Nmr-based method and system for identifying fluid occurrence types in tight oil reservoirs

Abstract

The present application provides a method and system for identifying fluid occurrence types in tight oil reservoirs based on nuclear magnetic resonance, belonging to the technical field of oil geological exploration and development. The method comprises: 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, the pore throat types are divided, and the T2 relaxation time is converted into the pore throat diameter; the fluids occurring in different types of pore throats are identified through nuclear magnetic resonance spectrum, the fluid occurrence types corresponding to different signal domain ranges are obtained, and the relative contents of each fluid occurrence type are calculated; based on the signal domain ranges of each fluid occurrence type of several samples, a nuclear magnetic resonance fluid occurrence type identification chart is established, and the identification standards of each fluid occurrence type are determined. The present application combines the pore size distribution of T2 relaxation time with the nuclear magnetic resonance spectrum, determines the pore size range corresponding to the fluid occurrence type, and calculates the relative content of the fluid through the signal intensity of each signal domain, which is more accurate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of petroleum geological exploration and development, and particularly relates to a method and system for identifying fluid occurrence types of tight oil reservoirs based on nuclear magnetic resonance. BACKGROUND

[0002] The tight oil reservoir has the characteristics of complex pore throat structure and strong heterogeneity, and the fluid occurrence types are various and difficult to identify.

[0003] The research on the fluid occurrence types of the tight oil reservoir is mainly based on the samples of the original oil-bearing state or the simulation samples of the saturated fluid.

[0004] (1) The oil film and oil bead two occurrence forms of the tight oil can be observed through the environmental scanning electron microscope;

[0005] (2) The three-dimensional reconstruction of the tight reservoir and the tight oil is performed by using the laser confocal scanning microscope technology, and the tight oil occurrence types are classified;

[0006] (3) The CT scanning is performed on the tight oil reservoir, and the three-dimensional images of the pore throat structure, the occurrence forms of the crude oil and water are obtained, so as to evaluate the occurrence types of the tight oil;

[0007] (4) The nuclear magnetic resonance is used to quantitatively test the pore structure, and the T2 spectrum before and after the centrifugation of the saturated oil sample is compared, so as to quantitatively calculate the occurrence proportion of the movable fluid in different size pores.

[0008] In the related technology, the environmental scanning electron microscope, the laser confocal scanning microscope and the CT scanning technology are used, a large amount of artificial oil-water micro-occurrence interpretation and comprehensive statistics are required, the accuracy of the quantitative evaluation of the fluid occurrence types of the tight oil reservoir is reduced, the microfluid migration is obviously insufficient, and it is difficult to accurately classify the pore throat types and the corresponding pore size distribution. SUMMARY

[0009] The application provides an accurate and reliable method and system for identifying the fluid occurrence types of the tight oil reservoir based on the nuclear magnetic resonance, the method is simple and effective, the accurate evaluation of the fluid occurrence types and the relative content of the tight oil reservoir is realized, the problem that the fluid occurrence types of the tight oil reservoir are difficult to identify in the prior art is solved, the fluid occurrence types and the corresponding pore interval of the tight oil reservoir are further revealed, and the identification result is more in line with the actual situation.

[0010] To achieve the above object, the present application provides a method for identifying fluid occurrence type in tight oil reservoir based on nuclear magnetic resonance, which comprises the following steps:

[0011] Based on the comparison between the T2 relaxation time cumulative distribution curve of the nuclear magnetic resonance and the high-pressure mercury injection pore throat diameter cumulative distribution curve of the tight oil reservoir sample, the types of pore throats are divided, the ranges of pore throat diameters of different types of pore throats and the corresponding T2 relaxation time ranges are determined, and the T2 relaxation time is converted into pore throat diameter.

[0012] The fluids occurring in different types of pore throats are identified by two-dimensional nuclear magnetic resonance spectrum, the fluid occurrence types corresponding to different signal domain ranges are obtained, and the relative contents of each fluid occurrence type are calculated.

[0013] Based on the signal domain ranges of each fluid occurrence type of a plurality of said tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, and the identification standards of each fluid occurrence type are determined.

[0014] The method for identifying fluid occurrence type in tight oil reservoir based on nuclear magnetic resonance provided by the technical scheme realizes the accurate division of pore throat types and the quantitative characterization of pore size distribution by comparing the T2 relaxation time cumulative distribution curve of nuclear magnetic resonance with the high-pressure mercury injection pore throat diameter cumulative distribution curve. By two-dimensional nuclear magnetic resonance spectrum analysis combined with pore throat type division, the fluid type can be accurately identified, and its relative content can be calculated, thereby improving the accuracy of identification. Meanwhile, by statistically analyzing a large amount of sample data, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, and the identification standards of each fluid type are determined, thereby providing a standardized tool for the evaluation of tight oil reservoirs.

[0015] According to embodiments of the present disclosure, the pore throat types include type I pore throats, type II pore throats and type III pore throats, and the division of the pore throat types comprises:

[0016] The type I pore throats are determined by marking the pore throat space of the unsaturated mercury part of the high-pressure mercury injection as the type I pore throats through high-pressure mercury injection analysis.

[0017] The T2 relaxation time of the pore throat space of the saturated mercury part of the high-pressure mercury injection and the high-pressure mercury injection pore throat diameter are subjected to correlation analysis, and a fitting curve in two sections is obtained.

[0018] Based on the inflection point of the fitting curve, the two sections of pore throat space bounded by the inflection point are marked as the type II pore throats and the type III pore throats, respectively.

[0019] According to embodiments of the present disclosure, the conversion of the pore throat diameter comprises:

[0020] acquire the T2 relaxation time and the pore throat diameter of the boundary of the I-type pore throat, the II-type pore throat and the III-type pore throat, and calculate the ratio of the T2 relaxation time and the pore throat diameter of the two boundaries;

[0021] According to the data of the two boundaries, a corresponding relationship between the T2 relaxation time and the pore throat diameter is established by using a geometric progression method, and the pore throat diameter corresponding to other T2 relaxation times is calculated based on the geometric progression, so as to obtain the pore throat diameter distribution of the tight oil reservoir sample based on the T2 relaxation time.

[0022] According to an embodiment of the present disclosure, the occurrence fluids in different types of pore throats are identified by two-dimensional nuclear magnetic resonance spectrum, including:

[0023] According to the T2 relaxation time range, the distribution intervals of different types of pore throats are drawn in the two-dimensional nuclear magnetic resonance spectrum;

[0024] Based on the nuclear magnetic resonance T1 and T2 characteristics corresponding to different fluids, the fluid signals occurring in each pore throat distribution interval are analyzed to identify the signal domain range and the fluid type of different fluids.

[0025] According to an embodiment of the present disclosure, the calculation of the relative content of each fluid occurrence type includes the following steps:

[0026] According to the T1 and T2 characteristics in the two-dimensional nuclear magnetic resonance spectrum, the cumulative signal intensity of different signal domain ranges is obtained;

[0027] According to the proportion of the cumulative signal intensity of each signal domain range in the total signal intensity, the relative content of each fluid occurrence type is determined.

[0028] According to an embodiment of the present disclosure, based on the signal domain range of each fluid occurrence type of a plurality of tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, including:

[0029] The signal domain range of each occurrence fluid in a plurality of the tight oil reservoir samples is acquired;

[0030] In the two-dimensional nuclear magnetic resonance spectrum, the entire coverage area of each occurrence fluid is plotted to establish a fluid occurrence type identification chart applicable to the region.

[0031] According to an embodiment of the present disclosure, the identification standard includes each fluid occurrence type, the corresponding pore throat diameter and T2 relaxation time, and the ratio range between T1 relaxation time and T2 relaxation time.

[0032] According to an embodiment of the present disclosure, the conversion of the pore throat diameter includes:

[0033] If multiple boundaries are shared among all pore throat types, the corresponding relationship between the T2 relaxation time and the pore throat diameter is established by using the equal ratio sequence 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 according to the equal ratio sequence.

[0034] According to embodiments of the present disclosure, the fluid occurrence types include bound water, adsorbed oil, movable fluid, movable water and movable oil.

[0035] According to embodiments of the present disclosure, the identification criteria include:

[0036] In the range of the type I pore throat, the A of the bound water signal is less than 0.5, and the A of the adsorbed oil signal is greater than 0.5;

[0037] In the range of the type II pore throat, the A of the movable water signal is 1-5, and the A of the adsorbed oil signal is greater than 5;

[0038] In the range of the type III pore throat, the A of the movable water signal is 0.5-5, and the A of the adsorbed oil signal is greater than 10;

[0039] Wherein, A is the ratio between the T1 relaxation time and the T2 relaxation time.

[0040] In another aspect of the present disclosure, a fluid occurrence type identification system based on nuclear magnetic resonance for compact oil reservoirs is also provided, which is used to implement the fluid occurrence type identification method of any one of the above technical solutions, and includes:

[0041] A pore throat type division and pore diameter distribution module is used to divide the type of pore throat, determine the T2 relaxation time range and pore throat diameter range corresponding to different types of pore throat, and convert the T2 relaxation time into pore throat diameter based on the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve and the high-pressure mercury injection pore throat diameter cumulative distribution curve of the compact oil reservoir sample.

[0042] A fluid type identification module is used to identify the occurrence fluid in different types of pore throat through two-dimensional nuclear magnetic resonance spectrum, obtain the fluid occurrence type corresponding to different signal domain ranges, and calculate the relative content of each fluid occurrence type.

[0043] A fluid type identification chart establishment module is used to establish a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart based on the signal domain range of each fluid occurrence type of a plurality of compact oil reservoir samples, and clearly define the identification criteria of each fluid occurrence type.

[0044] Compared with the prior art, the present application has the following advantages and positive effects:

[0045] 1. By comparing and analyzing the T2 relaxation time of nuclear magnetic resonance and the high-pressure mercury injection pore throat diameter, the accurate classification of pore throat types and the quantitative characterization of pore size distribution (pore throat diameter distribution) are realized, which can more accurately reflect the microstructure characteristics of tight oil reservoirs and provide a solid foundation for identifying the fluid occurrence type.

[0046] 2. By analyzing the fluid signals in different pore throat types using two-dimensional nuclear magnetic resonance spectroscopy, the fluid occurrence type in the pore throat can be accurately identified, and the relative content can be calculated through the signal intensity, effectively avoiding the uncertainty of artificial interpretation in traditional methods and improving the accuracy and reliability of the identification results.

[0047] 3. By statistically analyzing a large amount of sample data, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, and the identification criteria for each fluid type are clearly defined, 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.

[0048] The evaluation results in different regions are based on unified standards and methods, avoiding the result deviation caused by method differences, making the evaluation results more reliable.

[0049] 4. A high-efficiency and accurate fluid occurrence type identification method is provided, which can quickly evaluate the fluid occurrence state and recoverable reserves of tight oil reservoirs, which is of great significance for the exploration and development of tight oil and is conducive to improving resource utilization. BRIEF DESCRIPTION OF DRAWINGS

[0050] The drawings described herein are used to provide a further understanding of the present application, which forms a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0051] Figure 1 The flowchart of the tight oil reservoir fluid occurrence type identification method based on nuclear magnetic resonance provided by the present application;

[0052] Figure 2 The high-pressure mercury injection pore throat diameter cumulative distribution and nuclear magnetic resonance T2 relaxation time cumulative distribution comparison chart of a typical sample provided by the present application;

[0053] Figure 3 The high-pressure mercury injection pore throat diameter and nuclear T2 relaxation time conversion relationship of a typical sample provided by the present application;

[0054] Figure 4 The pore size distribution chart of a typical sample provided by the present application;

[0055] Figure 5 The two-dimensional nuclear magnetic resonance spectroscopy of a typical sample (dry sample) provided by the present application;

[0056] Figure 6 The two-dimensional nuclear magnetic resonance spectrum of a typical sample (saturated oil sample) provided by the present application;

[0057] Figure 7 The two-dimensional nuclear magnetic resonance-based fluid occurrence type identification chart of a typical sample provided by the present application. DETAILED DESCRIPTION

[0058] The technical solutions in the embodiments will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0059] In the description of the present application, it should be understood that the terms “center”, “transverse”, “longitudinal”, “upper”, “lower”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer” and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0060] The terms “first”, “second”, “third” are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with “first”, “second”, “third” can explicitly or implicitly include one or more of the features.

[0061] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms “mounting”, “connection”, “connection” should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0062] The tight oil reservoir has a complex pore throat structure and strong heterogeneity, and the traditional pore characterization method (such as scanning electron microscope, CT scanning, etc.) is difficult to accurately divide the pore throat type and the corresponding pore size distribution, and the existing fluid occurrence type identification method lacks a unified chart and standard, and cannot accurately distinguish the fluid type in different pore throat types, and the identification of fluid occurrence type makes it difficult to compare and apply the results between different studies.

[0063] To solve the above technical problems, the application provides a tight oil reservoir fluid occurrence type identification method based on nuclear magnetic resonance, which is simple and effective, realizes accurate evaluation of the tight oil reservoir fluid occurrence type and relative content, solves the problem that the tight oil reservoir fluid occurrence type is difficult to identify in the prior art, and can further reveal the tight oil reservoir fluid occurrence type and corresponding pore interval, so that the identification result is more in line with the actual situation.

[0064] The application provides a tight oil reservoir fluid occurrence type identification method based on nuclear magnetic resonance, which refers to Figure 1 and comprises the following steps:

[0065] S1, 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, the type of the pore throat is divided, and the T2 relaxation time is converted into a pore diameter;

[0066] S2, the occurrence fluid in different types of pore throats is identified by two-dimensional nuclear magnetic resonance spectrum, the fluid occurrence type corresponding to different signal domain ranges is obtained, and the relative content of each fluid occurrence type is calculated;

[0067] S3, based on the signal domain range of each fluid occurrence type of a plurality of tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, and the identification standard of each fluid occurrence type is determined.

[0068] The tight oil reservoir fluid occurrence type identification method based on nuclear magnetic resonance provided in the embodiment realizes accurate division of the pore throat type and quantitative characterization of the pore diameter distribution by comparing the nuclear magnetic resonance T2 relaxation time cumulative distribution curve with the high-pressure mercury injection pore throat diameter cumulative distribution curve. Through two-dimensional nuclear magnetic resonance spectrum analysis combined with pore throat type division, the fluid type can be accurately identified, and the relative content thereof 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 is established, and the identification standard of each fluid type is determined, thereby providing a standardized tool for evaluation of the tight oil reservoir.

[0069] Further, the pore throat type can at least include type I pore throat, type II pore throat and type III pore throat. The pore diameter range corresponding to the type II pore throat is smaller than that corresponding to the type III pore throat, and the pore diameter range corresponding to the type I pore throat is smaller than that corresponding to the type II pore throat.

[0070] Specifically, the division of the pore throat type comprises the following steps:

[0071] Through high-pressure mercury injection analysis, the high-pressure mercury injection pore throat diameter cumulative distribution curve is obtained, and the pore throat space of the unsaturated mercury part of the high-pressure mercury injection is marked as type I pore throat;

[0072] The T2 relaxation time of the pore throat space of the mercury-saturated part of the high-pressure mercury injection is correlated with the high-pressure mercury injection pore throat diameter to obtain a fitting curve with at least two sections;

[0073] Based on at least one inflection point of the fitting curve, at least two sections of the pore throat space bounded by the at least one inflection point are sequentially calibrated as type II pore throat, type III pore throat, and so on according to the pore throat diameter from small to large.

[0074] In the step S1, according to the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve and the high-pressure mercury injection pore throat diameter cumulative distribution curve of the tight oil reservoir sample, the T2 relaxation time range and the pore throat diameter range corresponding to different types of pore throat can be determined.

[0075] In the embodiment, the joint analysis of the high-pressure mercury injection and the nuclear magnetic resonance T2 relaxation time can more accurately divide the pore throat type and the corresponding pore diameter range. The pore throat space of the unsaturated part of the high-pressure mercury injection generally represents the micro-pore, which may be occupied by the bound fluid and is difficult to be saturated with mercury. The pore throat space is calibrated as type I pore throat, which can clearly determine the characteristics and distribution of the micro-pore.

[0076] In addition, the fitting curve with at least two sections obtained by the correlation analysis can clearly distinguish the pore throat space with medium pore diameter and large pore diameter, so that the characterization of the pore throat structure is more detailed and accurate.

[0077] It should be noted that the fitting curve with at least two sections can be a fitting curve with two sections or a fitting curve with three sections, and the fitting curve with at least two sections has at least one inflection point.

[0078] For example, if the T2 relaxation time of the pore throat space of the mercury-saturated part of the high-pressure mercury injection is correlated with the high-pressure mercury injection pore throat diameter, a fitting curve with two sections is obtained, and two sections of the pore throat space bounded by one inflection point of the fitting curve are calibrated as type II pore throat and type III pore throat, respectively.

[0079] In the embodiment, the conversion of the pore throat diameter can include:

[0080] The T2 relaxation time and the pore throat diameter at the boundary of the type I pore throat, the type II pore throat and the type III pore throat are obtained, and the ratio of the T2 relaxation time and the pore throat diameter of the two boundaries is calculated;

[0081] The corresponding relationship between the T2 relaxation time and the pore throat diameter is established by using the equal ratio series method based on the data of the two boundaries, and the pore throat diameter corresponding to other T2 relaxation time is calculated based on the equal ratio series to obtain the pore diameter distribution of the tight oil reservoir sample based on the T2 relaxation time.

[0082] Specifically, the T2 relaxation time and pore throat diameter of two boundaries are obtained, the ratio of the T2 relaxation time and pore throat diameter of two boundaries is calculated, and the data corresponding to the two boundaries are taken as known data for converting the T2 relaxation time to the pore throat diameter.

[0083] Based on the known data of the two boundaries, the corresponding relationship between the T2 relaxation time and the pore throat diameter is established by using the geometric progression represented by the following formula (1).

[0084] (1)

[0085] In the formula, is the ratio of the T2 relaxation time and the pore throat diameter of the nth data point, is the common ratio (constant).

[0086] It can be understood that the boundary between the I-type pore throat and the II-type pore throat is the boundary line between the pore throat space of the unsaturated part of the high-pressure mercury and the pore throat space of the saturated part of the high-pressure mercury, and the corresponding T2 relaxation time and pore throat diameter are the intersection point of the boundary line and the nuclear magnetic resonance T2 relaxation time cumulative distribution curve and the high-pressure mercury pore throat diameter cumulative distribution curve. The boundary between the II-type pore throat and the III-type pore throat is the inflection point of the fitting curve.

[0087] In this embodiment, by establishing the corresponding relationship between the T2 relaxation time and the pore throat diameter at the two boundaries of the I-type pore throat, the II-type pore throat and the III-type pore throat, the pore size distribution characteristics of the tight oil reservoir can be more truly reflected.

[0088] Through the unified pore size distribution characterization method, the tight oil reservoirs in different regions can be compared under the same evaluation standard. This standardization and comparability makes the evaluation of the tight oil reservoir more consistent, facilitating cross-regional research and development.

[0089] In other embodiments, if the pore throat type is greater than three types, that is, if there are multiple boundaries among all pore throat types, the conversion of the pore throat includes:

[0090] Based on the two adjacent boundaries, the corresponding relationship between the T2 relaxation time and the pore throat diameter is established by using the geometric progression method, and the T2 relaxation time corresponding to the pore throat interval based on the geometric progression is converted to the pore throat diameter.

[0091] It can be understood that in the description herein, "multiple" refers to not less than three.

[0092] Further, the occurrence of fluids in different types of pore throats is identified by two-dimensional nuclear magnetic resonance spectrum, including the following steps:

[0093] According to the T2 relaxation time range, the distribution interval of different types of pore throats is drawn in the two-dimensional nuclear magnetic resonance spectrum;

[0094] Based on the nuclear magnetic resonance characteristics of different fluids, the signals of different fluids in each pore throat distribution interval are analyzed to identify the signal domain range and type of different fluids.

[0095] In this embodiment, the fluids in different types of pore throats are identified by using two-dimensional nuclear magnetic resonance spectrum, which improves the accuracy of fluid occurrence type identification, reduces the uncertainty of human interpretation, and can more clearly understand the fluid occurrence state in different pore throat types, providing more reliable data support for reservoir evaluation.

[0096] It can be understood that the nuclear magnetic resonance characteristics can include T1 relaxation time and T2 relaxation time.

[0097] In this embodiment, the calculation of the relative content of each fluid occurrence type includes the following steps:

[0098] According to the T1 and T2 characteristics in the two-dimensional nuclear magnetic resonance spectrum, the cumulative signal intensity of different signal domain ranges is obtained;

[0099] According to the proportion of the cumulative signal intensity of each signal domain range in the total signal intensity, the relative content of each fluid occurrence type is determined.

[0100] It can be understood that the two-dimensional nuclear magnetic resonance spectrum can provide intensity information of fluid signals.

[0101] In the above embodiment, the quantitative evaluation of each occurrence fluid content is calculated by the signal intensity of each signal domain, which is more accurate and can help more accurately evaluate the fluid productivity of the reservoir.

[0102] Based on the signal domain range of each fluid occurrence type of a plurality of tight oil reservoir samples, a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart is established, which further includes:

[0103] Obtaining the signal domain range of each occurrence fluid in a plurality of tight oil reservoir samples;

[0104] In the two-dimensional nuclear magnetic resonance spectrum, the entire coverage area of each occurrence fluid is plotted to establish a fluid occurrence type identification chart applicable to the region.

[0105] In this embodiment, by statistically analyzing 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 determined, and a unified fluid occurrence type identification chart is established, which provides a standardized tool for fluid identification of tight oil reservoirs.

[0106] In some embodiments of the present application, the identification standard includes 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.

[0107] It should be noted that the T2 relaxation time is a nuclear magnetic resonance transverse relaxation time, and the T1 relaxation time is a nuclear magnetic resonance vertical relaxation time.

[0108] The fluid occurrence type can include bound water, adsorbed oil, movable fluid, movable water and movable oil. The adsorbed oil includes adsorbed oil (light component) and adsorbed oil (heavy component), and the movable fluid mainly contains oil and a small amount of water. By precisely dividing the fluid type, the potential of the tight oil reservoir can be more accurately evaluated.

[0109] In some embodiments of the present application, the identification criteria include:

[0110] In the range of the type I pore throat, the A of the bound water signal is less than 0.5, and the A of the adsorbed oil signal is greater than 0.5. The pore throat diameter is less than the pore throat diameter corresponding to the first boundary. The first boundary is a boundary line between the pore throat space of the unsaturated mercury part of the high-pressure mercury injection and the pore throat space of the saturated mercury part of the high-pressure mercury injection.

[0111] In the range of the type II pore throat, the A of the movable water signal is 1-5, and the A of the adsorbed oil signal is greater than 5. 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 an inflection point of the fitting curve in a two-segment distribution.

[0112] In the range of the type III pore throat, the A of the movable water signal is 0.5-5, the A of the adsorbed oil signal is greater than 10, and the pore throat diameter is greater than the pore throat diameter corresponding to the second boundary.

[0113] The A is a ratio between the T1 relaxation time and the T2 relaxation time.

[0114] In another aspect of the present application, a tight oil reservoir fluid occurrence type identification system based on nuclear magnetic resonance is also provided, which is used to implement the fluid occurrence type identification method of any one of the above technical solutions, and includes:

[0115] The pore throat type division and pore diameter distribution module is used to divide the type of the pore throat, determine the T2 relaxation time range and the pore diameter pore throat diameter range corresponding to different types of pore throats, and convert the T2 relaxation time into the pore throat diameter distribution based on the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve and the high-pressure mercury injection pore throat diameter cumulative distribution curve of the tight oil reservoir sample.

[0116] The fluid type identification module is used to identify the occurrence fluid in different types of pore throats through the two-dimensional nuclear magnetic resonance spectrum, obtain the fluid occurrence type corresponding to different signal domain ranges, and calculate the relative content of each fluid occurrence type.

[0117] The fluid type identification chart establishment module is configured to establish a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart based on signal domain ranges of each fluid occurrence type of a plurality of the tight oil reservoir samples, and to determine identification criteria for each fluid occurrence type.

[0118] In order to more clearly and specifically introduce the method for identifying the fluid occurrence type of the tight oil reservoir based on the nuclear magnetic resonance provided by the embodiments of the present application, the following will be described in combination with specific embodiments.

[0119] Embodiment 1

[0120] The specific implementation of the present application will be described by taking the tight oil reservoir of the fourth member of Shahejie Formation in Dongying Sag as an example.

[0121] (1) Pore throat type division and pore size distribution conversion

[0122] As shown in Figure 2 , the corresponding sample is the tight oil reservoir of 3217.3m of Well Fanxie 189, and the high-pressure mercury intrusion pore size cumulative distribution curve and the nuclear magnetic resonance T2 relaxation time cumulative distribution curve are superimposed and compared. The unsaturated mercury part of the high-pressure mercury intrusion corresponds to a cumulative distribution frequency range of 83.19%~100%, and the pore throat space corresponding to the frequency range is marked or defined as type I pore throat. Continuing to refer to Figure 2 , the nuclear magnetic resonance T2 relaxation time range is 0~0.8ms, and the pore throat diameter range is 0~0.126μm.

[0123] Continuing to refer to Figure 1 , the cumulative distribution frequency of the saturated mercury part of the high-pressure mercury intrusion pore throat space is 0~83.19%, and the T2 relaxation time with the same cumulative distribution frequency in this part is statistically analyzed with the high-pressure mercury intrusion pore throat diameter data. Through the nonlinear fitting of these data points, the fitting curve shown in Figure 2 is obtained.

[0124] Referring to Figure 3 , the fitting curve shape is obviously two-section distribution, and the inflection point of the fitting curve is taken as the boundary of the pore size interval of type II pore throat and type III pore throat, so as to determine that the nuclear magnetic T2 relaxation time range of type II pore throat is 0.8~41ms, and the pore throat diameter distribution range is 0.126~0.73μm; the nuclear magnetic 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.

[0125] According to the above steps, the nuclear magnetic resonance T2 relaxation time (the 63rd and 143rd T2 relaxation time from small to large) of the two boundaries of type I pore throat, type II pore throat and type III pore throat and the high-pressure mercury intrusion pore throat diameter are obtained, and are brought into formula (1) to calculate the ratio between the two, to obtain the following formulas (2) and (3).

[0126] Using the two boundaries as the standard, and following the geometric progression method, divide formula (3) by formula (2) to calculate the common ratio in formula (1). The value is equal to 1.015. Then, according to formula (1), the pore throat diameter corresponding to the T2 relaxation time of other data points in nuclear magnetic resonance is calculated, resulting in the following: Figure 4 The pore size distribution of this sample, shown, is based on the nuclear magnetic resonance T2 relaxation time. Figure 4 The vertical axis represents the nuclear magnetic resonance signal intensity.

[0127] (2)

[0128] (3)

[0129] In the formula, , These are the ratios of T2 relaxation time to pore throat diameter at the 63rd and 143rd data points (two dividing points), respectively. Common ratio (constant).

[0130] (2) Identification of different fluid occurrence types

[0131] The distribution ranges of type I, type II, and type III pore throats were delineated in the two-dimensional nuclear magnetic resonance spectrum, and then the different fluid signals contained in each pore throat distribution range were analyzed.

[0132] Generally, the T1 and T1 / T2 ratio A of oils are greater than those of water.

[0133] refer to Figure 5 , Figure 6 In the two-dimensional nuclear magnetic resonance spectra of unsaturated and saturated oil samples at 3217.3m in well Fanxie 189, different fluid signals in each pore throat distribution range showed cluster distribution characteristics, which can identify different types of existing fluids.

[0134] Within the type I pore throat range, the T1 / T2 ratio A of the bound water signal is <0.5, and the T1 / T2 ratio A of the adsorbed oil signal is >0.5. Signals with a T1 / T2 ratio A >100 are considered heavy components. For type II pore throats, the T1 / T2 ratio A of the movable water signal is 1~5, and the T1 / T2 ratio A of the adsorbed oil signal is >5. For type III pore throats, the T1 / T2 ratio A of the movable water signal is 0.5~5, and the T1 / T2 ratio A of the adsorbed oil signal is >10.

[0135] 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 nuclear magnetic resonance. Based on the proportion of the signal intensity of each signal domain in the total signal intensity of the two-dimensional nuclear magnetic resonance spectrum, the relative content of fluids of different fluid occurrence types is calculated (Table 2).

[0136] It should be noted that the total signal intensity of the two-dimensional nuclear magnetic resonance spectrum is the sum of the signal intensities of all signal domains.

[0137] Table 1 Two-dimensional nuclear magnetic resonance signal intensity table of sample 3217.3m of Well Fannian 189

[0138] Table 2 Fluid percentage content table of sample 3217.3m of Well Fannian 189

[0139]

[0140] (3) Determine the fluid occurrence type identification standard

[0141] Statistical signal domain range of each fluid occurrence type of a large number of samples to determine a more accurate identification standard (Table 3). The entire coverage area of each type of fluid signal domain is marked in the two-dimensional nuclear magnetic resonance spectrum, so as to establish the two-dimensional nuclear magnetic resonance fluid occurrence type identification chart as shown in Figure 7 The specific identification standard is shown in Figure 7 and Table 3.

[0142] Table 3 Two-dimensional nuclear magnetic resonance identification standard of each type of fluid occurrence

[0143]

[0144] The dense oil reservoir fluid occurrence type identification method based on nuclear magnetic resonance provided by the present application combines the pore size distribution of T2 relaxation time with the two-dimensional nuclear magnetic resonance spectrum, and clearly defines the pore size interval corresponding to each fluid occurrence type. 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 fluid occurrence type and relative content of the dense oil reservoir.

[0145] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any person skilled in the art can modify or change the above disclosed technical content to equivalent embodiments applied to other fields, but any simple modification, equivalent change and modification made on the basis of the technical essence of the present application to the above embodiments still belongs to the protection scope of the present application technical solution.

Claims

1. A method for identifying the fluid occurrence type of a tight oil reservoir based on nuclear magnetic resonance, characterized in that, The method comprises the following steps: The unsaturated mercury part of the high-pressure mercury injection is marked as the I-type pore throat according to the comparison between the T2 relaxation time cumulative distribution curve of the tight oil reservoir sample and the high-pressure mercury injection pore throat diameter cumulative distribution curve, and the pore throat space of the saturated mercury part of the high-pressure mercury injection is divided into at least the II-type pore throat and the III-type pore throat according to the correlation between the T2 relaxation time and the high-pressure mercury injection pore throat diameter, so as to divide the types of the pore throat, determine the range of the pore throat diameter of different types of the pore throat and the corresponding range of the T2 relaxation time; The pore throat types include the I-type pore throat, the II-type pore throat and the III-type pore throat, and the division of the pore throat types comprises: The high-pressure mercury injection pore throat diameter cumulative distribution curve is obtained through the high-pressure mercury injection analysis, the pore throat space of the unsaturated mercury part of the high-pressure mercury injection is marked as the I-type pore throat, the T2 relaxation time of the pore throat space of the saturated mercury part of the high-pressure mercury injection is correlated with the high-pressure mercury injection pore throat diameter to obtain a fitting curve in two sections, and the two sections of the pore throat space divided by the inflection point of the fitting curve are marked as the II-type pore throat and the III-type pore throat respectively; The corresponding relationship between the T2 relaxation time and the pore throat diameter is established by using the equal ratio sequence method with the demarcation between adjacent pore throat types as the standard, and the T2 relaxation time of the corresponding pore throat interval is converted into the pore throat diameter according to the equal ratio sequence; The occurrence fluid in different types of pore throat is identified through the two-dimensional nuclear magnetic resonance spectrum, the fluid occurrence type corresponding to different signal domain ranges is obtained, and the relative content of each fluid occurrence type is calculated; The two-dimensional nuclear magnetic resonance fluid occurrence type identification chart applicable to the region is established based on the signal domain range of each fluid occurrence type of a plurality of tight oil reservoir samples, and the identification standard of each fluid occurrence type is determined.

2. The nuclear magnetic resonance-based tight oil reservoir fluid occurrence type identification method of claim 1, wherein, The conversion of the pore throat diameter comprises: The T2 relaxation time and the pore throat diameter at the demarcation of the I-type pore throat, the II-type pore throat and the III-type pore throat are obtained, and the ratio of the T2 relaxation time and the pore throat diameter of the two demarcations is calculated; The corresponding relationship between the T2 relaxation time and the pore throat diameter is established by using the equal ratio sequence method with the data of the two demarcations as the standard, and the pore throat diameter corresponding to other T2 relaxation times is calculated according to the equal ratio sequence to obtain the pore size distribution of the tight oil reservoir sample based on the T2 relaxation time.

3. The method for identifying the fluid occurrence type of tight oil reservoirs based on nuclear magnetic resonance as described in claim 1, characterized in that, The occurrence fluid in different types of pore throat is identified through the two-dimensional nuclear magnetic resonance spectrum, which comprises: the distribution interval of different types of pore throat is drawn in the two-dimensional nuclear magnetic resonance spectrum according to the T2 relaxation time range; The fluid signal in each pore throat distribution interval is analyzed based on the nuclear magnetic resonance T1 and T2 characteristics corresponding to different fluids to identify the signal domain range and the fluid type of different fluids.

4. The nuclear magnetic resonance-based tight oil reservoir fluid occurrence type identification method of claim 1, wherein, The calculation of the relative content of each fluid occurrence type comprises the following steps: The cumulative signal intensity of different signal domain ranges is obtained according to the T1 and T2 characteristics in the two-dimensional nuclear magnetic resonance spectrum; The relative content 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.

5. The nuclear magnetic resonance-based tight oil reservoir fluid occurrence type identification method of claim 1, wherein, Based on the signal domain range of each fluid occurrence type of a plurality of 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 occurrence fluid in a plurality of tight oil reservoir samples; In the two-dimensional nuclear magnetic resonance spectrum, the entire coverage area of each occurrence fluid is plotted to establish a fluid occurrence type identification chart applicable to the region.

6. The nuclear magnetic resonance-based tight oil reservoir fluid occurrence type identification method of claim 1, wherein, 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.

7. The nuclear magnetic resonance-based tight oil reservoir fluid occurrence type identification method of claim 1, wherein, The identification criteria include: Within the range of the type I pore throat, the A of the bound water signal is less than 0.5, and the A of the adsorbed oil signal is greater than 0.5; Within the range of the type II pore throat, the A of the movable water signal is 1-5, and the A of the adsorbed oil signal is greater than 5; Within the range of the type III pore throat, the A of the movable water signal is 0.5-5, and the A of the adsorbed oil signal is greater than 10; Wherein, A is the ratio between T1 relaxation time and T2 relaxation time.

8. A system for identifying fluid occurrence type in tight oil reservoirs based on nuclear magnetic resonance, for implementing the method for identifying fluid occurrence type according to any one of claims 1-7, characterized in that, Including: A pore throat type division and pore size distribution module is used to divide the type of pore throat based on the comparison between the nuclear magnetic resonance T2 relaxation time cumulative distribution curve and the high-pressure mercury injection pore throat diameter cumulative distribution curve of the tight oil reservoir sample, determine the T2 relaxation time range and pore throat diameter range corresponding to different types of pore throat, and convert the T2 relaxation time into pore throat diameter; A fluid type identification module is used to identify the occurrence fluid in different types of pore throat through a two-dimensional nuclear magnetic resonance spectrum, obtain the fluid occurrence type corresponding to different signal domain ranges, and calculate the relative content of each fluid occurrence type; A fluid type identification chart establishment module is used to establish a two-dimensional nuclear magnetic resonance fluid occurrence type identification chart based on the signal domain range of each fluid occurrence type of a plurality of tight oil reservoir samples, and to clearly define the identification criteria for each fluid occurrence type.

Images