Method for acquiring content of unfrozen water in rock under freeze-thaw cycle condition
阅读说明：本技术 一种冻融循环条件下岩石中未冻水含量的获取方法 (Method for acquiring content of unfrozen water in rock under freeze-thaw cycle condition ) 是由 谭贤君 苏舟舟 陈卫忠 马伟 于 2019-11-20 设计创作，主要内容包括：本发明属于融冻岩石技术领域,公开了一种冻融循环条件下岩石中未冻水含量的获取方法,包括：制备岩石柱样,而后通过地层水饱和所述岩石柱样；对饱和地层水的所述岩石柱样进行核磁共振测试得到T2谱曲线；将所述T2谱曲线转换成核磁孔喉分布曲线f(r)；将所述核磁孔喉分布曲线f(r)带入到积分公式分别得到融化时和冻结时未冻结水含量与温度的关系曲线。本发明提供的冻融循环条件下岩石中未冻水含量的获取方法能够实现高精度,高可靠性,简便获取未冻水含量。(The invention belongs to the technical field of thawing rocks, and discloses a method for acquiring the content of unfrozen water in rocks under a freezing-thawing cycle condition, which comprises the following steps: preparing a rock column sample, and then saturating the rock column sample by formation water; performing nuclear magnetic resonance test on the rock column sample of the saturated formation water to obtain a T2 spectrum curve; converting the T2 spectrum curve to a nuclear magnetic pore throat distribution curve f (r); and substituting the nuclear magnetic pore throat distribution curve f (r) into an integral formula to respectively obtain the relationship curves of unfrozen water content and temperature during melting and freezing. The method for acquiring the content of unfrozen water in the rock under the freeze-thaw cycle condition can realize high precision and high reliability, and can simply and conveniently acquire the content of the unfrozen water.)
1. A method for obtaining the content of unfrozen water in rock under the condition of freeze-thaw cycle is characterized by comprising the following steps:
preparing a rock column sample, and then saturating the rock column sample by formation water;
performing nuclear magnetic resonance test on the rock column sample of the saturated formation water to obtain a T2 spectrum curve;
converting the T2 spectrum curve to a nuclear magnetic pore throat distribution curve f (r);
substituting the nuclear magnetic pore throat distribution curve f (r) into an integral formula to respectively obtain a relationship curve of unfrozen water content and temperature during melting and freezing;
wherein the integral formula is:
when the freezing is carried out, the freezing process is carried out,
when the melting process is carried out, the melting process r,
wherein r is the void radius, ρsIs the density of ice, TmAt the temperature at which the water melts,. DELTA.T is TmDifference from core temperature T at measurement, gammaiwH is the thickness of unfrozen water film between ice in frozen pores and pore walls, Delta H is the latent heat value of hydrothermal conversion, rmaxThe maximum pore size of the rock;
critical freezing pore diameter during freezing
Critical radius of fusion during fusion
2. The method of obtaining the unfrozen water content of a rock under freeze-thaw cycles of claim 1, wherein the nuclear magnetic pore throat distribution curve
Wherein p1 is 0.087, p2 is-11.41, p3 is 60.065, p4 is 1408.5, p5 is 8544.5, p6 is 46295.27, p7 is-5974, p8 is 10273, and p9 is 750.
Technical Field
The invention relates to the technical field of freeze-thaw rock measurement, in particular to a method for acquiring the content of unfrozen water in rock under the condition of freeze-thaw cycle.
Background
The method is significant for engineering construction of a freezing and thawing area by measuring the unfrozen water of the rock, and in the prior art, the unfrozen water is measured by a plurality of measuring schemes, but the defects of low precision, high requirement on experimental conditions, complex test operation, poor reliability and the like exist more or less.
Disclosure of Invention
The invention provides a method for acquiring the content of unfrozen water in rocks under a freeze-thaw cycle condition, and solves the technical problems of poor precision, complex operation and poor reliability in the prior art for measuring the content of the unfrozen water.
In order to solve the technical problem, the invention provides a method for acquiring the content of unfrozen water in rocks under the condition of freeze-thaw cycle, which comprises the following steps:
preparing a rock column sample, and then saturating the rock column sample by formation water;
performing nuclear magnetic resonance test on the rock column sample of the saturated formation water to obtain a T2 spectrum curve;
converting the T2 spectrum curve to a nuclear magnetic pore throat distribution curve f (r);
substituting the nuclear magnetic pore throat distribution curve f (r) into an integral formula to respectively obtain a relationship curve of unfrozen water content and temperature during melting and freezing;
wherein the integral formula is:
when the freezing is carried out, the freezing process is carried out,
when the melting process is carried out, the melting process r,
wherein r is the void radius, ρsIs the density of ice, TmAt the temperature at which the water melts,. DELTA.T is TmDifference from core temperature T at measurement, gammaiwH is the free energy of water-ice interface, H is the thickness of the unfrozen water film between ice in frozen pores and pore walls, Delta H is the latent heat released when water freezes, rmaxThe maximum pore size of the rock;
critical freezing pore diameter during freezing
When melting, the melting is criticalRadius of
Further, the nuclear magnetic pore throat distribution curve
Wherein p1 is 0.087, p2 is-11.41, p3 is 60.065, p4 is 1408.5, p5 is 8544.5, p6 is 46295.27, p7 is-5974, p8 is 10273, and p9 is 750.
One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:
according to the method for acquiring the content of the unfrozen water in the rock under the freeze-thaw cycle condition, the calculation of the content of the unfrozen water is theorized, so that the method is more popularized, meanwhile, the test process of the content of the unfrozen water is greatly simplified due to the theoretical formula, and the content of the unfrozen water at the moment can be acquired according to the relation curve between the temperature and the content of the unfrozen water only by measuring the temperature at a certain moment. The error is found to be very little with the comparison of experimental data to the result of theoretical calculation, has solved the loaded down with trivial details step when testing in general experiment, and measurement accuracy is relatively poor problem. The results can be obtained quickly and accurately.
Drawings
FIG. 1 is a graph of unfrozen water content versus temperature provided by an embodiment of the present invention.
Detailed Description
The embodiment of the application provides a method for obtaining the content of unfrozen water in rocks under a freeze-thaw cycle condition, and solves the technical problems of poor precision, complex operation and poor reliability in the prior art for measuring the content of the unfrozen water.
In order to better understand the technical solutions, the technical solutions will be described in detail below with reference to the drawings and the specific embodiments of the specification, and it should be understood that the embodiments and specific features of the embodiments of the present invention are detailed descriptions of the technical solutions of the present application, and are not limitations of the technical solutions of the present application, and the technical features of the embodiments and examples of the present application may be combined with each other without conflict.
The embodiment provides a method for acquiring the content of unfrozen water in rock under a freeze-thaw cycle condition, which comprises the following steps:
preparing a rock column sample, and then saturating the rock column sample by formation water;
performing nuclear magnetic resonance test on the rock column sample of the saturated formation water to obtain a T2 spectrum curve;
converting the T2 spectrum curve to a nuclear magnetic pore throat distribution curve f (r);
substituting the nuclear magnetic pore throat distribution curve f (r) into an integral formula to respectively obtain a relationship curve of unfrozen water content and temperature during melting and freezing;
wherein the integral formula is:
when the freezing is carried out, the freezing process is carried out,
when the melting process is carried out, the melting process r,
wherein r is the void radius, ρsIs the density of ice, TmAt the temperature at which the water melts,. DELTA.T is TmDifference from core temperature T at measurement, gammaiwH is the free energy of water-ice interface, H is the thickness of the unfrozen water film between ice in frozen pores and pore walls, Delta H is the latent heat released when water freezes, rmaxThe maximum pore size of the rock;
critical freezing pore diameter during freezing
Critical radius of fusion during fusion
Further, the nuclear magnetic pore throat distribution curve
Wherein p1 is 0.087, p2 is-11.41, p3 is 60.065, p4 is 1408.5, p5 is 8544.5, p6 is 46295.27, p7 is-5974, p8 is 10273, and p9 is 750.
The technical solution and principle of the present application will be specifically explained below.
The technical scheme of the invention is to provide a method for calculating by using an integral formula by using the radius, porosity, temperature and the like of unfrozen water, and the theoretical process of the method mainly comprises the following derivation steps:
classical thermodynamics can be used to describe the solidification process, i.e., the change from a liquid to a solid. At the equilibrium phase boundary, the specific gibbs free energy is the same in both phases on both sides. The phase change equilibrium equation on the ice-water interface can be obtained by the Gibbs-Duhem equation:
in the formula: rhosDensity of ice 0.9g/cm3；
L is latent heat released when water of unit mass is frozen; 1 kg of ice absorbs 334.3 kj of heat and converts it to liquid water.
Tm-temperature at melting 273K;
testing the central temperature of the rock sample at the time T-T;
ΔT—Tm-T test temperature and measured core temperature difference;
pl-water pressure at the interface;
ps-the ice pressure at the interface;
in the case of pl-pmWhen the pressure difference is generated (1) can be simplified into
According to the capillary theory oneAn assumption that when the temperature drops to TmThe equation can be derived when the Young-Laplace equation is applied to the pressure difference at the curved ice-water interface, when ice does not immediately penetrate into the voids in the soil:
these equations (2) and (3) are equivalent to each other:
the frozen ice body at this time is regarded as a circular cap, and the critical radius of the ice circular cap at this time is as follows:
wherein gamma isiwWater ice interface free energy 40.9X 10-3kg/s2；
rc-a critical freezing pore size;
the thickness of the adsorption film is linked to the surface and liquid properties, geometry and chemical potential, considering the simple case that the liquid film adsorbed on a plane surface causes only long range intermolecular (van der waals) interactions,
can obtain the product
In the formula:
h is the thickness of the film;
permeability of Pi-rock 1.4X 10-8md；
AsvlHamaker constant of water, 3.3X 10, by interposing liquid-solid-gas interactions- 20J。
Under the action of T<r0May not freeze.
Wherein f (r) -the pore volume fraction function, as converted from NMR experiments;
h is the thickness of the film;
W1-free part of unfrozen water;
W2-non-free part of unfrozen water;
when freezing:
wherein the shape of any of the circles or rectangles α is 2
rc-ice radius at freezing;
can obtain the product
When melting:
wherein the coefficient α takes a value of 2
rc' -critical radius upon melting;
to obtain
When melting:
rmax-maximum pore size of the rock;
practical calculation example:
referring to FIG. 1, data obtained by performing freeze-thaw experiments at-25, -20, -15, -10, -5, 0, 5, 10, 15, 20, and 25 ℃ respectively, with the maximum radius of 1000 μm, and introducing the relevant data into the above formula are shown in the following table
One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:
according to the method for acquiring the content of the unfrozen water in the rock under the freeze-thaw cycle condition, the calculation of the content of the unfrozen water is theorized, so that the method is more popularized, meanwhile, the test process of the content of the unfrozen water is greatly simplified due to the theoretical formula, and the content of the unfrozen water at the moment can be acquired according to the relation curve between the temperature and the content of the unfrozen water only by measuring the temperature at a certain moment. The error is found to be very little with the comparison of experimental data to the result of theoretical calculation, has solved the loaded down with trivial details step when testing in general experiment, and measurement accuracy is relatively poor problem. The results can be obtained quickly and accurately.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to examples, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
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