Reservoir monitoring device and acoustic and electromagnetic combined oil-water interface monitoring method

Abstract

The present invention relates to a reservoir monitoring device and an acoustic wave and electromagnetic combined oil-water interface monitoring method, characterized in that the reservoir monitoring device comprises an acoustic wave electromagnetic composite monitoring device, a monitoring subsystem and a ground processing subsystem; the acoustic wave electromagnetic composite monitoring device is arranged at a corresponding depth of the casing reservoir to be measured, and the acoustic wave electromagnetic composite monitoring device is used to obtain an acoustic wave response signal and an induced electromotive force signal at a corresponding depth of the casing reservoir to be measured; the monitoring subsystem is used to send the signal obtained by the acoustic wave electromagnetic composite monitoring device to the ground processing subsystem, and to power the acoustic wave electromagnetic composite monitoring device; the ground processing subsystem is used to determine the oil-water interface position of the casing reservoir to be measured based on the signal obtained by the acoustic wave electromagnetic composite monitoring device. The present invention can be widely used in the field of monitoring the water injection front of casing reservoirs.

Description

Technical Field

[0001] The invention relates to the field of water injection front monitoring for rear-casing reservoirs, and in particular to a reservoir monitoring device and an acoustic wave and electromagnetic combined oil-water interface monitoring method. Background Art

[0002] With the development of oil and gas wells, the heterogeneity of the cased reservoir is serious, the remaining crude oil is highly dispersed, the differences between the layers continue to increase, and the water drive wave and range are unpredictable. To better understand the situation of the cased reservoir and rationally develop the oil field, the analysis and determination of the cased reservoir is the most important issue in the comprehensive description and development design of the reservoir. As the main content of cased reservoir monitoring, oil-water interface monitoring and analysis is a hot topic among scholars. Advanced monitoring methods can not only accurately determine data such as porosity, resistivity, lithology, mud content, fluid saturation, and pressure in cased wells, but also collect formation fluid samples, providing original data for the evaluation of remaining oil.

[0003] Common oil-water interface monitoring methods include tracer methods, seismic monitoring, crosswell potential and electromagnetic monitoring, through-casing logging, and online monitoring methods in submersible electric pump wells or intelligent well systems. The tracer method, the earliest applied to reservoir dynamic monitoring, involves injecting a fluid containing a tracer. By analyzing the arrival time and concentration of the tracer in water samples from production wells throughout the test area, the azimuth, velocity, and direction of the water injection are determined. This method suffers from complex testing procedures, long testing cycles, and delayed test results. Seismic monitoring utilizes the differences in acoustic wave attenuation characteristics in gases, liquids, and solids. By detecting the acoustic wave attenuation and delay caused by gas-rich areas and their interfaces with sandstones and carbonates containing oil and water pores, the gas-affected region is identified. This method is primarily used to monitor the gas flooding front during gas injection to analyze the displacement effect and its impact on the reservoir. However, because injected water and formation water have essentially the same impact on acoustic waves, this method is difficult to adapt to monitoring injected water. Although acoustic wave monitoring in the wellbore can locate the front of the gas drive wave, the propagation distance of the acoustic waves generated by transducers made of piezoelectric or magnetostrictive materials is limited, and the bonding interface between the cement sheath, casing and formation has an attenuation effect on the acoustic waves, making it difficult to use downhole acoustic waves to monitor the displacement interface. The potential monitoring method uses a high-power current supplied downhole through the casing to establish a stable artificial electric field in the reservoir. Reservoir monitoring is achieved by measuring changes in surface potential. Due to the significant resistivity differences between the remaining oil, injected fluid, and surrounding reservoir rock, this resistivity difference strongly repels or attracts surrounding leakage current pathways, distorting the artificially established electric field within the measured area. If this distorted field reaches a sufficient intensity to reach the surface, the ground potential changes around the wellbore can be observed and, combined with appropriate processing, the distribution of subsurface oil and gas and the extent of water impact can be inferred, thereby enabling dynamic monitoring of the subsurface reservoir. Similar to seismic monitoring, the potential monitoring method requires a phased test: a background potential is measured before water (or gas) injection, followed by time-lapse measurements during the injection process. Dynamic monitoring of the reservoir under investigation is achieved by measuring the potential changes during these phases. Crosswell electromagnetic monitoring involves continuously moving a high-power electromagnetic transmitter in one well while a series of statically placed receivers, positioned from top to bottom, collect data in another well. Under low-frequency signal excitation, a magnetic or electric dipole transmitting coil transmits an electromagnetic field into the formation. The eddy currents induced by the primary field in turn generate a secondary alternating field, the strength of which is inversely proportional to the formation resistivity. Both the primary and secondary electromagnetic fields are detected at the receiver array. The specific measurement parameters of a crosswell electromagnetic measurement system depend on factors such as well spacing, transmitter and receiver spacing, casing type, operating frequency, and noise. Currently, practical approaches are very limited.Radioactive logging is currently the primary method for logging production wells. By testing the presence and relative concentrations of certain elements in the formation, it can identify producing and non-producing zones, understand the distribution of remaining oil in the block, detect fluid interfaces, and determine porosity. This is an essential tool for re-understanding the formations near the wellbore. However, the main problem with this monitoring method is its limited detection range, typically 0.25 to 0.4 meters.

[0004] Due to the complex reservoir media behind the casing, and the electromagnetic probe's emission-off cycle, the oil-water interface is constantly changing, which can lead to certain measurement errors. Although the corrosion rate of the metal casing downhole is much slower than the change rate of the reservoir oil-water interface, the influence of the metal casing can be used as a fixed background in the detection results. By comparing the early and late trends of the transient electromagnetic response over a period of time, the relative changes in the reservoir resistivity can be identified and analyzed, and the reservoir oil-water interface can be identified and analyzed. However, relying solely on the changes in the reservoir medium resistivity is still not enough to effectively and accurately analyze the reservoir oil-water interface. Summary of the Invention

[0005] In response to the above problems, the purpose of the present invention is to provide a reservoir monitoring device and a combined acoustic and electromagnetic oil-water interface monitoring method, which can solve the problem of difficulty in identifying the oil-water interface downhole and the inability to effectively and accurately analyze the oil-water interface in the reservoir.

[0006] To achieve the above-mentioned object, the present invention adopts the following technical solutions: On the one hand, a reservoir monitoring device is provided, comprising an acoustic wave electromagnetic composite monitoring device, a monitoring subsystem and a surface processing subsystem;

[0007] The acoustic wave electromagnetic composite monitoring device is set at the corresponding depth of the reservoir behind the casing to be measured, and the acoustic wave electromagnetic composite monitoring device is used to obtain the acoustic wave response signal and the induced electromotive force signal at the corresponding depth of the reservoir behind the casing to be measured;

[0008] The monitoring subsystem is used to send the signal obtained by the acoustic wave electromagnetic composite monitoring device to the ground processing subsystem, and to supply power to the acoustic wave electromagnetic composite monitoring device;

[0009] The surface processing subsystem is used to determine the oil-water interface position of the reservoir to be measured based on the signal obtained by the acoustic and electromagnetic composite monitoring device.

[0010] Furthermore, the acoustic wave and electromagnetic composite monitoring device includes an acoustic wave transducer, an electromagnetic probe and a controller;

[0011] The electromagnetic probe is fixedly arranged in the acoustic wave transducer, and the acoustic wave transducer is used to transmit an acoustic wave pulse signal and obtain an acoustic wave response signal of a corresponding depth of the reservoir behind the casing to be measured, and the electromagnetic probe is used to obtain an induced electromotive force signal of a corresponding depth of the reservoir behind the casing to be measured;

[0012] The controller is connected to the acoustic wave transducer, electromagnetic probe and monitoring subsystem respectively. The controller is used to select the working mode of the acoustic wave electromagnetic composite monitoring device, control the operation of the acoustic wave transducer and electromagnetic probe according to the selected working mode, and send the signals obtained by the acoustic wave transducer and electromagnetic probe to the monitoring subsystem.

[0013] Furthermore, the electromagnetic probe includes a magnetic core, a transmitting coil and a receiving coil;

[0014] The transmitting coil and the receiving coil are evenly wound on the magnetic core. The transmitting coil is used to transmit electromagnetic pulses to generate a primary magnetic field in space; the receiving coil is used to receive induced electromotive force signals that change with the reservoir medium.

[0015] Furthermore, the acoustic wave transducer includes an acoustic wave transmitting probe and an acoustic wave receiving probe;

[0016] The acoustic wave transmitting probe is used to transmit acoustic wave pulse signals;

[0017] The acoustic wave receiving probe is used to receive the acoustic wave response signal of the reservoir behind the casing to be tested.

[0018] Furthermore, the ground processing subsystem is provided with:

[0019] a data processing module for calculating the porosity and cementation index of each reservoir medium in the tested behind-the-casing reservoir according to the acoustic wave response signal at the corresponding depth of the tested behind-the-casing reservoir acquired by the acoustic wave transducer; and determining the dielectric resistivity of each reservoir medium in the tested behind-the-casing reservoir according to the induced electromotive force signal at the corresponding depth of the tested behind-the-casing reservoir acquired by the electromagnetic probe;

[0020] The oil-water interface position module is used to determine the oil-water interface position of the reservoir to be tested based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic wave response signal and the propagation relationship at the oil-water interface, and according to the medium resistivity, medium porosity and cementation index of each reservoir medium of the reservoir to be tested.

[0021] Furthermore, the electromagnetic probe adopts a focusing structure with both transmitting and receiving elements.

[0022] Furthermore, the acoustic wave transducer adopts a hollow cylindrical piezoelectric ceramic structure.

[0023] In another aspect, a method for monitoring an oil-water interface using a combination of acoustic and electromagnetic methods is provided, comprising:

[0024] Establishing a downhole layered columnar model of the casing reservoir to be tested, wherein the downhole layered columnar model includes a plurality of reservoir media from the inner layer to the outer layer;

[0025] The surface processing subsystem analyzes the post-casing energy distribution of the downhole layered columnar model, determines the corresponding relationship between the reservoir medium and the induced electromotive force signal and the acoustic response signal, as well as the propagation relationship at the oil-water interface, and calculates the electromagnetic response and acoustic response under the forward model;

[0026] The acoustic wave electromagnetic composite monitoring device is set at the corresponding depth of the reservoir to be tested;

[0027] The acoustic and electromagnetic composite monitoring device obtains the induced electromotive force signal and acoustic response signal of the corresponding depth of the reservoir behind the casing to be tested during the test period, and sends them to the surface processing subsystem through the monitoring subsystem;

[0028] The surface processing subsystem determines the oil-water interface position of the reservoir to be tested based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic wave response signal, the propagation relationship at the oil-water interface, and the electromagnetic response and acoustic wave response under the forward model. According to the signals obtained by the acoustic and electromagnetic composite monitoring device, the surface processing subsystem determines the oil-water interface position of the reservoir to be tested.

[0029] Furthermore, the surface processing subsystem determines the oil-water interface position of the reservoir to be tested based on the corresponding relationship between the reservoir medium and the induced electromotive force signal and the acoustic wave response signal, the propagation relationship at the oil-water interface, and the electromagnetic response and acoustic wave response under the forward model, and according to the signal obtained by the acoustic and electromagnetic composite monitoring device, including:

[0030] The surface processing subsystem determines the medium porosity, cementation index and medium resistivity of each reservoir medium behind the casing to be tested based on the acoustic response signal obtained by the acoustic transducer and the induced electromotive force signal obtained by the electromagnetic probe;

[0031] The surface processing subsystem inverts and obtains the medium radius of each reservoir medium in the reservoir to be tested based on the medium porosity, cementation index and medium resistivity of each reservoir medium in the reservoir to be tested;

[0032] The surface processing subsystem determines the oil-water interface position of the reservoir to be tested based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic response signal, the propagation relationship at the oil-water interface, and the electromagnetic response and acoustic response under the forward model, and according to the medium radius of each reservoir medium in the reservoir to be tested.

[0033] Furthermore, the reservoir media of the downhole layered columnar model are respectively iron core, air, instrument outer casing, well fluid, casing, cement sheath and formation from inner layer to outer layer.

[0034] The present invention has the following advantages due to the adoption of the above technical solution:

[0035] 1. The present invention solves the problem that traditional methods cannot effectively identify and accurately analyze the oil-water interface in reservoirs. At the same time, by iteratively analyzing the medium resistivity, medium porosity, cementation index and other parameters of the reservoir measured at different radial distances layer by layer, it can achieve high-precision monitoring of the oil-water interface position in the casing reservoir.

[0036] 2. The present invention can analyze the oil-water interface position by radially separating the cased reservoir layer by layer, thereby effectively improving the monitoring accuracy of the cased reservoir.

[0037] 3. The present invention can realize permanent monitoring of the reservoir behind the casing in the well. At the same time, it can realize high-precision analysis of the oil-water interface of the reservoir by measuring the medium resistivity, porosity, cementation index and other multi-parameter information of the reservoir and jointly interpreting them.

[0038] 4. Due to the complexity of the cased reservoir medium, it is difficult to accurately and effectively identify the oil-water interface solely based on medium resistivity information, and certain errors are inevitable. Therefore, the present invention uses a combination of acoustic and electromagnetic methods to perform radial stratification and separation of the cased reservoir medium layer by layer. The medium resistivity is combined with physical parameters such as formation porosity and Poisson's ratio measured by acoustic waves to comprehensively interpret the reservoir medium at different radial distances, thereby analyzing the downhole oil-water interface.

[0039] In summary, the present invention can be widely applied in the field of water injection advance front monitoring in casing-backed reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0041] Figure 1 Schematic diagram of the structure of a downhole layered columnar model provided by one embodiment of the present invention;

[0042] Figure 2 1 is a schematic structural diagram of a reservoir monitoring device provided by an embodiment of the present invention;

[0043] Figure 3 1 is a schematic structural diagram of an acoustic and electromagnetic composite monitoring device provided by one embodiment of the present invention;

[0044] Figure 4 1 is a flow chart of a combined acoustic and electromagnetic oil-water interface monitoring method according to an embodiment of the present invention;

[0045] Figure 5 This is a schematic diagram of an oil-water interface monitoring experiment provided by one embodiment of the present invention;

[0046] Figure 6 Schematic diagram of the change in distance between the oil-water interface position and the acoustic and electromagnetic composite monitoring device provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0047] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0048] It should be understood that the terms used herein are for the purpose of describing specific example embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "comprise", "include", "contain" and "have" are inclusive and therefore specify the presence of stated features, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring them to be performed in the specific order described or illustrated, unless the order of execution is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0049] Although the terms first, second, third, etc. can be used in the text to describe multiple elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or section from another region, layer or section. Unless the context clearly indicates otherwise, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer or section discussed below can be referred to as the second element, component, region, layer or section without departing from the teaching of the example embodiments.

[0050] In order to solve the problem of difficulty in identifying the oil-water interface in the well and the various obstacles that may occur during the logging process, the reservoir monitoring device and the acoustic and electromagnetic combined oil-water interface monitoring method provided by the embodiment of the present invention abstract the oil-water interface identification and monitoring model of the casing reservoir into the following form according to the reservoir medium characteristics: Figure 1The downhole layered columnar model shown in the figure first establishes a downhole layered columnar model, analyzes the electromagnetic and acoustic wave energy distribution, and determines the corresponding relationship between the response signal and the medium outside the casing of each layer, as well as the propagation relationship at the oil-water interface; secondly, the downhole acoustic and electromagnetic composite probe is used to monitor the reservoir section behind the casing, and the ground processing subsystem collects the response signal containing information such as the resistivity and porosity of the reservoir medium within the detection time; finally, by analyzing the energy distribution, the corresponding relationship between the response signal and the medium outside the casing of each layer, as well as the propagation relationship at the oil-water interface, is determined, and the resistivity and acoustic wave echo signal of each layer in the radial direction of the reservoir behind the casing are separated layer by layer along the radial direction of the wellbore, and the oil-water interface behind the reservoir casing is identified and analyzed, thereby realizing the oil-water interface monitoring behind the casing of high-porosity, high-permeability and large-thickness reservoirs.

[0051] Example 1

[0052] like Figure 2 and Figure 3 As shown, this embodiment provides a reservoir monitoring device, including an acoustic wave electromagnetic composite monitoring device 1, a monitoring subsystem 2 and a ground processing subsystem 3, wherein the acoustic wave electromagnetic composite monitoring device 1 includes an acoustic wave transducer 4, an electromagnetic probe 5 and a controller.

[0053] The acoustic wave electromagnetic composite monitoring device 1 is set at the corresponding depth of the reservoir behind the casing to be tested. The electromagnetic probe 5 is fixedly set in the acoustic wave transducer 4. The acoustic wave transducer 4 is used to transmit acoustic wave pulse signals and obtain acoustic wave response signals of reservoir fluid characteristics at the corresponding depth of the reservoir behind the casing to be tested. The electromagnetic probe 5 is used to obtain the secondary eddy current field signal, i.e., the induced electromotive force signal, at the corresponding depth of the reservoir behind the casing to be tested.

[0054] The controller is respectively connected to the acoustic wave transducer 4, the electromagnetic probe 5 and the monitoring subsystem 2. The monitoring subsystem 2 is also connected to the ground processing subsystem 3. The controller is used to select the working mode of the acoustic wave electromagnetic composite monitoring device 1, and control the operation of the acoustic wave transducer 4 and the electromagnetic probe 5 according to the selected working mode, and send the signals obtained by the acoustic wave transducer 4 and the electromagnetic probe 5 to the monitoring subsystem 2; the monitoring subsystem 2 is used to send the signals obtained by the acoustic wave transducer 4 and the electromagnetic probe 5 to the ground processing subsystem 3, and power the acoustic wave electromagnetic composite monitoring device 1; the ground processing subsystem 3 is used to calculate the medium porosity and cementation index of the corresponding depth of the reservoir to be tested based on the acoustic wave response signal of the reservoir fluid characteristics obtained by the acoustic wave transducer 4, and determine the oil-water interface position of the reservoir to be tested.

[0055] In a preferred embodiment, the electromagnetic probe 5 adopts a transceiver-integrated focusing structure, which is composed of a magnetic material wound with high-temperature enameled wire. This structural design can further improve the radial detection resolution and reduce the influence between the magnetic field and the sound wave.

[0056] Specifically, the electromagnetic probe 5 includes a magnetic core, a transmitting coil and a receiving coil. The transmitting coil and the receiving coil are evenly wound on the magnetic core. The transmitting coil is used to transmit electromagnetic pulses to generate a primary magnetic field in space, and the receiving coil is used to receive the induced electromotive force signal that changes with the reservoir medium.

[0057] By applying a bipolar ramp signal to the transmitting coil, the longitudinal magnetic field strength H of the receiving coil is obtained by solving the homogeneous and inhomogeneous Helmholtz equations according to Maxwell's equations. z (ω,r,μ,σ,ε,λ) is:

[0058]

[0059] Among them, f(ω,r,μ,σ,ε,λ)= j (ω,μ,σ,ε,λ)C1(ω,r,μ,σ,ε,λ)I1[x j (ω,μ,σ,ε,λ)], ω is the angular frequency, r is the medium radius, μ is the medium magnetic permeability, Θ is the medium conductivity, ε is the dielectric constant, x j and λ are introduced as intermediate variables, satisfying k j is the wave number, and μ j is the magnetic permeability of the jth layer from the inside to the outside of the reservoir to be tested; ε j is the dielectric constant of the jth layer from the inside to the outside of the reservoir to be tested; C1 is the undetermined coefficient, which can be obtained according to the boundary conditions of each layer; I1 is the first type modified Bessel function; N T is the number of turns of the transmitting coil; I T is the current applied to the transmitting coil.

[0060] In a preferred embodiment, the acoustic wave transducer 4 adopts a hollow cylindrical piezoelectric ceramic structure, including an acoustic wave transmitting probe 6 and an acoustic wave receiving probe 7. The acoustic wave transmitting probe 6 is used to transmit acoustic wave pulse signals, and the acoustic wave receiving probe 7 is used to receive acoustic wave response signals of the reservoir fluid characteristics of the reservoir to be tested.

[0061] Specifically, when the acoustic wave transmitter 6 emits an acoustic pulse signal, the acoustic wave propagates in all directions in the form of a longitudinal wave. When the acoustic wave encounters the well wall, it is reflected and refracted, and a portion of the energy entering the formation is converted into a sliding shear wave that continues to propagate. Assuming that the sound source spectrum function is S(ω), the sound pressure P(r,z,t) at any point in the well (except the sound source) is:

[0062]

[0063] Where P(r,z,t) is the time and space function of the sound field, r is the medium radius, z is the longitudinal magnetic field intensity, and t is the observation time; K0 is the second-order zero-order imaginary Bessel function, μ f is the Lame coefficient of the formation medium; A is the correlation coefficient of the pulse sound source; k is the wave number; I0 is the first kind of zero-order imaginary Bessel function.

[0064] In a preferred embodiment, a working mode selection module and a control module are provided in the controller.

[0065] The working mode selection module is used to select the working mode of the acoustic and electromagnetic composite monitoring device 1, including the electromagnetic priority working mode and the acoustic wave priority working mode. The electromagnetic priority working mode is to first turn on the electromagnetic probe 5 to obtain the signal and then turn on the acoustic wave transducer 4 to obtain the signal. The acoustic wave priority working mode is to first turn on the acoustic wave transducer 4 to obtain the signal and then turn on the electromagnetic probe 5 to obtain the signal.

[0066] The control module is used to control the opening or closing of the acoustic wave transducer 4 and the electromagnetic probe 5 according to the selected working mode.

[0067] In a preferred embodiment, the ground processing subsystem 3 is provided with a data processing module and an oil-water interface position module.

[0068] The data processing module is used for the layer-by-layer separation method. Based on the acoustic wave response signal of the reservoir fluid characteristics at the corresponding depth of the tested casing reservoir obtained by the acoustic wave transducer 4, the medium porosity and cementation index of each reservoir medium in the tested casing reservoir are calculated; and based on the induced electromotive force signal at the corresponding depth of the tested casing reservoir obtained by the electromagnetic probe 5, the medium resistivity of each reservoir medium in the tested casing reservoir is determined.

[0069] The oil-water interface position module is used to determine the oil-water interface position of the reservoir to be tested based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic wave response signal and the propagation relationship at the oil-water interface, and according to the medium resistivity, medium porosity and cementation index of each reservoir medium of the reservoir to be tested.

[0070] In a preferred embodiment, the acoustic wave electromagnetic composite monitoring device 1 is fixedly installed at the monitoring position of the reservoir behind the casing to be measured using a packer.

[0071] Example 2

[0072] like Figure 4 As shown, this embodiment provides a method for monitoring an oil-water interface by combining acoustic and electromagnetic methods, comprising the following steps:

[0073] 1) Establish a downhole layered columnar model of the reservoir to be tested. The reservoir media of the downhole layered columnar model are iron core, air, instrument outer casing, well fluid, casing, cement sheath and formation from inner layer to outer layer.

[0074] Specifically, the magnetic permeability, dielectric constant, dielectric conductivity and porosity of the innermost layer of the reservoir to be tested are set to μ1, ε1, σ1 and φ1 respectively; the magnetic permeability, dielectric constant, dielectric conductivity and porosity of the second layer from the inside to the outside of the reservoir to be tested are set to μ2, ε2, σ2 and φ2 respectively; the third layer from the inside to the outside of the reservoir to be tested to the outermost layer (the Jth layer) are set to the same value; the radius of each layer is r i =r1,r2,…,r J In the active region, there are both primary and secondary fields; in the passive region, there is only the secondary field.

[0075] 2) The surface processing subsystem 3 analyzes the post-casing energy distribution of the downhole layered columnar model, determines the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic response signal, and the propagation relationship at the oil-water interface, and calculates the electromagnetic response and acoustic response under the forward model based on the parameters of the transmitting coil and receiving coil of the electromagnetic probe 5 in the reservoir monitoring device.

[0076] Specifically, the post-casing energy distribution refers to the distribution of the oil-water interface in the post-casing reservoir. Different oil-water interface locations produce different energy levels within the formation. Different oil-water interface locations correspond to different induced electromotive force signals and acoustic response signals. Once the oil-water interface location changes, its propagation relationship in space changes, and the induced electromotive force signal and acoustic response signal also change accordingly.

[0077] Specifically, the surface processing subsystem 3 analyzes the induced EMF signal and the acoustic test signal to determine the correspondence between the reservoir medium and the induced EMF signal and the acoustic response signal, as well as the propagation relationship at the oil-water interface. The electromagnetic and acoustic responses in the forward model are calculated based on this correspondence and propagation relationship, as well as the parameters of the transmitting and receiving coils of the electromagnetic probe 5. By comparing the induced EMF signal and the acoustic test signal with the electromagnetic and acoustic responses calculated in the forward model, they can verify the accuracy of the correspondence and propagation relationships.

[0078] Specifically, the electromagnetic response characteristics of the receiving coil of the electromagnetic probe 5 and the echo response characteristics of the acoustic wave receiving probe 7 of the acoustic wave transducer 4 are analyzed. It is assumed that the wall thickness of the downhole casing remains unchanged for a period of time. Then, the induced electromotive force of the receiving coil of the electromagnetic probe 5 is related to the sampling time and the reservoir conductivity; the acoustic wave part adopts time difference and amplitude logging, and the acoustic wave receiving probe 7 receives the acoustic wave response signal containing the porosity of the reservoir medium and the reservoir fluid characteristics.

[0079] 3) The acoustic wave electromagnetic composite monitoring device 1 in Example 1 is set at the corresponding depth of the reservoir behind the casing to be measured. The controller selects the working mode of the acoustic wave electromagnetic composite monitoring device 1 and controls the operation of the acoustic wave transducer 4 and the electromagnetic probe 5 according to the selected working mode.

[0080] 4) The electromagnetic probe 5 obtains the induced electromotive force signal of the corresponding depth of the reservoir behind the casing to be tested during the test period, and the acoustic wave transducer 4 obtains the acoustic wave response signal of the reservoir fluid characteristics at the corresponding depth of the reservoir behind the casing to be tested during the test period. The monitoring subsystem 2 sends the signals obtained by the acoustic wave transducer 4 and the electromagnetic probe 5 to the ground processing subsystem 3.

[0081] Specifically, the electromagnetic probe 5 identifies the oil-water interface in the reservoir by extracting and analyzing the received secondary eddy current field signal that carries the resistivity information of the surrounding medium. According to the transient electromagnetic method theory, the induced electromotive force of the receiving coil of the electromagnetic probe 5 shows an exponential decay trend over time. The early signal is mainly due to the shallow medium, and the late signal is mainly due to the deep medium. Therefore, it is necessary to select a suitable sampling time to sample the induced electromotive force signal. Among them, the relationship between the diffusion time (the diffusion time is long and is not subject to human intervention; the sampling time is the sampling point corresponding to the discrete sampling of the diffusion time) and the detection depth is:

[0082]

[0083] Where, E is the induced electromotive force; M is the detection depth; t d is the diffusion time; μ0 is the magnetic permeability of air.

[0084] Specifically, once the sampling time is determined, the induced electromotive force is solely related to the conductivity of the reservoir behind the casing to be measured. This conductivity can be analyzed based on the induced electromotive force at different sampling times. The acoustic echo signal can be calculated based on the time difference signal to include information such as the porosity of the medium at different radial distances. Thus, the acoustic response signal received by the acoustic receiving probe 7 includes information about the reservoir behind the casing at different radial distances.

[0085] The longitudinal magnetic field strength of the receiving coil of the electromagnetic probe 5 can be obtained by solving the homogeneous and inhomogeneous Helmholtz equations. Then, through time domain conversion and combined with boundary conditions, the induced electromotive force V(t, r, μ, σ, ε, λ) of the receiving coil is obtained as follows:

[0086]

[0087] Among them, n R is the number of turns of the receiving coil; t of is the off time of the excitation signal; K p is the filter coefficient of the GS inverse transform; p is the pth order of the GS inverse transform; P is the total order of the GS inverse transform; sp is a variable whose value is pln2.

[0088] Specifically, the oil-water interface of the reservoir after casing can be further analyzed according to the above formula (4). Assuming that the total number of test cycles is W, the measurement starts from the i-th test cycle, and the induced electromotive force corresponding to the i-th test cycle is recorded as V i (t), then its matrix form is:

[0089] V i (t)=[V i (t1) V i (t2) … V i (t L )],i=1,2,…,W(5)

[0090] Among them, V i (t) is the total number of sampling points in each measurement cycle.

[0091] Specifically, the induced electromotive force within the test period is obtained according to the above formula (5), and the resistivity information of the casing reservoir can be obtained.

[0092] In addition, the time difference signal Δt received by the sound wave receiving probe 7 is:

[0093]

[0094] Where Δt f is the acoustic time difference of the fluid in the pore; Δt ma The acoustic time difference of the rock skeleton; is the formation porosity.

[0095] 5) The surface processing subsystem 3 adopts a layer-by-layer separation method to determine the porosity, cementation index, and resistivity of each reservoir medium in the reservoir behind the casing to be tested based on the acoustic response signal of the reservoir fluid characteristics obtained by the acoustic transducer 4 and the induced electromotive force signal obtained by the electromagnetic probe 5. Then, based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic response signal, the propagation relationship at the oil-water interface, and the electromagnetic response and acoustic response under the forward model, the oil-water interface position of the reservoir behind the casing to be tested is determined. Specifically,

[0096] 5.1) The surface processing subsystem 3 determines the porosity, cementation index and resistivity of each reservoir medium in the reservoir to be tested based on the acoustic response signal of the reservoir fluid characteristics obtained by the acoustic transducer 4 and the induced electromotive force signal obtained by the electromagnetic probe 5.

[0097] Specifically, the cementation index m of the reservoir at the corresponding depth after the casing to be tested is:

[0098]

[0099] Among them, A casing A is the casing wave amplitude of the target layer; max is the casing wave amplitude in the free casing section.

[0100] Specifically, the medium porosity can be obtained based on the acoustic wave response signal, and the medium resistivity can be obtained based on the induced electromotive force signal. The specific process will not be described in detail here.

[0101] 5.2) The surface processing subsystem 3 inverts the medium radius of each reservoir medium in the reservoir to be tested based on the medium porosity, cementation index and medium resistivity of each reservoir medium in the reservoir to be tested.

[0102] Specifically, due to the different media porosity, cementation index and media resistivity feedback of each radial layer of the cased reservoir, taking water flooding as an example, when the injected water advances into the wellbore, the affected area of the injected water will cause changes in the reservoir conductivity and media information, which will in turn cause changes in the induced electromotive force signal of the receiving coil and the acoustic wave response signal. Therefore, the media porosity, cementation index and media resistivity of each layer of the cased reservoir can be iteratively analyzed layer by layer according to the different radial radii, and a layer-by-layer separation method is adopted. This method uses the obtained media resistivity ρ, media porosity The distance of the wellbore, i.e. the medium radius r, is obtained by inverting parameters such as the cementation index layer by layer.

[0103] 5.3) The surface processing subsystem 3 determines the oil-water interface position of the tested reservoir based on the corresponding relationship between the reservoir medium and the induced electromotive force signal and the acoustic response signal, the propagation relationship at the oil-water interface, and the electromagnetic response and acoustic response under the forward model, and according to the medium radius of each reservoir medium in the tested reservoir.

[0104] Specifically, the obtained multi-parameter information of the reservoir behind the casing, such as dielectric resistivity, porosity and cementation index, is brought into the Alch formula to obtain the water saturation S of the reservoir behind the casing. w :

[0105]

[0106] Among them, R w is the formation water resistivity; R t is the formation resistivity, n is the saturation index; n and R w It is a constant for the downhole formation in a specific area.

[0107] The oil saturation Sh of the reservoir behind the casing to be tested can be further calculated by the above formula (8):

[0108] Sh=1-S w (9)

[0109] The water saturation of the casing reservoir to be measured is calculated by the above formula (8), and the oil saturation of the casing reservoir to be measured is calculated by the above formula (9). According to the medium radius of each reservoir medium of the casing reservoir to be measured and the detection depth M where the acoustic electromagnetic composite monitoring device 1 is located, the casing reservoir to be measured is interpreted radially layer by layer. Based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic wave response signal and the propagation relationship at the oil-water interface, as well as the electromagnetic response and acoustic wave response under the forward model, the oil-water interface position of the casing reservoir to be measured is determined, providing a basis and reference for accurate reservoir evaluation.

[0110] The following describes in detail the acoustic wave and electromagnetic combined oil-water interface monitoring method of the present invention through specific embodiments:

[0111] like Figure 5 As shown, the vertical boundary between oil and water is used to simulate the position of the oil-water interface in the reservoir, and the distance detection performance and detection accuracy of the acoustic wave electromagnetic composite monitoring device 1 are verified by changing the distance between the acoustic wave electromagnetic composite monitoring device 1 and the oil-water interface.

[0112] By monitoring the oil-water interface at different distances for a long time, optimizing the sampling time in each test cycle, and accumulating the receiving response at the optimized sampling time, the oil-water interface position monitoring results are obtained, such as Figure 6 It can be seen that the method of the present invention can clearly identify the change in the distance between the oil-water interface and the acoustic-wave electromagnetic composite monitoring device 1, and the closer the distance between the oil-water interface and the acoustic-wave electromagnetic composite monitoring device 1, the better the monitoring effect, and the farthest monitoring distance can reach 9m.

[0113] The above embodiments are only used to illustrate the present invention, wherein the structure, connection mode and manufacturing process of each component can be changed. Any equivalent transformations and improvements based on the technical solution of the present invention should not be excluded from the scope of protection of the present invention.

Claims

1. A reservoir monitoring device, characterized in that: It includes an acoustic and electromagnetic composite monitoring device, a monitoring subsystem and a ground processing subsystem; The acoustic wave electromagnetic composite monitoring device is set at the corresponding depth of the reservoir behind the casing to be measured, and the acoustic wave electromagnetic composite monitoring device is used to obtain the acoustic wave response signal and the induced electromotive force signal at the corresponding depth of the reservoir behind the casing to be measured; The monitoring subsystem is used to send the signal obtained by the acoustic wave electromagnetic composite monitoring device to the ground processing subsystem, and to supply power to the acoustic wave electromagnetic composite monitoring device; The surface processing subsystem is used to determine the oil-water interface position of the reservoir to be tested based on the signal obtained by the acoustic and electromagnetic composite monitoring device; The acoustic wave electromagnetic composite monitoring device includes an acoustic wave transducer, an electromagnetic probe and a controller; The electromagnetic probe is fixedly arranged in the acoustic wave transducer, and the acoustic wave transducer is used to transmit an acoustic wave pulse signal and obtain an acoustic wave response signal of a corresponding depth of the reservoir behind the casing to be measured, and the electromagnetic probe is used to obtain an induced electromotive force signal of a corresponding depth of the reservoir behind the casing to be measured; The controller is connected to the acoustic wave transducer, electromagnetic probe and monitoring subsystem respectively, and is used to select an operating mode of the acoustic wave electromagnetic composite monitoring device, control the operation of the acoustic wave transducer and electromagnetic probe according to the selected operating mode, and send signals obtained by the acoustic wave transducer and electromagnetic probe to the monitoring subsystem; The ground processing subsystem is provided with: a data processing module for calculating the porosity and cementation index of each reservoir medium in the tested behind-the-casing reservoir according to the acoustic wave response signal at the corresponding depth of the tested behind-the-casing reservoir acquired by the acoustic wave transducer; and determining the dielectric resistivity of each reservoir medium in the tested behind-the-casing reservoir according to the induced electromotive force signal at the corresponding depth of the tested behind-the-casing reservoir acquired by the electromagnetic probe; The oil-water interface position module is used to determine the oil-water interface position of the reservoir to be tested based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic wave response signal and the propagation relationship at the oil-water interface, and according to the medium resistivity, medium porosity and cementation index of each reservoir medium of the reservoir to be tested.

2. A reservoir monitoring device according to claim 1, characterized in that: The electromagnetic probe includes a magnetic core, a transmitting coil and a receiving coil; The transmitting coil and the receiving coil are evenly wound on the magnetic core. The transmitting coil is used to transmit electromagnetic pulses to generate a primary magnetic field in space; the receiving coil is used to receive induced electromotive force signals that change with the reservoir medium.

3. A reservoir monitoring device according to claim 2, characterized in that: The acoustic wave transducer comprises an acoustic wave transmitting probe and an acoustic wave receiving probe; The acoustic wave transmitting probe is used to transmit acoustic wave pulse signals; The acoustic wave receiving probe is used to receive the acoustic wave response signal of the reservoir behind the casing to be tested.

4. A reservoir monitoring device according to claim 1, characterized in that: The electromagnetic probe adopts a focusing structure integrating transmission and reception.

5. A reservoir monitoring device according to claim 1, characterized in that: The acoustic wave transducer adopts a hollow cylindrical piezoelectric ceramic structure.

6. A combined acoustic and electromagnetic oil-water interface monitoring method, characterized in that: include: Establishing a downhole layered columnar model of the casing reservoir to be tested, wherein the downhole layered columnar model includes a plurality of reservoir media from the inner layer to the outer layer; The surface processing subsystem analyzes the post-casing energy distribution of the downhole layered columnar model, determines the corresponding relationship between the reservoir medium and the induced electromotive force signal and the acoustic response signal, as well as the propagation relationship at the oil-water interface, and calculates the electromagnetic response and acoustic response under the forward model; The acoustic wave electromagnetic composite monitoring device according to any one of claims 1 to 5 is set at a corresponding depth of the reservoir behind the casing to be measured; The acoustic and electromagnetic composite monitoring device obtains the induced electromotive force signal and acoustic response signal of the corresponding depth of the reservoir behind the casing to be tested during the test period, and sends them to the surface processing subsystem through the monitoring subsystem; The surface processing subsystem determines the oil-water interface position of the reservoir to be tested based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic wave response signal, the propagation relationship at the oil-water interface, and the electromagnetic response and acoustic wave response under the forward model. According to the signals obtained by the acoustic and electromagnetic composite monitoring device, the surface processing subsystem determines the oil-water interface position of the reservoir to be tested.

7. The method for monitoring the oil-water interface by combining acoustic and electromagnetic methods according to claim 6, wherein: The surface processing subsystem determines the oil-water interface position of the reservoir to be tested based on the corresponding relationship between the reservoir medium and the induced electromotive force signal and the acoustic wave response signal, the propagation relationship at the oil-water interface, and the electromagnetic response and acoustic wave response under the forward model, and the signal obtained by the acoustic and electromagnetic composite monitoring device, including: The surface processing subsystem determines the medium porosity, cementation index and medium resistivity of each reservoir medium behind the casing to be tested based on the acoustic response signal obtained by the acoustic transducer and the induced electromotive force signal obtained by the electromagnetic probe; The surface processing subsystem inverts and obtains the medium radius of each reservoir medium in the reservoir to be tested based on the medium porosity, cementation index and medium resistivity of each reservoir medium in the reservoir to be tested; The surface processing subsystem determines the oil-water interface position of the reservoir to be tested based on the correspondence between the reservoir medium and the induced electromotive force signal and the acoustic response signal, the propagation relationship at the oil-water interface, and the electromagnetic response and acoustic response under the forward model, and according to the medium radius of each reservoir medium in the reservoir to be tested.

8. The method for monitoring the oil-water interface by combining acoustic and electromagnetic methods according to claim 6, wherein: The reservoir media of the downhole layered columnar model are respectively iron core, air, instrument outer casing, well fluid, casing, cement sheath and formation from inner layer to outer layer.

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