阅读说明：本技术 一种页岩储层含油饱和度的电化学预测方法 (Electrochemical prediction method for shale reservoir oil saturation ) 是由 祝瑜 吴伟 张召才 于静 冯阵东 刘高峰 刘惟庆 李晓斌 高迪 于 2020-05-13 设计创作，主要内容包括：本发明公开了一种页岩储层含油饱和度的电化学预测方法,包括以下步骤：(a)在页岩试件的两端放置电极片,通过导线将电极片与电化学工作站数据采集系统连接,再与计算机数据处理系统连接；(b)对页岩试件施加电压或电流扰动信号,输入的扰动信号经过试件后产生相应的响应信号,响应信号经过电化学工作站数据采集系统和计算机数据处理系统处理,得到试件的电化学阻抗谱；(c)通过分析电化学阻抗谱的特征变化,对实测数据电化学阻抗谱进行拟合,建立页岩固-液渗透等效电路模型,通过渗透扩散引起的法拉第阻抗参数的理论计算,建立页岩储层含油饱和度的预测模型。本发明操作简单,方便快捷,样品预处理简单,能够满足大量样品测试需求。(The invention discloses an electrochemical prediction method for oil saturation of a shale reservoir, which comprises the following steps: (a) placing electrode plates at two ends of a shale test piece, connecting the electrode plates with a data acquisition system of an electrochemical workstation through a lead, and then connecting the electrode plates with a computer data processing system; (b) applying a voltage or current disturbance signal to the shale test piece, generating a corresponding response signal after the input disturbance signal passes through the test piece, and processing the response signal by an electrochemical workstation data acquisition system and a computer data processing system to obtain an electrochemical impedance spectrum of the test piece; (c) the method comprises the steps of fitting an electrochemical impedance spectrum of actually measured data by analyzing characteristic changes of the electrochemical impedance spectrum, establishing a shale solid-liquid permeation equivalent circuit model, and establishing a prediction model of the oil saturation of a shale reservoir by theoretical calculation of Faraday impedance parameters caused by permeation diffusion. The method is simple to operate, convenient and quick, simple in sample pretreatment and capable of meeting the test requirements of a large number of samples.)

1. An electrochemical prediction method for the oil saturation of a shale reservoir is characterized by comprising the following steps:

(a) placing electrode plates at two ends of a shale test piece, connecting the electrode plates with a data acquisition system of an electrochemical workstation through a lead, and then connecting the electrode plates with a computer data processing system;

(b) applying sinusoidal alternating current voltage or sinusoidal alternating current disturbance signals with different frequencies to a shale test piece, generating corresponding response signals, namely sinusoidal alternating current or sinusoidal alternating current voltage signals, after the input disturbance signals pass through the shale test piece, and processing the response signals by an electrochemical workstation data acquisition system and a computer data processing system to obtain an electrochemical impedance spectrum of the shale test piece;

(c) the method comprises the steps of fitting an electrochemical impedance spectrum of actually measured data by analyzing characteristic changes of the electrochemical impedance spectrum, establishing a shale solid-liquid permeation equivalent circuit model, and establishing a prediction model of the oil saturation of a shale reservoir by theoretical calculation of Faraday impedance parameters caused by permeation diffusion.

2. The method for electrochemically predicting the oil saturation of a shale reservoir as claimed in claim 1, wherein the number of the electrode sheets in the step (a) is at least two, and the positions are placed in a uniformly distributed or non-uniformly distributed manner.

3. The method for electrochemically predicting the oil saturation of a shale reservoir according to claim 1, wherein the frequency range of the disturbance signal in the step (b) is 1Hz-10 MHz.

4. The method of claim 1, wherein the sinusoidal ac voltage amplitude in step (b) is less than 20 mV.

5. The method of claim 1, wherein the sinusoidal ac current amplitude in step (b) is less than 50 mA.

6. The method for electrochemically predicting the oil saturation of shale reservoirs according to claim 1, wherein the method for representing the electrochemical impedance spectrum of the shale test pieces obtained in the step (b) comprises a Warburg diagram, an admittance diagram, a capacitance diagram, a Nyquist diagram and a Bode diagram.

7. The method for electrochemically predicting the oil saturation of shale reservoirs according to claim 6, wherein the representation method of the electrochemical impedance spectrum of the shale test pieces obtained in the step (b) is preferably a Nyquist diagram and a Bode diagram.

8. The method for electrochemically predicting the oil saturation of a shale reservoir according to claim 1, wherein the characteristic change of the electrochemical impedance spectrum of the shale sample in the step (c) is a change condition corresponding to the increase or decrease of the phase angle, the angular frequency, the impedance vector and the impedance mode value with the frequency in a certain frequency range.

9. The method for electrochemically predicting the oil saturation of the shale reservoir according to claim 1, wherein the characteristic change of the electrochemical impedance spectrum of the shale sample in the step (c) is in a corresponding relation with the oil saturation.

Technical Field

The invention relates to a natural gas exploration technology, in particular to an electrochemical prediction method for oil saturation of a shale reservoir.

Background

Shale oil exists in shale reservoirs in a free state, a dissolved state and an adsorption state, wherein the free shale oil is mainly stored in micro-nano pores and cracks, and the shale oil has the best mobility and is easy to recover and is a main source for forming industrial oil flow in the shale reservoirs. The dissolved shale oil is mainly added into residual pores formed by organic hydrocarbon generation, has certain fluidity and contributes to development of the shale oil, and the higher the organic content is, the more the formed organic hydrocarbon generation residual pores are. The shale oil in an adsorption state is mainly attached to the surfaces of kerogen and mineral particles, and a widely distributed kerogen network can provide a large specific surface for shale oil adsorption.

The characterization parameters of the oil content of the shale can be divided into organic geochemical parameters and core physical parameters. The most representative of the organic geochemical parameters are residual hydrocarbon S1 and chloroform bitumen "a", both of which are influenced primarily by the abundance, type and degree of thermal evolution of the organic material, both of which can quantitatively characterize the oiliness of shale reservoirs. The common physical parameter of the core is oil saturation S0, which is often used for oil-bearing characterization of conventional reservoirs, and the oil saturation is generally obtained by an oil washing method, so that the core can only characterize free hydrocarbons in connected pores, and cannot calculate adsorbed hydrocarbons and liquid hydrocarbons in closed pores. Therefore, the establishment of a prediction method capable of comprehensively evaluating the oil saturation of the shale reservoir is an urgent problem to be solved by the technical personnel in the field.

An Electrochemical Impedance Spectroscopy (EIS) can reflect a new method of the internal structure of the material, and can discuss the relationship between the Electrochemical Impedance Spectroscopy characteristic and the shale oil saturation.

Disclosure of Invention

The invention aims to provide an electrochemical prediction method for shale reservoir oil saturation, which can comprehensively evaluate the shale reservoir oil saturation. The method analyzes the development change condition of the shale pore structure on the theoretical basis of researching the oil saturation of the shale by adopting the electrochemical impedance spectroscopy principle, thereby being capable of monitoring the dynamic evolution process of the shale pore structure.

The invention makes the following description on the principle of an electrochemical prediction method of the oil saturation of the shale reservoir.

The electrochemical impedance spectrum is to apply a small amplitude AC potential wave with different frequencies to an electrochemical system, measure the change of the ratio of the AC potential to a current signal along with the frequency of a sine wave, and the ratio is the impedance of the system, or measure the change of the phase angle of the impedance of the system along with the frequency of the sine wave. The method is a frequency domain measurement method, the measurable frequency range is wide, and more kinetic information and electrode interface structure information can be obtained compared with the conventional electrochemical method. Because the system is perturbed by a small amplitude sinusoidal potential signal, the oxidation and reduction processes alternately occur at the electrodes. Therefore, even if the disturbing signal acts on the electrode for a long time, the accumulative development of the polarization phenomenon and the accumulative change of the surface state of the electrode are not caused. Because of the linear relation between the potential and the current, the electrode is in a quasi-steady state in the measuring process, so that the digital processing of the measuring result is simplified.

The invention relates to a method for continuously and automatically monitoring and recording electrochemical impedance spectrum characteristic parameter data by an electrochemical system consisting of a shale test piece, an electrode slice, a lead, an electrochemical workstation and a computer and judging the oil saturation of the test piece according to the change of the electrochemical impedance spectrum characteristic parameter. The electrochemical system can be regarded as an equivalent circuit, and the equivalent circuit is formed by combining basic elements such as a resistor, a capacitor, an inductor and the like according to different modes such as series connection, parallel connection and the like. The structure of the equivalent circuit and the size of each element can be measured by electrochemical impedance spectroscopy, and the structure of the electrochemical system and the properties of the electrode process can be analyzed by using the electrochemical meanings of the elements. The shale test piece is a special electrochemical system, electrodes are arranged at two ends of the test piece, when the shale oil saturation is different, capacitance is increased in the test piece, so that the impedance of the test piece under different frequencies changes, electrochemical parameter values of the test piece under different frequencies are obtained through analysis of an electrochemical workstation, an electrochemical impedance map of the test piece is obtained through drawing of a computer, the characteristic change of the electrochemical impedance map corresponds to the shale oil saturation, and the shale pore structure and the development condition of the shale pore structure can be well reflected.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

an electrochemical prediction method for shale reservoir oil saturation comprises the following steps:

(a) placing electrode plates at two ends of a shale test piece, connecting the electrode plates with a data acquisition system of an electrochemical workstation through a lead, and then connecting the electrode plates with a computer data processing system;

(b) applying sinusoidal alternating current voltage or sinusoidal alternating current disturbance signals with different frequencies to a shale test piece, generating corresponding response signals, namely sinusoidal alternating current or sinusoidal alternating current voltage signals, after the input disturbance signals pass through the shale test piece, and processing the response signals by an electrochemical workstation data acquisition system and a computer data processing system to obtain an electrochemical impedance spectrum of the shale test piece;

(c) the method comprises the steps of fitting an electrochemical impedance spectrum of actually measured data by analyzing characteristic changes of the electrochemical impedance spectrum, establishing a shale solid-liquid permeation equivalent circuit model, and establishing a prediction model of the oil saturation of a shale reservoir by theoretical calculation of Faraday impedance parameters caused by permeation diffusion.

Further, the number of the electrode plates in the step (a) is at least two, and the electrode plates are placed in a uniformly distributed or non-uniformly distributed mode.

Further, the frequency range of the disturbing signal in the step (b) is 1Hz-10 MHz.

Further, the sinusoidal alternating voltage amplitude in step (b) is less than 20 mV.

Further, the amplitude of the sinusoidal alternating current in the step (b) is lower than 50 mA.

Further, the method for representing the electrochemical impedance spectrum of the shale test piece obtained in the step (b) comprises a Warburg diagram, an admittance diagram, a capacitance diagram, a Nyquist diagram and a Bode diagram.

Furthermore, the method for representing the electrochemical impedance spectrum of the shale test piece obtained in the step (b) is preferably a Nyquist diagram and a Bode diagram.

Further, the characteristic change of the electrochemical impedance spectrum of the shale test piece in the step (c) refers to a change condition corresponding to the increase or decrease of the phase angle, the angular frequency, the impedance vector and the impedance mode value along with the frequency in a certain frequency range.

Further, the characteristic change of the electrochemical impedance spectrum of the shale test piece in the step (c) has a corresponding relation with the oil saturation of the shale test piece.

Compared with the prior art, the invention has the beneficial effects that:

1. according to the electrochemical prediction method for the oil saturation of the shale reservoir, the prediction area of the shale test piece is not limited by the structure and the space position of the shale, and the application range is wide.

2. The electrochemical prediction method for the oil saturation of the shale reservoir can comprehensively evaluate the oil saturation of the shale reservoir and solve the technical problem that the oil saturation of the shale reservoir cannot be comprehensively evaluated in the prior art.

Drawings

FIG. 1 is a schematic diagram of an electrochemical prediction method for oil saturation of a shale reservoir according to the present invention;

FIG. 2 is a Nyquist curve of the shale test piece obtained in example 1 of the present invention;

FIG. 3 is a fitting curve of a Nyquist curve of the shale test piece obtained in example 1 of the present invention;

FIG. 4a is an impedance spectrum of a shale water-gap solid-liquid permeability model in embodiment 1 of the present invention;

FIG. 4b is an equivalent circuit of a shale water-gap solid-liquid permeation model in embodiment 1 of the present invention;

FIG. 4c is the Faraday impedance of the shale water-gap solid-liquid permeation model equivalent circuit in embodiment 1 of the present invention;

FIG. 5a is an impedance spectrum of a shale oil-water pore solid-liquid permeation model I based on R in the lower oil saturation condition in the embodiment 1 of the present invention_xPredicting oil saturation: r1 < R2 < R3;

FIG. 5b is an equivalent circuit of a shale oil-water pore solid-liquid permeation model I under the condition of low oil saturation in the embodiment 1 of the present invention, wherein R is based on_xPredicting oil saturation: r1 < R2 < R3;

FIG. 5c is the Faraday impedance of the equivalent circuit of the shale oil-water pore solid-liquid permeation model I under the condition of lower oil saturation in the embodiment 1 of the present invention, wherein R is based on_xPredicting oil saturation: r1 < R2 < R3;

FIG. 6a is an impedance spectrum of a shale oil water-pore solid-liquid permeability model II under the condition of medium oil saturation in the embodiment 1 of the present invention, wherein Z_wThe larger the value, the higher the oil saturation;

FIG. 6b is an equivalent circuit of shale oil water-pore solid-liquid permeation model II under the condition of medium oil saturation in the embodiment 1 of the present invention, wherein Z is_wThe larger the value, the higher the oil saturation;

FIG. 6c is the impedance of the oil-water semi-infinite diffusion layer of the shale oil water pore solid-liquid permeability model II under the condition of medium oil saturation in the embodiment 1 of the present invention, wherein Z is_wThe larger the value, the higher the oil saturation;

FIG. 7a is an impedance spectrum of a shale oil-water pore solid-liquid permeation model III under the condition of higher oil saturation in the embodiment 1 of the present invention, wherein Z is_TThe larger the value, the higher the oil saturation;

FIG. 7b is an equivalent circuit of a shale oil-water pore solid-liquid permeation model III under the condition of higher oil saturation in the embodiment 1 of the present invention, wherein Z is_TThe larger the value, the higher the oil saturation;

FIG. 7c is a graph showing the diffusion resistance of the oil-water barrier layer in the shale oil-water pore solid-liquid permeation model III under the condition of higher oil saturation in the embodiment 1 of the present invention, wherein the larger the ZT value is, the higher the oil saturation is;

in the figure, the electrochemical device comprises a first working electrode 1, a first working electrode 2, a reference electrode 3, a second working electrode 4, an auxiliary electrode 5, an electrode plate 6, an electrochemical workstation data acquisition system 7 and a computer data processing system.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.