Method for transient temperature equivalence to transient pressure effect in fracturability studies

Abstract

The application discloses a method for instant temperature equivalent to instant pressure effect in fracturability research, which comprises the following steps: (1) obtaining fracturability F by basic characteristic data and comparing with mechanical parameters; (2) given a specific temperature t0, calculating the fracturability by changing confining pressure σ constantly, fitting F(σ)=f t0 (σ) and curve; (3) given a specific confining pressure σ0, calculating the fracturability by changing temperature t constantly, fitting F(t)=f σ0 (t) and curve; (4) making fitting change curves of confining pressure σ and F(σ), temperature t and F(t) in a double y-axis coordinate system respectively, and letting F(σ)=F(t), so that the corresponding confining pressure value σ n of a certain temperature value t n under the confining pressure σ0 is obtained. The method can calculate the corresponding confining pressure value under the temperature t0 equivalent to a certain temperature value under the confining pressure σ0, and can perfect the analysis model of rock mechanics properties affected by temperature and pressure.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of oil and gas basin reservoir fracturing evaluation, and particularly relates to a method for equivalent effect of instantaneous temperature to instantaneous pressure in fracturability research. BACKGROUND

[0002] Formation temperature and pressure are important factors for controlling oil and gas generation, evolution and occurrence state in oil and gas bearing basin. Both of them are interrelated and jointly act in the process of oil and gas reservoir formation, and control the distribution of oil and gas. In addition, formation temperature and pressure are important factors affecting the mechanical properties of formation rock.

[0003] Fracturability evaluation is of great significance for reservoir reconstruction and oil and gas development. The characterization of fracturability and fracturing reconstruction cannot be separated from the discussion of rock mechanical properties. With the increase of burial depth, temperature and pressure change to different degrees, and the influence degree of both on rock mechanical properties and fracturing difficulty is also obviously different. The different changes of temperature and pressure have great obstacles for reservoir development evaluation. SUMMARY

[0004] The application aims to provide a method for equivalent effect of instantaneous temperature to instantaneous pressure in fracturability research, and provide certain reference for subsequent oil and gas reservoir development evaluation and reservoir volume fracturing by equivalent estimation of instantaneous temperature and instantaneous pressure.

[0005] In order to achieve the above purpose, the technical solution adopted by the application is:

[0006] A method for equivalent effect of instantaneous temperature to instantaneous pressure in fracturability research, comprising the following steps:

[0007] (1) data preparation, the data including measured data of fractures and mechanical parameter data of mechanical test, and the fracturability F of rock is obtained through the measured data and the mechanical parameter data;

[0008] (2) a specific temperature t0 is given, the temperature is kept unchanged, the confining pressure sigma is changed constantly to carry out the mechanical experiment of the characterization parameter and calculate the fracturability, the scatter point relation of the fracturability and the confining pressure at the temperature is obtained, and the formula F(sigma)=f t0 (sigma) and the curve are fitted out;

[0009] (3) a specific confining pressure sigma0 is given, the confining pressure is kept unchanged, the temperature t is changed constantly to carry out the mechanical experiment of the characterization parameter and calculate the fracturability, the relation of the fracturability and the temperature at the confining pressure is obtained, and the formula F(t)=f σ0 (t) and the curve are fitted out;

[0010] (4) in the double y-axis coordinate system, make fitting change curves of confining pressure sigma and F(sigma), temperature t and F(t) respectively, let F(sigma)=F(t), then the corresponding confining pressure value sigma under the equivalent temperature t0 of a certain temperature value under confining pressure sigma0 is obtained n The corresponding confining pressure value sigma under the equivalent temperature t0 of a certain temperature value under confining pressure sigma0 is obtained n .

[0011] Preferably, the measured data of the fracture is the basic characteristic data of the actually measured core or field profile fracture, and the mechanical parameters capable of reflecting the characteristics of the fracture are screened out for weighted combination to comprehensively represent the fracturing property F of the rock.

[0012] Preferably, the basic characteristic data of the fracture includes the area density, length, width and filling degree of the fracture.

[0013] Preferably, the mechanical experiment is an experiment affecting the mechanical properties of the rock; the mechanical experiment includes a conventional or true triaxial experiment, a fracture toughness experiment, a ground stress experiment, a compressive strength experiment and a tensile strength experiment.

[0014] Preferably, the mechanical parameter is a parameter affecting the mechanical properties of the rock; the mechanical parameter includes Young's modulus, Poisson's ratio, fracture toughness, ground stress, compressive strength and tensile strength.

[0015] Preferably, the rock types include various types of terrigenous clastic rocks, various types of volcanic rocks, volcanic clastic rocks and metamorphic rocks.

[0016] Preferably, when the confining pressure sigma is changed continuously, the change of the confining pressure sigma can be a certain confining pressure interval, or a continuously increasing or decreasing confining pressure.

[0017] Preferably, when the temperature t is changed continuously, the change of the temperature t can be a certain temperature interval, or a continuously increasing or decreasing temperature.

[0018] The beneficial effects of the present application are:

[0019] In the method for equivalent instantaneous temperature in the fracturing property research, the method can calculate the corresponding confining pressure value under the equivalent temperature t0 of a certain temperature value under confining pressure sigma0, can perfect the analysis model of the influence of the temperature and pressure on the mechanical properties of the rock, and is convenient for the theoretical discussion of the change of the mechanical properties of the rock with the depth. Meanwhile, the method is also convenient for the evaluation and calculation of the fracturing property of the formation, and is beneficial to guide the development and fracturing of oil and gas. The theoretical basis of the method is simple and reliable, can conveniently solve the problem of the change of the temperature and pressure with the increase of the depth, and has strong practicability. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a flow chart of the method for equivalent instantaneous temperature in the fracturing property research.

[0021] Figure 2 is a schematic diagram of the instantaneous temperature equivalent to the instantaneous pressure effect in the fracturability study.

[0022] Figure 3 is a scatter plot of the fracturability index and confining pressure in Example 3.

[0023] Figure 4 is a scatter plot of the fracturability index and temperature in Example 3.

[0024] Figure 5 is a graph of the fracturability index in a double-y coordinate system with respect to temperature and confining pressure in Example 3. DETAILED DESCRIPTION

[0025] The present application will be described in detail below with reference to the accompanying drawings:

[0026] Example 1

[0027] In combination Figures 1 to 5 , a method for instantaneous temperature equivalent to instantaneous pressure effect in fracturability study, comprising the following steps:

[0028] (1) Data preparation, the data includes measured data of fractures and mechanical parameter data of mechanical tests, and the fracturability F of the rock is obtained by the measured data and the mechanical parameter data. The measured data of the fractures is basic characteristic data of actually measured core or field section fractures, and the mechanical parameters capable of reflecting the characteristics of the fractures are further screened and combined with weights to comprehensively characterize the fracturability F of the rock. The basic characteristic data of the fractures includes the surface density, length, width and filling degree of the fractures.

[0029] (2) Given a specific temperature t0, keep the temperature unchanged, and continuously change the confining pressure σ condition to perform a mechanical test of the characterization parameter and calculate the fracturability, obtain the scatter plot of the fracturability and the confining pressure at the temperature, and fit the formula F(σ)=f t0 (σ) and the curve.

[0030] The measured data of the fractures is basic characteristic data of actually measured core or field section fractures, and the mechanical parameters capable of reflecting the characteristics of the fractures are further screened and combined with weights to comprehensively characterize the fracturability F of the rock. The basic characteristic data of the fractures includes the surface density, length, width and filling degree of the fractures. The mechanical test is an experiment affecting the mechanical properties of the rock, and the mechanical test includes a conventional or true triaxial test, a fracture toughness test, a in-situ stress test, a compressive strength test and a tensile strength test. The mechanical parameter is a parameter affecting the mechanical properties of the rock, and the mechanical parameter includes Young's modulus, Poisson's ratio, fracture toughness, in-situ stress, compressive strength and tensile strength.

[0031] (3) Given a specific confining pressure σ0, and keeping the confining pressure constant, conduct mechanical experiments to characterize the parameters by continuously changing the temperature t, and then calculate the fracturing capability. Obtain the relationship between the fracturing capability and temperature under the confining pressure, and fit the formula F(t) = f σ0 (t) and curve.

[0032] (4) Combination Figure 2 Plot the fitted curves of confining pressure σ versus F(σ) and temperature t versus F(t) in a dual y-axis coordinate system. Let F(σ) = F(t) to obtain a certain temperature value t under confining pressure σ0. n The equivalent confining pressure σ at temperature t0 n .

[0033] The rocks mentioned are generally various types of terrigenous clastic rocks, various types of volcanic rocks, volcanic clastic rocks, and metamorphic rocks.

[0034] When the confining pressure σ is continuously changed, the change in confining pressure σ can be either a certain confining pressure interval or a continuous increase or decrease in confining pressure. Similarly, when the temperature t is continuously changed, the change in temperature t can be either a certain temperature interval or a continuous increase or decrease in temperature.

[0035] Example 2

[0036] This paper presents an evaluation method for assessing the effect of instantaneous temperature on instantaneous pressure in a field study of the fracturability of a measured core sample. Through equivalent estimation of instantaneous temperature and pressure, this method provides a reference for subsequent oil and gas reservoir development evaluation and guidance on reservoir volumetric fracturing. The specific steps include:

[0037] The basic characteristic data of the actual rock core were measured and compared with the mechanical parameters of mechanical experiments. Mechanical parameters that reflect the characteristics of the fractures were selected and weighted together to comprehensively characterize the rock's fracturability (F). The basic characteristic data of the fractures measured in the actual rock core included the areal density, length, width, and degree of filling of the fractures.

[0038] Mechanical experiments include various tests that affect the mechanical properties of rocks, such as conventional or true triaxial tests, fracture toughness tests, in-situ stress tests, compressive strength tests, and tensile strength tests. Depending on the type of test, mechanical parameters include various parameters that affect the mechanical properties of rocks, including Young's modulus, Poisson's ratio, fracture toughness, in-situ stress, compressive strength, and tensile strength.

[0039] Given a specific temperature t0, and keeping that temperature constant, mechanical experiments are conducted to characterize the parameters by continuously changing the confining pressure. This allows for the calculation of fracturability, yielding a scatter plot relationship between fracturability and confining pressure at that temperature. Finally, the formula F(σ) = f(t0) is fitted to derive the relationship between fracturability and temperature. t0(σ) and curve. Wherein, the constantly changing confining pressure conditions can be a certain confining pressure interval, or a continuous increase or decrease in confining pressure.

[0040] Given a certain confining pressure σ0, keep the confining pressure unchanged, constantly change the temperature conditions to characterize the mechanical experiment of the parameter and then calculate the fracturability, obtain the fracturability and temperature scatter plot relationship under the confining pressure, and fit the formula of fracturability and temperature F(t) = f σ0 (t) and curve. Wherein, the constantly changing temperature conditions can be a certain temperature interval, or a continuous increase or decrease in temperature. Make the fitting change curve of confining pressure σ and F(σ), temperature t and F(t) in the double y-axis coordinate system, let F(σ) = F(t), and then obtain the corresponding confining pressure value σ n of the equivalent temperature t0 under a certain temperature value t n .

[0041] As shown in Figure 2 , the method for equivalent temperature in fracturability research is shown in the schematic diagram of the effect of instantaneous pressure. When the temperature is constant, with the increase of pressure, the fracturability F(σ) of the rock will increase, and the relationship curve may be a straight line or a curve. When the confining pressure is constant, with the increase of temperature, the fracturability F(t) of the rock will decrease, and the relationship curve may be a straight line or a curve. Taking the two relationship curve values when the fracturability is equal, that is, the corresponding confining pressure value under a certain temperature value under a certain confining pressure.

[0042] In summary, the method can calculate the corresponding confining pressure value under the temperature t0 equivalent to the temperature value under the confining pressure σ0, can perfect the analysis model of the influence of temperature and pressure on the mechanical properties of rock, and is convenient for the theoretical discussion of the change of rock mechanical properties with depth. At the same time, it is also convenient for the evaluation and calculation of the fracturability of the stratum, which is beneficial to guide the development and fracturing of oil and gas. The theoretical basis of the method is simple and reliable, which can solve the problem of temperature and pressure change with depth increase, and has strong practicability.

[0043] Example 3

[0044] Combined Figures 1 to 5 , a method for equivalent temperature in fracturability research is taken as an example, the XX layer (depth about 2000m, stratum temperature about 40℃, stratum confining pressure about 30MPa) of a certain depression area, the specific steps are as follows:

[0045] (1) Through the core statistics of the fracture data, including the fracture density, the fracture length and the filling degree. The mechanical experiments in this embodiment include the conventional triaxial experiment and the chevron notched Brazilian disc experiment (CCNBD). The mechanical parameters include the Young's modulus, the Poisson's ratio and the compressive strength obtained by the conventional triaxial experiment and the fracture toughness obtained by the chevron notched Brazilian disc experiment (CCNBD). Through the comparison of the fracture data and the mechanical parameters, it is found that the fracture density and the brittleness index, the fracture toughness and the triaxial compressive strength have good correlation, so the brittleness index (BI), the fracture toughness (K IC ) and the triaxial compressive strength (σ 3c ) are comprehensively used to represent the fracturing property (F) of the rock, and the representation formula is as follows:

[0046] F=BI / (K Ic *σ 3c )

[0047] It is to be noted that there are many representation methods of the fracturing property, and the representation method used in this embodiment is only one method suitable for the actual situation of the research area, and the fracturing property in this embodiment refers to the fracturing property index obtained by all representation methods.

[0048] (2) Given a specific temperature of 40℃, the mechanical experiments are respectively carried out at 0, 10, 20, 30, 40, 50 and 60 MPa with an interval of 10 MPa, and the related data are obtained (as shown in Table 1, Table 1 is the mechanical parameters at different confining pressures at the temperature of 40℃ in this embodiment), the scatter point relationship between the fracturing property and the confining pressure at this temperature is obtained (as shown in Figure 3 ), and the formula and the curve of the fracturing property and the confining pressure can be fitted.

[0049] Table 1

[0050]

[0051] (3) Given a specific confining pressure of 30 MPa, the mechanical experiments are respectively carried out at 0, 10, 20, 30, 40, 50 and 60℃ with an interval of 10℃, and the related data are obtained (as shown in Table 2, Table 2 is the mechanical parameters at different temperatures at the confining pressure of 30 MPa), the scatter point relationship between the fracturing property and the temperature at this confining pressure is obtained (as shown in Figure 4 ), and the formula and the curve of the fracturing property and the temperature can be fitted.

[0052] Table 2

[0053]

[0054] (4) In the double y-axis coordinate system, taking the fracturing index as the X-axis, the fitting change curves of confining pressure-fracturing index F(σ) and temperature-fracturing index F(t) are drawn respectively. Letting F(σ)=F(t), the corresponding confining pressure value at a temperature of 40℃ equivalent to the temperature value at a confining pressure of 30MPa is obtained.

[0055] It should be noted that, in the case of limited samples, only the corresponding confining pressure value at a certain temperature equivalent to the temperature value at a certain confining pressure can be obtained. In the case of absolutely sufficient samples, the method can be extended to draw a fracturing index-temperature, confining pressure relationship chart, so as to obtain the corresponding confining pressure value at any temperature equivalent to the temperature value at any confining pressure.

[0056] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or replacements made by the skilled in the art within the essential scope of the present application shall also fall within the protection scope of the present application.

Claims

1. A method for investigating the effect of instantaneous temperature equivalence to instantaneous pressure in fracturing, characterized by, It comprises the following steps: (1) data preparation, the data including the measured data of the fracture and the mechanical parameter data of the mechanical test, and the comprehensive representation of the fracturing property F of the rock is obtained through the measured data and the mechanical parameter data; (2) Given a certain temperature t0, keep the temperature unchanged, constantly change the confining pressure σ condition to characterize the mechanical experiment of the parameter and then calculate the fracturability, get the scatter point relationship between the fracturability and the confining pressure at this temperature, and fit the formula F(σ) = f t0 (σ) and the curve; (3) Given a certain confining pressure σ0, keep the confining pressure unchanged, constantly change the temperature t condition to characterize the mechanical experiment of the parameter and then calculate the fracturability, get the relationship between the fracturability and the temperature under the confining pressure, and fit the formula F(t) = f σ0 (t) and the curve; (4) In the double y-axis coordinate system, make fitting change curves of confining pressure σ and F(σ), temperature t and F(t) respectively, let F(σ)=F(t), then the temperature value t corresponding to confining pressure σ0 n is obtained n .

2. A method for investigating the effect of transient temperature equivalence to transient pressure in fracturability studies according to claim 1, characterized in that, The measured data of the fracture is the basic characteristic data of the actually measured core or field profile fracture, the mechanical parameters reflecting the fracture characteristics are screened out and combined to comprehensively represent the fracturing property F of the rock.

3. A method for investigating the effect of transient temperature equivalence to transient pressure in fracturability studies according to claim 2, characterized in that, The basic characteristic data of the fracture includes the surface density, length, width and filling degree of the fracture.

4. The method for transient temperature equivalent to transient pressure effect in fracturability study according to claim 1, characterized in that, The mechanical test is the test affecting the mechanical property of the rock; the mechanical test includes the conventional triaxial test, true triaxial test, fracture toughness test, in-situ stress test, compressive strength test and tensile strength test.

5. A method for investigating the effect of transient temperature equivalence to transient pressure in fracturability studies according to claim 1, characterized in that, The mechanical parameter is the parameter affecting the mechanical property of the rock; the mechanical parameter includes the Young's modulus, Poisson's ratio, fracture toughness, in-situ stress, compressive strength and tensile strength.

6. A method for investigating the effect of transient temperature equivalence to transient pressure in fracturability studies according to claim 1, characterized in that, The rock types include various terrigenous clastic rocks, various volcanic rocks, volcaniclastic rocks and metamorphic rocks.

7. A method for investigating the effect of transient temperature equivalence to transient pressure in fracturability studies according to claim 1, characterized in that, The confining pressure σ is changed in a certain confining pressure interval or continuously increased or continuously decreased.

8. A method for investigating the effect of transient temperature equivalence to transient pressure in fracturability studies according to claim 1, characterized in that, The temperature t is changed in a certain temperature interval or continuously increased or continuously decreased.

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