A method for evaluating TOC of hydrocarbon source rock by using T1-T2 two-dimensional nuclear magnetic resonance

Abstract

The application provides a method for evaluating TOC of a hydrocarbon source rock by using T1-T2 two-dimensional nuclear magnetic resonance, and the method comprises the following steps: obtaining high-quality T1-T2 spectrum signals, and then establishing a signal area percentage S of a signal representing TOC on the T1-T2 spectrum TOC A relationship model between the measured total organic carbon content TOC and the signal area percentage S, so as to calculate the total organic carbon content TOC of the hydrocarbon source rock to be measured, overcome the uncertainty and inaccuracy in the characterization of the TOC content of the hydrocarbon source rock caused by different instrument parameters and different measurement parameters, realize the evaluation of the characteristics of the hydrocarbon source rock while evaluating the oiliness and wateriness of the hydrocarbon source rock, fill the blank of the evaluation of TOC by using T1-T2 spectrum, and have simple operation, high accuracy, and very wide application range and prospect.

Description

Technical Field

[0001] This invention relates to the field of nuclear magnetic resonance evaluation of oil and gas engineering technology, and specifically designs a method for evaluating the total organic matter (TOC) of source rocks using T1-T2 two-dimensional nuclear magnetic resonance. Background Technology

[0002] Two-dimensional nuclear magnetic resonance (T1-T2) of source rocks can identify multiple pore fluid components in a single analysis, making it a hot technology for evaluating source rock oil and gas reservoirs. However, T1-T2 measurements are affected by multiple factors such as instruments, samples, and operations, resulting in significant differences between the spectral results and the interpretation results.

[0003] Instrument and operational factors include magnetic field strength, echo interval, probe aperture, measurement parameters, and inversion algorithm; sample factors include the airtightness of storage, temperature, and timeliness of analysis. Due to the numerous influencing factors, the number of T1-T2 signal peaks varies greatly, ranging from one to five or six peaks, and fluid signals and noise signals coexist, making the identification and verification of signal peaks difficult.

[0004] For the T1-T2 spectra of source rock oil reservoirs, the hydrocarbon signals interpreted are mainly of five types: (1) kerogen / solid bitumen, adsorbed oil, and movable oil (Jinbu Li, 2020); (2) kerogen or organic matter, and methane (Marc Fleury, 2016; Han Jiang, 2019; Xinhua Ma, 2020); (3) high-viscosity hydrocarbons, immovable oil, and movable oil (Andrew C. Johnson, 2021); (4) kerogen (not visible on low-field NMR), bitumen (partially visible), oil in organic pores (movable and immovable), and oil in inorganic pores (Ravinath Kausik, 2015); (5) kerogen, oil / bitumen (Mohammad Sadegh Zamiri, 2021). It can be seen that the understanding of kerogen, bitumen, organic matter, and oil in organic pores is relatively chaotic and mainly qualitative, without achieving a quantitative evaluation of total organic carbon (TOC). Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention aims to overcome the uncertainties in current two-dimensional nuclear magnetic resonance (NMR) measurements and interpretations of multi-component information (T1-T2) in source rock reservoirs, achieve high-precision quantitative calculation of TOC content, and provide reliable technical support for TOC evaluation of source rock oil and gas reservoirs.

[0006] This invention proposes a method for evaluating the total organic matter (TOC) of source rocks using T1-T2 two-dimensional nuclear magnetic resonance (NMR), comprising the following steps:

[0007] Step 1: Establish the percentage of signal area S representing TOC on the T1-T2 spectrum of the source rock.TOC A model relating the total organic carbon (TOC) content of the corresponding source rock to the measured total organic carbon (TOC) content.

[0008] Step 2: Perform T1-T2 two-dimensional nuclear magnetic resonance analysis on the source rock to be tested to obtain the T1-T2 spectrum of the source rock;

[0009] Step 3: Calculate the TOC of the source rock to be tested based on the relational model obtained in Step 1.

[0010] As a specific embodiment of the present invention, step 1 includes:

[0011] Step 11: Perform T1-T2 two-dimensional nuclear magnetic resonance analysis on the source rock to obtain the T1-T2 spectrum of the source rock;

[0012] Step 12: The total organic carbon content of the source rock is measured by rock pyrolysis to obtain the measured total organic carbon content (TOC) of the corresponding source rock;

[0013] Step 13: Based on the T1-T2 spectra of the source rock obtained in Step 11 and the measured total organic carbon (TOC) content of the corresponding source rock obtained in Step 12, obtain the percentage of the signal area S representing TOC on the T1-T2 spectra of the source rock. TOC A model relating the total organic carbon (TOC) content of the corresponding source rock to the measured total organic carbon (TOC) content.

[0014] As a specific embodiment of the present invention, in step 11 and / or step 2, the T1-T2 two-dimensional nuclear magnetic resonance analysis parameters are: magnetic field strength of 20±5MHz, probe aperture of not less than 15mm, pulse sequence of inversion recovery method IR-CPMG, echo interval TE of 0.06ms, waiting time TW of 10ms, and inversion method of regularization method.

[0015] As a specific embodiment of the present invention, the T1-T2 spectrum signal-to-noise ratio (SNR) measured in step 11 and / or step 2 is >1000, and the number of signal peaks is not less than 3.

[0016] It should be noted that the measured T1-T2 spectrum signal-to-noise ratio (SNR) is >1000, which is a high SNR. This is necessary to suppress the noise signal and obtain a high-quality, high-resolution T1-T2 spectrum with high separation. This is a prerequisite and key factor for subsequent modeling and TOC calculation.

[0017] As a specific embodiment of the present invention, step 13 further includes the following steps:

[0018] Step 13a: Calculate or read the area A of the T1-T2 spectrum signal. TOC ,

[0019] Step 13b: Calculate or read the total effective area ∑A of the T1-T2 spectrum. i ,

[0020] Step 13c: Calculate A TOC account for ∑A i percentage S TOC :

[0021] S TOC =(A TOC / ∑A i Formula 1 (100%)

[0022] Step 13d: Establish S through linear regression. TOC Relationship model with TOC:

[0023] TOC = a × S TOC Formula 2 +b

[0024] In the formula, a and b are regression coefficients, where a is the slope of the regression line and b is the intercept of the regression line.

[0025] As a specific embodiment of the present invention, in step 13a, the area of ​​the T1-T2 spectrum signal cannot be calculated or read due to signal overlap. The signals need to be separated before subsequent modeling calculations can be performed. Therefore, if the signals overlap, the lowest value between the signal peaks can be used as the dividing point by adjusting the contour lines of the T1-T2 two-dimensional spectrum or by finding the lowest value between the signal peaks in the spectrum data table.

[0026] In a specific embodiment of the present invention, in step 13b, the effective area does not include noise signals.

[0027] As a specific embodiment of the present invention, T1 takes the value range of [15, 500]; T1 / T2 takes the value range of [30, 600].

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. This invention acquires high-quality T1-T2 spectral signals and establishes the percentage S of the signal area representing TOC on the T1-T2 spectrum. TOC The invention establishes a relationship model between the measured total organic carbon (TOC) content and the total organic carbon (TOC) content of the source rock to be tested, thereby calculating the TOC content. Compared with existing technologies, this invention overcomes the uncertainty and inaccuracy in the characterization of TOC content in source rocks caused by different instrument parameters and measurement parameters. It enables the evaluation of source rock characteristics while simultaneously evaluating the oil and water content of the source rock reservoir, filling the gap in TOC evaluation through T1-T2 spectra. The invention is simple to operate, highly accurate, and has a wide range of applications and prospects.

[0030] 2. This invention can accurately identify the pore fluid type and occurrence state of hydrocarbon source rock reservoirs using T1-T2 two-dimensional nuclear magnetic resonance, while simultaneously evaluating the TOC content. No sample processing or additional technical means are required, making it economical to measure and accurate in evaluation. Attached Figure Description

[0031] Figure 1 The T1-T2 NMR spectrum of sample Wooh-1 in Example 1 of this invention;

[0032] Figure 2 The T1-T2 NMR spectrum of sample Wooh-2 in Example 2 of this invention;

[0033] Figure 3 This is a graph showing the linear regression modeling data of samples Wooh-1 and Wooh-2 in Examples 1 and 2 of the present invention.

[0034] Figure 4 The T1-T2 NMR spectrum of the sample in Comparative Example 1;

[0035] Figure 5 The T1-T2 NMR spectrum of the sample in Comparative Example 2;

[0036] Figure 6 The T1-T2 NMR spectra of the sample in Comparative Example 3;

[0037] Figure 7 The T1-T2 nuclear magnetic resonance spectrum obtained in Example 3 of this invention;

[0038] Figure 8 This is a graph of linear regression modeling data obtained in Embodiment 3 of the present invention.

[0039] Among them, 1-kerogen signal; 2-adsorbed oil signal; 3-mobile oil signal; 4-structural water signal; 5-mobile water signal; 6-adsorbed water signal; 7-kerogen signal; 8-mobile oil signal; 9-structural water signal; 10-pore water signal; 11-crack water signal; 12-kerogen signal; 13-hydroxyl signal; 14-methane signal in porous media; 15-water (clay, intergranular) signal. Detailed Implementation

[0040] To make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments and accompanying drawings. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present invention.

[0041] The nuclear magnetic resonance instrument used in the various embodiments of the present invention is a MesoMR23-040V, which uses SR-CPMG pulse sequence for measurement and the instrument's built-in data acquisition software for data acquisition.

[0042] Example 1

[0043] This embodiment provides a method for evaluating the total organic matter (TOC) of source rocks using T1-T2 two-dimensional nuclear magnetic resonance (NMR). This method was used to test shale core samples from Well W, a shale oil well. During core selection, pressure-maintaining drilling was performed to obtain the core from the target stratum, and the core samples were then frozen with liquid nitrogen. The core sample was designated Wooh-1, and its lithology is fine-grained siltstone and mudstone. Specific details are as follows:

[0044] Step 1: The T1-T2 spectrum was measured using Wooh-1 at a resonant frequency of 19MHz, a probe coil diameter of 25mm, a backlash interval TE of 0.06ms, and a waiting time TW of 10ms. (See attached image.) Figure 1 ;

[0045] Figure 1 It can be seen that the T1-T2 spectrum of Wooh-1 sample has a high signal-to-noise ratio and good separation. Among them, the T1-T2 spectrum of Wooh-1 has 5 signal peaks, and the TOC signal is very weak and almost invisible.

[0046] Step 2: Calculate or read the total effective area ∑A of the T1-T2 spectrum of Wooh-1. i And calculate A TOC account for ∑A i percentage S TOC :

[0047] S TOC =(A TOC / ∑A i ) × 100% = 0.85%;

[0048] Step 3: Establish S TOC The relationship model with TOC, see Figure 3 The TOC of Wooh-1 is calculated using modeling formula two:

[0049] TOC = a × S TOC +b = 1.02%

[0050] The data obtained in Example 1 were analyzed: Figure 3 It is not difficult to see that the S of the Wooh-1 sample TOC The TOC data points are located on both sides of the modeling regression line and are concentrated, which shows strong representativeness.

[0051] Two Wooh-1 shale samples from Example 1 were subjected to rock pyrolysis measurements, and the resulting TOC values ​​were 0.82%. (See attached data.) Figure 3 .

[0052] In this embodiment, the absolute error between the calculated TOC and the measured TOC of sample Wooh-1 is 0.20%, indicating that the data is valid and highly reliable.

[0053] Example 2

[0054] This embodiment provides a method for evaluating the total organic matter (TOC) of source rocks using T1-T2 two-dimensional nuclear magnetic resonance (NMR). This method was used to test shale core samples from Well W, a shale oil well. During core selection, pressure-maintaining drilling was performed to obtain the core from the target stratum, and the core samples were then frozen with liquid nitrogen. The core sample was designated Wooh-2, and its lithology consisted of silty mudstone and bioclastic fine-grained dolomite. Specific details are as follows:

[0055] Step 1: The T1-T2 spectrum was measured using the Wooh-2 at a resonant frequency of 19MHz, a probe coil diameter of 25mm, a backlash interval TE of 0.06ms, and a waiting time TW of 10ms. (See attached image.) Figure 2 ;

[0056] Figure 2 It can be seen that the T1-T2 spectrum of Wooh-2 sample has a high signal-to-noise ratio and good separation. The T1-T2 spectrum of Wooh-2 has 4 signal peaks and the TOC signal is relatively strong.

[0057] Step 2: Calculate or read the total effective area ∑A of the T1-T2 spectrum of Wooh-2. i And calculate A TOC account for ∑A i percentage S TOC :

[0058] S TOC =(A TOC / ∑A i ) × 100% = 6.36%

[0059] Step 3: Establish S TOC The relationship model with TOC, see Figure 4 The TOC of Wooh-2 is calculated using modeling formula two:

[0060] TOC = a × S TOC +b = 2.47%

[0061] The data obtained in Example 2 were analyzed: Figure 3 It is not difficult to see that the S of sample Wooh-2 TOC The TOC data points are located on both sides of the modeling regression line and are concentrated, which shows strong representativeness.

[0062] The Wooh-2 sample from Example 2 was subjected to rock pyrolysis analysis, and the resulting TOC was 2.63%. (See attached data.) Figure 3 .

[0063] In this embodiment, the absolute error between the calculated TOC and the measured TOC of sample Wooh-2 is 0.16%.

[0064] The mean absolute error between the TOC results obtained in Examples 1 and 2 and the actual measurements was 0.18%. Figure 3 In the sample Wooh-1 and sample Wooh-2, S TOC The TOC data points are located on both sides and at both ends of the modeling regression line, which is highly representative, indicating that the evaluation method provided by this invention is reliable.

[0065] Comparative Example 1

[0066] This comparative example uses sample D-1, which is shale. The T1-T2 spectra were obtained using nuclear magnetic resonance at a magnetic field strength of 21.36 MHz. See [link to T1-T2 spectrum]. Figure 4 The signal analysis is as follows:

[0067] The NMR test sample D-1, using a magnetic field strength of 21.36 MHz, yielded hydrocarbon signals including kerogen 1, adsorbed oil 2, and mobile oil 3; water signals including structural water 4, mobile water 5, and adsorbed water 6; from Figure 4 As can be seen, the T1-T2 spectra obtained from sample D-1 all exhibit overlapping peak shapes.

[0068] Comparative Example 2

[0069] This comparative example uses sample D-2, which is shale. The T1-T2 spectra were obtained using nuclear magnetic resonance at a magnetic field strength of 12 MHz. Figure 5 The signal analysis is as follows:

[0070] The NMR test sample D-2, with a magnetic field strength of 12 MHz, yielded hydrocarbon signals including kerogen signal 7 and movable oil signal 8; water signals including structural water signal 9, pore water signal 10, and fracture water signal 11; from Figure 5 As can be seen, the T1-T2 spectrum obtained from sample D-2 shows a superposition of peaks for kerogen signal 7 and water signal 9. The position of kerogen signal 7 is similar to that of comparative example 1. Figure 4 quite.

[0071] Comparative Example 3

[0072] This comparative example uses sample D-3, which is shale. The T1-T2 spectra were obtained using nuclear magnetic resonance at a magnetic field strength of 23.7 MHz. See [link to T1-T2 spectrum]. Figure 6 The signal analysis is as follows:

[0073] The NMR sample D-3, with a magnetic field strength of 23.7 MHz, was used. The hydrocarbon signals in the obtained T1-T2 spectra included kerogen signal 12 and methane signal 14 from the porous medium; hydroxyl signal 13 and water (clay, intergranular) signal 15. Figure 6 As can be seen, the T1-T2 spectrum obtained from sample D-3 shows a superposition of peaks for kerogen signal 12 and hydroxide signal 13; the long axis direction of kerogen signal 12 is parallel to... Figure 4 , Figure 5 There are differences.

[0074] The hydrocarbon signals in the T1-T2 spectra obtained by Comparative Examples 1 to 3 all exhibit peak superposition, which can be used for qualitative analysis. However, for quantitative analysis, these signals have low signal-to-noise ratios, poor separation, inconsistent interpretations, and poor signal quality.

[0075] Example 3

[0076] This embodiment provides a method for testing shale oil core samples Y-1 to Y-10 from well Y using the coupling of nuclear magnetic resonance instruments and parameters according to the present invention. (See...) Figure 7 , Figure 8 The specific data analysis is as follows:

[0077] The parameters of the nuclear magnetic resonance instrument were as follows: magnetic field strength of 20 MHz, pulse sequence of inversion recovery method IR-CPMG, echo interval TE of 0.06 ms, waiting time TW of 10 ms, and inversion method of regularization method.

[0078] in, Figure 7 The T1-T2 spectrum obtained from shale oil core sample Y-1 shows that the spectrum has a high signal-to-noise ratio and four signal peaks. The TOC signal peak and the signal peak of movable oil on the right can be clearly separated by adjusting the amplitude contour lines.

[0079] Figure 8 The percentage of TOC signal peaks in the T1-T2 spectra obtained from shale oil core samples Y-1 to Y-10 is S. TOC The correlation analysis chart with TOC from rock pyrolysis shows that the correlation is very high, with a correlation coefficient of 0.96.

[0080] In summary, the method of this invention eliminates the need for sample processing and can identify multiple components of source rock reservoirs using T1-T2 two-dimensional nuclear magnetic resonance technology. Furthermore, it calculates the total organic carbon (TOC) content by obtaining high-quality T1-T2 spectra, overcoming the uncertainties in characterizing the kerogen and organic matter content of source rocks caused by different instrument parameters and measurement parameters. This achieves high-precision quantitative calculation of TOC content, enabling the evaluation of source rock characteristics while assessing the oil and water content of source rock reservoirs. This provides reliable technical support for the evaluation of sweet spots in source rock oil and gas.

[0081] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0082] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for evaluating the total chemical content (TOC) of source rocks using T1-T2 two-dimensional nuclear magnetic resonance (NMR), characterized in that, Includes the following steps: Step 1: Establishing the signal area percentage S of the signal representing TOC on the T1-T2 spectrum of the hydrocarbon source rock TOC The relationship model between the signal area percentage S and the measured total organic carbon content TOC of the corresponding hydrocarbon source rock; Step 2: Perform T1-T2 two-dimensional nuclear magnetic resonance analysis on the source rock to be tested to obtain the T1-T2 spectrum of the source rock; Step 3: Calculate the TOC of the source rock to be tested based on the relationship model obtained in Step 1. Step 1 includes: Step 11: Perform T1-T2 two-dimensional nuclear magnetic resonance analysis on the source rock to obtain the T1-T2 spectrum of the source rock; Step 12: The total organic carbon content of the source rock is measured by rock pyrolysis to obtain the measured total organic carbon content (TOC) of the corresponding source rock; Step 13: obtaining the signal area percentage S on the T1-T2 spectrum of the source rock representing TOC of the source rock based on the T1-T2 spectrum of the source rock obtained in step 11 and the measured total organic carbon content TOC of the corresponding source rock obtained in step 12 TOC a relationship model between the signal area percentage S on the T1-T2 spectrum of the source rock representing TOC of the source rock and the measured total organic carbon content TOC of the corresponding source rock, Step 13 also includes the following steps: Step 13a: Calculate or read T1-T2 spectral signal area A TOC , Step 13b: Calculate or read the total effective area of the T1-T2 spectrum, ∑A i , Step 13c: Calculate A TOC Percentage S of ∑A i TOC :​ S TOC = (A TOC / ∑A i Formula 1 (100%) Step 13d: Establish S by linear regression TOC Relationship model with TOC: TOC = a x S TOC + b Equation Two In the formula, a and b are regression coefficients, where a is the slope of the regression line, with a value of 0.2631; and b is the intercept of the regression line, with a value of 0.7951. In steps 11 and 2, the magnetic field strength for the T1-T2 two-dimensional nuclear magnetic resonance analysis is 20±5 MHz, the probe aperture is not less than 15 mm, the pulse sequence is IR-CPMG (Inversion Recovery Method), the echo interval TE is 0.06 ms, the waiting time TW is 10 ms, and the inversion method is the regularization method. The T1-T2 spectral signal-to-noise ratio (SNR) measured in step 11 and / or step 2 is >1000, and the number of signal peaks is not less than 3. T1 ranges from [15, 500]; T1 / T2 ranges from [30, 600].

2. The method for evaluating the TOC of source rocks according to claim 1, characterized in that, In step 13b, the effective area does not include noise signals.

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