Porosity-based hydration correction method for shale acoustic velocity

Abstract

The present invention relates to a shale acoustic wave velocity hydration correction method based on porosity, comprising the following steps: preparing cores with different bedding angles; conducting shale hydration experiments, acoustic wave experiments, and nuclear magnetic resonance experiments to obtain parameters such as acoustic wave velocity and nuclear magnetic porosity of shale at different hydration times; studying the response relationship between shale acoustic wave velocity and porosity, and establishing a quantitative evaluation model for shale shear wave velocity and porosity; determining unknown parameters in the shale shear wave velocity and porosity quantitative evaluation model, and constructing an inversion model including the initial wave velocity and initial porosity of shale; combining the measured acoustic wave velocity and porosity of shale at different hydration times, calculating the acoustic wave velocity before hydration of shale, and realizing shale acoustic wave velocity hydration correction. The present application can eliminate the influence of hydration on the acoustic wave velocity of shale to a certain extent, and can obtain the acoustic wave velocity of shale in its original state.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploration and development, and in particular to a shale acoustic wave velocity hydration correction method based on porosity. Background Art

[0002] During the drilling process of shale reservoirs, it is inevitable that the water-based working fluid contacts the formation. During the contact between the working fluid and the shale reservoir, the original physical and chemical conditions change, causing the various equilibrium states in the shale formation to be broken, causing a series of physical and chemical reactions between shale and water, causing the microstructure of shale rocks to change dynamically, and leading to significant changes in the physical and mechanical properties of shale formation rocks. These changes will have an important impact on the various physical and mechanical properties of the formation obtained by applying geophysical logging research. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a shale acoustic wave velocity hydration correction method based on porosity.

[0004] The present invention is achieved through the following technical solutions:

[0005] The porosity-based shale acoustic velocity hydration correction method comprises the following steps:

[0006] Prepare cores with different bedding angles;

[0007] Conduct shale hydration experiments, acoustic wave experiments, and nuclear magnetic resonance experiments to obtain the acoustic wave velocity and porosity parameters of shale at different hydration times;

[0008] Study the changing law of shale porosity during shale hydration, clarify the relationship between shale porosity and hydration, and establish a quantitative evaluation model between shale porosity and hydration by the least squares method;

[0009] The response relationship between shale acoustic wave velocity and porosity is studied, and a quantitative evaluation model of shale shear wave velocity and porosity is established by the least square method;

[0010] Determine the unknown parameters in the quantitative evaluation model of shale shear wave velocity and porosity, and construct an inversion model including the initial wave velocity and initial porosity of shale;

[0011] Based on the inversion model including the initial wave velocity and initial porosity of shale, combined with the measured acoustic wave velocity and porosity of shale at different hydration times, the acoustic wave velocity of shale before hydration is calculated to realize the acoustic wave hydration correction of shale.

[0012] Among them, the shale porosity is obtained by nuclear magnetic resonance experimental method.

[0013] The method for establishing a quantitative evaluation model of shale shear wave velocity and porosity includes:

[0014] Study the relationship between shale porosity and hydration time at different bedding angles, establish a mathematical model for the porosity and hydration time of hydrated shale, and construct a quantitative evaluation model between shale porosity and hydration;

[0015] Based on the experimental data of shale porosity and shear wave velocity, the response relationship between shale shear wave velocity and shale porosity is studied. By establishing a mathematical model for shale shear wave velocity and porosity at different hydration times, the shale shear wave velocity and porosity quantitative evaluation model is constructed.

[0016] The quantitative evaluation model between shale porosity and hydration is:

[0017] Φ n =Aln(t)+Φ0

[0018] In the formula, Φ n is the porosity of shale, %; t is the hydration time of shale, h; A is a constant; Φ0 is close to the initial porosity of shale.

[0019] The quantitative evaluation model of shale shear wave velocity and porosity is as follows:

[0020] V st =MΦ t +N

[0021] Where V st is the shear wave velocity of shale during water-rock interaction, m / s; Φ t is the porosity of shale during water-rock interaction, %; M, N—constants.

[0022] The method for determining the unknown parameter N in the quantitative evaluation model of shale shear wave velocity and porosity is as follows:

[0023]

[0024] Where V st and V s(t-1) is the wave velocity at different hydration times, Φ t and Φ (t-1) is the porosity at different hydration times; the value of N is determined using the shear wave velocity and porosity parameters at different hydration times.

[0025] The method for determining the unknown parameter M in the shale shear wave velocity and porosity quantitative evaluation model is as follows:

[0026]

[0027] Where Vst is the shear wave velocity of shale during water-rock interaction, m / s; V s0 is the initial shear wave velocity of shale, m / s; Φ t —Porosity of shale during water-rock interaction, %; Φ0—initial porosity of shale, %.

[0028] The inversion model including the initial wave velocity and the initial porosity is:

[0029]

[0030] Where V s0 is the initial wave velocity of shale, V st 、V s(t-1) is the shear wave velocity of shale at different times during the water-rock interaction process, m / s; Φ0 is the initial porosity, Φ t , Φ (t-1) is the porosity of shale at different times during water-rock interaction, %.

[0031] Compared with the prior art, this application has at least the following beneficial effects:

[0032] The present application can eliminate the influence of hydration on the acoustic wave velocity of shale to a certain extent, and the acoustic wave velocity of the shale in its original state is obtained with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 This is a graph showing changes in shale porosity at different hydration times in the embodiment;

[0035] Figure 2 Graph showing the relationship between shear wave velocity and porosity in the embodiment. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0037] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.

[0038] The porosity-based shale acoustic velocity hydration correction method disclosed in this embodiment specifically includes the following steps:

[0039] S1, collect relevant data on geology, well logging, coring, etc. in the study area.

[0040] Among them, geological data include logging core profiles, stratigraphic divisions and other data; logging data include conventional logging data such as compensated sonic waves, compensated neutrons, and compensated density; coring data include downhole coring and outcrop coring in the study area.

[0041] S2, core preparation.

[0042] The method for preparing the experimental core is based on the relevant requirements of the Engineering Rock Mass Test Method Standard GB / T 50266-99. Considering the hydration characteristics of shale, this embodiment uses liquid nitrogen coring to prepare the core. The specific process includes:

[0043] (1) Coring from the target strata in the study area;

[0044] (2) Processing the collected rock samples into a shape that is convenient for the drilling machine to fix;

[0045] (3) Place the processed core in a container and add liquid nitrogen to freeze the core for 2 hours;

[0046] (4) Fix the frozen rock sample on a drilling machine, use liquid nitrogen to cool the drill bit, and drill the core;

[0047] (5) Cut both ends of the successfully drilled core flat and grind the end face of the core column according to the relevant requirements of the Engineering Rock Mass Test Method Standard GB / T50266-99 (use liquid nitrogen or air to cool the blade during grinding).

[0048] (6) Select shale cores with well-developed bedding (containing different bedding angles). The bedding angle of shale is 0-90°, the length of the rock sample is 50 mm, and the diameter is 25 mm. The bedding angle is defined as the angle between the bedding plane and the normal line of the core end face. In this embodiment, the bedding angles of the experimental rock samples are mainly selected as: 0°, 50°, and 90°.

[0049] S3, conduct hydration experiment on the core, soak the core with distilled water as the soaking solution, take out the core after soaking time of 1h, 6h, 12h, 24h and 48h, conduct acoustic wave velocity measurement experiment and porosity measurement experiment on the core, and obtain parameters such as acoustic wave velocity and resonance porosity of the core with different soaking time.

[0050] Optionally, the shale porosity is obtained using a nuclear magnetic resonance experimental method.

[0051] The relationship between hydration time and shale porosity is analyzed. The results are as follows: Figure 1 As shown, it can be seen that with the increase of immersion time, the shale porosity increases linearly in a logarithmic function; by establishing a mathematical model of the porosity and hydration time of hydrated shales with different bedding angles, the fitting results are shown in Table (1), and the average correlation coefficient is 0.9824.

[0052] Table 1: Shale porosity evolution model

[0053]

[0054] The above mathematical model can be used to construct a quantitative evaluation model between shale porosity and hydration, as shown in formula (1):

[0055] Φ n =A ln(t)+Φ0 (1)

[0056] In formula (1), Φ n is the porosity of shale, %; t is the hydration time of shale, h; A is a constant; Φ0 is close to the initial porosity of shale.

[0057] After clarifying the relationship between shale porosity and hydration, a quantitative relationship model between shale porosity and hydration is established by the least squares method. n and t can be obtained through the resonance experiment of rocks after hydration, and the porosity Φ of shale at different hydration times obtained in the experiment is n By substituting the hydration time t into formula (1), the unknown parameters A and Φ0 in the shale porosity prediction model can be calculated. Substituting the unknown parameter A into formula (1) can obtain the quantitative evaluation model between shale porosity and hydration.

[0058] S4. Using time as a unit of measurement in data analysis cannot accurately describe the inherent laws of shale porosity and acoustic wave changes. Therefore, this embodiment combines porosity and shear wave velocity for data analysis. The analysis results are as follows: Figure 2 As shown in the figure, it can be seen that the shale shear wave velocity and porosity have a good linear relationship under different hydration times. The fitting function relationship results are shown in Table 2, and the average correlation coefficient is 0.9458.

[0059] Table 2: Relationship between shear wave velocity and porosity

[0060]

[0061] S5. Using the shale shear wave velocity and porosity data analysis results, a quantitative evaluation model for shale shear wave velocity and porosity is established, as shown in formula (2):

[0062] V st =MΦ t +N (2)

[0063] In formula (2), V st is the shear wave velocity of shale during water-rock interaction, m / s; Φ t is the porosity of shale during water-rock interaction, %; M, N—constants.

[0064] The response relationship between shale acoustic wave velocity and porosity is studied, and a quantitative evaluation model of shale shear wave velocity and porosity is established by the least squares method. Specifically, M and N are unknown constants. In the quantitative relationship model, M is taken as the slope of the function. Therefore, according to the slope definition, M can be expressed by the wave velocity and porosity at any different hydration time, as shown in formula (3); N is taken as the intercept of the function. In a conventional linear function, the intercept should be the ordinate value corresponding to the horizontal coordinate Φ being 0. That is, when Φ=0, the wave velocity. Because this function is a linear function, the wave velocity and porosity at different hydration times can be arbitrarily selected. Combining formulas (2) and (3), the calculation formula of N can be obtained (formula (4).

[0065]

[0066]

[0067] Where: V st and V s(t-1) is the wave velocity at different hydration times; Φ t and Φ (t-1) is the porosity at different hydration times.

[0068] After the value of N is determined using the shear wave velocity and porosity parameters at different hydration times, the value of N is now a known quantity.

[0069] S6. When constructing a quantitative evaluation model for shale shear wave velocity and porosity, M is used as the slope of a linear function. The initial porosity and the corresponding initial wave velocity can be taken into account. The expression of M is shown in formula (5):

[0070]

[0071] Where V stis the shear wave velocity of shale during water-rock interaction, m / s; V s0 is the initial shear wave velocity of shale, m / s; Φ t —Porosity of shale during water-rock interaction, %; Φ0—initial porosity of shale, %.

[0072] In formula (5), the initial porosity Φ0 and the initial wave velocity V s0 is an unknown parameter. Since the initial porosity Φ0 of shale is difficult to obtain under actual working conditions, based on the porosity prediction model of shale under different hydration times, the porosity of shale under different hydration times is obtained through experiments. The experimental results are substituted into formula (1) to obtain the initial porosity Φ0 of shale through the prediction model; the unknown parameter in formula (5) is only the initial wave velocity V of shale s0 Substituting equation (5) and intercept N into equation (2) yields equation (6). Simplifying equation (6) yields the inversion model including initial wave velocity and initial porosity, as shown in equation (7):

[0073]

[0074] Where: V s(t-1) —The shear wave velocity of shale at different times during the water-rock interaction, m / s; Φ (t-1) —Porosity of shale at different times during water-rock interaction, %.

[0075] S7, based on the experimental data, is substituted into formula (7) to calculate the acoustic wave velocity of the shale before hydration, and the initial acoustic wave velocity of the hydration experimental core is restored and predicted to complete the shale acoustic hydration correction. The prediction results are shown in Table 1. It can be seen that based on the quantitative relationship model between porosity and shear wave velocity during hydration, the shear wave velocity of the shale before hydration is predicted. Compared with the measured velocity, the maximum relative error is 2.72%. The accuracy of the predicted velocity is verified, and the correctness and applicability of the wave velocity prediction based on the quantitative relationship model are also demonstrated.

[0076] Table 3: Wave velocity prediction results and error analysis

[0077]

[0078] In order to eliminate the influence of hydration on the acoustic velocity of shale and obtain the acoustic velocity of shale in its original state, this embodiment uses the resonance porosity data of shale at different hydration times, combined with the acoustic velocity of shale at different hydration times, to construct a shale acoustic velocity correction equation, thereby achieving the purpose of calculating the acoustic velocity of shale in its original state.

[0079] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A porosity-based shale acoustic velocity hydration correction method, characterized in that: The following steps are involved: Prepare cores with different bedding angles; Conduct shale hydration experiments, sonic experiments, and nuclear magnetic resonance experiments to obtain the sonic velocity and nuclear magnetic porosity parameters of shale at different hydration times; Study the changing law of shale porosity during shale hydration, clarify the relationship between shale porosity and hydration, and establish a quantitative evaluation model between shale porosity and hydration by the least squares method; The response relationship between shale acoustic wave velocity and shale porosity was studied, and a quantitative evaluation model of shale shear wave velocity and porosity was established by the least square method. Determine the unknown parameters in the quantitative evaluation model of shale shear wave velocity and porosity, and construct an inversion model including the initial shear wave velocity and initial porosity of shale; Based on the inversion model including the initial shear wave velocity and initial porosity of the shale, combined with the measured shear wave velocity and porosity of the shale at different hydration times, the acoustic wave velocity of the shale before hydration is calculated to achieve hydration correction of the acoustic wave velocity of the shale; The method for establishing a quantitative evaluation model for shale shear wave velocity and porosity includes: The relationship between shale porosity and hydration time at different bedding angles is studied, and a mathematical model fitting relationship between the porosity and hydration time of hydrated shale is established to construct a quantitative evaluation model between shale porosity and hydration. Based on the experimental data of shale porosity and shear wave velocity, the response relationship between shale shear wave velocity and shale porosity is studied, and a mathematical model of shale shear wave velocity and porosity under different hydration times is established to construct the shale shear wave velocity and porosity quantitative evaluation model; The quantitative evaluation model between shale porosity and hydration is: F n =Aln(t)+Φ0 In the formula, Φ n is the porosity of shale, in %; t is the hydration time of shale, in h; A is a constant; Φ0 is close to the initial porosity of shale.

2. The porosity-based shale acoustic velocity hydration correction method according to claim 1, characterized in that: The shale porosity is obtained by nuclear magnetic resonance experimental method.

3. The porosity-based shale acoustic velocity hydration correction method according to claim 1, characterized in that: The quantitative evaluation model of shale shear wave velocity and porosity is: V st =MΦ t +N Where V st is the shear wave velocity of shale at different hydration times, in m / s; Φ t is the porosity of shale at different hydration times, in %; M and N are constants.

4. The porosity-based shale acoustic velocity hydration correction method according to any one of claims 1 to 3, characterized in that: The method for determining the unknown parameter N in the quantitative evaluation model of shale shear wave velocity and porosity is: Where V st and V s(t-1) is the shear wave velocity of shale at different hydration times, Φ t and Φ (t-1) is the porosity of shale at different hydration times; The value of N is determined by using the shear wave velocity and porosity parameters of shale at different hydration times.

5. The porosity-based shale acoustic velocity hydration correction method according to any one of claims 1 to 3, characterized in that: The method for determining the unknown parameter M in the quantitative evaluation model of shale shear wave velocity and porosity is: Where V st is the shear wave velocity of shale at different hydration times, in m / s; V s0 is the initial shear wave velocity of shale, in m / s; Φ t is the porosity of shale at different hydration times, in %; Φ0 is the initial porosity of shale, in %.

6. The porosity-based shale acoustic velocity hydration correction method according to claim 1, characterized in that: The inversion model including the initial shear wave velocity and initial porosity of shale is: Where V s0 is the initial shear wave velocity of shale, V st 、V s(t-1) is the shear wave velocity of shale at different hydration times, in m / s; Φ0 is the initial porosity of shale, Φ t , Φ (t-1) is the porosity of shale at different hydration times, in %.

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