A forward-focusing electromagnetic logging method while drilling

Abstract

This invention relates to electromagnetic logging technology and discloses a forward-focusing electromagnetic logging method while drilling, comprising two stages: (1) Pre-testing stage: using a magnetic ring antenna array arranged in a straight line along the drill collar, the last antenna is used as a reference antenna to transmit signals, and the preceding antennas simultaneously receive them, so as to synchronously acquire the amplitude and phase delay of the received signals of each preceding antenna. (2) Forward focusing stage: configuring the transmission parameters for the preceding antennas, setting their initial phase to the negative value of the measured phase delay, and calculating an inversely proportional weighting coefficient based on the received amplitude, thereby configuring the driving amplitude of each preceding antenna; finally, driving the reference antenna and the configured preceding antennas to transmit synchronously, and coherently superimposing them in front of the drill bit to form a focused beam, while weakening the signal interference from the instrument's sides and back to the formation. This invention does not require pre-setting equipment in un-drilled formations, is fully compatible with existing instruments, and can significantly improve the signal strength and signal-to-noise ratio of forward detection.

Description

Technical Field

[0001] This invention relates to electromagnetic logging technology, and particularly to a forward focusing electromagnetic logging method while drilling. Background Technology

[0002] Forward electromagnetic logging (WELM) technology detects the electromagnetic properties of the formation within tens of meters in front of the drill bit, providing crucial information for precise landing in low-angle wells and early warning of faults or formation boundaries in high-angle / horizontal wells. This technology is of great significance for reducing drilling risks, improving drilling efficiency, and enhancing oil and gas recovery.

[0003] Existing technologies for forward detection while drilling mainly rely on functional expansion of traditional electromagnetic remote detection instruments, but they all have inherent bottlenecks in their physical principles, resulting in insufficient forward detection capabilities.

[0004] 1. Indirect detection method based on lateral probing principle: This method utilizes the instrument's ability to probe deep formations laterally within the wellbore. Under large well inclination angles, it indirectly infers formation changes ahead by measuring the lateral resistivity behind the drill string. However, this method is essentially lateral probing, and its detection effectiveness heavily relies on specific formation structure models and accurate well inclination data. It is not true forward probing by the drill bit, and its applicability is limited and highly uncertain.

[0005] 2. Omnidirectional Detection and Inversion Method Based on Remote Detection Instruments: This method expands the instrument's detection depth by increasing the transmitter-receiver spacing and reducing the operating frequency, and attempts to simultaneously extract lateral and forward formation parameters from a mixed signal containing information across the entire space using a large-scale inversion algorithm. However, the electromagnetic field generated by the transmitter exhibits an omnidirectional diffusion mode, resulting in the dominant response from the wellbore periphery and lateral formations in the measurement signal, while the signal from the target formation ahead of the drill bit is extremely weak. In conductive formations, electromagnetic wave attenuation is severe, making this problem of weak forward signal even more pronounced.

[0006] The fundamental drawback of the aforementioned technologies lies in the lack of forward focusing capability of the emitted electromagnetic field. The omnidirectional diffusion of the field distribution prevents energy from being effectively concentrated in the area in front of the drill bit, resulting in low sensitivity to forward formation changes. In formations with low resistivity contrast, the effective detection distance is short; furthermore, because the useful forward signal is submerged in strong lateral background signals, measurement accuracy and reliability are poor. Therefore, developing a logging-while-drilling method that can enhance forward radiation and increase the proportion of forward signal has become a pressing technical challenge in this field.

[0007] To address the aforementioned technical bottlenecks, related research has explored a new approach to forward focusing based on the electromagnetic reciprocity principle. For example, the applicant has proposed a method that, by deploying a test antenna at a hypothetical position in front of the drill bit and adjusting the excitation parameters of the rear transmitting antenna in reverse according to the reciprocity theorem, theoretically, energy can be focused towards this preset point. (Hao Peng. Research and Application of Electromagnetic Detection and Positioning Methods in Non-uniform Underground Media [D]. University of Electronic Science and Technology of China, 2022.)

[0008] However, when applied to actual logging-while-drilling engineering, the underlying assumptions of this scheme are difficult to apply to real-world operating environments, resulting in limitations in its practical application.

[0009] 1. Focusing algorithms rely on pre-positioning a receiving antenna in the un-drilled formation to obtain a reference signal. However, in actual drilling operations, the formation ahead of the drill bit is completely unknown, making it physically impossible to pre-deploy any sensors. Therefore, the amplitude and phase calibration steps of this scheme lack the prerequisites for engineering implementation and are difficult to put into practice.

[0010] 2. The radiating element used is a solenoid coil antenna. However, in current logging-while-drilling instruments widely used in the petroleum industry, radially radiating magnetic loop antennas are a common design to adapt to the high-intensity, small-size drill collar environment. The proposed antenna type is incompatible with the mainstream instrument structure, which means that this solution is difficult to modify or verify based on existing logging equipment, resulting in low engineering portability and applicability.

[0011] Therefore, existing technologies cannot solve the practical engineering challenges of forward drilling detection. As oil and gas exploration and development extend to deeper and more complex geological formations, the need for real-time and accurate detection of un-drilled formation information within tens of meters ahead of the drill bit is becoming increasingly urgent. Existing forward drilling electromagnetic detection technologies suffer from systemic bottlenecks in both physical principles and engineering implementation, making it difficult to meet this practical need. Specifically:

[0012] 1. Existing forward detection schemes for drilling are unable to effectively concentrate limited energy in the target area ahead of the drill bit due to the omnidirectional diffusion of the launch field. This results in extremely weak response signals of the instrument to forward formation parameters, low signal-to-noise ratio, and measurement data mainly dominated by strong lateral background signals. In complex formations, the effective detection distance and resolution of the formation ahead of the drill bit are seriously insufficient.

[0013] 2. Existing focusing methods based on the reciprocity principle rely on pre-setting receiving sensors in un-drilled formations to obtain reference signals. This prerequisite limits the theoretical methods to the simulation stage, making them unsuitable for actual drilling operations and lacking engineering feasibility. Furthermore, the solenoid coil antenna used in this study is incompatible with the magnetic loop antenna structure of existing forward electromagnetic logging-while-drilling (WSLD) instruments, making it difficult to modify, verify, and apply on existing instrument platforms. This results in high technology transfer costs and low applicability. Summary of the Invention

[0014] The technical problem to be solved by the present invention is to provide a forward focusing electromagnetic logging method that does not rely on the pre-deployment of test equipment in front of the drill bit, is compatible with the standard magnetic loop antenna of existing logging-while-drilling instruments, can effectively focus the transmission field on the formation in front, and at the same time weaken useless lateral signals and enhance the strength and signal-to-noise ratio of the forward signal.

[0015] The technical solution adopted by this invention to solve the above-mentioned technical problems is a forward-focusing electromagnetic logging method while drilling, comprising the following steps:

[0016] Preliminary testing phase: An antenna array is constructed using several magnetic loop antennas arranged in a straight line along the drill collar axis. The antenna located at the rear of the array is used as a reference antenna, and the remaining antennas located in front of the reference antenna are used as preceding antennas.

[0017] The reference antenna is used as a transmitting source to radiate test signals, and each preceding antenna is used as a receiving antenna to obtain the amplitude and phase information of the test signals received by each preceding antenna. The amplitude and phase information characterizes the channel response of the electromagnetic propagation path from the reference antenna to each preceding antenna.

[0018] Forward focusing phase: Based on the amplitude and phase information obtained in the pre-test phase, the transmission excitation parameters of the preceding antenna are configured; after configuration, the reference antenna and the configured preceding antenna are driven to synchronously transmit electromagnetic waves to achieve energy focusing in the formation in front of the drill bit.

[0019] This invention proposes a holistic forward focusing detection method that first performs a rear array channel reception test, and then performs forward compensation focusing transmission based on the measured channel response. First, a self-transmit / receive test is conducted using the drill collar's rear antenna array to obtain the amplitude and phase response of the forward propagation channel. Then, based on this measured response, the transmission parameters of the same array are configured with reverse amplitude and phase compensation, thereby achieving directional energy focusing towards the front of the drill bit.

[0020] During the preliminary testing phase, the last of the multiple magnetic loop antennas arranged on the drill collar is used as the transmitting source, and the remaining multiple antennas in front are used as the receiving array. The amplitude and phase information of the signal at each receiving point relative to the transmitting source are obtained synchronously through a single transmission and multiple reception.

[0021] During the forward focusing phase, the initial phase of each transmitting antenna is set to the negative of the corresponding phase delay measured in the first phase, and the amplitude of each transmitting antenna is set to be inversely proportional to the corresponding received amplitude measured in the first phase for amplitude and phase compensation.

[0022] Specifically, the transmit excitation parameters of the preceding antenna are configured, including:

[0023] For each preceding antenna to be configured, its initial phase of transmission is set to the compensation value of the corresponding phase information of the antenna measured in the pre-test phase;

[0024] For each preceding antenna to be configured, a transmit amplitude weighting coefficient is calculated based on the amplitude information corresponding to the antenna measured in the pre-test phase. The transmit amplitude weighting coefficient is inversely proportional to the received signal amplitude value represented by the amplitude information. The driving amplitude of the preceding antenna is set according to the transmit amplitude weighting coefficient.

[0025] This invention establishes an active and controllable electromagnetic field forward focusing mechanism. By optimizing the transmission parameters of the rear array, it achieves directional energy convergence in front of the drill bit. It eliminates the need to deploy any testing equipment in the unexplored area in front of the drill bit and is compatible with the antenna structure of existing forward electromagnetic logging-while-drilling instruments, ensuring the feasibility of real-time field operation. Ultimately, it enables long-distance, high signal-to-noise ratio detection of resistivity changes in unexplored formations in front of the drill bit, improving geological guidance and risk warning capabilities. This method is theoretically feasible and has practical engineering value.

[0026] The beneficial effects of this invention are:

[0027] 1. Significantly improved the detection range and signal strength of forward probes, enhancing the forward probe performance of existing drilling-while-drilling instruments:

[0028] Addressing the current technological bottleneck: the omnidirectional radiation characteristics of the antenna result in weak forward signals, which are drowned out by the background noise of strong lateral detection signals.

[0029] This invention utilizes measured channel response data to perform precise amplitude and phase pre-compensation on the forward transmitting array. Phase compensation achieves wavefront synchronization in the target area, while amplitude-weighted propagation attenuation is balanced. When the array transmits synchronously, the wavelets of each transmitting antenna undergo constructive interference in front of the drill bit, allowing energy to superimpose and concentrate, forming a high-intensity focused beam. Laterally and backward, phase mismatch weakens each other, fundamentally enhancing the signal ratio of the effective forward signal and relatively suppressing interference from useless directions, ultimately achieving an overall improvement in detection range and signal strength.

[0030] 2. It has practical engineering applicability in actual well logging operations and is easy to implement:

[0031] Addressing the current technological bottlenecks: Pre-setting test antennas in un-drilled formations is not feasible in actual well logging operations, lacks engineering practicality, and is difficult to implement.

[0032] This invention uses the last antenna on the drill collar as the transmitting source and the remaining front antennas as the receiving array. It actively measures the actual electromagnetic propagation path response of each array element from the rear to the front within the drilled, operable well section, eliminating the need for pre-installed testing equipment in the unexplored area in front of the drill bit. This has practical engineering application value. Furthermore, the antenna structure used in this invention is compatible with existing logging-while-drilling instruments, offering high adaptability and low technology transfer costs. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating the acquisition of phase amplitude information by the array during the pre-test phase.

[0034] Figure 2 A schematic diagram illustrating forward focusing achieved through array-coordinated forwarding during the forward focusing phase;

[0035] Figure 3 A schematic diagram of the drill bit's forward focusing effect in the embodiment. Detailed Implementation

[0036] A forward-focusing electromagnetic logging method based on rear-end array coordination is proposed. Its core lies in its independent use of any prior deployment or new antenna structures in unknown areas ahead of the drill bit. It fully utilizes existing standard magnetic loop antennas and their arrays behind the drill bit, and achieves directional and efficient focusing of electromagnetic energy towards the formation ahead of the drill bit through an active control process involving rear-end array channel reception testing and compensated transmission. This method is implemented through two coordinated stages:

[0037] I. Preliminary testing phase, used for array channel reception testing:

[0038] An antenna array formed by multiple magnetic loop antennas arranged in a single line near the drill bit, such as... Figure 1 As shown. By designating the last antenna in the array as the reference antenna, the remaining antennas in the array, because they are all positioned before the reference antenna, are called preceding antennas.

[0039] In the pre-test phase, the reference antenna is used as the source of the test signal, and the preceding antennas receive it simultaneously. This allows for the active measurement of the channel response of the electromagnetic propagation path from the rear reference antenna to each preceding antenna, accurately acquiring key characteristic data, including amplitude information reflected by signal attenuation and phase information reflected by propagation delay.

[0040] The purpose of this stage is to actively detect the electromagnetic propagation channel characteristics from the rear reference antenna to each preceding antenna using the antenna array on the drill collar, so as to provide amplitude and phase information for focused transmission.

[0041] The array arrangement is as follows: near the drill bit, multiple magnetic loop antennas are arranged at certain intervals (equal or optimized intervals) along the drill collar axis, denoted as... , , … .in, This represents the number of magnetic ring antennas behind the drill bit. This is the frontmost antenna of the array, and also the one closest to the drill bit. … All are preceding antennas. This is the reference antenna at the very end of the array.

[0042] The polarization direction of each antenna in an antenna array can be radial. , Direction, or axial direction The direction can be any tilt; antennas can be arranged at equal intervals or at arbitrary intervals.

[0043] Channel sensing excitation method: The reference antenna located at the rear end of the array As a transmitting antenna, it radiates a known test signal that excites an electromagnetic field in the formation and propagates in all directions, including the path forward of the drill bit.

[0044] Amplitude and phase information acquisition method: located in the array Forward front-end antenna … … Simultaneously serving as a receiving antenna, the preceding antenna number... , Receive from reference antenna The received radiation signal is measured and its amplitude and phase information is recorded. ,in, For the preceding antenna The amplitude of the received radiation signal; For each preceding antenna Relative to the reference antenna Phase delay at the time of transmission. Due to the reference antenna. When the radiated signal propagates forward towards the drill bit, it is affected by the attenuation of the formation medium. The amplitude relationship of the radiated signals received by each preceding antenna satisfies... .

[0045] Amplitude and phase information collected during this stage Characterized from the reference antenna To each preceding antenna The forward propagation channel response.

[0046] II. Forward focusing phase, used for forward compensation focusing and transmission:

[0047] n-1 preceding antennas in the pre-test phase … and reference antenna Together, they serve as the transmitting antennas in this stage. Before radiating the signal, keeping the excitation parameters of the reference antenna unchanged, and based on the amplitude and phase information obtained in the pre-test phase to characterize the forward propagation channel response, the excitation parameters of the n-1 preceding antennas are optimized. The excitation parameters include the initial phase and the transmit amplitude weighting coefficient:

[0048] Each preceding antenna The initial phase is set to the corresponding phase delay. The negative value is used to compensate for the measured phase delay and counteract the inherent hysteresis of wavefront propagation. That is, to achieve in-phase superposition of the radiated wavefronts of each antenna in the array in front of the drill bit, each preceding antenna... The initial transmit phase is set to When the electromagnetic waves radiated by each preceding antenna propagate toward the drill bit, they will automatically compensate for the previously detected phase lag, thereby achieving phase synchronization in the target area and realizing coherent enhancement.

[0049] Meanwhile, to balance the attenuation differences caused by different propagation distances, each transmitting antenna is adjusted based on the received amplitude measured during the pre-test phase. For each transmitting antenna Calculate a transmit amplitude weighting coefficient The coefficient and Proportional to the received amplitude Inversely proportional, that is, satisfying The relationship between them. The final driving amplitude of each preceding antenna is determined according to the weighting coefficient. This configuration allows for stronger transmission power to be compensated for antennas that are farther away from the drill bit and have greater attenuation, thereby creating a more uniform field strength superposition in the target area in front of the drill bit.

[0050] Presequence antenna According to their respective optimized incentive parameters After amplitude and phase configuration, the configured preceding antenna and reference antenna simultaneously transmit electromagnetic waves of the same frequency. Based on the reciprocity of electromagnetic wave propagation and the principle of coherent superposition, the wavefronts radiated by each antenna will achieve constructive interference and amplitude equalization in a predetermined area in front of the drill bit, forming a focused beam with concentrated energy. Simultaneously, in the non-target areas to the side and rear of the drill bit, phase mismatch caused by path differences will weaken the radiated fields.

[0051] This phase utilizes the channel response data acquired in the pre-test phase to reverse-configure the transmission parameters, enabling the antennas of the forward-transmitting array to work together and focus energy in front of the drill bit, such as... Figure 2 As shown.

[0052] Optionally, during the forward focusing phase, the signal-to-noise ratio and other factors measured in the pre-test phase can be adjusted based on the preceding antenna. to A selection of high-performance antennas are chosen to form a forward-transmitting array together with a reference antenna. For example, the excitation parameters of a leading antenna with a received signal-to-noise ratio higher than a preset threshold are configured, and it is then combined with the reference antenna to form a forward-transmitting array.

[0053] Optionally, the reference antenna radiated signal has the same frequency as the electromagnetic wave signal synchronously transmitted by the antenna array during the forward focusing phase.

[0054] The example of the pre-drilling focused electromagnetic detection instrument is at 25 In the drilled strata, there is 250 ahead. In a high-resistivity geological formation with an operating frequency of 100kHz, according to the method of the present invention, five magnetic loop antennas are installed behind the drill bit. , … The formed antenna array, after passing through the pre-testing phase and the forward focusing phase, is then... Figure 3 As shown in the simulation results, the forward field of the antenna array is improved by about 8dB, while the lateral and backward fields are weakened by about 10dB. This is equivalent to improving the signal-to-noise ratio of the forward field signal in the total detection signal by about 18dB, which proves the effectiveness and feasibility of the technical solution of the present invention.

Claims

1. A forward-focusing electromagnetic logging method while drilling, characterized in that, Includes the following steps: Preliminary testing phase: An antenna array is constructed using several magnetic loop antennas arranged in a straight line along the drill collar axis. The antenna located at the rear of the array is used as a reference antenna, and the remaining antennas located in front of the reference antenna are used as preceding antennas. The reference antenna is used as a transmitting source to radiate test signals, and each preceding antenna is used as a receiving antenna to obtain the amplitude and phase information of the test signals received by each preceding antenna. The amplitude and phase information characterizes the channel response of the electromagnetic propagation path from the reference antenna to each preceding antenna. Forward focusing phase: Based on the amplitude and phase information obtained in the pre-test phase, the transmit excitation parameters of the preceding antenna are configured; Once configured, the drive reference antenna and the configured preceding antenna synchronously transmit electromagnetic waves to focus energy in the formation in front of the drill bit. In the forward focusing phase, the transmit excitation parameters of the preceding antenna are configured, including: For each preceding antenna to be configured, its initial phase of transmission is set to the compensation value of the corresponding phase information of the antenna measured in the pre-test phase; For each preceding antenna to be configured, a transmit amplitude weighting coefficient is calculated based on the amplitude information corresponding to the antenna measured in the pre-test phase. The transmit amplitude weighting coefficient is inversely proportional to the received signal amplitude value represented by the amplitude information. The driving amplitude of the preceding antenna is set according to the transmit amplitude weighting coefficient.

2. The method as described in claim 1, characterized in that, In the antenna array, the polarization direction of each antenna is radial, axial, or tilted relative to the axis of the drill collar.

3. The method as described in claim 1, characterized in that, In the antenna array, each antenna is arranged at equal or non-equal intervals along the axis of the drill collar.

4. The method as described in claim 1, characterized in that, Transmit excitation parameters are configured only for preceding antennas whose signal-to-noise ratio of received test signals is higher than a preset threshold during the pre-test phase.

5. The method as described in claim 1, characterized in that, During the preliminary testing phase, the test signal radiated by the reference antenna has the same frequency as the electromagnetic wave signal synchronously transmitted during the forward focusing phase.

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