleton point, the standardized correction amount of the lithologic density curve is determined to be -0.02 g / cm 3 The standardized correction values ​​of the compensated neutron and acoustic time difference curves are 0P.U and 0μs / ft respectively. By adding the logging values ​​of the lithology density, compensated neutron and acoustic time difference curves to the standardized correction values ​​of the above curves, we can get the standardized lithology density curve, the standardized compensated neutron curve and the standardized acoustic time difference curve.

[0048] The cross-plot of the normalized compensated neutron and lithology density of the pure anhydrite section and the pure tight limestone section of Well A in the P gas field is shown in the figure. Figure 4As shown in the figure, it can be seen that the logging sample points of the lithology density and compensated neutron intersection diagram of the pure anhydrite rock section and the pure tight limestone section after standardization fall on the theoretical skeleton point positions. Since the standardized correction amounts of the compensated neutron and acoustic time difference curves are 0P.U and 0μs / ft respectively, the compensated neutron curve logging value is equal to the standardized compensated neutron curve logging value, and the acoustic time difference curve logging value is equal to the standardized acoustic time difference curve logging value.

[0049] The conventional logging combination results of Well A in P gas field and the identification results of the gas layer dominated by intragranular dissolved pores are shown in the figure below. Figure 5 As shown, Figure 5 The solid line in the fourth track is the lithology density curve, and the dotted line in the fourth track is the standardized lithology density curve.

[0050] 2) In the section to be identified in a single well, fixed scale intervals are set for the standardized lithology density, the standardized compensated neutron, and the standardized acoustic time difference curve, respectively, and the standardized lithology density and the standardized compensated neutron curve are further placed on the same curve track, and the standardized lithology density and the standardized acoustic time difference curve are placed on the same curve track.

[0051] In dolomite gas layers, reservoirs of various pore types all exhibit logging response characteristics of lower lithologic density, higher acoustic time difference, and higher compensated neutrons, and there is no uniform dividing line for the values ​​of lithologic density, acoustic time difference, and compensated neutron logging curves. However, through the calibration of the pore types of core analysis on the logging curves, it is found that the total porosity of reservoirs dominated by intragranular dissolved pores is mostly larger than that of reservoirs dominated by intergranular dissolved pores or reservoirs dominated by matrix pores. Because lithologic density is the only logging curve that can accurately reflect the total porosity of the reservoir in dolomite gas layers, reservoirs dominated by intragranular dissolved pores mostly have lower lithologic density values ​​than those dominated by intergranular dissolved pores or reservoirs dominated by matrix pores.

[0052] Acoustic waves have the characteristic of selective propagation, that is, they always propagate along the skeleton of rock particles. The propagation path of acoustic waves in reservoir rocks dominated by intragranular dissolved pores is more tortuous and complex than that in reservoir rocks dominated by intergranular dissolved pores or matrix pores. In reservoirs dominated by intergranular dissolved pores or matrix pores, the acoustic time difference reflects the size of the reservoir matrix porosity. The smaller the acoustic time difference, the stronger the reservoir dissolution and transformation effect. In reservoirs dominated by intragranular dissolved pores, the acoustic time difference reflects the size of the reservoir framework rock porosity. The larger the acoustic time difference, the stronger the reservoir dissolution and transformation effect. Therefore, it is difficult to distinguish between reservoirs dominated by intergranular dissolved pores or matrix pores and reservoirs dominated by intragranular dissolved pores only by relying on the acoustic time difference.

[0053] The compensatory neutrons in dolomite gas layers often show a decreasing trend due to the mining effect. In reservoirs dominated by intragranular dissolved pores, due to the gas-saturated characteristics of the intragranular dissolved pores, the compensatory neutron mining effect is more significant than that of reservoirs dominated by intergranular dissolved pores or reservoirs dominated by matrix pores, and the decreasing trend of the compensatory neutrons is also more obvious. However, the existing technology does not have a means to measure this trend. It is also difficult to distinguish between reservoirs dominated by intergranular dissolved pores or reservoirs dominated by matrix pores and reservoirs dominated by intragranular dissolved pores only by relying on the compensatory neutrons.

[0054] Based on the logging response characteristics of the above-mentioned lithology density, acoustic time difference, and compensated neutron curves, although it is difficult to identify the reservoir dominated by intragranular dissolved pores using only one curve, the comprehensive use of the logging response characteristics of lithology density, acoustic time difference, and compensated neutron, and the calibration of the pore type of core analysis on the logging curve found that when the fixed scale interval of the standardized lithology density curve in step 1 is set to 2.2-3.05 g / cm 3 , when the fixed scale interval of the standardized compensated neutron curve is set to 30~-20P.U, and the fixed scale interval of the standardized acoustic time difference curve is set to 90~20μs / ft, in the intersection of the standardized lithology density and the standardized compensated neutron curve, and in the intersection of the standardized lithology density and the standardized acoustic time difference curve, the sample points of the reservoir dominated by intergranular dissolved pores or matrix-dominated reservoirs and the reservoir dominated by intragranular dissolved pores are differentiated. Specifically, the sample points of the reservoir dominated by intragranular dissolved pores fall at the position that satisfies the following two conditions at the same time: Condition 1 is that the standardized lithology density curve is on the left side of the standardized compensated neutron curve, and Condition 2 is that the standardized lithology density curve is on the left side of the standardized acoustic time difference curve;

[0055] In the section 5564-5612 m to be identified in Well A, the fixed scale interval of the standardized lithology density curve is set to 2.2-3.05 g / cm 3 The fixed scale interval of the compensated neutron curve is 30~-20P.U, and the fixed scale interval of the acoustic time difference curve is 90~20μs / ft. The standardized lithology density and the compensated neutron curve are placed in the same channel. The standardized lithology density and the compensated neutron curve are placed in the same channel. Figure 5 The solid lines in the fifth and sixth tracks are the standardized lithology density curves drawn according to the above-mentioned fixed scale interval, the dotted line in the fifth track is the compensated neutron curve drawn according to the above-mentioned fixed scale interval, and the dotted line in the sixth track is the sonic time difference curve drawn according to the above-mentioned fixed scale interval.

[0056] 3) In the section to be identified in a single well, the positional relationship between the standardized lithology density and the standardized compensated neutron curve in the gas layer section, and the positional relationship between the standardized lithology density and the standardized acoustic time difference curve in the gas layer section are comprehensively compared. When the standardized lithology density curve is on the left side of the standardized compensated neutron curve, and the standardized lithology density curve is on the left side of the standardized acoustic time difference curve, the section in the gas layer section that meets the above conditions is determined to be a reservoir section dominated by intragranular dissolved pores.

[0057] The gas layer section in the well section to be identified in the single well is the gas layer section in the well section to be identified in the single well interpreted by the conventional logging data of the target single well. In this embodiment, the well section 5564-5612m to be identified in Well A is identified. In the dolomite gas layer sections 18-21, by comparing Figure 5 The positional relationship between the two curves in the fifth and sixth tracks is that when the standardized lithology density curve in the fifth track is on the left side of the compensated neutron curve, and the standardized lithology density curve in the sixth track is on the left side of the acoustic time difference curve, the section in the gas layer that meets the above conditions is determined to be a reservoir section dominated by intragranular dissolved pores. Figure 5 The eighth track is the reservoir section dominated by intragranular solution pores and the reservoir section dominated by non-intragranular solution pores identified and screened out using the method of the present invention.

[0058] The present invention is Figure 5 The results of the reservoir section dominated by intragranular dissolved pores selected from the above analysis were verified. Figure 5 The intragranular dissolved pores selected from the reservoir are mainly selected for core sampling and core analysis to determine whether they are mainly intragranular dissolved pores. Figure 6 The figure shows a cast thin section of the core analysis at a depth of 5592.1 m in Well A of the P gas field. From this figure, it can be judged that it belongs to residual oolite dolomite with intergranular dissolved pores as the main feature. Figure 7 The figure shows a cast thin section of the core analysis at a depth of 5601m in Well A of the P gas field. From this figure, it can be judged that it belongs to residual oolitic dolomite with intragranular dissolved pores as the main component. Comparative analysis shows that the gas layer segments of various pore types identified by the method of the present invention using conventional logging data are consistent with the description of the gas layer pore types of core analysis, proving that the identification method of the dolomite gas layer pore type is feasible and effective, and can provide technical support for the accurate characterization and precise classification of the permeability of the gas layer, thereby realizing the rational and efficient development of the target gas reservoir.

[0059] In order to facilitate the comparison of the positional relationship between the two standardized curves, this embodiment sets fixed scale intervals for the standardized lithology density, the standardized compensated neutron, and the standardized acoustic wave time difference curves. As other implementation methods, the values ​​of the scale intervals can be changed according to actual conditions.

[0060] Example 2 of the method for identifying the pore type of dolomite gas layer:

[0061] This embodiment takes Well B of the P gas field as an example to introduce a method for identifying the pore type of a dolomite gas layer. The specific implementation steps of the method for identifying the pore type of a dolomite gas layer adopted in this embodiment are the same as those in Embodiment 1.

[0062] The compensated neutron and lithology density cross-plot of the pure anhydrite rock section and the pure tight limestone section of Well B in P gas field before normalization is shown in the figure below. Figure 8 As shown in the figure, the compensated neutron and acoustic time difference cross-plot of the pure anhydrite rock section and the pure tight limestone section of Well B in the P gas field before standardization is as follows: Fig. 9 As shown. Figure 8 and Fig. 9 It can be seen that there are differences between the lithology density and theoretical skeleton values ​​of the pure anhydrite rock section and the pure tight limestone section of Well B, while the compensated neutron and acoustic wave time difference of the pure anhydrite rock section and the pure tight limestone section are consistent with the theoretical skeleton values. By moving the sample points of the pure anhydrite rock section and the pure tight limestone section in the lithology density and compensated neutron intersection diagram to the position of the theoretical skeleton point, the standardized correction amount of the lithology density curve is determined to be -0.04g / cm 3 The standardized correction values ​​of the compensated neutron and acoustic time difference curves are 0P.U and 0μs / ft respectively. By adding the logging values ​​of the lithology density, compensated neutron and acoustic time difference curves to the standardized correction values ​​of the above curves, we can get the standardized lithology density curve, the standardized compensated neutron curve and the standardized acoustic time difference curve.

[0063] The cross-plot of normalized compensated neutron and lithology density of pure anhydrite section and pure tight limestone section of Well B is shown in the figure. Fig.10 As shown in the figure, it can be seen that the logging sample points of the lithology density and compensated neutron intersection diagram of the pure anhydrite rock section and the pure tight limestone section after standardization fall on the theoretical skeleton point positions, realizing the standardized processing of the lithology density, and the compensated neutron curve logging value is equal to the standardized compensated neutron curve logging value, and the sonic time difference curve logging value is equal to the standardized sonic time difference curve logging value.

[0064] In the section 5348-5431 m to be identified in Well B, the fixed scale interval of the standardized lithology density curve is set to 2.2-3.05 g / cm 3 The fixed scale interval of the compensated neutron curve is set to 30~-20P.U, the fixed scale interval of the acoustic time difference curve is set to 90~20μs / ft, and the standardized lithology density and the compensated neutron curve are placed in the same channel. The standardized lithology density and the compensated neutron curve are placed in the same channel. Fig.11The solid lines in the fifth and sixth tracks are the standardized lithology density curves drawn according to the above-mentioned fixed scale interval, the dotted line in the fifth track is the compensated neutron curve drawn according to the above-mentioned fixed scale interval, and the dotted line in the sixth track is the sonic time difference curve drawn according to the above-mentioned fixed scale interval.

[0065] The unidentified section 5348-5431m of Well B was identified. In the dolomite gas layer sections 76-79, by comparing Fig.11 The positional relationship between the two curves in the fifth and sixth tracks is that when the standardized lithology density curve in the fifth track is on the left side of the compensated neutron curve, and the standardized lithology density curve in the sixth track is on the left side of the acoustic time difference curve, the section in the gas layer that meets the above conditions is determined to be a reservoir section dominated by intragranular dissolved pores. Fig.11 The eighth track is the reservoir section dominated by intragranular solution pores and the reservoir section dominated by non-intragranular solution pores identified and screened out using the method of the present invention.

[0066] The present invention is Fig.11 The results of the reservoir section dominated by intragranular dissolved pores selected from the above analysis were verified. Fig.11 The intragranular dissolved pores selected from the reservoir are mainly selected for core sampling and core analysis to determine whether they are mainly intragranular dissolved pores. Fig.12 The figure shows a thin-section image of the core analyzed at a depth of 5362.8 m in Well B of the P gas field. From this image, it can be judged that it is residual oolite dolomite with intergranular dissolved pores as the main component. Fig.13 The figure shows a thin-section image of the core analysis at a depth of 5380.5m in Well B of the P gas field. From this figure, it can be judged that it belongs to residual oolitic dolomite with intragranular dissolved pores as the main components. Comparative analysis shows that the gas layer sections of various pore types identified by the method of the present invention using conventional logging data are consistent with the description of the gas layer pore types of the core analysis, which once again proves that the identification method of the dolomite gas layer pore type is feasible and effective.

[0067] Example 3 of the method for identifying the pore type of dolomite gas layer

[0068] The difference between this embodiment and Embodiment 1 and Embodiment 2 is that this embodiment specifically utilizes the frequency histogram method to perform standardization processing on the lithology density, compensated neutron and acoustic wave time difference curves.

[0069] In carbonate oil and gas reservoirs, the frequency histogram method is also the most commonly used method in the standardization of logging lithology density, compensated neutron, and acoustic time difference curves. Its principle is also based on the difference between the logging sample point value and the theoretical skeleton value of the lithology density, compensated neutron, and acoustic time difference curves in the pure anhydrite rock section or pure tight limestone section as the standardized correction amount of each curve, and then the lithology density, compensated neutron, and acoustic time difference curves are added with the corresponding standardized correction amount to obtain the standardized lithology density curve, the standardized compensated neutron curve, and the standardized acoustic time difference curve;

[0070] The process of standardizing the lithology density, compensated neutron and acoustic time difference curves using the frequency histogram method is as follows:

[0071] a. Comprehensively utilize the logging lithology description and the logging response characteristics of each logging curve to determine the pure anhydrite rock section or pure dense limestone section of a single well;

[0072] b. Make the frequency histogram of lithology density, compensated neutron and acoustic wave time difference in pure anhydrite rock section or pure dense limestone section respectively;

[0073] c. Determine the standardized correction amount corresponding to the lithology density, compensated neutron and acoustic time difference curve by moving the peak of each frequency histogram of the pure anhydrite rock section or the pure dense limestone section to the corresponding theoretical skeleton point of the pure anhydrite rock or the pure dense limestone;

[0074] d. Using the lithology density, compensated neutron and acoustic time difference curves and adding the corresponding standardized correction amount, a standardized lithology density curve, a standardized compensated neutron curve and a standardized acoustic time difference curve are obtained.

Claims

1. A method for identifying pore types of dolomite gas layers, characterized in that: The following steps are involved: 1) Obtaining the lithology density, compensated neutron and acoustic wave time difference curves of the well section to be identified in a single well, and performing standardization processing on the lithology density, compensated neutron and acoustic wave time difference curves of the well section to be identified in a single well; 2) Set fixed scale intervals for the standardized lithology density, the standardized compensated neutron, and the standardized acoustic time difference curves, respectively, put the standardized lithology density curve and the standardized compensated neutron curve on the same curve track, and put the standardized lithology density curve and the standardized acoustic time difference curve on the same curve track; 3) Comprehensively compare the positional relationship between the standardized lithology density curve and the standardized compensated neutron curve in a gas layer section, as well as the positional relationship between the standardized lithology density curve and the standardized acoustic wave time difference curve, and determine that the gas layer section is a reservoir section dominated by intragranular dissolved pores when the set conditions are met; The setting condition is that the lithology density curve after the standardization process is on the left side of the compensated neutron curve after the standardization process, and the lithology density curve after the standardization process is on the left side of the acoustic time difference curve after the standardization process.

2. The method for identifying pore types of dolomite gas layers according to claim 1, characterized in that: The lithology density, compensated neutron and sonic time difference curves are standardized using the cross plot method or frequency histogram method.

3. The method for identifying pore types of dolomite gas layers according to claim 2, characterized in that: The steps of standardizing the lithology density, compensated neutron and sonic time difference curves using the cross plot method include: A. Comprehensively utilize the logging lithology description and the logging response characteristics of each logging curve to determine the pure anhydrite rock section or pure tight limestone section of a single well; B. Make any two cross-plots of the compensated neutron and lithology density, the compensated neutron and acoustic wave time difference, and the lithology density and acoustic wave time difference in the pure anhydrite rock section or the pure tight limestone section; C. Determine the standardized correction amount corresponding to the lithology density, compensated neutron and acoustic time difference curves by moving the sample point position of the pure anhydrite rock section or the pure dense limestone section in the intersection diagram to the corresponding pure anhydrite rock or pure dense limestone theoretical skeleton point; D. Use the lithology density, compensated neutron and acoustic time difference curves and add the corresponding standardized correction amount to obtain the standardized lithology density curve, the standardized compensated neutron curve and the standardized acoustic time difference curve.

4. The method for identifying pore types of dolomite gas layers according to claim 2, characterized in that: The steps of standardizing the lithology density, compensated neutron and sonic time difference curves using the frequency histogram method include: a. Comprehensively utilize the logging lithology description and the logging response characteristics of each logging curve to determine the pure anhydrite rock section or pure dense limestone section of a single well; b. Make the frequency histogram of lithology density, compensated neutron and acoustic wave time difference in pure anhydrite rock section or pure dense limestone section respectively; c. Determine the standardized correction amount corresponding to the lithology density, compensated neutron and acoustic time difference curve by moving the peak of each frequency histogram of the pure anhydrite rock section or the pure dense limestone section to the corresponding theoretical skeleton point of the pure anhydrite rock or the pure dense limestone; d. Using the lithology density, compensated neutron and acoustic time difference curves and adding the corresponding standardized correction amount, a standardized lithology density curve, a standardized compensated neutron curve and a standardized acoustic time difference curve are obtained.

5. The method for identifying pore types of dolomite gas layers according to claim 1, characterized in that: The fixed scale interval set for the standardized lithology density curve is 2.2~3.05g / cm 3 The fixed scale interval set for the standardized compensated neutron curve is 30 to -20P.U, and the fixed scale interval set for the standardized acoustic time difference curve is 90 to 20μs / ft.

6. The method for identifying pore types of dolomite gas layers according to claim 1, characterized in that: The gas layer section in the well section to be identified in the single well is the gas layer section in the well section to be identified in the single well interpreted by conventional well logging data of the target single well.

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