WO2019214267A1 - 一种考虑驰豫组分区间的致密岩心核磁共振孔隙度校正方法 - Google Patents

一种考虑驰豫组分区间的致密岩心核磁共振孔隙度校正方法 Download PDF

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WO2019214267A1
WO2019214267A1 PCT/CN2018/125986 CN2018125986W WO2019214267A1 WO 2019214267 A1 WO2019214267 A1 WO 2019214267A1 CN 2018125986 W CN2018125986 W CN 2018125986W WO 2019214267 A1 WO2019214267 A1 WO 2019214267A1
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milliseconds
porosity
magnetic resonance
core
relaxation
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French (fr)
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葛新民
范宜仁
刘建宇
邢东辉
胡法龙
邓少贵
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中国石油大学(华东)
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Publication of WO2019214267A1 publication Critical patent/WO2019214267A1/zh

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01VGEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/18Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
    • G01V3/32Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with electron or nuclear magnetic resonance
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01VGEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/38Processing data, e.g. for analysis, for interpretation, for correction
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/30Assessment of water resources

Definitions

  • the present invention belongs to the field of geophysical logging, and in particular relates to a compact core NMR porosity correction method that considers a relaxation component interval.
  • Nuclear magnetic resonance is the only geophysical technology that can simultaneously reflect pore and fluid information. It has been widely used in petrophysical experiments and well logging evaluation, and has achieved good results in reservoir physical property calculation and fluid identification.
  • the echo interval is an important factor affecting the accuracy of nuclear magnetic resonance measurement. For rocks with good physical properties and large apertures, the results of nuclear magnetic resonance measurements are less affected by the echo interval. However, the dense rock has a small aperture, a complex relaxation characteristic, a high proportion of short relaxation components, and a large influence of the nuclear magnetic resonance signal on the echo interval, resulting in inversion of the NMR T2 spectrum and the porosity distortion obtained by the scale. Core NMR can reduce the echo interval to 0.1ms or less, which can minimize the impact of molecular diffusion on NMR. However, the existing downhole NMR instruments have higher echo intervals. Except for Schlumberger's NMR logging instruments, the shortest echo interval is 0.2ms. The NMR logging tools produced by other companies are the shortest. The echo spacing is generally greater than 0.6 ms, and the application capacity in complex and conventional oil and gas such as compact and shale is limited.
  • the present invention provides a method for correcting a dense core NMR hole porosity considering a relaxation component interval.
  • a compact core NMR porosity correction method considering a relaxation component interval comprising the following steps: [0007] (1) Drilling, cutting, washing oil, washing salt and drying treatment on the dense core, measuring the core length and diameter, placing the core into the saturation meter, so that the core pores are completely saturated with water;
  • the waiting time of the core NMR apparatus is set to 6 seconds, the number of scans is set to 256 times, and the total water-bearing core is measured at intervals of 0.2 milliseconds, 0.3 milliseconds, 0.6 milliseconds, 0.9 milliseconds, and 1.2 milliseconds. And a magnetization vector decay curve at 2.4 ms, and inverting the magnetization vector decay curve into a T2 spectrum;
  • the waiting time of the core NMR apparatus is set to 6 seconds, the number of scans is set to 256 times, and the standard samples with known porosity are measured at echo intervals of 0.2 milliseconds, 0.3 milliseconds, 0.6 milliseconds, 0.9.
  • the magnetization vector decay curve in milliseconds, 1. 2 milliseconds and 2.4 milliseconds, and the magnetization vector attenuation curve is inverted into the T2 spectrum, and the relationship between the porosity and the nuclear magnetic resonance response is established by the spectral area method;
  • (6) determining a T2 distribution range of different relaxation component intervals, a T2 distribution range of the first relaxation component interval is 0.01 milliseconds to a millisecond; and a T2 distribution range of the second relaxation component interval is a millisecond Up to b milliseconds, the T2 distribution of the third relaxation component interval ranges from b milliseconds to 10000 milliseconds;
  • the echo interval is the
  • the echo interval is the
  • the core frequency magnetic resonance instrument has a dominant frequency of 2 MHz.
  • the a is 0.3 milliseconds and b is 7 milliseconds.
  • the present invention considers the influence of the echo interval on different relaxation component intervals, and can accurately correct the NMR porosity of any echo interval, and eliminates the low precision of the simple correction method of the previous component of the relaxation component.
  • the defects greatly improve the accuracy of NMR porosity measurement of dense cores, and have important significance for the porosity correction measured by downhole NMR instruments.
  • 1 is a flow chart of a method for correcting a dense core NMR porosity considering a relaxation component interval according to the present invention.
  • the waiting time is 6 seconds and the number of scans is 256 times in a core NMR apparatus having a frequency of 2 MHz.
  • the E2 spectrum of the echo interval (T E ) is 0.2 milliseconds, 0.3 milliseconds, 0.6 milliseconds, 0.9 milliseconds, 1.2 milliseconds, and 2.4 milliseconds, respectively.
  • T E is the second-order difference of the T2 spectrum at 0.2 milliseconds.
  • 4a is a comparison of porosity measured by an initial relaxation component at an echo interval of 0.2 milliseconds and 0.3 milliseconds, respectively, in an embodiment of the present invention (magnetic resonance porosity measured on an abscissa of 0.3 milliseconds, and an ordinate of 0.2). MRI porosity measured in milliseconds);
  • 4b is a comparison of the porosity of the first relaxation component measured at echo intervals of 0.2 milliseconds and 0.6 milliseconds, respectively, in the embodiment of the present invention (the nuclear magnetic resonance porosity measured on the abscissa of 0.6 milliseconds, the ordinate is 0.2) MRI porosity measured in milliseconds);
  • 4c is a comparison of porosity measured by the first relaxation component in the echo interval of 0.2 milliseconds and 0.9 milliseconds respectively (the abscissa is 0.9 milliseconds measured nuclear magnetic resonance porosity, and the ordinate is 0.2). MRI porosity measured in milliseconds);
  • 4d is a comparison of porosity measured by the first relaxation component in the echo interval of 0.2 milliseconds and 1.2 milliseconds, respectively, in the embodiment of the present invention (the nuclear magnetic resonance porosity measured on the abscissa of 1.2 milliseconds, the ordinate is 0.2) MRI porosity measured in milliseconds);
  • 4e is a comparison of the porosity of the first relaxation component measured at echo intervals of 0.2 milliseconds and 2.4 milliseconds, respectively, in the embodiment of the present invention (magnetic resonance porosity measured on the abscissa of 2.4 milliseconds, the ordinate is 0.2) Millisecond measurement of NMR porosity).
  • 5a is a comparison of porosity measured by an echo fraction at intervals of 0.2 milliseconds and 0.3 milliseconds, respectively, in an embodiment of the present invention (magnetic resonance porosity measured on an abscissa of 0.3 milliseconds, and an ordinate of 0.2) MRI porosity measured in milliseconds);
  • 5b is a comparison of porosity measured by the second relaxation component in the echo interval of 0.2 milliseconds and 0.6 milliseconds respectively (the abscissa is 0.6 milliseconds measured nuclear magnetic resonance porosity, and the ordinate is 0.2). MRI porosity measured in milliseconds);
  • 5c is a comparison of porosity measured by the second relaxation component in the echo interval of 0.2 milliseconds and 0.9 milliseconds respectively (the abscissa is 0.9 milliseconds measured nuclear magnetic resonance porosity, and the ordinate is 0.2). MRI porosity measured in milliseconds);
  • 5d is a comparison of the porosity of the second relaxation component measured at echo intervals of 0.2 milliseconds and 1.2 milliseconds, respectively, in the embodiment of the present invention (the magnetic resonance porosity measured on the abscissa of 1.2 milliseconds, the ordinate is 0.2) MRI porosity measured in milliseconds); 5e is a comparison of porosity measured by an echo fraction at intervals of 0.2 milliseconds and 2.4 milliseconds, respectively, in an embodiment of the present invention (magnetic resonance porosity measured on an abscissa of 2.4 milliseconds, and an ordinate of 0.2) Millisecond measurement of NMR porosity).
  • 6a is a comparison of porosity measured by an echo fraction at intervals of 0.2 milliseconds and 0.3 milliseconds, respectively, in an embodiment of the present invention (magnetic resonance porosity measured on an abscissa of 0.3 milliseconds, and an ordinate of 0.2) MRI porosity measured in milliseconds);
  • 6b is a comparison of porosity measured by an echo fraction at intervals of 0.2 milliseconds and 0.6 milliseconds, respectively, in an embodiment of the present invention (magnetic resonance porosity measured on an abscissa of 0.6 milliseconds, and an ordinate of 0.2) MRI porosity measured in milliseconds);
  • 6c is a comparison of porosity measured by an echo fraction at intervals of 0.2 milliseconds and 0.9 milliseconds, respectively, in an embodiment of the present invention (magnetic resonance porosity measured on an abscissa of 0.9 milliseconds, and an ordinate of 0.2) MRI porosity measured in milliseconds);
  • 6d is a comparison of the porosity of the third relaxation component measured at echo intervals of 0.2 milliseconds and 1.2 milliseconds, respectively, in the embodiment of the present invention (magnetic resonance porosity measured on the abscissa of 1.2 milliseconds, the ordinate is 0.2) MRI porosity measured in milliseconds);
  • 6e is a comparison of porosity measured by an echo fraction at intervals of 0.2 milliseconds and 2.4 milliseconds, respectively, in an embodiment of the present invention (magnetic resonance porosity measured on an abscissa of 2.4 milliseconds, and an ordinate of 0.2) Millisecond measurement of NMR porosity).
  • NMR porosity correction formula for different echo intervals and different relaxation component intervals in an embodiment of the present invention.
  • the present invention proposes a reasonable and effective nuclear magnetic resonance porosity correction method, specifically to establish a compact core NMR porosity correction method considering the relaxation component interval, so as to effectively solve the existing nuclear magnetic resonance logging
  • the shortest echo spacing of the instrument is typically greater than 0.6 ms, and the application capacity in dense cores is limited.
  • the invention measures nuclear magnetic resonance under different echo spacing conditions by measuring dense cores with complete water content
  • the vibration attenuation curves are inverted into T2 spectra and scaled into porosity.
  • the relationship between the amplitude of the T 2 spectrum of different relaxation components and the echo interval is compared, and the amplitude reduction of different relaxation components is established.
  • the relationship with the echo interval, the data is corrected to the value measured at the shortest echo interval, and the NMR porosity is effectively corrected, thereby effectively improving the ability of the nuclear magnetic resonance logging data to characterize the reservoir.
  • a compact core NMR porosity correction method considering a relaxation component interval comprising the following steps:
  • the waiting time of the core NMR apparatus with a frequency of 2 MHz is set to 6 seconds, the number of scans is set to 256 times, and the total water-bearing core is measured at intervals of 0.2 milliseconds, 0.3 milliseconds, and 0.6.
  • the waiting time of the core NMR apparatus with a dominant frequency of 2 MHz is set to 6 seconds, the number of scans is set to 256 times, and the standard samples with known porosity are measured at an echo interval of 0.2 milliseconds, respectively.
  • the magnetization vector decay curves at 0.3 milliseconds, 0.6 milliseconds, 0.9 milliseconds, 1.2 milliseconds, and 2.4 milliseconds, and the magnetization vector attenuation curve is inverted into a T2 spectrum, and the relationship between the porosity and the nuclear magnetic resonance response, that is, the T2 spectrum, is established by the spectral area method;
  • (6) determining a T2 distribution range of different relaxation component intervals, a T2 distribution range of the first relaxation component interval is 0.01 milliseconds to a millisecond; and a T2 distribution range of the second relaxation component interval is a millisecond Up to b milliseconds, the T2 distribution of the third relaxation component interval ranges from b milliseconds to 10,000 milliseconds.
  • the echo interval is the
  • the echo interval is the
  • the echo interval is the
  • the above-mentioned porosity correction formulas for establishing different echo intervals and different relaxation components are specifically referred to respectively.
  • the data correction relationship is established when the echo interval is 0.3 milliseconds, 0.6 milliseconds, 0.9 milliseconds, 1.2 milliseconds, and 2.4 milliseconds, and the echo interval is 0.2 milliseconds (the shortest echo interval). For example, when the echo interval is 0.6 milliseconds, the data correction relationship with the shortest echo interval of 0.2 milliseconds is established. In this case, in equations (1) to (3),
  • the corrected NMR porosity of the first, second, and third relaxation components when the echo interval is 0.2 milliseconds, respectively;
  • the NMR porosity of the first, second, and third relaxation components when the echo interval is 0.6 milliseconds, respectively;
  • the corrected NMR porosity of the first, second, and third relaxation components when the echo interval is 0.2 milliseconds, respectively;
  • the NMR porosity of the first, second, and third relaxation components when the echo interval is 0.9 milliseconds, respectively;
  • the correction factor is the echo interval of 0.9 milliseconds.
  • the correction factor when the echo interval is 0.6 msec and the correction coefficient when the echo interval is 0.9 msec are not the same.
  • the magnetization vector attenuation curve measured in the downhole can be inverted into a T 2 spectrum, and then the signal of the three relaxation component intervals is scaled into a porosity by the spectral area method, and then substituted into the porosity correction.
  • the corrected porosity is obtained by equations (1) to (4).
  • the core NMR apparatus is applicable to other main frequencies in addition to the main frequency of 2 MHz.
  • the parameters described in steps (2) and (3) can also be adjusted as needed.
  • the relaxation component interval may not be limited to three, and may be dynamically adjusted according to test results of different regions and different products.
  • the a is generally 0.3 milliseconds
  • b is generally 7 milliseconds
  • the two parameters are empirical statistics, and can also be dynamically adjusted according to test results of different regions and different samples.
  • a compact core NMR porosity correction method considering a relaxation component interval performing nuclear magnetic resonance measurement and inversion on a completely water-bearing rock under different echo intervals to obtain a nuclear magnetic resonance T 2 spectrum, and T 2 spectrum scale into porosity.
  • the second-order difference is made to the NMR T 2 spectrum of the shortest echo interval measured by the experiment, and the relaxation component interval is determined according to the second-order differential zero point, and the rock relaxation information is divided into a plurality of intervals.
  • the relationship between the NMR porosity of the shortest echo interval and the NMR porosity under different echo intervals is established for each relaxation component interval, and the NMR pores of each relaxation component interval are realized. Degree correction.
  • the NMR porosity of the corrected plurality of relaxation component intervals is accumulated to obtain the corrected dense rock NMR porosity.
  • the smaller the relaxation time and the larger the echo interval the larger the correction amount of the NMR porosity.
  • 1 is a compact core NMR porosity correction method considering the relaxation component interval, which mainly includes multiple sets of echo-interval rock and standard nuclear magnetic resonance signal measurement, nuclear magnetic resonance T 2 spectral inversion and pores. Degree scale, relaxation component interval and 1 ⁇ distribution range determination based on second-order difference, NMR porosity correction of different relaxation components, and compact rock NMR porosity correction are indispensable, and the order is not available. reverse.
  • the waiting time is 6 seconds and the number of scans is 256 times in a core NMR apparatus with a frequency of 2 MHz.
  • the echo interval (T E ) is 1 ⁇ 2 spectrum at 0.2 milliseconds, 0.3 milliseconds, 0.6 milliseconds, 0.9 milliseconds, 1.2 milliseconds, and 2.4 milliseconds. It can be seen from the figure that with the increase of the echo interval, the area of the NMR spectrum is gradually reduced, and the interval of the short relaxation component with the smaller relaxation time is the largest.
  • Echo interval (T E ) is the second-order difference of the 1 ⁇ spectrum at 0.2 ms.
  • the T 2 distribution of the first relaxation component interval ranges from about 0.01 milliseconds to 0.3 milliseconds; the T 2 distribution of the second relaxation component interval ranges from about 0.3 milliseconds to 7 milliseconds; the third relaxation group
  • the T 2 distribution of the bins ranges from about 7 milliseconds to 10,000 milliseconds.
  • FIG. 4 to FIG. 6 are respectively the relationship between the NMR porosity of the first, second and third relaxation components at the shortest echo interval and the NMR porosity of other echo intervals in the embodiment of the present invention. As can be seen from the figure, they all show a good linear relationship.
  • NMR porosity correction formula for different echo intervals and different relaxation component intervals according to an embodiment of the present invention, and linear magnetic fitting can be used to correct the nuclear magnetic porosity of each relaxation component interval to the shortest time. Wave-interval NMR porosity.
  • the abscissa is the nuclear magnetic resonance porosity measured when the core interval is 0.2 milliseconds, and the ordinate is the corrected nuclear magnetic field).
  • Resonance porosity It can be seen from the figure that after calibration, the NMR porosity measured at any echo interval is basically the same as the porosity measured by the shortest echo interval, and the average relative error is less than 3%, indicating that the calibration result is very effective.

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Abstract

一种考虑弛豫组分区间的致密岩心核磁共振孔隙度校正方法,通过对完全含水岩石开展不同回波间隔条件下的核磁共振测量并反演得到核磁共振T2谱,并将T2谱刻度成孔隙度;对实验测得的最短回波间隔的核磁共振T2谱做二阶差分,根据二阶差分为零的点确定弛豫组分区间;针对多个弛豫组分区间,分别建立最短回波间隔核磁共振孔隙度与不同回波间隔条件下核磁共振孔隙度的关系,进而实现各个弛豫组分区间的核磁共振孔隙度校正;最后将校正后的多个弛豫组分区间的核磁共振孔隙度累加,即可得到经过校正后的致密岩石核磁共振孔隙度。考虑了回波间隔对不同弛豫组分区间的影响,可实现任意回波间隔的核磁共振孔隙度精确校正。

Description

一种考虑驰豫组分区间的致密岩心核磁共振孔隙度校正 方法
技术领域
[0001] 本发明属于地球物理测井领域, 具体地说是涉及一种考虑弛豫组分区间的致密 岩心核磁共振孔隙度校正方法。
背景技术
[0002] 核磁共振是目前唯一能同时反映孔隙和流体信息的地球物理技术, 已广泛应用 于岩石物理实验和测井评价领域, 在储层物性参数计算和流体识别中取得较好 的效果。
[0003] 回波间隔是影响核磁共振测量精度的重要因素, 对于物性好、 孔径大的岩石来 说, 核磁共振测量结果受回波间隔影响小。 然而, 致密岩石的孔径小, 弛豫特 征复杂, 短弛豫组分占比高, 核磁共振信号受回波间隔影响大, 导致反演得到 的核磁共振 T2谱和刻度得到的孔隙度失真。 岩心核磁共振仪可以将回波间隔降 至 0.1ms甚至更低, 能最大程度地降低分子扩散对核磁共振的影响。 但现有的井 下核磁共振仪器的回波间隔较高, 除斯伦贝谢公司的核磁共振测井仪器其最短 回波间隔为 0.2ms外, 其它公司所生产的核磁共振测井仪器, 其最短回波间隔一 般大于 0.6ms, 在致密、 页岩等复杂及常规油气中的应用能力受到限制。
发明概述
技术问题
问题的解决方案
技术解决方案
[0004] 基于上述技术问题, 本发明提供一种考虑驰豫组分区间的致密岩心核磁共振孔 隙度校正方法。
[0005] 本发明所采用的技术解决方案是:
[0006] 一种考虑驰豫组分区间的致密岩心核磁共振孔隙度校正方法, 包括以下步骤: [0007] ( 1) 对致密岩心依次进行钻取、 切割、 洗油、 洗盐、 烘干处理, 测量岩心 长度和直径, 将岩心放入饱和仪, 使岩心孔隙完全饱和水;
[0008] (2) 将岩心核磁共振仪的等待时间设为 6秒, 扫描次数设为 256次, 测量完 全含水岩心在回波间隔分别为 0.2毫秒、 0.3毫秒、 0.6毫秒、 0.9毫秒、 1.2毫秒和 2 .4毫秒时的磁化矢量衰减曲线, 并将磁化矢量衰减曲线反演成 T2谱;
[0009] (3) 将岩心核磁共振仪的等待时间设为 6秒, 扫描次数设为 256次, 测量孔 隙度已知的标准样品在回波间隔分别为 0.2毫秒、 0.3毫秒、 0.6毫秒、 0.9毫秒、 1. 2毫秒和 2.4毫秒时的磁化矢量衰减曲线, 并将磁化矢量衰减曲线反演成 T2谱, 采 用谱面积法建立孔隙度与核磁共振响应的关系;
[0010] (4) 根据步骤 (3) 建立的孔隙度与核磁共振响应的关系, 将步骤 ⑵ 所 测的核磁信号转换成岩心孔隙度;
[0011] (5) 对完全含水岩心在回波间隔为 0.2毫秒时所测得的 T2谱进行二阶差分, 将二阶差分值为零的点记为弛豫组分的截止值, 分别为 a, b;
[0012] (6) 确定不同弛豫组分区间的 T2分布范围, 第一弛豫组分区间的 T2分布范 围为 0.01毫秒至 a毫秒; 第二弛豫组分区间的 T2分布范围为 a毫秒至 b毫秒, 第三 弛豫组分区间的 T2分布范围为 b毫秒至 10000毫秒;
[0013] (7) 采用谱面积法将三个弛豫组分区间的信号刻度成孔隙度, 建立不同回波 间隔、 不同弛豫组分的孔隙度校正公式, 如式 ( 1) 至式 (3) :
[0014]
[数]
Figure imgf000004_0001
[0015]
[数]
Figure imgf000004_0002
[0016] [数]
Figure imgf000005_0001
[0017] 式中:
[数]
[数]
分别为回波间隔为
[数]
TE
时第一、 第二、 第三弛豫组分的校正后核磁共振孔隙度;
[数]
[数]
[数] 分别为回波间隔为
[数]
时第一、 第二、 第三弛豫组分的核磁共振孔隙度;
[数]
[数]
[数]
[数]
分别为回波间隔为
[数]
T
^ E 时的校正系数;
[0018] (8) 根据步骤 (7) 确定的不同弛豫组分孔隙度校正公式, 得到校正后的致 密岩心核磁共振孔隙度, 如式 (4) :
[0019]
[数]
Figure imgf000007_0001
⑷。
[0020] 优选的, 所述岩心核磁共振仪的主频为 2兆赫兹。
[0021] 优选的, 所述 a为 0.3毫秒, b为 7毫秒。
发明的有益效果
有益效果
[0022] 本发明的有益技术效果是:
[0023] 本发明考虑了回波间隔对不同弛豫组分区间的影响, 可实现任意回波间隔的核 磁共振孔隙度精确校正, 摒弃了以往不分弛豫组分区间的简单校正方法精度低 的缺陷, 大大提升了致密岩心的核磁共振孔隙度测量精度, 对井下核磁共振仪 器测量的孔隙度校正具有重要意义。
对附图的简要说明
附图说明
[0024] 下面结合附图与具体实施方式对本发明作更进一步的说明:
[0025] 图 1为本发明提供的一种考虑弛豫组分区间的致密岩心核磁共振孔隙度校正方 法的流程图。
[0026] 图 2为本发明实施例中某地区完全含水的致密岩心 (孔隙度为 5.9%) 分别在主 频为 2兆赫兹的岩心核磁共振仪中等待时间为 6秒, 扫描次数为 256次, 回波间隔 (T E) 分别为 0.2毫秒、 0.3毫秒、 0.6毫秒、 0.9毫秒、 1.2毫秒和 2.4毫秒时的 T2谱
[0027] 图 3为本发明实施例中某地区完全含水的致密岩心 (孔隙度为 5.9%) 在主频为 2 兆赫兹的岩心核磁共振仪中等待时间为 6秒, 扫描次数为 256次, 回波间隔 (T E ) 为 0.2毫秒时的 T2谱的二阶差分。
[0028] 图 4a为本发明实施例中第一弛豫组分在回波间隔分别为 0.2毫秒和 0.3毫秒测量 的孔隙度对比 (横坐标为 0.3毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0029] 图 4b为本发明实施例中第一弛豫组分在回波间隔分别为 0.2毫秒和 0.6毫秒测量 的孔隙度对比 (横坐标为 0.6毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0030] 图 4c为本发明实施例中第一弛豫组分在回波间隔分别为 0.2毫秒和 0.9毫秒测量 的孔隙度对比 (横坐标为 0.9毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0031] 图 4d为本发明实施例中第一弛豫组分在回波间隔分别为 0.2毫秒和 1.2毫秒测量 的孔隙度对比 (横坐标为 1.2毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0032] 图 4e为本发明实施例中第一弛豫组分在回波间隔分别为 0.2毫秒和 2.4毫秒测量 的孔隙度对比 (横坐标为 2.4毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) 。
[0033] 图 5a为本发明实施例中第二弛豫组分在回波间隔分别为 0.2毫秒和 0.3毫秒测量 的孔隙度对比 (横坐标为 0.3毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0034] 图 5b为本发明实施例中第二弛豫组分在回波间隔分别为 0.2毫秒和 0.6毫秒测量 的孔隙度对比 (横坐标为 0.6毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0035] 图 5c为本发明实施例中第二弛豫组分在回波间隔分别为 0.2毫秒和 0.9毫秒测量 的孔隙度对比 (横坐标为 0.9毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0036] 图 5d为本发明实施例中第二弛豫组分在回波间隔分别为 0.2毫秒和 1.2毫秒测量 的孔隙度对比 (横坐标为 1.2毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ; [0037] 图 5e为本发明实施例中第二弛豫组分在回波间隔分别为 0.2毫秒和 2.4毫秒测量 的孔隙度对比 (横坐标为 2.4毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) 。
[0038] 图 6a为本发明实施例中第三弛豫组分在回波间隔分别为 0.2毫秒和 0.3毫秒测量 的孔隙度对比 (横坐标为 0.3毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0039] 图 6b为本发明实施例中第三弛豫组分在回波间隔分别为 0.2毫秒和 0.6毫秒测量 的孔隙度对比 (横坐标为 0.6毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0040] 图 6c为本发明实施例中第三弛豫组分在回波间隔分别为 0.2毫秒和 0.9毫秒测量 的孔隙度对比 (横坐标为 0.9毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0041] 图 6d为本发明实施例中第三弛豫组分在回波间隔分别为 0.2毫秒和 1.2毫秒测量 的孔隙度对比 (横坐标为 1.2毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) ;
[0042] 图 6e为本发明实施例中第三弛豫组分在回波间隔分别为 0.2毫秒和 2.4毫秒测量 的孔隙度对比 (横坐标为 2.4毫秒测量的核磁共振孔隙度, 纵坐标为 0.2毫秒测量 的核磁共振孔隙度) 。
[0043] 图 7为本发明实施例中不同回波间隔、 不同弛豫组分区间的核磁共振孔隙度校 正公式。
[0044] 图 8为本发明实施例中不同回波间隔的核磁共振孔隙度效果对比 (横坐标为 0.2 毫秒测量的核磁共振孔隙度, 纵坐标为校正后的核磁共振孔隙度) 。
发明实施例
本发明的实施方式
[0045] 本发明提出一种合理有效的核磁共振孔隙度校正方法, 具体地说是建立一种考 虑弛豫组分区间的致密岩心核磁共振孔隙度校正方法, 以有效解决现有核磁共 振测井仪器的最短回波间隔一般大于 0.6ms, 在致密岩心中的应用能力受到限制 的问题。 本发明通过测量完全含水的致密岩心在不同回波间隔条件下的核磁共 振衰减曲线, 将它们反演成 T2谱, 并刻度成孔隙度; 对比不同弛豫组分区间段 T 2谱的幅度与回波间隔的关系, 建立不同弛豫组分区间段幅度减小量与回波间隔 的关系, 将数据校正到最短回波间隔时所测值, 实现核磁共振孔隙度的有效校 正, 进而有效提升核磁共振测井资料表征储层的能力。
[0046] 一种考虑驰豫组分区间的致密岩心核磁共振孔隙度校正方法, 包括以下步骤:
[0047] ( 1) 对致密岩心依次开展钻取、 切割、 洗油、 洗盐、 烘干等预处理, 得到 预处理后的柱状岩心, 测量岩心长度和直径, 将岩心放入饱和仪, 使岩心孔隙 完全饱和水。
[0048] (2) 将主频为 2兆赫兹的岩心核磁共振仪的等待时间设为 6秒, 扫描次数设 为 256次, 测量完全含水岩心在回波间隔分别为 0.2毫秒、 0.3毫秒、 0.6毫秒、 0.9 毫秒、 1.2毫秒和 2.4毫秒时的磁化矢量衰减曲线, 并采用仪器自带软件将磁化矢 量衰减曲线反演成 T2谱。
[0049] (3) 将主频为 2兆赫兹的岩心核磁共振仪的等待时间设为 6秒, 扫描次数设 为 256次, 测量孔隙度已知的标准样品在回波间隔分别为 0.2毫秒、 0.3毫秒、 0.6 毫秒、 0.9毫秒、 1.2毫秒和 2.4毫秒时的磁化矢量衰减曲线, 并将磁化矢量衰减曲 线反演成 T2谱, 采用谱面积法建立孔隙度与核磁共振响应即 T2谱的关系;
[0050] (4) 根据步骤 (3) 建立的孔隙度与核磁共振响应的关系, 将步骤 ⑵ 所 测的核磁信号或者说 T2谱转换成岩心孔隙度。
[0051] (5) 对完全含水岩心所测得的 T2谱进行二阶差分, 将二阶差分值为零的点 记为弛豫组分的截止值, 分别为 a, b。
[0052] (6) 确定不同弛豫组分区间的 T2分布范围, 第一弛豫组分区间的 T2分布范 围为 0.01毫秒至 a毫秒; 第二弛豫组分区间的 T2分布范围为 a毫秒至 b毫秒, 第三 弛豫组分区间的 T2分布范围为 b毫秒至 10000毫秒。
[0053] (7) 采用谱面积法将三个弛豫组分区间的信号刻度成孔隙度, 建立不同回波 间隔、 不同弛豫组分的孔隙度校正公式, 如式 ( 1) 至式 (3) :
[0054]
[数]
Figure imgf000010_0001
(D
[0055]
[数]
Figure imgf000011_0001
[0056]
[数]
Figure imgf000011_0002
[0057] 式中:
[数]
[数]
4
分别为回波间隔为
[数]
时第一、 第二、 第三弛豫组分的校正后核磁共振孔隙度;
[数] [数]
[数]
分别为回波间隔为
[数]
时第一、 第二、 第三弛豫组分的核磁共振孔隙度;
[数]
xiT_
[数]
Xw
[数]
X3:T£
[数]
[数] [数]
分别为回波间隔为
[数]
时的校正系数。
[0058] 需要进一步说明的是, 由于回波间隔为 0.2毫秒时测得的孔隙度是比较准确的, 因此上述建立不同回波间隔、 不同驰豫组分的孔隙度校正公式, 具体是指分别 建立回波间隔为 0.3毫秒、 0.6毫秒、 0.9毫秒、 1.2毫秒和 2.4毫秒时, 与回波间隔 为 0.2毫秒时 (最短回波间隔) 的数据校正关系。 比如说建立回波间隔为 0.6毫秒 时与最短回波间隔 0.2毫秒的数据校正关系, 此时, 式 (1) 至式 (3) 中,
[数]
分别为回波间隔为 0.2毫秒时第一、 第二、 第三弛豫组分的校正后核磁共振孔隙 度;
[数] [数]
[数]
分别为回波间隔为 0.6毫秒时第一、 第二、 第三弛豫组分的核磁共振孔隙度;
[数]
[数]
X—
[数]
[数]
[数]
.)?
[数] Mi} 分别为回波间隔为 0.6毫秒时的校正系数。 又如, 建立回波间隔为 0.9毫秒时与最 短回波间隔 0.2毫秒的数据校正关系, 此时, 式 (1) 至式 (3) 中,
[数]
[数]
分别为回波间隔为 0.2毫秒时第一、 第二、 第三弛豫组分的校正后核磁共振孔隙 度;
[数]
[数]
[数]
分别为回波间隔为 0.9毫秒时第一、 第二、 第三弛豫组分的核磁共振孔隙度;
[数] [数]
[数]
[数]
[数]
分别为回波间隔为 0.9毫秒时的校正系数。 当然, 回波间隔为 0.6毫秒时的校正系 数和回波间隔为 0.9毫秒时的校正系数是不一样的。
[0059] (8) 根据步骤 (7) 确定的不同弛豫组分孔隙度校正公式, 得到校正后的致 密岩心核磁共振孔隙度, 如式 (4) :
[0060] [数]
Figure imgf000016_0001
⑷。
[0061] 具体应用时, 可根据井下测得的磁化矢量衰减曲线, 反演成 T 2谱, 然后采用谱 面积法将三个弛豫组分区间的信号刻度成孔隙度, 再代入孔隙度校正公式 (1) 至 (4) , 即可得到校正后的孔隙度。 [0062] 上述步骤中: 岩心核磁共振仪除选用 2兆赫兹的主频外, 也适用于其它主频。 当然, 步骤 (2) 和步骤 (3) 中所述的参数也可根据需要进行调整。
[0063] 上述步骤中: 所述的弛豫组分区间也可不仅仅限于三个, 可根据不同地区、 不 同样品的测试结果进行动态调整。
[0064] 上述步骤中: 所述的 a—般为 0.3毫秒, b—般为 7毫秒, 这 2个参数为经验统计值 , 也可根据不同地区、 不同样品的测试结果进行动态调整。
[0065] 下面结合附图对本发明进行更为具体的说明。
[0066] 一种考虑弛豫组分区间的致密岩心核磁共振孔隙度校正方法, 通过对完全含水 岩石开展不同回波间隔条件下的核磁共振测量并反演得到核磁共振 T 2谱、 并将 T 2谱刻度成孔隙度。 对实验测得的最短回波间隔的核磁共振 T 2谱做二阶差分, 根 据二阶差分为零的点确定弛豫组分区间, 将岩石弛豫信息分为多个区间。 在此 基础上, 针对多个弛豫组分区间, 分别建立最短回波间隔核磁共振孔隙度与不 同回波间隔条件下核磁共振孔隙度的关系, 进而实现各个弛豫组分区间的核磁 共振孔隙度校正。 最后将校正后的多个弛豫组分区间的核磁共振孔隙度累加, 即可得到经过校正后的致密岩石核磁共振孔隙度。 一般而言, 弛豫时间越小、 回波间隔越大, 核磁共振孔隙度的校正量越大。
[0067] 图 1是一种考虑弛豫组分区间的致密岩心核磁共振孔隙度校正方法, 主要包括 多组回波间隔的岩石及标样核磁共振信号测量、 核磁共振 T 2谱反演及孔隙度刻 度、 基于二阶差分的弛豫组分区间及 1\分布范围确定, 不同弛豫组分区间核磁 共振孔隙度校正, 致密岩石核磁共振孔隙度校正这五部分, 缺一不可, 且顺序 不可颠倒。
[0068] 图 2是本发明实施例中某地区完全含水的致密岩心 (孔隙度为 5.9%) 分别在主 频为 2兆赫兹的岩心核磁共振仪中等待时间为 6秒, 扫描次数为 256次, 回波间隔 (T E) 为 0.2毫秒、 0.3毫秒、 0.6毫秒、 0.9毫秒、 1.2毫秒和 2.4毫秒时的 1^ 2谱。 从 图中可知, 随着回波间隔的增大, 核磁共振!^谱面积逐步减小, 弛豫时间较小 的短弛豫组分区间的减小幅度最大。
[0069] 图 3是本发明实施例中某地区完全含水的致密岩心 (孔隙度为 5.9%) 在主频为 2 兆赫兹的岩心核磁共振仪中等待时间为 6秒, 扫描次数为 256次, 回波间隔 (T E ) 为 0.2毫秒时的 1\谱的二阶差分。 从图中可知, 第一弛豫组分区间的 T 2分布范 围约为 0.01毫秒至 0.3毫秒; 第二弛豫组分区间的 T 2分布范围约为 0.3毫秒至 7毫秒 ; 第三弛豫组分区间的 T 2分布范围约为 7毫秒至 10000毫秒。
[0070] 图 4至图 6分别是本发明实施例中第一、 第二和第三弛豫组分在最短回波间隔的 核磁共振孔隙度与其它回波间隔的核磁共振孔隙度的关系。 从图中可知, 它们 均呈现良好线性关系。
[0071] 图 7为本发明实施例中不同回波间隔、 不同弛豫组分区间的核磁共振孔隙度校 正公式, 采用线性拟合可将各弛豫组分区间的核磁孔隙度校正到最短回波间隔 的核磁共振孔隙度。
[0072] 图 8为本发明实施例中不同回波间隔的核磁共振孔隙度效果对比 (横坐标为岩 心在回波间隔为 0.2毫秒时测得的核磁共振孔隙度, 纵坐标为校正后的核磁共振 孔隙度) 。 从图中可知, 经过校正后, 任意回波间隔下测量得到的核磁共振孔 隙度与最短回波间隔测量得到的孔隙度基本一致, 平均相对误差基本小于 3%, 说明校正结果十分有效。

Claims

权利要求书
[权利要求 1] 一种考虑驰豫组分区间的致密岩心核磁共振孔隙度校正方法, 其特征 在于包括以下步骤:
( D 对致密岩心依次进行钻取、 切割、 洗油、 洗盐、 烘干处理, 测量岩心长度和直径, 将岩心放入饱和仪, 使岩心孔隙完全饱和水;
(2) 将岩心核磁共振仪的等待时间设为 6秒, 扫描次数设为 256次 , 测量完全含水岩心在回波间隔分别为 0.2毫秒、 0.3毫秒、 0.6毫秒、 0.9毫秒、 1.2毫秒和 2.4毫秒时的磁化矢量衰减曲线, 并将磁化矢量衰 减曲线反演成 T 2谱;
(3) 将岩心核磁共振仪的等待时间设为 6秒, 扫描次数设为 256次
, 测量孔隙度已知的标准样品在回波间隔分别为 0.2毫秒、 0.3毫秒、 0 .6毫秒、 0.9毫秒、 1.2毫秒和 2.4毫秒时的磁化矢量衰减曲线, 并将磁 化矢量衰减曲线反演成 T2谱, 采用谱面积法建立孔隙度与核磁共振 响应的关系;
(4) 根据步骤 (3) 建立的孔隙度与核磁共振响应的关系, 将步骤 (2) 所测的核磁信号转换成岩心孔隙度;
(5) 对完全含水岩心所测得的 T 2谱进行二阶差分, 将二阶差分值 为零的点记为弛豫组分的截止值, 分别为 a, b;
(6) 确定不同弛豫组分区间的 T 2
分布范围, 第一弛豫组分区间的 T 2分布范围为 0.01毫秒至 a毫秒; 第 二弛豫组分区间的 T 2分布范围为 a毫秒至 b毫秒, 第三弛豫组分区间 的 T 2分布范围为 b毫秒至 10000毫秒;
(7) 采用谱面积法将三个弛豫组分区间的信号刻度成孔隙度, 建立 不同回波间隔、 不同弛豫组分的孔隙度校正公式, 如式 ( 1) 至式 (3
Figure imgf000019_0001
Figure imgf000020_0001
时第一、 第二、 第三弛豫组分的校正后核磁共振孔隙度;
Figure imgf000020_0002
Figure imgf000020_0003
Figure imgf000020_0004
分别为回波间隔为
Figure imgf000021_0001
时第一、 第二、 第三弛豫组分的核磁共振孔隙度; xnv
Figure imgf000021_0002
Figure imgf000021_0003
Figure imgf000021_0004
Figure imgf000021_0005
Figure imgf000021_0006
分别为回波间隔为
TE 时的校正系数;
(8) 根据步骤 (7) 确定的不同弛豫组分孔隙度校正公式, 得到校 正后的致密岩心核磁共振孔隙度, 如式 (4) :
Figure imgf000021_0007
(4)。 。
[权利要求 2] 根据权利要求 1所述的一种考虑驰豫组分区间的致密岩心核磁共振孔 隙度校正方法, 其特征在于: 所述岩心核磁共振仪的主频为 2兆赫玆
[权利要求 3] 根据权利要求 1所述的一种考虑驰豫组分区间的致密岩心核磁共振孔 隙度校正方法, 其特征在于: 所述 a为 0.3毫秒, b为 7毫秒。
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