Well-ground near-source transient electromagnetic high-precision exploration method

Abstract

The invention belongs to the technical field of geological exploration, and provides a well-ground near-source transient electromagnetic high-precision exploration method, which is a technical innovation and breakthrough of applying electrical exploration to low-porosity and low-permeability gas reservoir gas-water identification by adopting a BSEM well-to-ground electrical method to acquire and obtain high-precision geoelectric data for processing and explaining for the first time. The high-precision electrical method gas-water identification method is a novel and effective gas-water identification method besides conventional well logging and seismic exploration, the achievement of the high-precision electrical method gas-water identification method can directly evaluate a gas-containing target qualitatively and quantitatively, the high-precision electrical method gas-water identification method is a gas-water identification technology capable of indicating the boundary and the range of the gas-containing target, and the high-precision electrical method gas-water identification method is a new and effective gas-water identification method for developing well network deployment. Particularly, high-gas-content target indication is provided for horizontal well deployment, and the benefit development target of few wells and high yield is achieved; high-resolution and large-radius transverse resistivity detection of target layer resistivity can be realized at the same time; the method is an effective geophysical detection means for unconventional oil-gas-water detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of geological exploration, and particularly relates to a high-precision exploration method for well-to-surface near-source transient electromagnetic method. Background Art

[0002] Since unconventional oil and gas reservoirs generally have a large burial depth, the target reservoirs have the characteristics of multiple layers in one well, multiple segments in the same layer, complex oil and gas relationships, and strong reservoir heterogeneity. Conventional surface controlled-source time-frequency electromagnetic (TFEM) has been unable to meet the production requirements for oil and gas water identification in the exploration and development of unconventional oil and gas reservoirs. The well-to-surface time-domain induced polarization electromagnetic method (BSTEM) can maximize the elimination of the influence of interference layers by placing the transmitting electrode along the wellbore at specific depth interfaces at the top and bottom of the target layer, highlighting the oil and gas reservoir response of the target layer in the time-domain induced polarization electromagnetic excitation mode. As early as the 1970s, experts proposed using the well-to-surface electrical method to delineate the oil and gas boundaries. The well-to-surface electromagnetic exploration method is a type of electromagnetic method that supplies current in the well and receives electromagnetic fields on the ground, mainly used for delineating the boundaries of oil and gas reservoirs and predicting favorable oil and gas-bearing areas around known oil and gas reservoirs. The present invention proposes a near-source acquisition method and processing and interpretation technology based on the well-to-surface time-domain induced polarization electromagnetic method. Through the acquisition of secondary field signals, it realizes a "magnifying glass" for high-resolution resistivity of the target layer and a "telescope" for detecting large-radius oil and gas water boundaries. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a high-precision exploration method for well-to-surface near-source transient electromagnetic method to solve the problems in the prior art. The technical solution adopted by the present invention is as follows:

[0004] A high-precision exploration method for well-to-surface near-source transient electromagnetic method includes the following steps:

[0005] Step 1: Data acquisition is carried out in the form of fixed ground reception and mobile wellbore transmission, including: arranging a plurality of receivers along the survey line on the ground with a spacing of 50 meters; arranging a mobile transmitting electrode in the wellbore, and the mobile transmitting electrode includes three positions: B1, B2, B3, and arranging a fixed transmitting electrode A at the ground wellhead position;

[0006] Step 2: Through the fixed transmitting electrode A and the mobile transmitting electrode at B3, a bipolar rectangular zero-crossing step current is transmitted to the periphery of the wellbore with a current intensity of 40 A; by arranging a plurality of receivers along the survey line on the ground, the electromagnetic component data Ex AB3 (t) is observed and recorded;

[0007] Step 3: Lift the moving transmitting electrode from position B3 to position B2 in the well. By fixing the transmitting electrode A and the moving transmitting electrode at B2, a bipolar rectangular zero-crossing step current with a current intensity of 40 A is transmitted to the periphery of the wellbore. By arranging multiple receivers along the survey line on the ground, the electromagnetic component data Ex AB2 (t) is observed and recorded;

[0008] Step 4: Lift the moving transmitting electrode from position B2 to position B1 in the well. By fixing the transmitting electrode A and the moving transmitting electrode at B1, a bipolar rectangular zero-crossing step current with a current intensity of 40 A is transmitted to the periphery of the wellbore. By arranging multiple receivers along the survey line on the ground, the electromagnetic component data Ex AB1 (t) is observed and recorded;

[0009] Step 5: Obtain the apparent resistivity value of the target layer according to the observed and recorded electric field component data.

[0010] Furthermore, the electric field component data of the target layer is:

[0011] Ex(t) = Ex AB3 (t) - Ex AB1 (t) (1)

[0012] Ex AB3 (t): The electric field energy recorded when the fixed transmitting electrode A and electrode B3 are excited; Ex AB1 (t): The electric field energy recorded when the fixed transmitting electrode A and electrode B2 are excited;

[0013] Calculate the apparent resistivity data of the target layer according to the following formula:

[0014] R(t) = K1M 2 / 3 / Ex(t) 2 / 3 t 5 / 3 (2)

[0015] M is the transmitting magnetic moment; the K value is the conductivity constant, which is calibrated by well logging data;

[0016] Calculate the conductivity constant K value according to the following formula

[0017] K = Ha / ((Ra(t) 2 *t / μ)) (3)

[0018] Ra(t) is the well logging resistivity, and Ha is the depth corresponding to Ra(t)

[0019] Draw a profile according to the calculated apparent resistivity data of the target layer.

[0020] The present invention has the following beneficial effects:

[0021] The present invention first adopts the form of in-well emission - surface reception for electrical method acquisition. The high-precision geoelectric data obtained, combined with the cross-domain big data processing and interpretation of seismo-electricity, has been successfully applied to the gas-water identification of the water-rich tight sandstone gas reservoir in the western Sulige area. This is a technological innovation and breakthrough in the application of electrical method exploration to gas-water identification in low-porosity and low-permeability gas reservoirs. The high-precision electrical method for gas-water identification is a new and effective gas-water identification method in addition to conventional logging and seismic exploration. Its results can directly qualitatively and quantitatively evaluate gas-bearing targets, and it is a gas-water identification technology that can indicate the boundaries and scope of gas-bearing targets, providing high-gas-bearing target indications for the deployment of development well patterns, especially horizontal well patterns, and achieving the benefit development goal of high production with fewer wells. It breaks through the detection dilemma of the limited view of the wellbore in conventional logging and realizes the resistivity detection of the target layer with a large radius in the wellbore. It combines high-resolution resistivity of the target layer with large-radius lateral resistivity detection and is an effective geophysical detection means for unconventional oil and gas water detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the schematic diagram of the well - ground electromagnetic method acquisition;

[0023] Figure 2 is the well depth conversion process for well calibration beside the well;

[0024] Figure 3 is the 2D depth domain profile of the electrical method survey line;

[0025] Figure 4 is the resistivity profile of the 2D depth domain of the electrical method survey line. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following will combine the Figures 1-4 in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. If not specifically specified, the technical means used in the embodiments are conventional means well-known to those skilled in the art.

[0027] A well - ground near-source transient electromagnetic high-precision exploration method includes:

[0028] Adopting the form of fixed reception - mobile emission for data acquisition:

[0029] The acquisition working principle is as Figure 1As shown, this method is particularly applicable to the implementation of long wire source time-domain zero-crossing electrical pulse emission in casing wells and cylinders. The transmitting electrodes are respectively placed at different depths (B1, B2, B3) of the top and bottom interfaces of the target layer through armored cables to emit a bipolar rectangular zero-crossing step current with an emission intensity of 30 - 50A. On the ground, MN electrodes with a channel spacing of 50 meters are arranged according to geological requirements to record the Ex component of the secondary field excited from underground when the step zero-crossing power-off occurs. This observation system can improve the signal-to-noise ratio of the observed signal. In addition, it also reduces the influence of the volume effect of the conventional TFEM acquisition body, improving the resolution and accuracy of the data processing results.

[0030] A high-precision exploration method for borehole-to-surface near-source transient electromagnetic method, comprising the following steps:

[0031] Step 1: Data acquisition is carried out in the form of fixed ground reception and mobile wellbore emission, including: arranging multiple receivers along the survey line on the ground with a spacing of 50 meters; arranging a mobile transmitting electrode in the wellbore, and the mobile transmitting electrode includes three positions: B1, B2, B3, and arranging a fixed transmitting electrode A at the wellhead position on the ground;

[0032] Step 2: Through the fixed transmitting electrode A and the mobile transmitting electrode at B3, a bipolar rectangular zero-crossing step current is emitted to the periphery of the wellbore with a current intensity of 40A; by arranging multiple receivers along the survey line on the ground, the electromagnetic component data Ex AB3 (t) is observed and recorded;

[0033] Step 3: Lift the mobile transmitting electrode from the B3 position to the B2 position in the wellbore. Through the fixed transmitting electrode A and the mobile transmitting electrode at B2, a bipolar rectangular zero-crossing step current is emitted to the periphery of the wellbore with a current intensity of 40A; by arranging multiple receivers along the survey line on the ground, the electromagnetic component data Ex AB2 (t) is observed and recorded;

[0034] Step 4: Lift the mobile transmitting electrode from the B2 position to the B1 position in the wellbore. Through the fixed transmitting electrode A and the mobile transmitting electrode at B1, a bipolar rectangular zero-crossing step current is emitted to the periphery of the wellbore with a current intensity of 40A; by arranging multiple receivers along the survey line on the ground, the electromagnetic component data Ex AB1 (t) is observed and recorded;

[0035] Step 5: According to the observed and recorded electric field component data, the apparent resistivity value of the target layer is obtained.

[0036] Furthermore:

[0037] The electric field component data of the target layer is:

[0038] Ex(t) = Ex AB3 (t) - Ex AB1 (t) (1)

[0039] Ex AB3 (t): Electric field energy recorded when fixed transmitting electrode A and electrode B3 are excited; Ex AB1 (t): electric field energy recorded when the fixed transmitting electrode A and electrode B2 are excited;

[0040] Calculate the apparent resistivity data of the target layer according to the following formula:

[0041] R(t)=K1M 2 / 3 / Ex(t) 2 / 3 t 5 / 3 (2)

[0042] M is the emission magnetic moment; K is the conductivity constant, which is calibrated by the logging data;

[0043] The conductivity constant K value is calculated according to the following formula

[0044] K=Ha / ((Ra(t) 2 *t / μ)) (3)

[0045] Ra(t) is the logging resistivity, Ha is the depth corresponding to Ra(t)

[0046] Draw a profile diagram based on the calculated apparent resistivity data of the target layer.

[0047] Through the steps of the present invention, the apparent resistivity varying with depth can be obtained.

[0048] The present invention adopts BSEM well-geoelectric acquisition for the first time, and the high-precision geoelectric data obtained are combined with seismic-electric cross-domain big data processing and interpretation, and successfully applied to the gas-water identification of water-rich tight sandstone gas reservoirs in the western area of ​​Sulige. It is a technical innovation and breakthrough in the application of electrical exploration to gas-water identification in low-porosity and low-permeability gas reservoirs; the high-precision electrical gas-water identification method is a new and effective gas-water identification method after conventional well logging and seismic exploration. Its results can directly evaluate the gas-bearing targets qualitatively and quantitatively. It is a gas-water identification technology that can indicate the boundaries and ranges of gas-bearing targets, and provide high-gas target indications for development well network deployment, especially horizontal well deployment, to achieve the efficient development goal of fewer wells and more production; it breaks through the conventional well logging detection dilemma of one-hole detection in the wellbore, and realizes the resistivity detection of the target layer in the wellbore for most of the radius. High-resolution resistivity of the target layer and large-radius lateral resistivity detection are both achieved; it is an effective geophysical detection means for unconventional oil, gas and water detection.

[0049] like Figure 1, by using the method of the present invention, high-quality exploration electromagnetic field data can be obtained: there are two transmitting electrodes for the transmitting source, one is buried in the ground and the other is attached to the wellbore wall; the ground transmitter supplies power to the two transmitting electrodes, and the power supply mode is time mode. The transmitting electrode buried in the ground is in a fixed position, and the transmitting electrode attached to the wellbore wall is in a moving mode. After each power supply ends, it moves up or down one position along the wellbore and supplies power again; the receiving device is fixed at the ground position and needs to receive electromagnetic signals of different combinations of transmitting electrodes. The received electromagnetic signals are related to geological bodies and are signals induced by geological bodies.

[0050] Such as Figure 2 , according to the obtained high-quality exploration electromagnetic field data, the apparent resistivity value of the target horizon closely related to the remaining geological body properties is calculated. Finally, based on the apparent resistivity value of the horizon, the oil-bearing position is inferred. The flow chart shows how to convert the observation time-related data into depth-related data and how to convert the observed voltage signal into apparent resistivity data.

[0051] Such as Figure 4 , the technical implementation effect diagram of the present invention. The part with high apparent resistivity is dark in color, and the part with low apparent resistivity is light in color. The part with high apparent resistivity is related to the oil and gas layer, and three boreholes are drilled at the positions with high apparent resistivity, and oil and gas are found. The part with low apparent resistivity is related to the overlying layer. The vertical coordinate represents depth, and the horizontal coordinate represents the horizontal distance. The color scale on the right is the apparent resistivity.

[0052] The embodiments described above are only descriptions of the preferred modes of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, variations, modifications, and substitutions made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A well-ground near-source transient electromagnetic high-precision exploration method, characterized in that: The following steps are involved: Step 1, data collection is performed in the form of fixed reception on the ground and mobile transmission in the well, including: multiple receivers are arranged along the survey line on the ground, with a spacing of 50 meters; mobile transmitting electrodes are arranged in the well, and the mobile transmitting electrodes include three positions: B1, B2, and B3, and a fixed transmitting electrode A is arranged at the wellhead position on the ground; Step 2: Use the fixed transmitting electrode A and the mobile transmitting electrode at B3 to transmit a bipolar rectangular zero-crossing step current with a current intensity of 40A to the periphery of the wellbore; and deploy multiple receivers along the survey line on the ground to observe and record the electromagnetic component data Ex AB3 (t); Step 3: In the well, the mobile transmitting electrode is lifted from position B3 to position B2, and a bipolar rectangular zero-crossing step current with a current intensity of 40A is emitted to the periphery of the wellbore through the mobile transmitting electrode at the fixed transmitting electrode A and B2; multiple receivers are arranged along the survey line on the ground to observe and record the electromagnetic component data Ex AB2 (t); Step 4: In the well, the mobile transmitting electrode is lifted from position B2 to position B1, and a bipolar rectangular zero-crossing step current with a current intensity of 40A is emitted to the periphery of the wellbore through the fixed transmitting electrodes A and the mobile transmitting electrodes at B1; multiple receivers are arranged on the ground along the survey line to observe and record the electromagnetic component data Ex AB1 (t); Step 5, obtaining the apparent resistivity value of the target layer according to the electric field component data recorded in the observation, and inferring the oil-bearing location according to the apparent resistivity value of the layer.

2. A well-ground near-source transient electromagnetic high-precision exploration method according to claim 1, characterized in that: The electric field component data of the target layer are: Ex(t)=Ex AB3 (t)-Ex AB1 (t) (1) Ex AB3 (t): Electric field energy recorded when fixed transmitting electrode A and electrode B3 are excited; Ex AB1 (t): electric field energy recorded when the fixed transmitting electrode A and electrode B2 are excited; Calculate the apparent resistivity data of the target layer according to the following formula: R(t)=K1M 2 / 3 / Ex(t) 2 / 3 t 5 / 3 (2) M is the emission magnetic moment; K is the conductivity constant, which is calibrated by the logging data; The conductivity constant K value is calculated according to the following formula KHHa / ((Ra(t) 2 *t / µ)) (3) Ra(t) is the logging resistivity, Ha is the depth corresponding to Ra(t) Draw a profile diagram based on the calculated apparent resistivity data of the target layer.

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