CN111577266A - Electrochemical prediction method for shale reservoir oil saturation - Google Patents

Abstract

The invention discloses an electrochemical prediction method for oil saturation of a shale reservoir, comprising the following steps: (a) placing electrode sheets at both ends of a shale test piece, and connecting the electrode sheets with a data acquisition system of an electrochemical workstation through a wire (b) Apply a voltage or current disturbance signal to the shale specimen, and the input disturbance signal will generate a corresponding response signal after passing through the specimen, and the response signal will pass through the electrochemical workstation data acquisition system and computer. The electrochemical impedance spectrum of the specimen is obtained by processing the data processing system; (c) by analyzing the characteristic changes of the electrochemical impedance spectrum, the measured data electrochemical impedance spectrum is fitted, and the shale solid-liquid permeation equivalent circuit model is established, The prediction model of oil saturation in shale reservoirs is established by theoretical calculation of Faraday impedance parameters caused by permeation diffusion. The invention is simple to operate, convenient and quick, and the sample pretreatment is simple, and can meet the testing requirements of a large number of samples.

Description

An electrochemical prediction method for oil saturation in shale reservoirs

technical field

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

Background technique

Shale oil occurs in shale reservoirs in free, dissolved and adsorbed states. Free shale oil is mainly stored in micro-nano-scale pores and fractures. This type of shale oil has the best fluidity and Easy to mine, it is the main source of industrial oil flow from shale reservoirs. Dissolved shale oil mainly occurs in the residual pores formed by organic hydrocarbon generation. It has a certain fluidity and has a certain contribution to the development of shale oil. The higher the organic matter content, the more organic hydrocarbon generation residual pores are formed. Adsorbed shale oil is mainly attached to the surface of kerogen and mineral particles, and the widely distributed kerogen network can provide a large specific surface area for shale oil adsorption.

The characterization parameters of shale oiliness can be divided into organic geochemical parameters and core physical parameters. The most representative organic geochemical parameters are residual hydrocarbon S1 and chloroform bitumen “A”, these two parameters are mainly affected by the abundance, type and thermal evolution degree of organic matter, both of which can quantitatively characterize shale reservoirs of oiliness. The commonly used core physical parameters is the oil saturation S0, which is often used for the oil-bearing characterization of conventional reservoirs. Generally, the oil-bearing saturation is obtained by the method of oil washing, so it can only characterize the free hydrocarbons in the connected pores. Calculates adsorbed hydrocarbons and liquid hydrocarbons in closed pores. Therefore, establishing a prediction method capable of comprehensively evaluating the oil saturation of shale reservoirs is an urgent problem for those skilled in the art.

Electrochemical Impedance Spectroscopy (EIS) is a new method that can reflect the internal structure of materials, and can explore the relationship between EIS characteristics and shale oil saturation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an electrochemical prediction method for the oil saturation of shale reservoirs to comprehensively evaluate the oil saturation of shale reservoirs. The method uses electrochemical impedance spectroscopy to study the theoretical basis of shale oil saturation, and analyzes the development and changes of shale pore structure, so as to monitor the dynamic evolution process of shale pore structure.

In the present invention, the principle of an electrochemical prediction method for oil saturation of a shale reservoir is described below.

Electrochemical impedance spectroscopy is to apply a small-amplitude AC potential wave with different frequencies to the electrochemical system, and measure the ratio of the AC potential to the current signal as a function of the frequency of the sine wave. Changes in the frequency of a sine wave. It is a frequency domain measurement method, which can measure a wide frequency range and can obtain more kinetic information and electrode interface structure information than conventional electrochemical methods. Owing to the perturbation of the system with a small amplitude sinusoidal potential signal, the oxidation and reduction processes alternately occur on the electrodes. Therefore, even if the perturbation signal acts on the electrode for a long time, it will not lead to the cumulative development of the polarization phenomenon and the cumulative change of the electrode surface state. Due to the linear relationship between the potential and the current, the electrodes are in a quasi-steady state during the measurement process, which simplifies the digital processing of the measurement results.

The invention realizes the continuous and automatic monitoring and recording of the characteristic parameter data of the electrochemical impedance spectrum by an electrochemical system composed of a shale test piece, an electrode sheet, a lead wire, an electrochemical workstation and a computer. A method for judging the oil saturation of the test piece. The electrochemical system can be regarded as an equivalent circuit, which is composed of basic elements such as resistance, capacitance and inductance in different ways such as series and parallel. Through electrochemical impedance spectroscopy, the composition of the equivalent circuit and the size of each element can be determined, and the electrochemical meaning of these elements can be used to analyze the structure of the electrochemical system and the properties of the electrode process. The shale specimen is a special electrochemical system. Electrodes are placed at both ends of the specimen. When the oil saturation of the shale is different, it is equivalent to increasing the capacitance in the specimen, resulting in the impedance of the specimen at different frequencies. Through the analysis of the electrochemical workstation, the electrochemical parameter values of the specimen at different frequencies are obtained, and the electrochemical impedance spectrum of the specimen is drawn by the computer. The characteristic change of the electrochemical impedance spectrum has a corresponding relationship with the shale oil saturation. , which can well reflect the shale pore structure and its development.

To achieve the above object, the technical scheme of the present invention is achieved in this way:

An electrochemical prediction method for oil saturation of a shale reservoir, comprising the following steps:

(a) Place electrode sheets at both ends of the shale specimen, connect the electrode sheets to the electrochemical workstation data acquisition system through wires, and then connect to the computer data processing system;

(b) Apply sinusoidal AC voltage or sinusoidal AC current disturbance signals of different frequencies to the shale specimen, and the input disturbance signal generates a corresponding response signal after passing through the shale specimen, that is, sinusoidal AC current or sinusoidal AC voltage signal, and the response signal After the electrochemical workstation data acquisition system and the computer data processing system, the electrochemical impedance spectrum of the shale specimen was obtained;

(c) By analyzing the characteristic changes of the electrochemical impedance spectrum, fitting the electrochemical impedance spectrum of the measured data, establishing an equivalent circuit model of shale solid-liquid permeation, and establishing a page through the theoretical calculation of the Faraday impedance parameter caused by permeation diffusion A prediction model for oil saturation in rock reservoirs.

Further, in the step (a), the number of electrode sheets is at least two, and the positions are placed in a manner of uniform distribution or non-uniform distribution.

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

Further, in the step (b), the amplitude of the sinusoidal AC voltage is lower than 20mV.

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

Further, the representation methods of the electrochemical impedance spectrum of the shale specimen obtained in the step (b) include Warburg diagram, admittance diagram, capacitance diagram, Nyquist diagram and Bode diagram.

Further, the representation methods of the electrochemical impedance spectrum of the shale specimen obtained in the step (b) are preferably Nyquist diagram and Bode diagram.

Further, the characteristic change of the electrochemical impedance spectrum of the shale specimen in the step (c) refers to the corresponding phase angle, angular frequency, impedance vector and impedance modulus value in a certain frequency range as the frequency increases or decreases. changes.

Further, in the step (c), the characteristic change of the electrochemical impedance spectrum of the shale specimen has a corresponding relationship with its oil saturation.

Compared with the prior art, the beneficial effects of the present invention are:

1. In the electrochemical prediction method of oil saturation in shale reservoirs of the present invention, the prediction area of the shale specimen is not limited by the structure and spatial position of the shale, and has a wide range of applications.

2. The electrochemical prediction method for oil saturation of shale reservoirs of the present invention can comprehensively evaluate the oil saturation of shale reservoirs, and solves the technical problem that the prior art cannot fully evaluate the oil saturation of shale reservoirs.

Description of drawings

Fig. 1 is the schematic diagram of the electrochemical prediction method of shale reservoir oil saturation of the present invention;

Fig. 2 is the Nyquist curve of the shale specimen obtained in Example 1 of the present invention;

Fig. 3 is the fitting curve of the Nyquist curve of the shale specimen obtained in Example 1 of the present invention;

Fig. 4a is the impedance spectrum of the shale water layer gap solid-liquid permeability model in implementation 1 of the present invention;

Fig. 4b is the equivalent circuit of the solid-liquid permeation model of the shale water layer gap in implementation 1 of the present invention;

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

Fig. 5a is the impedance spectrum of shale oil-water interstitial solid-liquid permeability model I under the condition of low oil saturation in implementation 1 of the present invention, and the oil saturation is predicted based on R _x in the figure: R1 < R2 <R3;

Fig. 5b is the equivalent circuit of the solid-liquid permeability model I of shale oil-water interstices under the condition of low oil saturation in implementation 1 of the present invention, and the oil saturation is predicted based on R _x in the figure: R1 < R2 <R3;

Figure 5c is the Faraday impedance of the equivalent circuit of the solid-liquid permeability model I of the shale oil-water gap under the condition of low oil saturation in implementation 1 of the present invention. In the figure, the oil saturation _is predicted based on Rx: R1<R2<R3;

Fig. 6a is the impedance spectrum of shale oil-water interstitial solid-liquid permeability model II under the condition of medium oil saturation in implementation 1 of the present invention, the larger the Z _w value in the figure, the higher the oil saturation;

Fig. 6b is the equivalent circuit of the solid-liquid permeability model II of the shale oil-water layer gap under the condition of medium oil saturation in implementation 1 of the present invention, the larger the Z _w value in the figure, the higher the oil saturation;

Figure 6c is the impedance of the oil-water semi-infinite diffusion layer of the shale oil-water interstitial solid-liquid permeability model II under the condition of medium oil saturation in the embodiment 1 of the present invention, the larger the Z _w value in the figure, the higher the oil saturation;

Fig. 7a is the impedance spectrum of shale oil-water interstitial solid-liquid permeability model III under the condition of high oil saturation in implementation 1 of the present invention, the larger the Z _T value in the figure, the higher the oil saturation;

Fig. 7b is the equivalent circuit of the solid-liquid permeability model III of the shale oil-water gap under the condition of high oil saturation in implementation 1 of the present invention, the larger the Z _T value in the figure, the higher the oil saturation;

Fig. 7c shows the diffusion impedance of oil-water barrier layer in shale oil-water interstitial solid-liquid permeability model III under the condition of high oil saturation in implementation 1 of the present invention, the larger the ZT value in the figure, the higher the oil saturation;

In the figure, 1, the first working electrode, 2, the reference electrode, 3, the second working electrode, 4, the auxiliary electrode, 5, the electrode sheet, 6, the electrochemical workstation data acquisition system, 7, the computer data processing system.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

FIG. 1 shows a schematic diagram of the electrochemical prediction method for oil saturation of a shale reservoir in this embodiment. As shown in Figure 1, the electrochemical prediction method of oil saturation in shale reservoirs includes the following steps:

(1) Production of shale specimens

In the specific embodiment of the present invention, the shale specimen required by the present invention is prepared by but not limited to the following methods.

The collected bulk shale samples were cut into cylindrical samples with a diameter of 50 mm and saturated with water. A saturated sponge should be placed on the upper and lower ends of the sample to ensure close contact between the sample and the electrode pads.

(2) Build a monitoring system

An electrode sheet 5 is placed on each end of the shale specimen, and the electrode sheet 5 is connected to the electrochemical workstation data acquisition system 6 through wires, and then connected to the computer data processing system 7; wherein, the electrochemical workstation data acquisition system 6 includes: Electrochemical workstation, first working electrode 1, reference electrode 2, second working electrode 3, auxiliary electrode 4, connect the first working electrode 1 and reference electrode 2 to the electrode sheet 5 at one end of the shale specimen, and the second working electrode The electrode 3 and the auxiliary electrode 4 are connected to the electrode sheet 5 at the other end of the shale specimen; wherein, the first working electrode 1 and the second working electrode 3 are stainless steel, nickel, and copper; they can be self-made or purchased, in this embodiment It is stainless steel; the reference electrode 2 is a saturated calomel electrode; the auxiliary electrode 4 is a platinum wire electrode.

(2) A sinusoidal AC voltage disturbance signal with a frequency of 1Hz to 10MHz and an amplitude of 5mV is applied to the shale specimen through the electrode sheet 5, and the response signal, that is, the sinusoidal AC current signal, is collected by the electrochemical workstation data acquisition system 6. The computer data processing system 7 processes the collected response signals, and records the Nyquist curve in the electrochemical impedance spectrum of the test piece, as shown in FIG. 2 .

(3) By analyzing the characteristic changes of the electrochemical impedance spectrum, fitting the electrochemical impedance spectrum of the measured data, establishing an equivalent circuit model of shale solid-liquid permeation, and establishing a page through the theoretical calculation of the Faraday impedance parameter caused by permeation diffusion A prediction model for oil saturation in rock reservoirs.

计算Zw。The Nyquist curve in Fig. 2 is fitted by the equivalent circuit of "Shale oil-water interstitial solid-liquid permeability model II under the condition of moderate oil saturation", as shown in Fig. 3. According to the impedance of the oil-water semi-infinite diffusion layer

Calculate Zw.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the present invention is defined by the appended claims and their equivalents.

Claims (9)

1. an electrochemical prediction method of shale reservoir oil saturation, is characterized in that, this method comprises the following steps: (a) Place electrode sheets at both ends of the shale specimen, connect the electrode sheets to the electrochemical workstation data acquisition system through wires, and then connect to the computer data processing system; (b) Apply sinusoidal AC voltage or sinusoidal AC current disturbance signals of different frequencies to the shale specimen, and the input disturbance signal generates a corresponding response signal after passing through the shale specimen, that is, sinusoidal AC current or sinusoidal AC voltage signal, and the response signal After the electrochemical workstation data acquisition system and the computer data processing system, the electrochemical impedance spectrum of the shale specimen was obtained; (c) By analyzing the characteristic changes of the electrochemical impedance spectrum, fitting the electrochemical impedance spectrum of the measured data, establishing the shale solid-liquid permeation equivalent circuit model, and establishing the shale through the theoretical calculation of the Faraday impedance parameter caused by permeation diffusion A prediction model for oil saturation in rock reservoirs. 2 . The electrochemical prediction method for oil saturation of shale reservoir according to claim 1 , wherein the number of electrode sheets in the step (a) is at least two, and the positions are distributed uniformly or non-uniformly. 3 . way to place. 3 . The electrochemical prediction method for oil saturation of a shale reservoir according to claim 1 , wherein the frequency range of the disturbance signal in the step (b) is 1 Hz-10 MHz. 4 . 4 . The electrochemical prediction method for oil saturation of a shale reservoir according to claim 1 , wherein the amplitude of the sinusoidal AC voltage in the step (b) is lower than 20mV. 5 . 5 . The electrochemical prediction method for oil saturation of a shale reservoir according to claim 1 , wherein the amplitude of the sinusoidal alternating current in the step (b) is lower than 50 mA. 6 . 6 . The electrochemical prediction method for oil saturation of shale reservoir according to claim 1 , wherein the representation method of the electrochemical impedance spectrum of the shale specimen obtained in the step (b) includes a Warburg diagram. 7 . , Admittance, Capacitance, Nyquist, and Bode plots. 7 . The electrochemical prediction method for oil saturation of shale reservoir according to claim 6 , wherein the representation method of the electrochemical impedance spectrum of the shale specimen obtained in the step (b) is preferably Nyquist. 8 . Figures and Bode diagrams. 8 . The method for electrochemical prediction of oil saturation in shale reservoirs according to claim 1 , wherein the characteristic change of the electrochemical impedance spectrum of the shale specimen in the step (c) refers to a certain frequency The phase angle, angular frequency, impedance vector, and impedance modulus value within the range change with increasing or decreasing frequency. 9 . The electrochemical prediction method for oil saturation of shale reservoir according to claim 1 , wherein the characteristic change of the electrochemical impedance spectrum of the shale specimen in the step (c) is associated with its oil saturation. 10 . Correspondence.

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