Tight oil reservoir fluid occurrence type identification method and system based on nuclear magnetic resonance

Abstract

The invention provides a tight oil reservoir fluid occurrence type identification method and system based on nuclear magnetic resonance, and belongs to the technical field of petroleum geology exploration and development. The method comprises the following steps: on the basis of comparison between a nuclear magnetic resonance T2 relaxation time cumulative distribution curve of a tight oil reservoir sample and a high-pressure mercury injection pore throat diameter cumulative distribution curve, dividing pore throat types, and converting T2 relaxation time into pore throat diameters; judging occurrence fluids in different types of pore throats through a nuclear magnetic resonance spectrum to obtain fluid occurrence types corresponding to different signal domain ranges, and calculating the relative fluid content of each fluid occurrence type; and based on the signal domain range of each fluid occurrence type of the plurality of samples, establishing a nuclear magnetic resonance fluid occurrence type identification chart, and defining an identification standard of each fluid occurrence type. According to the method, the pore size distribution of the T2 relaxation time is combined with the nuclear magnetic resonance spectrum, the pore size range corresponding to the fluid occurrence type is determined, and the relative content of the fluid is calculated through the signal intensity of each signal domain, so that the accuracy is higher.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum geological exploration and development, and in particular relates to a method and system for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance. Background Art

[0002] Tight oil reservoirs have the characteristics of complex pore throat structure and strong heterogeneity. The fluid occurrence types are diverse and difficult to identify. Accurate identification of the fluid occurrence types in tight oil reservoirs is of great significance to the evaluation, exploration and development of tight oil.

[0003] The research on the occurrence type of fluid in tight oil reservoirs is mainly based on samples of the original oil-bearing state of tight oil reservoirs or simulated samples of saturated fluids. At present, the main methods for identifying the occurrence type of fluid in tight oil reservoirs are: (1) Through environmental scanning electron microscopy, two types of tight oil occurrence forms, oil film and oil droplets, can be observed; (2) Using laser confocal scanning microscopy technology, three-dimensional reconstruction of tight reservoirs and tight oil was performed to classify the occurrence types of tight oil; (3) Perform CT scanning on tight oil reservoirs to obtain three-dimensional images of pore throat structure, crude oil and water occurrence forms, thereby evaluating the occurrence type of tight oil; (4) Use nuclear magnetic resonance to quantitatively test the pore structure, compare the T2 spectra of saturated oil samples before and after centrifugation, and quantitatively calculate the distribution ratio of movable fluid in pores of different sizes.

[0004] In the related technologies, the use of environmental scanning electron microscope, laser confocal scanning microscope, CT scanning and other technologies requires a lot of manual interpretation and comprehensive statistics of oil and water microscopic occurrence, which reduces the accuracy of quantitative evaluation of fluid occurrence types in tight oil reservoirs, and the depiction of microscopic fluid migration is obviously insufficient, making it difficult to accurately divide pore throat types and corresponding pore size distribution. Nuclear magnetic resonance technology focuses on the characterization of movable fluids by nuclear magnetic resonance T2 spectra before and after centrifugation, but this identification method lacks a unified chart, has poor accuracy, and fails to explain the differences in the occurrence characteristics of oil and water in each pore throat during the centrifugation process. Summary of the invention

[0005] In response to the above technical problems, the present invention proposes an accurate and reliable method and system for identifying the fluid occurrence type of tight oil reservoirs based on nuclear magnetic resonance. The identification method is simple and effective, and can achieve accurate evaluation of the fluid occurrence type and relative content of tight oil reservoirs, solving the problem of difficulty in identifying the fluid occurrence type of tight oil reservoirs in the prior art, and can further reveal the fluid occurrence type and corresponding pore interval of tight oil reservoirs, so that the identification results are more in line with the actual situation.

[0006] In order to achieve the above object, the present invention provides a method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance, which comprises the following steps: Based on the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve of tight oil reservoir samples and the high-pressure mercury injection pore throat diameter cumulative distribution curve, the types of pore throats are classified, the ranges of pore throat diameters of different types of pore throats and their corresponding T2 relaxation time ranges are determined, and the T2 relaxation time is converted into pore throat diameters; The fluids in different types of pore throats are identified by two-dimensional nuclear magnetic resonance spectra, the fluid occurrence types corresponding to different signal domain ranges are obtained, and the relative content of fluids in each fluid occurrence type is calculated; Based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, and the identification criteria of each fluid occurrence type are clarified.

[0007] This technical solution provides a method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance. By comparing the cumulative distribution curve of nuclear magnetic resonance T2 relaxation time with the cumulative distribution curve of high-pressure mercury injection pore throat diameter, it realizes the accurate classification of pore throat types and the quantitative characterization of pore size distribution. Through two-dimensional nuclear magnetic resonance spectrum analysis, combined with the classification of pore throat types, it is possible to accurately identify the fluid type and calculate its relative content, thereby improving the accuracy of identification. At the same time, by statistically analyzing a large amount of sample data, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart was established, and the identification criteria for each fluid type were clarified, providing a standardized tool for the evaluation of tight oil reservoirs.

[0008] According to an embodiment of the present disclosure, the pore throat types include type I pore throat, type II pore throat and type III pore throat, and the classification of the pore throat types includes: Through high-pressure mercury injection analysis, a high-pressure mercury injection pore throat diameter cumulative distribution curve is obtained, and the pore throat space of the unsaturated mercury portion of the high-pressure mercury injection is calibrated as the type I pore throat; The correlation analysis between the nuclear magnetic resonance T2 relaxation time of the pore throat space of the mercury saturated part of the high-pressure mercury injection and the pore throat diameter of the high-pressure mercury injection was performed to obtain a fitting curve with a two-stage distribution. Based on the inflection point of the fitting curve, two sections of pore throat space bounded by the inflection point are respectively calibrated as the type II pore throat and the type III pore throat.

[0009] According to an embodiment of the present disclosure, the conversion of the pore throat diameter includes: Obtaining the T2 relaxation time and pore throat diameter of the boundaries of type I pore throat, type II pore throat and type III pore throat, and calculating the ratio of the T2 relaxation time to the pore throat diameter of the two boundaries; Taking the data of the two boundaries as the standard, the geometric progression method is used to establish the corresponding relationship between the T2 relaxation time and the pore throat diameter, and the pore throat diameters corresponding to other T2 relaxation times are calculated based on the geometric progression to obtain the pore throat diameter distribution of the tight oil reservoir sample based on the T2 relaxation time.

[0010] According to an embodiment of the present disclosure, the fluids in different types of pore throats are identified by two-dimensional nuclear magnetic resonance spectra, including: According to the T2 relaxation time range, the distribution intervals of different types of pore throats are delineated in the two-dimensional nuclear magnetic resonance spectrum; Based on the NMR T1 and T2 characteristics corresponding to different fluids, the fluid signals present in each pore throat distribution interval are analyzed to identify the signal domain range and fluid type of different fluids.

[0011] According to an embodiment of the present disclosure, the calculation of the relative content of fluid of each fluid occurrence type includes the following steps: According to the T1 and T2 characteristics in the two-dimensional NMR spectrum, the cumulative signal intensity in different signal domains is obtained; The relative content of fluid of each fluid occurrence type is determined according to the proportion of the cumulative signal intensity of each signal domain range in the total signal intensity.

[0012] According to an embodiment of the present disclosure, based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, including: Obtaining the signal domain range of each fluid in the plurality of tight oil reservoir samples; In the two-dimensional nuclear magnetic resonance spectrum, the entire coverage area of ​​each fluid occurrence is drawn, and a fluid occurrence type identification plate applicable to the region is established.

[0013] According to an embodiment of the present disclosure, the identification criteria include each fluid occurrence type and its corresponding pore throat diameter, T2 relaxation time, and the ratio range between T1 relaxation time and T2 relaxation time.

[0014] According to an embodiment of the present disclosure, the conversion of the pore throat diameter includes: If there are multiple boundaries between all pore throat types, the corresponding relationship between the T2 relaxation time and the pore throat diameter is established using the geometric progression method with adjacent boundaries as the standard, and the T2 relaxation time of the corresponding pore throat interval is converted into the pore throat diameter based on the geometric progression.

[0015] According to an embodiment of the present disclosure, the fluid occurrence types include bound water, adsorbed oil, movable fluid, movable water, and movable oil.

[0016] According to an embodiment of the present disclosure, the identification criteria include: Within the scope of the type I pore throat, A of the bound water signal is <0.5, and A of the adsorbed oil signal is >0.5; Within the range of the type II pore throats, the A of the movable water signal is 1-5, and the A of the adsorbed oil signal is >5; Within the range of the type III pore throats, the A of the movable water signal is 0.5-5, and the A of the adsorbed oil signal is >10; Where A is the ratio between T1 relaxation time and T2 relaxation time.

[0017] In another aspect, the present invention further provides a system for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance, which is used to implement the method for identifying the occurrence type of fluid described in any one of the above technical solutions, and comprises: The pore throat type classification and pore size distribution module is used to classify the pore throat types based on the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve of the tight oil reservoir sample and the high-pressure mercury injection pore throat diameter cumulative distribution curve, determine the T2 relaxation time range and pore throat diameter range corresponding to different types of pore throats, and convert the T2 relaxation time into pore throat diameter; The fluid type identification module is used to identify the fluids in different types of pore throats through two-dimensional nuclear magnetic resonance spectra, obtain the fluid occurrence types corresponding to different signal domain ranges, and calculate the relative content of fluids of each fluid occurrence type; The fluid type identification plate establishment module is used to establish a two-dimensional nuclear magnetic resonance fluid occurrence type identification plate based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, and to clarify the identification criteria of each fluid occurrence type.

[0018] Compared with the prior art, the advantages and positive effects of the present invention are: 1. Through comparative analysis of NMR T2 relaxation time and high-pressure mercury injection pore throat diameter, the precise classification of pore throat types and quantitative characterization of pore size distribution (pore throat diameter distribution) are achieved, which can more accurately reflect the microstructural characteristics of tight oil reservoirs and provide a solid foundation for the identification of fluid occurrence types.

[0019] 2. The two-dimensional nuclear magnetic resonance spectrum is used to analyze the fluid signals in different pore throat types, which can accurately identify the fluid occurrence type in the pore throat and calculate its relative content by signal intensity, effectively avoiding the uncertainty of human interpretation in traditional methods and improving the accuracy and reliability of the identification results.

[0020] 3. By statistically analyzing a large amount of sample data, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart was established, and the identification criteria for each fluid type were clarified, providing a standardized tool for identifying the fluid occurrence type of tight oil reservoirs, making the evaluation of tight oil reservoirs in different regions more consistent and comparable.

[0021] The evaluation results of different regions are based on unified standards and methods, which avoids the deviation of results caused by differences in methods and makes the evaluation results more reliable.

[0022] 4. It provides an efficient and accurate method for identifying fluid occurrence types, which can quickly evaluate the fluid occurrence status and recoverable reserves of tight oil reservoirs. It is of great significance for the exploration and development of tight oil and is conducive to improving resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 A flow chart of a method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance provided by the present invention; Figure 2 A comparison diagram of the cumulative distribution of high-pressure mercury injection pore throat diameters and the cumulative distribution of nuclear magnetic resonance T2 relaxation times of typical samples provided by the present invention; Figure 3 The conversion relationship between the high-pressure mercury injection pore throat diameter and the nuclear magnetic T2 relaxation time of the typical sample provided by the present invention; Figure 4 A pore size distribution diagram of a typical sample provided by the present invention; Figure 5 A two-dimensional nuclear magnetic resonance spectrum of a typical sample (dry sample) provided by the present invention; Figure 6 A two-dimensional nuclear magnetic resonance spectrum of a typical sample (saturated oil sample) provided by the present invention; Figure 7 The present invention provides a typical sample based on two-dimensional nuclear magnetic resonance fluid occurrence type identification plate. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments. 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 making creative work are within the scope of protection of the present invention.

[0025] In the description of the present invention, it should be understood that the terms "center", "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0026] The terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Thus, a feature defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] Tight oil reservoirs have complex pore throat structures and strong heterogeneity. Traditional pore characterization methods (such as scanning electron microscopy, CT scanning, etc.) are difficult to accurately divide pore throat types and corresponding pore size distributions. Existing methods for identifying fluid occurrence types lack unified charts and standards, and are unable to accurately distinguish fluid types in different pore throat types. The identification of fluid occurrence types makes it difficult to compare and apply the results of different studies.

[0029] In order to solve the above technical problems, the present invention provides a method for identifying the fluid occurrence type of tight oil reservoirs based on nuclear magnetic resonance. The identification method is simple and effective, and can achieve accurate evaluation of the fluid occurrence type and relative content of tight oil reservoirs, thereby solving the problem of difficulty in identifying the fluid occurrence type of tight oil reservoirs in the prior art, and can further reveal the fluid occurrence type and corresponding pore interval of the tight oil reservoir, so that the identification results are more in line with the actual situation.

[0030] The present invention provides a method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance. Figure 1 , which comprises the following steps: S1. Based on the comparison between the cumulative distribution curve of nuclear magnetic resonance T2 relaxation time of tight oil reservoir samples and the cumulative distribution curve of high-pressure mercury injection pore throat diameter, the types of pore throats are classified, and the T2 relaxation time is converted into pore diameter; S2. Identify the fluids in different types of pore throats through two-dimensional nuclear magnetic resonance spectra, obtain the fluid occurrence types corresponding to different signal domain ranges, and calculate the relative content of fluids in each fluid occurrence type; S3. Based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, and the identification criteria of each fluid occurrence type are clarified.

[0031] The present embodiment provides a method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance, which achieves accurate classification of pore throat types and quantitative characterization of pore size distribution by comparing the cumulative distribution curve of nuclear magnetic resonance T2 relaxation time with the cumulative distribution curve of high-pressure mercury injection pore throat diameter. Through two-dimensional nuclear magnetic resonance spectrum analysis, combined with the classification of pore throat types, the fluid type can be accurately identified and its relative content can be calculated, thereby improving the accuracy of identification. At the same time, by statistically analyzing a large amount of sample data, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart was established, and the identification criteria for each fluid type were clarified, providing a standardized tool for the evaluation of tight oil reservoirs.

[0032] Furthermore, the pore throat types may include at least type I pore throats, type II pore throats and type III pore throats, wherein the pore diameter range corresponding to type II pore throats is smaller than the pore diameter range corresponding to type III pore throats, and the pore diameter range corresponding to type I pore throats is smaller than the pore diameter range corresponding to type II pore throats.

[0033] Specifically, the classification of pore throat types includes the following steps: Through high-pressure mercury injection analysis, the cumulative distribution curve of high-pressure mercury injection pore throat diameter is obtained, and the pore throat space of the unsaturated mercury part of high-pressure mercury injection is calibrated as type I pore throat; The correlation analysis is performed between the nuclear magnetic resonance T2 relaxation time of the pore throat space of the mercury saturated part of the high-pressure mercury injection and the pore throat diameter of the high-pressure mercury injection to obtain a fitting curve with at least two sections; Based on at least one inflection point of the fitting curve, at least two sections of pore throat space bounded by at least one inflection point are calibrated as type II pore throat, type III pore throat, etc. in order from small to large pore throat diameters.

[0034] In the above step S1, the T2 relaxation time range and pore throat diameter range corresponding to different types of pore throats can be determined by comparing the nuclear magnetic resonance T2 relaxation time cumulative distribution curve of the tight oil reservoir sample with the high-pressure mercury injection pore throat diameter cumulative distribution curve.

[0035] In this embodiment, the pore throat types and their corresponding pore size ranges can be more accurately divided by the joint analysis of high-pressure mercury injection and nuclear magnetic resonance T2 relaxation time. The pore throat space in the unsaturated part of high-pressure mercury injection usually represents tiny pores, which may be occupied by bound fluids and difficult to be saturated with mercury. They are marked as type I pore throats, which can clarify the characteristics and distribution of these tiny pores.

[0036] In addition, the fitting curve with at least two-segment distribution obtained through correlation analysis can clearly distinguish the pore throat space between medium pore size and large pore size, making the characterization of the pore throat structure more detailed and accurate.

[0037] It should be noted that the fitting curve with at least two-stage distribution may be a fitting curve with two-stage distribution or a fitting curve with three-stage distribution, and the fitting curve with at least two-stage distribution has at least one inflection point.

[0038] For example, if a correlation analysis is performed between the nuclear magnetic resonance T2 relaxation time of the pore throat space of the mercury-saturated part of the high-pressure mercury injection and the high-pressure mercury injection pore throat diameter, a fitting curve with a two-segment distribution is obtained, and the two segments of the pore throat space separated by an inflection point of the fitting curve are respectively calibrated as type II pore throat and type III pore throat.

[0039] In this embodiment, the conversion of the pore throat diameter may include: Obtain the T2 relaxation time and pore throat diameter at the boundary of type I pore throat, type II pore throat and type III pore throat, and calculate the ratio of T2 relaxation time to pore throat diameter at the two boundaries; Taking the data of the two boundaries as the standard, the geometric progression method is used to establish the corresponding relationship between T2 relaxation time and pore throat diameter, and the pore throat diameters corresponding to other T2 relaxation times are calculated based on the geometric progression to obtain the pore size distribution of tight oil reservoir samples based on T2 relaxation time.

[0040] Specifically, the T2 relaxation time and pore throat diameter of the two boundaries are obtained, and the ratio of the T2 relaxation time to the pore throat diameter of the two boundaries is calculated. The data corresponding to the two boundaries are used as known data for converting T2 relaxation time to pore throat diameter.

[0041] Taking the known data of the two boundaries as the standard, the geometric progression expressed by the following formula (1) is used to establish the corresponding relationship between T2 relaxation time and pore throat diameter.

[0042] (1) In the formula, is the ratio of the T2 relaxation time to the pore throat diameter at the nth data point, is a common ratio (constant).

[0043] It can be understood that the boundary between type I pore throat and type II pore throat is the boundary between the pore throat space of the unsaturated part of high-pressure mercury injection and the pore throat space of the saturated part of high-pressure mercury injection. The corresponding T2 relaxation time and pore throat diameter are the intersection of the boundary line and the cumulative distribution curve of nuclear magnetic resonance T2 relaxation time and the cumulative distribution curve of high-pressure mercury injection pore throat diameter. The boundary between type II pore throat and type III pore throat is the inflection point of the fitting curve.

[0044] In this embodiment, by establishing the corresponding relationship between the T2 relaxation time and the pore throat diameter at the two boundaries of type I pore throat, type II pore throat and type III pore throat, the pore size distribution characteristics of the tight oil reservoir can be more realistically reflected.

[0045] Through the unified pore size distribution characterization method, tight oil reservoirs in different regions can be compared under the same evaluation criteria. This standardization and comparability makes the evaluation of tight oil reservoirs more consistent and facilitates cross-regional research and development.

[0046] In some other embodiments, if there are more than three types of pore throats, that is, if there are multiple boundaries between all pore throat types, the transformation of pore throats includes: Taking two adjacent boundaries as the standard, the geometric progression method is used to establish the corresponding relationship between T2 relaxation time and pore throat diameter, and the T2 relaxation time of the corresponding pore throat interval is converted into pore throat diameter according to the geometric progression.

[0047] It can be understood that, in the description herein, “plurality” refers to no less than three.

[0048] Furthermore, the identification of the fluids in different types of pore throats is performed by two-dimensional nuclear magnetic resonance spectra, including the following steps: According to the range of T2 relaxation time, the distribution range of different types of pore throats is delineated in the two-dimensional NMR spectrum; Based on the nuclear magnetic resonance characteristics of different fluids, the different fluid signals existing in each pore throat distribution interval are analyzed to identify the signal domain range and type of different fluids.

[0049] In this embodiment, two-dimensional nuclear magnetic resonance spectra are used to identify the fluids in different types of pore throats, which improves the accuracy of fluid occurrence type identification, reduces the uncertainty of human interpretation, and enables a clearer understanding of the fluid occurrence status in different pore throat types, providing more reliable data support for reservoir evaluation.

[0050] It will be appreciated that the NMR characteristics may include T1 relaxation time and T2 relaxation time.

[0051] In this embodiment, the calculation of the relative content of fluid of each fluid occurrence type includes the following steps: According to the T1 and T2 characteristics in the two-dimensional NMR spectrum, the cumulative signal intensity in different signal domains is obtained; The relative content of fluid in each fluid occurrence type is determined based on the proportion of the cumulative signal intensity of each signal domain range in the total signal intensity.

[0052] It can be understood that the two-dimensional NMR spectrum can provide the intensity information of the fluid signal.

[0053] In the above embodiment, the quantitative evaluation of the content of each stored fluid is calculated by the signal intensity of each signal domain, which is more accurate and can help to more accurately evaluate the fluid recoverability of the reservoir.

[0054] Based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, further including: Obtaining the signal domain range of each fluid in the plurality of tight oil reservoir samples; In the two-dimensional nuclear magnetic resonance spectrum, the entire coverage area of ​​each fluid occurrence is drawn, and a fluid occurrence type identification plate applicable to the region is established.

[0055] In this embodiment, by counting the signal domain range of the occurrence fluid of a large number of tight oil reservoir samples, the coverage range of the same fluid is defined, and a unified fluid occurrence type identification plate is established, thereby providing a standardized tool for fluid identification in tight oil reservoirs.

[0056] In some embodiments of the present application, the identification criteria include each fluid occurrence type and its corresponding pore throat diameter (pore throat type), T2 relaxation time, and the ratio range between T1 relaxation time and T2 relaxation time.

[0057] It should be noted that the T2 relaxation time is the transverse relaxation time of nuclear magnetic resonance, and the T1 relaxation time is the vertical relaxation time of nuclear magnetic resonance.

[0058] Fluid occurrence types can include bound water, adsorbed oil, movable fluid, movable water, and movable oil. Among them, adsorbed oil includes adsorbed oil (light component) and adsorbed oil (heavy component), and movable fluid is mainly oil with a small amount of water. By carefully dividing fluid types, the potential of tight oil reservoirs can be more accurately evaluated.

[0059] In some embodiments of the present application, the identification criteria include: Within the range of type I pore throats, A of bound water signal is less than 0.5, and A of adsorbed oil signal is greater than 0.5. Among them, the pore throat diameter is less than the pore throat diameter corresponding to the first boundary. The first boundary is the boundary between the pore throat space of the unsaturated mercury part of high-pressure mercury injection and the pore throat space of the saturated mercury part of high-pressure mercury injection.

[0060] In the range of type II pore throats, the A of the movable water signal is 1-5, and the A of the adsorbed oil signal is > 5. Among them, the pore throat diameter is between the pore throat diameter corresponding to the first boundary and the pore throat diameter corresponding to the second boundary. The second boundary is the inflection point of the fitting curve with a two-stage distribution.

[0061] Within the range of type III pore throats, the A of the movable water signal is 0.5~5, the A of the adsorbed oil signal is >10, and the pore throat diameter is > the pore throat diameter corresponding to the second boundary.

[0062] Where A is the ratio between T1 relaxation time and T2 relaxation time.

[0063] In another aspect, the present invention further provides a system for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance, which is used to implement the method for identifying the occurrence type of fluid described in any one of the above technical solutions, and comprises: The pore throat type classification and pore size distribution module is used to classify the pore throat types based on the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve of the tight oil reservoir sample and the high-pressure mercury injection pore throat diameter cumulative distribution curve, determine the T2 relaxation time range and pore throat diameter range corresponding to different types of pore throats, and convert the T2 relaxation time into pore throat diameter distribution; The fluid type identification module is used to identify the fluids in different types of pore throats through two-dimensional nuclear magnetic resonance spectra, obtain the fluid occurrence types corresponding to different signal domain ranges, and calculate the relative content of fluids of each fluid occurrence type; The fluid type identification plate establishment module is used to establish a two-dimensional nuclear magnetic resonance fluid occurrence type identification plate based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, and to clarify the identification criteria of each fluid occurrence type.

[0064] In order to more clearly and in detail introduce the method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance provided by the embodiment of the present invention, it will be described below in conjunction with specific embodiments.

[0065] Example 1 The specific implementation scheme of the present invention is described by taking the tight oil reservoir of the fourth member of the Shahejie Formation in the Dongying Depression as an example.

[0066] (1) Pore throat type classification and pore size distribution transformation like Figure 2 The corresponding sample is the tight oil reservoir of 3217.3m in Fanxie 189 well. The cumulative distribution curve of high-pressure mercury injection pore size and the cumulative distribution curve of nuclear magnetic resonance T2 relaxation time are superimposed and compared. The corresponding cumulative distribution frequency range of the part of high-pressure mercury injection unsaturated mercury is 83.19%~100%. The pore throat space corresponding to this frequency range is calibrated or defined as type I pore throat. Figure 2 , the NMR T2 relaxation time ranges from 0 to 0.8 ms, and the pore throat diameter ranges from 0 to 0.126 μm.

[0067] Continue to refer Figure 1 The corresponding cumulative distribution frequency of the pore throat space saturated with mercury under high-pressure mercury injection is 0~83.19%. The T2 relaxation time and the pore throat diameter data with the same cumulative distribution frequency in this part are statistically analyzed. Through the nonlinear fitting of these data points, we can get Figure 2The fitting curve is shown.

[0068] refer to Figure 3 The fitting curve shows an obvious two-stage distribution. The inflection point of the fitting curve is used as the boundary of the pore size range of type II pore throat and type III pore throat, so that the NMR T2 relaxation time range of type II pore throat is determined to be 0.8~41ms, and the pore throat diameter distribution range is 0.126~0.73μm; the NMR T2 relaxation time range of type III pore throat is greater than 41ms, and the pore throat diameter distribution range is greater than 0.73μm.

[0069] According to the above steps, the two boundary NMR T2 relaxation times of type I pore throat, type II pore throat and type III pore throat (the 63rd and 143rd T2 relaxation times from small to large) and the high-pressure mercury injection pore throat diameter are obtained, and the ratio between the two is calculated by substituting them into formula (1), and the following formulas (2) and (3) are obtained.

[0070] Taking the two boundaries as the standard, according to the geometric progression method, divide formula (3) by formula (2) to calculate the common ratio in formula (1): =1.015, and then the pore throat diameter corresponding to the NMR T2 relaxation time of other data points is calculated according to formula (1), and the following is obtained: Figure 4 The pore size distribution of this sample based on the NMR T2 relaxation time is shown, where Figure 4 The vertical axis is the NMR signal intensity.

[0071] (2) (3) In the formula, , are the ratios of the T2 relaxation time and pore throat diameter of the 63rd and 143th data points (two dividing points), Refers to the common ratio (constant).

[0072] (2) Identification of different fluid occurrence types The distribution intervals of type I pore throats, type II pore throats, and type III pore throats are delineated in the two-dimensional nuclear magnetic resonance spectrum, and then the different fluid signals existing in each pore throat distribution interval are analyzed.

[0073] Generally, the T1 and T1 / T2 ratio A of oil substances are respectively greater than the T1 and T1 / T2 ratio A of water.

[0074] refer to Figure 5 , Figure 6 In the two-dimensional nuclear magnetic resonance spectra of the unsaturated oil and saturated oil samples at 3217.3 m in the Fanxie 189 well, the different fluid signals in each pore throat distribution interval have the characteristics of cluster distribution, which can identify different types of stored fluids.

[0075] Among them, within the range of type I pore throats, the T1 / T2 ratio of bound water signal A<0.5, and the T1 / T2 ratio of adsorbed oil signal A>0.5, where the signal domain with a high T1 / T2 ratio A (>100) is considered as a heavy component. For type II pore throats, the T1 / T2 ratio A of movable water signal is 1~5, and the T1 / T2 ratio A of adsorbed oil signal is>5. For type III pore throats, the T1 / T2 ratio A of movable water signal is 0.5~5, and the T1 / T2 ratio A of adsorbed oil signal is>10.

[0076] Furthermore, referring to Table 1 below, the cumulative signal intensity of different signal domains is obtained through the T1 and T2 characteristic data of two-dimensional NMR, and the relative content of fluids of different fluid occurrence types is calculated according to the proportion of the signal intensity of each signal domain in the total signal intensity of the two-dimensional NMR spectrum (Table 2).

[0077] It should be noted that the total signal intensity of the two-dimensional NMR spectrum is the sum of the signal intensities of all signal domains.

[0078] Table 1 2D NMR signal intensity of the 3217.3 m sample from Well Fanxie 189 Table 2 Percentage of fluid content in the 3217.3 m sample from Fanxie 189 well

[0079] (3) Determine the criteria for identifying fluid occurrence types The signal domain range of each fluid occurrence type of a large number of samples was counted to determine a more accurate identification standard (Table 3). The entire coverage area of ​​each type of fluid signal domain was marked in the two-dimensional NMR spectrum to establish a Figure 7 The two-dimensional NMR fluid occurrence type identification chart shown in the figure has specific identification criteria such as Figure 7 And as shown in Table 3.

[0080] Table 3 Identification criteria for various fluid occurrence types using 2D NMR

[0081] The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance provided by the present invention combines the pore size distribution of T2 relaxation time with the two-dimensional nuclear magnetic resonance spectrum to clarify the pore size interval corresponding to the occurrence type of fluid. The quantitative evaluation of the content of each occurrence fluid is calculated by the signal intensity of each signal domain, which is more accurate and realizes the accurate evaluation of the occurrence type and relative content of fluid in tight oil reservoirs.

[0082] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance, characterized in that: The following steps are involved: Based on the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve of tight oil reservoir samples and the high-pressure mercury injection pore throat diameter cumulative distribution curve, the types of pore throats are classified, the ranges of pore throat diameters of different types of pore throats and their corresponding T2 relaxation time ranges are determined, and the T2 relaxation time is converted into pore throat diameters; The fluids in different types of pore throats are identified by two-dimensional nuclear magnetic resonance spectra, the fluid occurrence types corresponding to different signal domain ranges are obtained, and the relative content of fluids in each fluid occurrence type is calculated; Based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, and the identification criteria of each fluid occurrence type are clarified.

2. The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance according to claim 1, characterized in that: The pore throat types include type I pore throat, type II pore throat and type III pore throat. The classification of the pore throat types includes: Through high-pressure mercury injection analysis, a high-pressure mercury injection pore throat diameter cumulative distribution curve is obtained, and the pore throat space of the unsaturated mercury portion of the high-pressure mercury injection is calibrated as the type I pore throat; The correlation analysis between the nuclear magnetic resonance T2 relaxation time of the pore throat space of the mercury saturated part of the high-pressure mercury injection and the pore throat diameter of the high-pressure mercury injection was performed to obtain a fitting curve with a two-stage distribution. Based on the inflection point of the fitting curve, two sections of pore throat space bounded by the inflection point are respectively calibrated as the type II pore throat and the type III pore throat.

3. The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance according to claim 2, characterized in that: The conversion of the pore throat diameter includes: Obtaining the T2 relaxation time and pore throat diameter at the boundaries of type I pore throat, type II pore throat and type III pore throat, and calculating the ratio of the T2 relaxation time to the pore throat diameter at the two boundaries; Taking the data of the two boundaries as the standard, the geometric progression method is used to establish the corresponding relationship between the T2 relaxation time and the pore throat diameter, and the pore throat diameters corresponding to other T2 relaxation times are calculated based on the geometric progression to obtain the pore size distribution of the tight oil reservoir sample based on the T2 relaxation time.

4. The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance according to claim 1 or 2, characterized in that: The two-dimensional nuclear magnetic resonance spectrum is used to identify the fluids in different types of pore throats, including: According to the T2 relaxation time range, the distribution intervals of different types of pore throats are delineated in the two-dimensional nuclear magnetic resonance spectrum; Based on the NMR T1 and T2 characteristics corresponding to different fluids, the fluid signals present in each pore throat distribution interval are analyzed to identify the signal domain range and fluid type of different fluids.

5. The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance according to claim 1 or 2, characterized in that: The calculation of the relative content of fluid of each fluid occurrence type comprises the following steps: According to the T1 and T2 characteristics in the two-dimensional NMR spectrum, the cumulative signal intensity in different signal domains is obtained; The relative content of fluid of each fluid occurrence type is determined according to the proportion of the cumulative signal intensity of each signal domain range in the total signal intensity.

6. The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance according to claim 1 or 2, characterized in that: Based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, a two-dimensional NMR fluid occurrence type identification chart is established, including: Obtaining the signal domain range of each fluid in the plurality of tight oil reservoir samples; In the two-dimensional nuclear magnetic resonance spectrum, the entire coverage area of ​​each fluid occurrence is drawn, and a fluid occurrence type identification plate applicable to the region is established.

7. The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance according to claim 1 or 2, characterized in that: The identification criteria include each fluid occurrence type and its corresponding pore throat diameter, T2 relaxation time, and the ratio range between T1 relaxation time and T2 relaxation time.

8. The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance according to claim 1, characterized in that: If there are multiple boundaries between all the pore throat types, the conversion of the pore throat diameter includes: Taking adjacent boundaries as the standard, the geometric progression method is used to establish the corresponding relationship between the T2 relaxation time and the pore throat diameter, and the T2 relaxation time of the corresponding pore throat interval is converted into the pore throat diameter based on the geometric progression.

9. The method for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance according to claim 2, characterized in that: The identification criteria include: Within the scope of the type I pore throat, A of the bound water signal is <0.5, and A of the adsorbed oil signal is >0.5; Within the range of the type II pore throats, the A of the movable water signal is 1-5, and the A of the adsorbed oil signal is >5; Within the range of the type III pore throats, the A of the movable water signal is 0.5-5, and the A of the adsorbed oil signal is >10; Where A is the ratio between T1 relaxation time and T2 relaxation time.

10. A system for identifying the occurrence type of fluid in tight oil reservoirs based on nuclear magnetic resonance, used to implement the method for identifying the occurrence type of fluid according to any one of claims 1 to 9, characterized in that: include: The pore throat type classification and pore size distribution module is used to classify the pore throat types based on the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve of the tight oil reservoir sample and the high-pressure mercury injection pore throat diameter cumulative distribution curve, determine the T2 relaxation time range and pore throat diameter range corresponding to different types of pore throats, and convert the T2 relaxation time into pore throat diameter; The fluid type identification module is used to identify the fluids in different types of pore throats through two-dimensional nuclear magnetic resonance spectra, obtain the fluid occurrence types corresponding to different signal domain ranges, and calculate the relative content of fluids of each fluid occurrence type; The fluid type identification plate establishment module is used to establish a two-dimensional nuclear magnetic resonance fluid occurrence type identification plate based on the signal domain range of each fluid occurrence type of several tight oil reservoir samples, and to clarify the identification criteria of each fluid occurrence type.

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