CN114460136B - Oil-gas fracturing monitoring electrical model building method and application method - Google Patents

Abstract

The method for establishing the oil gas fracturing monitoring electrical model and the application method thereof comprises the following steps: equivalent fracturing fluid wave and body are equivalent to a first miniature resistor-capacitor model formed by connecting a first equivalent resistor and a first equivalent capacitor in series; the stratum between the upper surface of the fracturing fluid wave and the ground is equivalent to a second miniature resistor-capacitor model, and the second miniature resistor-capacitor model comprises a second equivalent resistor and a second equivalent capacitor which are connected in series, and a third equivalent capacitor connected in parallel with the second equivalent resistor; the first micro resistance capacitance model and the second micro resistance capacitance model are connected in series to form a fracturing monitoring electricity model; and analyzing potential difference data acquired by the monitoring points based on the fracturing monitoring electrical model to obtain the morphological data of the crack corresponding to the position where the monitoring points are detected. The method solves the problems that the traditional process for analyzing the voltage signal is complex, the human resource consumption is high, and the sweep process and sweep range of the crack in the fracturing process cannot be intuitively described.

Description

A method for establishing an electrical model for oil and gas fracturing monitoring and its application method

Technical Field

The invention belongs to the field of oil and gas fracturing monitoring, and in particular relates to an oil and gas fracturing monitoring electrical model establishment method and an application method.

Background Art

Fracturing crack monitoring technology refers to the real-time monitoring and testing and evaluation of the entire fracturing process of coalbed methane, oil, shale gas, etc. through certain instruments and technical means. Through data processing, the direction, length, width, height, conductivity, filtration coefficient of fracturing fluid, predicted production, calculation of fracturing benefits, etc. of the cracks are obtained, thereby evaluating the fracturing effect.

Since a large amount of water or fracturing fluid needs to be injected during the fracturing process, the fracturing fluid will flow along the microcracks and continuously expand the cracks during the fracturing process. When the fracturing fluid exists in the cracks, it exhibits low resistivity and high polarizability, which is convenient for monitoring by electromagnetic detection methods. According to the voltage signal extracted by the collector, the parameters such as the length, height, and width of the fracturing layer can be described after analysis and interpretation. However, the traditional analytical process is relatively complicated, mainly using a large amount of data to derive and verify empirical formulas. This process requires a lot of human resources, and the derived empirical formulas are less applicable. When facing different geological environments, they need to be re-derived, and a lot of time is needed for repetitive work. Therefore, there is an urgent need for a more intuitive way to describe the fracturing process to reduce repetitive work.

Summary of the invention

The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for establishing an electrical model for oil and gas fracturing monitoring, which solves the problem that the traditional process of analyzing voltage signals is complicated, consumes a lot of human resources, and cannot intuitively describe the spread process and spread range of cracks during fracturing.

The embodiment of the present invention also provides an application method of an electrical model for oil and gas fracturing monitoring.

According to the first embodiment of the present invention, the method for establishing an electrical model for oil and gas fracturing monitoring comprises the following steps:

The fracturing fluid affected body is equivalent to a first micro resistor-capacitor model consisting of a first equivalent resistor and a first equivalent capacitor connected in series;

Equivalently converting the stratum between the upper surface of the fracturing fluid affected body and the ground into a second micro-resistance-capacitance model, wherein the second micro-resistance-capacitance model includes a second equivalent resistor and a second equivalent capacitor connected in series, and a third equivalent capacitor connected in parallel with the second equivalent resistor;

Connecting the first micro-resistance-capacitance model and the second micro-resistance-capacitance model in series to form a fracturing monitoring electrical model;

The potential difference data collected at the monitoring point is analyzed based on the fracturing monitoring electrical model to obtain the morphological data of the crack corresponding to the detection position of the monitoring point; the monitoring point is arranged on the ground above the crack, and is used to collect the potential difference data between the wellbore and the monitoring point when the transmitting system sends a test AC signal to the wellbore.

The method for establishing an electrical model for oil and gas fracturing monitoring according to an embodiment of the present invention has at least the following technical effects: after the transmitting system sends a test alternating current signal to the wellbore, the values of the first equivalent resistance and the first equivalent capacitance in the first micro-resistance-capacitance model will change with the change in the volume of the fracturing fluid affected body; the second micro-resistance-capacitance model is used to describe the potential difference data between the upper surface of the fracturing fluid affected body and the ground as a static background; through the change of the first micro-resistance-capacitance model relative to the second micro-resistance-capacitance model, the morphological data of the crack corresponding to the location where the monitoring point is detected can be obtained, which solves the problem that the traditional process of analyzing voltage signals is complicated, consumes a lot of human resources, and cannot intuitively describe the affected process and affected range of the cracks during the fracturing process.

According to some embodiments of the present invention, the first equivalent capacitance is obtained by the following steps:

The upper surface of the fracturing fluid affected body is equivalent to the upper plate of the first equivalent capacitor;

The lower surface of the fracturing fluid affected body is equivalent to the lower plate of the first equivalent capacitor.

According to some embodiments of the present invention, the second equivalent capacitance is obtained by the following steps:

The upper surface of the fracturing fluid affected body is equivalent to the lower plate of the second equivalent capacitor;

The ground is equivalent to the upper plate of the second equivalent capacitor.

According to the application method of the electrical model for oil and gas fracturing monitoring according to the second embodiment of the present invention, based on the electrical model for oil and gas fracturing monitoring in the first embodiment, the application method comprises the following steps:

Setting up a plurality of monitoring points on the ground, and connecting the plurality of monitoring points to a receiving system;

Injecting fracturing fluid into the wellbore to form the fracturing fluid affected body, and starting a transmitting system, wherein the transmitting system is used to apply a test alternating current signal to the fracturing fluid affected body;

receiving, by a receiving system, data of a potential difference between the wellbore and the ground;

The potential difference data is analyzed according to the fracturing monitoring electrical model to obtain the morphological data of the crack corresponding to the location where the monitoring point is detected.

The application method of the electrical model for oil and gas fracturing monitoring according to the embodiment of the present invention has at least the following technical effects: by setting a plurality of monitoring points on the ground and connecting the plurality of monitoring points to the receiving system, after the setting is completed, fracturing fluid can be injected into the wellbore to form a fracturing fluid affected body, and the transmitting system is started to apply a test AC signal to the fracturing fluid affected body, and at the same time, the potential difference data between the wellbore and the ground is received by the receiving system, so that the potential difference data can be analyzed according to the fracturing monitoring electrical model to obtain the morphological data of the crack corresponding to the detection position of the monitoring point, thereby solving the problem that the traditional process of analyzing voltage signals is complicated, consumes a lot of human resources, and cannot intuitively describe the affected process and affected range of the cracks during the fracturing process.

According to some embodiments of the present invention, the wellbore is a horizontal well, and the plurality of monitoring points are arranged in an array structure.

According to some embodiments of the present invention, the wellbore is a vertical well, and the plurality of monitoring points are arranged in a radial structure.

According to some embodiments of the present invention, the monitoring point uses a metal sensor.

Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

FIG1 is a schematic diagram of the layout of a fracturing monitoring system according to an embodiment of the present invention;

FIG2 is a schematic diagram of the layout of a fracturing monitoring system according to another embodiment of the present invention;

FIG3 is a schematic diagram of an electrical model for fracturing monitoring according to an embodiment of the present invention;

FIG4 is a waveform diagram of a test AC signal according to an embodiment of the present invention;

5 is a waveform diagram of a signal detected by a monitoring point according to an embodiment of the present invention;

6 is a flow chart of a method for establishing an electrical model for oil and gas fracturing monitoring according to an embodiment of the present invention;

FIG. 7 is a flow chart of a method for applying an electrical model for oil and gas fracturing monitoring according to an embodiment of the present invention.

Reference numerals:

Wellbore 100;

Launch system 200;

Receiving system 300.

DETAILED DESCRIPTION

Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

In order to better describe the method for establishing and applying the electrical model for oil and gas fracturing monitoring according to the embodiment of the present invention, a brief description of the actual fracturing monitoring system according to the embodiment of the present invention is given here.

As shown in FIG. 1 and FIG. 2, FIG. 1 and FIG. 2 are two different layout schematic diagrams of the fracturing monitoring system, respectively. The transmitting system 200 includes two emitters A and B. The emitter A is connected to the wellhead of the wellbore 100, and the emitter B is connected to infinity (which can be understood as grounding). After the emitter A transmits the test AC signal to the wellhead, the emitter A can form a loop with the emitter B through the earth, thereby completing the transmission of the test AC signal to the wellbore 100. The receiving system 300 includes a common electrode N and multiple receiving electrodes, and the multiple receiving electrodes are all used to receive the potential difference data collected by multiple monitoring points. The multiple monitoring points are M1, M2, ..., M2n, etc. shown in FIG. 1 and FIG. 2. The common electrode N of the receiving system 300 is connected to the wellhead of the wellbore 100, so that a loop can be formed with multiple monitoring points and the potential difference data detected by each monitoring point can be guaranteed to have the same reference. After the transmitting system 200 transmits the test AC to the wellbore 100, each monitoring point can detect the potential difference data, and then the potential difference data can be used to complete the analysis of the fracture morphology.

The following describes a method for establishing an electrical model for oil and gas fracturing monitoring according to an embodiment of the first aspect of the present invention with reference to FIGS. 1 to 7 .

The method for establishing an electrical model for oil and gas fracturing monitoring according to an embodiment of the present invention comprises the following steps:

The fracturing fluid affected body is equivalent to a first micro resistor-capacitor model consisting of a first equivalent resistor and a first equivalent capacitor connected in series;

The stratum between the upper surface of the fracturing fluid affected body and the ground is equivalent to a second micro-resistance-capacitance model, wherein the second micro-resistance-capacitance model includes a second equivalent resistor and a second equivalent capacitor connected in series, and a third equivalent capacitor connected in parallel with the second equivalent resistor;

The first micro-resistance and capacitance model and the second micro-resistance and capacitance model are connected in series to form a fracturing monitoring electrical model;

The potential difference data collected at the monitoring point is analyzed based on the electrical model of fracturing monitoring to obtain the morphological data of the crack corresponding to the location where the monitoring point is detected; the monitoring point is arranged on the ground above the crack, and is used to collect the potential difference data between the wellbore 100 and the monitoring point when the transmitting system 200 sends a test AC signal to the wellbore 100.

When fracturing operations are carried out, solutions containing electrolytes, such as fracturing fluids, have very low resistivity relative to the surrounding rocks and can be regarded as ideal conductors. By charging these electrolytes and observing the distribution of the charging electric field, it is possible to infer the electrical distribution of the entire fracturing fluid and the surrounding rocks, thereby explaining the propagation process and range of the fracturing cracks. As shown in FIG3 , the second micro-resistance-capacitance model is equivalent to the formation part. Theoretically, during the fracturing process, the values of the second equivalent resistance and the second equivalent capacitance themselves will not change, and can be regarded as a static background (i.e., it can be treated as a larger constant). The fracturing fluid affected body is equivalent to the first micro-resistance-capacitance model composed of the first equivalent resistance and the first equivalent capacitance in series, and the upper surface and the lower surface of the fracturing fluid affected body can be equivalent to the upper plate and the lower plate of the first equivalent capacitor. After the fracturing fluid is injected into the wellbore 100, as the volume of the fracturing fluid affected body continues to change, the distance between the upper plate and the lower plate equivalent to the first equivalent capacitor and the plate area are constantly changing, so the values of the first equivalent resistance and the first equivalent capacitance are also changing. Therefore, based on the electrical model of fracturing monitoring, the collected potential difference data will also change accordingly, and this change is also caused by the change of the first micro-resistance-capacitance model. The potential difference data detected at different monitoring points are different, so the potential difference data collected at the monitoring points can be analyzed based on the fracturing monitoring electrical model to obtain the morphological data of the crack corresponding to the location of the monitoring point detection. The morphological data can specifically be the height and area data of the crack.

According to the method for establishing an electrical model for oil and gas fracturing monitoring in an embodiment of the present invention, after the transmitting system 200 sends a test alternating current signal to the wellbore 100, the values of the first equivalent resistance and the first equivalent capacitance in the first micro-resistance-capacitance model will change with the change in the volume of the body affected by the fracturing fluid; the second micro-resistance-capacitance model is used to describe the potential difference data between the upper surface of the body affected by the fracturing fluid and the ground, as a static background; through the change of the first micro-resistance-capacitance model relative to the second micro-resistance-capacitance model, the height and area data of the crack corresponding to the location where the monitoring point is detected can be obtained, which solves the problem that the traditional process of analyzing voltage signals is complicated, consumes a lot of human resources, and cannot intuitively describe the spread process and spread range of the cracks during the fracturing process.

In some embodiments of the present invention, referring to FIG. 3 to FIG. 5 , the first equivalent capacitance is obtained by the following steps:

The upper surface of the fracturing fluid affected body is equivalent to the upper plate of the first equivalent capacitor;

The lower surface of the fracturing fluid affected body is equivalent to the lower plate of the first equivalent capacitor.

The upper surface and lower surface of the fracturing fluid affected body can be equivalent to the upper plate and lower plate of the first equivalent capacitor, respectively, and the fracturing fluid affected body is equivalent to the conductive medium of the first equivalent capacitor. Then the actual crack height h can be equivalent to the distance d between the two plates of the first equivalent capacitor. The physical formula of the first equivalent capacitor is:

The area between the curved waveform and the square wave in FIG5 can be regarded as the characteristic parameter U _c , and the calculation formula of U _c is:

Where R is the resistance of the first equivalent resistor. Define β as the engineering correction coefficient, then:

β can be obtained through model measurement, that is, different characteristic parameters can correspond to a set of β values, and then β can be treated as a constant in a certain state, while S can be directly treated as a unit area by the dissection method, so that the correlation between the characteristic parameters and the crack height can be established. The characteristic parameters are obtained by the potential difference data collected at the monitoring point (i.e., the waveform in Figure 5), so different crack heights can be simulated by equivalent to a resistance-capacitance model, that is, different crack heights can be simulated by simply adjusting the value of C.

In some embodiments of the present invention, referring to FIG. 3 , the first equivalent capacitance is obtained by the following steps:

The upper surface of the fracturing fluid affected body is equivalent to the lower plate of the second equivalent capacitor;

The ground is equivalent to the upper plate of the second equivalent capacitor.

The upper surface of the fracturing fluid affected body and the ground are two equipotential surfaces, which can be equivalent to the lower plate and upper plate of the second equivalent capacitor respectively, and the stratum between the upper surface of the fracturing fluid affected body and the ground is equivalent to the conductive medium of the second equivalent capacitor. The resistance value of the second equivalent resistor in the second micro-resistance-capacitance model is much larger than the first equivalent resistor. Therefore, the second micro-resistance-capacitance model is actually used as a static background, and the height and area data of the crack are analyzed by the change of the first micro-resistance-capacitance model relative to the second micro-resistance-capacitance model.

The following describes an application method of the electrical model for oil and gas fracturing monitoring according to an embodiment of the second aspect of the present invention with reference to FIGS. 1 to 7 .

The application method of the electrical model for oil and gas fracturing monitoring according to an embodiment of the present invention comprises the following steps:

A plurality of monitoring points are set up on the ground, and the plurality of monitoring points are all connected to the receiving system 300;

Injecting fracturing fluid into the wellbore 100 to form a fracturing fluid affected body, and starting the transmitting system 200, the transmitting system 200 is used to apply a test AC signal to the fracturing fluid affected body;

Receiving potential difference data between the wellbore 100 and the ground through the receiving system 300;

The potential difference data is analyzed according to the fracturing monitoring electrical model to obtain the morphological data of the crack corresponding to the location of the monitoring point detection.

As the fracturing fluid is continuously injected, the affected range of the fracturing fluid body corresponding to different monitoring points is different. Therefore, setting multiple monitoring points corresponding to multiple monitoring points on the ground can collect different changing potential difference data, and then analyze the potential difference data according to the fracturing monitoring electrical model to obtain the height and area data of the crack corresponding to the detection location of the monitoring point, which can intuitively describe the spread process and range of the crack.

The application method of the electrical model for oil and gas fracturing monitoring according to the embodiment of the present invention has at least the following technical effects: by setting a plurality of monitoring points on the ground and connecting the plurality of monitoring points to the receiving system 300, after the setting is completed, fracturing fluid can be injected into the wellbore 100 to form a fracturing fluid affected body, and the transmitting system 200 is started to apply a test AC signal to the fracturing fluid affected body, and at the same time, the potential difference data between the wellbore 100 and the ground is received by the receiving system 300, so that the potential difference data can be analyzed according to the fracturing monitoring electrical model to obtain the height and area data of the crack corresponding to the detection position of the monitoring point, thereby solving the problem that the traditional process of analyzing voltage signals is complicated, consumes a lot of human resources, and cannot intuitively describe the affected process and affected range of the cracks during the fracturing process.

In some embodiments of the present invention, referring to FIG. 2 and FIG. 3 , the wellbore 100 is a horizontal well, and a plurality of monitoring points are arranged in an array structure. The wellhead of the wellbore 100 is taken as the base value of the measuring electrode, and this base value is defined as zero, then at any monitoring point on the ground (i.e., M1, M2, ..., M2n shown in FIG. 2 and FIG. 3 ), a potential difference can be formed with the wellhead. Therefore, when the wellbore 100 is a horizontal well, a plurality of monitoring points can be arranged in an array structure on the ground, and the array structure is also a well-shaped structure, including a plurality of parallel measuring lines and vertical measuring lines, and a sufficient distance is maintained between two adjacent measuring lines, and each parallel measuring line and vertical measuring line has a plurality of equally spaced monitoring points, all of which are used to collect the potential difference data between the wellbore 100 and the ground. When fracturing fluid is injected into the wellbore 100, the fracturing fluid flows horizontally along the wellbore 100. When the transmitting system 200 applies a test AC signal to the fracturing fluid affected body, a line power supply is formed for the horizontal well. The potential difference data collected by the monitoring points on the ground corresponding to different points in the horizontal direction of the fracturing fluid affected body are different. The change pattern of the collected potential difference data can be used to analyze the changes in the cracks during the fracturing process, thereby obtaining the height and area data of the cracks during the fracturing process.

In some embodiments of the present invention, referring to FIG1, the wellbore 100 is a vertical well, and multiple monitoring points are arranged in a ray structure. As shown in FIG1, the ray structure is also called a ring structure, including multiple ring measuring lines, all of which are centered on the wellhead of the wellbore 100, and a sufficient distance is maintained between two adjacent measuring lines. There are multiple equally spaced monitoring points in each ring measuring line. When the fracturing fluid is injected into the wellbore 100, the fracturing fluid flows downward in the vertical direction along the wellbore 100. When the transmitting system 200 applies a test AC signal to the fracturing fluid affected body, a point power source is formed for the vertical well, and the fracturing fluid affected body diverges in a direction away from the wellbore 100. Therefore, the potential difference data collected by multiple monitoring points in the multiple ring measuring lines can reflect the changes in the cracks during the fracturing process, so as to obtain the height and area data of the cracks during the fracturing process.

In some embodiments of the present invention, metal sensors are used at monitoring points. The metal sheet sensors can detect the electric field signals of the fracturing fluid in the formation, and the metal sheet sensors are small in size, easy to set up, and low in cost, and can meet the requirements of setting up multiple monitoring points of the present invention.

In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

Although the embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, the present invention is not limited to the above embodiments. Those skilled in the art will understand that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and purpose of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims (5)

1. The method for establishing the oil-gas fracturing monitoring electrical model is characterized by comprising the following steps of:

equivalent fracturing fluid wave and body are equivalent to a first miniature resistor-capacitor model formed by connecting a first equivalent resistor and a first equivalent capacitor in series;

The stratum between the upper surface of the fracturing fluid wave and the ground is equivalent to a second miniature resistance-capacitance model, and the second miniature resistance-capacitance model comprises a second equivalent resistor and a second equivalent capacitor which are connected in series, and a third equivalent capacitor which is connected in parallel with the second equivalent resistor;

the first micro resistance capacitance model and the second micro resistance capacitance model are connected in series to form a fracturing monitoring electricity model;

Analyzing potential difference data acquired by monitoring points based on the fracturing monitoring electrical model to obtain morphological data of cracks corresponding to positions where the monitoring points are detected; the monitoring points are arranged on the ground above the cracks and are used for collecting potential difference data between the shaft and the monitoring points when the transmitting system transmits test alternating current signals to the shaft;

the first equivalent capacitance is obtained by the following steps:

equivalent the upper surface of the fracturing fluid wave and body to the upper polar plate of the first equivalent capacitor;

equivalent the lower surface of the fracturing fluid wave and body to the lower polar plate of the first equivalent capacitor;

the second equivalent capacitance is obtained by the following steps:

equivalent the upper surface of the fracturing fluid wave and body to the lower polar plate of the second equivalent capacitance;

And the ground is equivalent to an upper polar plate of the second equivalent capacitor.

2. An application method of an oil gas fracturing monitoring electrical model, which is based on the oil gas fracturing monitoring electrical model obtained by the establishment method of the oil gas fracturing monitoring electrical model according to claim 1, and is characterized by comprising the following steps:

Setting a plurality of monitoring points on the ground, and connecting the monitoring points to a receiving system;

Injecting a fracturing fluid into a wellbore to form a fracturing fluid wave and body, and activating a transmitting system for applying a test alternating current signal to the fracturing fluid wave and body;

receiving, by a receiving system, potential difference data between the wellbore and the surface;

And analyzing the potential difference data according to the fracturing monitoring electrical model to obtain the morphological data of the crack corresponding to the position where the monitoring point is detected.

3. The method of claim 2, wherein the well bore is a horizontal well and the plurality of monitoring points are arranged in a matrix configuration.

4. The method of claim 2, wherein the wellbore is a vertical well and the plurality of monitoring points are deployed in a radial configuration.

5. The method of claim 2, wherein the monitoring point is a metal sensor.