Method for quantitative evaluation of oil content

Abstract

The present invention provides a method for quantitatively evaluating oil content. The method comprises the following steps: obtaining core analysis data and actual well logging data; reconstructing a 100% water-bearing nuclear magnetic resonance T2 spectrum based on the core's pore structure type using a piecewise power function; and quantitatively determining the oil saturation of the reservoir. This method addresses the difficulty of quantitative evaluation in existing oil content evaluation methods.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum and natural gas geology and exploration and development equipment, and in particular to a method for quantitatively evaluating oil content. Background Art

[0002] Currently, the main methods for evaluating the oil content of oil and gas reservoirs are the Archie formula method for electrical logging, the difference spectrum method for nuclear magnetic resonance logging, the shift spectrum method for nuclear magnetic resonance logging, and artificial intelligence. Each of these methods has its advantages, but also has limitations. The Archie formula method for electrical logging is relatively well-established for calculating oil saturation in conventional reservoirs. However, for unconventional reservoirs with complex lithology, strong heterogeneity, and low matrix porosity, the resistivity logging response is significantly affected by the core skeleton and pore structure, providing weak information on reservoir pore fluid properties, making quantitative assessment of oil content difficult. The shift spectrum method and difference spectrum method for nuclear magnetic resonance logging can only provide qualitative, not quantitative, evaluation of oil content. Artificial intelligence is a purely mathematical model deduction lacking a petrophysical foundation or geological significance.

[0003] In other words, the oil content evaluation method in the prior art has the problem of difficulty in quantitative evaluation. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for quantitatively evaluating oil content, so as to solve the problem that the oil content evaluation method in the prior art has difficulty in quantitative evaluation.

[0005] To achieve the above-mentioned object, the present invention provides a method for quantitatively evaluating oil content, comprising the following steps: obtaining experimental analysis data and actual well logging data of a rock core; reconstructing a 100% water-bearing nuclear magnetic resonance T2 spectrum based on a piecewise power function according to the pore structure type of the rock core; and quantitatively determining the oil saturation of the reservoir.

[0006] Furthermore, the experimental analysis data include: mercury injection curve, nuclear magnetic resonance experimental T2 spectrum, sealed coring saturation data, core wettability analysis data, and crude oil analysis data; the actual logging data include: conventional logging data and nuclear magnetic resonance logging data.

[0007] Furthermore, according to the pore structure type of the core, based on the piecewise power function, reconstructing the 100% water-containing nuclear magnetic resonance T2 spectrum includes the following steps: establishing a conversion relationship between the mercury injection curve and the nuclear magnetic resonance experimental T2 spectrum; and reconstructing the 100% water-containing nuclear magnetic resonance T2 spectrum using the mercury injection curve.

[0008] Furthermore, the conversion relationship between the mercury injection curve and the T2 spectrum of the nuclear magnetic resonance experiment is:

[0009]

[0010] Where Pc represents the capillary pressure in dyn / cm2; T2 represents the transverse relaxation time in ms; m and n represent the model parameters corresponding to different pore structures; i = 1, 2, 3, ... n corresponds to different pore structures respectively.

[0011] Furthermore, quantitatively determining the oil saturation of the reservoir includes the following steps: constructing a nuclear magnetic resonance logging oil sensitivity factor λ; establishing a quantitative relationship using sealed coring saturation data and the nuclear magnetic resonance logging oil sensitivity factor λ to quantitatively determine the oil saturation of the reservoir.

[0012] Furthermore, constructing the oil-bearing sensitivity factor of the nuclear magnetic resonance logging includes: extracting the geometric mean T of the nuclear magnetic resonance logging T2 spectrum 2lm_o ; Extract the geometric mean T of the 100% water NMR T2 spectrum 2lm_w ; The oil content sensitivity factor λ of nuclear magnetic resonance logging satisfies: Among them, the geometric mean T 2lm_o The unit is ms, the geometric mean T 2lm_w The unit is ms.

[0013] Furthermore, in the process of establishing a quantitative relationship using the sealed coring saturation data and the oil-bearing sensitivity factor of nuclear magnetic resonance logging, the quantitative relationship satisfies the following formula:

[0014] S o =t(λ);

[0015] Among them, S o It represents oil saturation in %; t(λ) represents the function with λ as the independent variable.

[0016] Furthermore, the mercury injection curve, nuclear magnetic resonance experimental T2 spectrum and sealed coring saturation data are obtained from experimental data measured on the same core.

[0017] Furthermore, the sealed coring saturation data is the oil saturation data obtained after the core is corrected for mud invasion.

[0018] Furthermore, the wettability of the core is hydrophilic or neutral.

[0019] Furthermore, the crude oil analysis data is data obtained by analyzing light crude oil.

[0020] Applying the technical solution of the present invention, a method for quantitatively evaluating oil content includes the following steps: obtaining experimental analysis data and actual well logging data of the core; reconstructing a 100% water-containing nuclear magnetic resonance T2 spectrum based on a piecewise power function according to the pore structure type of the core; and quantitatively determining the oil saturation of the reservoir.

[0021] Through experimental analysis and actual well logging of cores, we can obtain experimental analysis data and actual well logging data. We analyze the core's pore structure type and, based on this, reconstruct a 100% water-bearing NMR T2 spectrum using a three-segment piecewise power function. We then use the experimental analysis data, actual well logging data, and the 100% water-bearing NMR T2 spectrum to quantitatively determine the reservoir's oil saturation. This setup enables quantitative evaluation of reservoir oil content, resolving the difficulty of quantitative oil content assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 FIG2 shows a cross-plot of T2 time and mercury injection pressure in a nuclear magnetic resonance experiment according to an optional embodiment of the present invention;

[0024] Figure 2 The figure shows the measurement of the core a of the present invention and the comparison of the 100% water-containing nuclear magnetic resonance T2 spectrum of the core constructed using the mercury injection curve;

[0025] Figure 3 The figure shows the measurement of the core b of the present invention and the comparison of the 100% water-containing nuclear magnetic resonance T2 spectrum of the core constructed using the mercury injection curve;

[0026] Figure 4 A relationship diagram of the sealed coring oil saturation and the T2 geometric mean ratio λ of the present invention is shown;

[0027] Figure 5 A comparison diagram of the predicted oil saturation and the sealed coring saturation of the present invention is shown. DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0029] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by ordinary technicians in the technical field to which this application belongs.

[0030] In the present invention, unless otherwise specified, the directional words used, such as "up, down, top, bottom", usually refer to the directions shown in the drawings, or to the components themselves in the vertical, perpendicular or gravity direction; similarly, for ease of understanding and description, "inside and outside" refer to the inside and outside relative to the outline of each component itself, but the above directional words are not used to limit the present invention.

[0031] In order to solve the problem that the oil content evaluation method in the prior art has difficulty in quantitative evaluation, the present invention provides a method for quantitative evaluation of oil content.

[0032] like Figures 1 to 5 As shown, the method for quantitative evaluation of oil content includes the following steps: obtaining core experimental analysis data and actual logging data; reconstructing a 100% water-bearing nuclear magnetic resonance T2 spectrum based on the piecewise power function according to the pore structure type of the core; and quantitatively determining the oil saturation of the reservoir.

[0033] Through experimental analysis and actual well logging of cores, we can obtain experimental analysis data and actual well logging data. We analyze the core's pore structure type and, based on this, reconstruct a 100% water-bearing NMR T2 spectrum using a three-segment piecewise power function. We then use the experimental analysis data, actual well logging data, and the 100% water-bearing NMR T2 spectrum to quantitatively determine the reservoir's oil saturation. This setup enables quantitative evaluation of reservoir oil content, resolving the difficulty of quantitative oil content assessment.

[0034] Specifically, experimental analysis data includes mercury injection curves, nuclear magnetic resonance (NMR) T2 spectra, sealed coring saturation data, core wettability analysis data, and crude oil analysis data; actual well logging data includes conventional logging data and NMR logging data. Reservoir oil saturation is quantitatively determined using these data, enabling quantitative evaluation of reservoir oil content.

[0035] Specifically, based on the pore structure type of the core, reconstructing the 100% water-containing NMR T2 spectrum using a piecewise power function includes the following steps: establishing a conversion relationship between the mercury injection curve and the NMR experimental T2 spectrum; and reconstructing the 100% water-containing NMR T2 spectrum using the mercury injection curve. This setup enables conversion between the mercury injection curve and the NMR experimental T2 spectrum. Furthermore, the 100% water-containing NMR T2 spectrum is reconstructed using the mercury injection curve. Without changing the shape of the mercury injection curve, cubic spline interpolation is used to unify the mercury injection pressure values ​​and the NMR experimental T2 time of the NMR experimental T2 spectrum accumulation curve to a fixed water saturation. By plotting the cross-plot, it is found that the relationship between the NMR experimental T2 time and the mercury injection pressure is represented by multiple lines with different slopes on a double logarithmic coordinate line. Each slope corresponds to the conversion relationship between capillary pressure and NMR experimental T2 spectrum for different pore structures in the core.

[0036] In this embodiment, the conversion relationship between the mercury intrusion curve and the T2 spectrum of the nuclear magnetic resonance experiment is:

[0037]

[0038] Where Pc represents the capillary pressure in dyn / cm²; T² represents the transverse relaxation time in milliseconds; m and n represent model parameters corresponding to different pore structures; i = 1, 2, 3, ..., n corresponds to different pore structures. The conversion relationship between the mercury intrusion curve and the T² spectrum from the NMR experiment is related to the pore structure, resulting in different conversion relationships between the mercury intrusion curve and the T² spectrum from the NMR experiment.

[0039] Specifically, quantitatively determining reservoir oil saturation includes the following steps: constructing a nuclear magnetic resonance (NMR) logging oil sensitivity factor λ; and establishing a quantitative relationship between sealed coring saturation data and the NMR logging oil sensitivity factor λ to quantitatively determine the reservoir's oil saturation. The NMR logging oil sensitivity factor can determine whether a reservoir contains oil. Establishing a quantitative relationship between the sealed coring saturation data and the NMR logging oil sensitivity factor λ allows quantitative determination of the reservoir's oil saturation, thereby quantitatively evaluating its oil content.

[0040] Specifically, the construction of the oil-bearing sensitivity factor of the nuclear magnetic resonance logging includes: extracting the geometric mean T of the nuclear magnetic resonance logging T2 spectrum 2lm_o ; Extract the geometric mean T of the 100% water NMR T2 spectrum 2lm_w ; The oil content sensitivity factor λ of nuclear magnetic resonance logging satisfies: Among them, the geometric mean T 2lm_o The unit is ms, the geometric mean T 2lm_wThe unit is ms. The geometric mean of the NMR T2 spectra under different oil-bearing conditions and the geometric mean of the reconstructed 100% water-bearing NMR T2 spectra were extracted, and the ratio of the two was used as the sensitivity factor for the oil-bearing evaluation of NMR logging.

[0041] In this embodiment, in the process of establishing a quantitative relationship using the sealed coring saturation data and the nuclear magnetic resonance logging oil-bearing sensitivity factor, the quantitative relationship satisfies the following formula:

[0042] S o =t(λ);

[0043] Among them, S o It represents oil saturation in %; t(λ) represents the function with λ as the independent variable.

[0044] It should be noted that t(λ) can be a linear function or a nonlinear function, and the parameters in t(λ) are obtained through regression.

[0045] Specifically, the mercury injection curve, NMR T2 spectrum, and sealed coring saturation data are derived from experimental data measured on the same core. This avoids differences in experimental data from different cores, reduces errors, and enables accurate quantitative evaluation of oil content.

[0046] Specifically, sealed coring saturation data is the oil saturation data obtained after the core has been corrected for mud intrusion. This provides more accurate oil saturation data and reduces errors.

[0047] Specifically, the wettability of the core is hydrophilic or neutral. It is only necessary to ensure that the wettability of the core is not oleophilic.

[0048] Specifically, crude oil analysis data is obtained by analyzing light crude oil. Light crude oil has good fluidity at bottom temperature conditions, and the density of crude oil is generally less than 0.9g / cm3.

[0049] Figure 1 This is a cross-plot of the T2 time from the NMR experiment and the inverse of the mercury injection pressure, showing a three-segmented structure on the double logarithmic coordinate line. Combined with lithologic characteristics, the long relaxation time portion primarily reflects the relaxation properties of large reservoir pores (curve "I" in the figure); the medium relaxation time portion primarily reflects the relaxation properties of medium reservoir pores (curve "II" in the figure); and the short relaxation time portion primarily reflects the relaxation properties of small reservoir pores (curve "III" in the figure).

[0050] Figure 2 A comparison of the core a measured and the core a constructed using mercury injection curve 100% water-containing nuclear magnetic resonance T2 spectrum. Figure 3b is a comparison of the core measurement and the core 100% water-containing NMR T2 spectrum constructed using the mercury injection curve. Figure 2 The former is a circle and the latter is a triangle, and the two are basically coincident, indicating that the model is highly reliable. It should be noted that the difference between core a and core b lies in the different pore structures. Core a has more large pore spaces and less small pore spaces (geologically known as good physical properties); core b has less large pore spaces and more small pore spaces (poor physical properties). Figure 2 and Figure 3 The two examples illustrate that the method of the present application can be used in rocks with good and poor material properties.

[0051] Figure 4 This figure shows the relationship between oil saturation and the ratio of the T2 geometric mean value for sealed core sampling. A logarithmic function was used to fit the figure, and the correlation coefficient of the fitting function was 0.79, indicating that the model is highly reliable.

[0052] This method achieves the goal of quantitatively predicting reservoir oil saturation using mercury injection curves and nuclear magnetic resonance logging. It has a strong core physics foundation, high accuracy, and a wide range of applications. The process meets the needs of logging reservoir evaluation and has strong field application value.

[0053] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the technical process of the present invention is described in detail based on 11 typical core plug samples in a specific well and the oil saturation measurement results of the 11 cores taken from the sealed coring. However, this should not be construed as limiting the scope of implementation of the present invention.

[0054] 1) Obtain conventional core experimental analysis data, including mercury injection curves, nuclear magnetic resonance experimental T2 spectra, sealed coring saturation data, core wettability analysis data, and crude oil analysis data; actual well logging data, including conventional logging data and nuclear magnetic resonance logging data.

[0055] 2) According to the pore structure type of the core, a conversion relationship between the mercury injection curve and the nuclear magnetic resonance experimental T2 spectrum was established based on the piecewise power function, and the 100% water-containing nuclear magnetic resonance T2 spectrum was reconstructed using the mercury injection curve.

[0056] The mercury injection capillary pressure curve and the nuclear magnetic resonance experiment T2 spectrum data collected from the same core can be used, or the above two experimental data can be measured simultaneously on the same core. Without changing the shape of the curve, the cubic spline interpolation method is used to unify the value of the mercury injection pressure and the nuclear magnetic resonance experiment T2 time of the nuclear magnetic resonance experiment T2 spectrum accumulation curve to a fixed water saturation. By drawing the intersection diagram, it is found that the nuclear magnetic resonance experiment T2 time and the inverse of the mercury injection pressure show a "three-segment" segmented feature on the double logarithmic coordinate line. The large, medium and small pore models in the "three-segment" correspond to Figure 1 Based on the multivariate statistical regression model, the parameters of the large, medium and small pore models can be obtained, thus establishing the correlation between the T2 time of the nuclear magnetic resonance experiment and the mercury injection pressure. That is:

[0057] Large hole:

[0058] Middle hole:

[0059] Small hole:

[0060] Where: Pc is the capillary pressure, dyn / cm2; T2 is the transverse relaxation time, ms.

[0061] 3) The T2 geometric mean values ​​of the NMR logging T2 spectrum and the reconstructed 100% water-bearing NMR T2 spectrum were extracted, and the ratio of the two was used as the NMR logging oil content sensitivity factor. A quantitative relationship was established between the sealed coring oil saturation and the NMR oil content sensitivity factor to determine the reservoir oil saturation.

[0062] The geometric mean parameters of the 100% water-containing NMR T2 spectrum and the oil-saturated NMR T2 spectrum were extracted, and the ratio of the two was used to construct the NMR logging oil content evaluation sensitivity factor, namely:

[0063]

[0064] Where: T 2lm_w represents the T2 geometric mean of the 100% water NMR T2 spectrum, ms;

[0065] T 2lm_o represents the T2 geometric mean of the NMR T2 spectra under different oil content conditions, ms;

[0066] λ represents the ratio of the geometric means of T2.

[0067] Then, the oil saturation measured by the sealed coring experiment was related to the nuclear magnetic resonance logging oil content evaluation sensitivity factor λ. Through regression, the model for calculating oil saturation using the nuclear magnetic resonance oil content sensitivity factor was obtained as follows:

[0068] S o =20.836*ln(λ)+33.53 (5)

[0069] Where: S o Indicates oil saturation, %.

[0070] In order to test the application effect of the invention, the present invention selected actual logging data that were not involved in the research for processing and interpretation.

[0071] Figure 5 A comparison chart of the oil saturation predicted by this method and the core oil saturation for a specific well is shown. The predicted oil saturation is relatively close to the actual oil saturation obtained from sealed coring, with an average absolute error of 8.74%, meeting the requirements of well logging reservoir evaluation.

[0072] Obviously, the embodiments described above are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0073] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, tasks, devices, components and / or combinations thereof.

[0074] It should be noted that the terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0075] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for quantitatively evaluating oil content, characterized in that: The steps include: Obtain core experimental analysis data and actual logging data; The experimental analysis data include: mercury injection curve, nuclear magnetic resonance experiment T2 spectrum, closed coring saturation data, core wettability analysis data, crude oil analysis data; The actual logging data include: conventional logging data and nuclear magnetic resonance logging data; According to the pore structure type of the core, a 100% water-containing nuclear magnetic resonance T2 spectrum is reconstructed based on a piecewise power function; Quantitatively determine the oil saturation of the reservoir; The quantitative determination of the oil saturation of the reservoir comprises the following steps: Construct the oil-bearing sensitivity factor λ of NMR logging; Establishing a quantitative relationship using the sealed coring saturation data and the nuclear magnetic resonance logging oil sensitivity factor λ to quantitatively determine the oil saturation of the reservoir; The construction of the oil-bearing sensitivity factor of nuclear magnetic resonance logging includes: Extract the geometric mean T of the nuclear magnetic resonance logging T2 spectrum of the actual logging data 2lm_o ; Extract the geometric mean T of the 100% water NMR T2 spectrum 2lm_w ; The oil content sensitivity factor λ of the nuclear magnetic resonance logging satisfies: Among them, the geometric mean T 2lm_o The unit is ms, the geometric mean T 2lm_w The unit is ms; In the process of establishing a quantitative relationship using the sealed coring saturation data and the nuclear magnetic resonance logging oil-bearing sensitivity factor, the quantitative relationship satisfies the following formula: S o =t(λ); Among them, S o Indicates oil saturation, unit is %; t(λ) represents a function with λ as the independent variable.

2. The method for quantitatively evaluating oil content according to claim 1, wherein: The reconstructing of the 100% water-containing nuclear magnetic resonance T2 spectrum based on the pore structure type of the core and the piecewise power function comprises the following steps: Establishing a conversion relationship between the mercury intrusion curve and the nuclear magnetic resonance experiment T2 spectrum; The 100% water-containing nuclear magnetic resonance T2 spectrum was reconstructed using the mercury intrusion curve.

3. The method for quantitatively evaluating oil content according to claim 2, wherein: The conversion relationship between the mercury intrusion curve and the nuclear magnetic resonance experiment T2 spectrum is: Where Pc represents the capillary pressure in dyn / cm2; T2 represents the transverse relaxation time, in ms; m and n represent the model parameters corresponding to different pore structures; i=1, 2, 3, ...n correspond to different pore structures respectively.

4. The method for quantitatively evaluating oil content according to any one of claims 2 to 3, characterized in that: The mercury injection curve, the nuclear magnetic resonance experimental T2 spectrum and the closed coring saturation data are obtained from experimental data measured on the same piece of core.

5. The method for quantitatively evaluating oil content according to any one of claims 2 to 3, characterized in that: The sealed coring saturation data is the oil saturation data obtained after the core is corrected for mud invasion.

6. The method for quantitatively evaluating oil content according to claim 5, wherein: The wettability of the core is hydrophilic or neutral.

7. The method for quantitatively evaluating oil content according to any one of claims 2 to 3, characterized in that: The crude oil analysis data is data obtained by analyzing light crude oil.

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