A method for identifying drill string status in torsional drilling based on wellhead impedance

Abstract

This invention discloses a method for identifying the drill string status in torsional drilling based on wellhead impedance, relating to the field of drilling technology. The method includes: S1, applying a periodic torque load to the drill string at the wellhead, and measuring the rotational speed and torque during the torsional drilling process using a wellhead measurement sub; S2, segmenting the rotational speed and torque signals to obtain segmented signals, performing a Fourier transform on the segmented signals to obtain their frequency domain response, constructing an equivalent torsional impedance function, and calculating the amplitude-frequency and phase-frequency characteristics; S3, obtaining the phase response curve based on the phase-frequency characteristics, and performing a discrete cosine transform on the phase response curve based on the amplitude-frequency characteristics; S4, identifying the drill string status based on the discrete cosine transform decomposition of the signal. This invention proposes a method to determine the drill string status during torsional drilling using only wellhead signals.

Description

Technical Field

[0001] This invention relates to the field of drilling technology, and more specifically to a method for identifying the state of a torsional drilling string based on wellhead impedance. Background Technology

[0002] The deep shale gas deposits in the Sichuan Basin are characterized by deep burial, high reservoir temperatures, and are mostly located in complex structural zones with well-developed faults and large formation dip angles. This presents challenges such as frequent wellbore trajectory adjustments in horizontal sections and difficulty in hitting the target. Excessive friction between the drill string and the wellbore results in slow response times when adjusting the tool face angle via surface rotation, leading to over-reliance on the driller's experience and repeated trial and error. This results in low trajectory control efficiency, poor wellbore quality, and further exacerbates the friction between the drill string and the wellbore, significantly limiting the ultimate extension capability of the horizontal section. The drill string torsion swing system, using conventional directional drilling tools, incorporates riser pressure, top drive inverter torque, and directional well data. By controlling the top drive to apply reciprocating rotation to the drill string, it releases most of the static friction of the drill string, improving the low mechanical speed and wellbore trajectory control challenges caused by high drill string friction during horizontal well sliding drilling.

[0003] During torsional drilling, the drill string exhibits different dynamic states under different well sections and frictional conditions. Wellhead torque and rotational speed are important dynamic characteristics reflecting the downhole drill string's motion state. Existing technologies mainly rely on downhole measurement results or empirical judgment to analyze the tool face and drill string status, lacking a method that fully utilizes measurable signals at the wellhead and can identify the drill string status without relying on downhole information. Summary of the Invention

[0004] To address at least one of the aforementioned problems, this invention proposes a method for identifying the state of a torsional drilling string based on wellhead impedance.

[0005] The technical solution of this invention to solve the above problems is as follows: A method for identifying the state of a torsional drilling string based on wellhead impedance, comprising: S1. Apply a periodic torque load to the wellhead drill string and measure the rotational speed and torque during the torsional drilling process based on the wellhead measurement sub. S2. The speed signal and torque signal are segmented to obtain segmented signals. The segmented signals are then subjected to Fourier transform to obtain their frequency domain response. The equivalent torsional impedance function is then constructed, and the amplitude frequency characteristic and phase frequency characteristic are calculated. S3. Obtain the phase response curve based on the phase frequency characteristics, and perform a discrete cosine transform on the phase response curve based on the amplitude frequency characteristics. S4. Identify the drill string status based on the discrete cosine transform decomposition of the signal.

[0006] The advantages of this invention are as follows: This invention proposes a method for determining the drill string status during oscillating drilling using only wellhead signals. Compared to conventional methods, it eliminates the need for downhole signals, reduces costs, and provides more timely and reliable results. Attached Figure Description

[0007] Figure 1 This is a flowchart of the method according to an embodiment of the present invention; Figure 2 The phase response curve, amplitude-frequency curve, and consistency plot are for a time window with a torque of 1000 N·m. Figure 3 The phase response curve, amplitude-frequency curve, and consistency plot are shown for a time window when the torque is 2000 N·m. Figure 4 The phase response curve, amplitude-frequency curve, and consistency plot are shown for a time window when the torque is 3000 N·m. Figure 5 The phase response curve, amplitude-frequency curve, and consistency plot are shown for a time window when the torque is 4000 N·m. Figure 6 The phase response curve, amplitude-frequency curve, and consistency plot are for a time window when the torque is 5000 N·m. Figure 7 The phase response curve, amplitude-frequency curve, and consistency plot are shown for a time window when the torque is 6000 N·m. Figure 8 The phase response curve, amplitude-frequency curve, and consistency plot are shown for a time window when the torque is 7000 N·m. Figure 9 The phase response curve, amplitude-frequency curve, and consistency plot are shown for a time window when the torque is 8000 N·m. Figure 10 This is a graph of the discrete cosine transform decomposed signal. Detailed Implementation

[0008] The specific embodiments of the present invention will be clearly and completely described below with reference to examples. Obviously, the described examples are only some embodiments of the present invention, and not all embodiments.

[0009] like Figure 1 As shown, a method for identifying the state of a torsional drilling string based on wellhead impedance includes: S1. Apply a periodic torque load to the wellhead drill string and measure the rotational speed and torque during the torsional drilling process based on the wellhead measurement sub. In this step, the wellhead measurement sub is a common wellhead facility used to monitor and measure the condition of the wellhead portion of the drill string. For example, it can be equipped with common measuring components such as temperature sensors. In this embodiment, a torque measuring unit and a rotational speed measuring unit are installed on the measurement sub, which are used to measure the torque and rotational speed of the drill string, respectively.

[0010] The torque measurement unit employs a full-bridge resistance strain gauge array, symmetrically arranged along a ±45° spiral direction. During actual operation, the measuring sub section generates shear strain signals under the torque load at the wellhead. These full-bridge resistance strain gauges measure these shear strain signals to obtain the torque. Simultaneously, axial strain gauges can also be installed for decoupling analysis of axial tensile stress and torque.

[0011] The rotational speed measurement unit uses either a MEMS gyroscope or a Hall effect angular velocity sensor, which can measure the drill string angular velocity and instantaneous rotational speed changes.

[0012] Of course, a synchronous acquisition and processing unit for signal conversion can also be set on the wellhead measurement sub. This unit includes an analog-to-digital conversion module, a processor, and a unified clock module. Through the unified clock module, the torque measurement unit and the speed measurement unit are controlled to trigger sampling synchronously, eliminating time drift errors.

[0013] A communication unit can also be installed on the wellhead measurement sub. The communication unit can use Wi-Fi, Bluetooth, LoRa or industrial-grade wireless data transmission modules to transmit the data obtained by the synchronous acquisition and processing unit.

[0014] In some embodiments, the periodic torque load is obtained by superimposing a constant load and a periodic load, wherein the waveform of the periodic load is one of a sine wave, cosine wave, triangular wave, or trapezoidal wave. Furthermore, in actual implementation, those skilled in the art will know that the magnitude of the periodic torque load is always greater than 0.

[0015] Meanwhile, when measuring speed and torque, in order to ensure that the data has good effect in subsequent processes, the data acquisition frequency should not be lower than 500Hz.

[0016] S2. The speed signal and torque signal are segmented to obtain segmented signals. The segmented signals are then subjected to Fourier transform to obtain their frequency domain response. The equivalent torsional impedance function is then constructed, and the amplitude frequency characteristic and phase frequency characteristic are calculated. In this embodiment, a Hanning sliding window is used to segment the speed and torque signals. The window length of the Hanning sliding window is 10-20 seconds, and the step size is 0.5 seconds. Of course, those skilled in the art can adjust the window length and step size appropriately, such as adjusting the step size to 0.8 seconds or 1 second.

[0017] In this step, the Fourier transform can be either the common Fast Fourier Transform (FFT) or Short-Time Fourier Transform (STFT). In this embodiment, FFT is chosen as the frequency domain response tool.

[0018] The final equivalent torsional resistance function is: In the formula, Characterizes the dynamic response characteristics of the drill string system to torsional excitation, that is, the torque response capability corresponding to a unit angular velocity input; This represents the complex frequency domain expression of the torque time-domain signal T(t) after Fourier transform; The complex frequency domain representation of the time-domain signal ω(t) representing rotational speed after Fourier transform; The final amplitude-frequency and phase-frequency characteristics are as follows: , In the formula, Indicates amplitude-frequency response; Indicates phase frequency characteristics; express The real part; express The imaginary part; This represents the arctangent function in the four quadrants.

[0019] S3. Obtain the phase response curve based on the phase frequency characteristics, and perform a discrete cosine transform on the phase response curve based on the amplitude frequency characteristics; this step includes the following sub-steps: S31. Calculate the impedance phase response curve based on the phase frequency characteristics, and select the upper limit of the effective frequency band based on the amplitude frequency characteristics. And for the frequency range [0, ...] of the impedance phase response curve. Discretization is performed to obtain a sequence of multiple sampling points. In the formula, This represents the value of the nth sampling point in the sequence, where N represents the maximum number of sampling points. S32. Perform phase expansion on the sampling points: In the formula, express The expanded value; Indicates phase untangling; and for Normalization process is performed to obtain ; S33, to Performing a DCT-II transformation yields the discrete cosine coefficients: In the formula, Indicates the first Discrete cosine transform coefficients; Represents the normalization coefficient; Number the DCT coefficients.

[0020] In S31, the method of calculating the phase response curve using phase frequency characteristics is a conventional operation in this field. That is, the curve drawn with the frequency in the phase frequency characteristics as the horizontal axis and the phase angle as the vertical axis is the phase response curve.

[0021] In S32, phase expansion is performed primarily to eliminate phase abrupt changes, ensuring the continuity of the curve. Simultaneously, standardization is applied to eliminate the influence of dimensions and amplitude.

[0022] The standardized procedures in this step are as follows: In the formula, This represents the mean of the sampled point sequence after phase expansion; The standard deviation of the expanded phase sampling point sequence.

[0023] S4. Identify the drill string status based on the discrete cosine transform decomposition of the signal.

[0024] Specifically, the rules for identifying the drill string status in this step are as follows: For a continuous segmented signal, if the first characteristic coefficient of its discrete cosine transform decomposed signal is negative and the second characteristic coefficient is positive, then the state of the drill string under this state is determined to be the state dominated by inertia in the vertical well section. In the subsequent process, if the first two characteristic coefficients of the discrete cosine transform decomposed signal are completely reversed relative to the previous state, that is, the first characteristic coefficient is positive and the second characteristic coefficient is negative, then the state of the drill string in this state is determined to be the horizontal section friction dissipation state. In the subsequent process, if the first two characteristic coefficients of the discrete cosine transform decomposed signal are completely reversed again compared to the previous state, that is, the first characteristic coefficient is negative and the second characteristic coefficient is positive, then the state of the drill string in this state is determined to be the horizontal segment inertia-dominated state.

[0025] Simultaneously, amplitude-frequency characteristics are used to generate amplitude-frequency curves, and these curves are then used to assist in the identification of drill string conditions. When it is initially determined that the drill string is in a state dominated by inertia in the vertical section or the horizontal section, the low-frequency energy proportion is high and the harmonic distortion coefficient shows an upward trend in the amplitude-frequency curve. The proportion of low-frequency energy is calculated using impedance amplitude-frequency curves. For each signal segment, within the effective analysis frequency band... Within, calculate the low-frequency range. The ratio of the sum of squares of the internal impedance magnitudes to the sum of squares of the total impedance magnitudes across the entire frequency band is used as the proportion of low-frequency energy. in, To select the upper limit of the low-frequency range The corresponding low-frequency torsional oscillation response range; The upper limit of the effective analysis frequency band determined for the amplitude-frequency response. When Greater than the preset threshold It is determined that the low-frequency energy proportion of this segmented signal is relatively high; when Less than the preset threshold When the low-frequency energy proportion of the segmented signal is low, it is determined that the low-frequency energy proportion is relatively low. Between and When in between, the segmented signal is treated as an intermediate or uncertain state. Threshold and Its value can be determined adaptively through experimental bench calibration or on-site initial stabilization time window.

[0026] When it is initially determined that the drill string is in a horizontal section of frictional dissipation state, the concentration of the main peak in the amplitude-frequency curve increases and the harmonic distortion coefficient is low. If the preliminary judgment result and the amplitude-frequency curve result are inconsistent, the signal segment is marked as uncertain, and corrected by combining the results of adjacent signal segments: if the drill string state is the same in two adjacent signal segments, the drill string state represented by the signal segment is adjusted to the drill string state of the adjacent signal segment; if the drill string state is different in two adjacent signal segments, the drill string state is kept as the preliminary judgment state. To facilitate understanding of the present invention by those skilled in the art, specific test examples are given below.

[0027] During the drilling process of the horizontal well, the torque was increased sequentially to obtain different torque and speed measurement results. Following the method described in the above embodiment, the torque and speed were segmented, and a random segment under each torque condition was selected to calculate its phase response curve and amplitude-frequency curve. The final results are as follows. Figures 2-9 As shown. Figures 2-9 In the figure, each graph, from top to bottom, consists of a phase response curve, an amplitude-frequency curve, and a consistency curve. The consistency curve represents the degree of linear consistency between torque and speed response in the frequency domain. The closer it is to 1, the higher the reliability of the amplitude-frequency curve and the phase response curve at that frequency.

[0028] Based on the method of the embodiments of the present invention, for Figures 2-9 The discrete cosine transform decomposition yields the following decomposed signal: Figure 10 As shown, from Figure 10It can be determined that the state of the drill string is different under different torque conditions: when the torque is 1000~2000 N·m, C1 is negative and C2 is positive, indicating the inertia state of the vertical well section; when the torque is 3000 N·m, C1 is positive and C2 is negative, indicating the friction dissipation state of the horizontal well section; when the torque is greater than 3000 N·m, C1 is negative and C2 is positive, indicating the inertia state of the horizontal well.

[0029] The present invention has been disclosed above with preferred embodiments. However, those skilled in the art should understand that these embodiments are only for describing the present invention and should not be construed as limiting the scope of the present invention. Further improvements can be made without departing from the principles of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for recognizing the state of a torsion pendulum drilling string based on wellhead impedance, characterized in that, Includes the following steps: S1. Apply a periodic torque load to the wellhead drill string and measure the rotational speed and torque during the torsional drilling process based on the wellhead measurement sub. S2. The speed signal and torque signal are segmented to obtain segmented signals. The segmented signals are then subjected to Fourier transform to obtain their frequency domain response. The equivalent torsional impedance function is then constructed, and the amplitude frequency characteristic and phase frequency characteristic are calculated. S3. Obtain the phase response curve based on the phase frequency characteristics, and perform a discrete cosine transform on the phase response curve based on the amplitude frequency characteristics. It includes the following steps: S31, calculating an impedance phase response curve based on the phase-frequency characteristic, and selecting an upper limit of an effective frequency band based on the amplitude-frequency characteristic , and performing discrete processing on a frequency interval [0, ] of the impedance phase response curve to obtain a plurality of sample point sequences , wherein, n represents a value of an nth sample point in the sequence, and N represents a maximum number of sample points. S32. Perform phase expansion on the sampling points: In the formula, express The expanded value; Indicates phase untangling; and for Normalization process is performed to obtain ; S33, to Performing a DCT-II transformation yields the discrete cosine coefficients: In the formula, Indicates the first Discrete cosine transform coefficients; Represents the normalization coefficient; Indicates the DCT coefficient number; S4. The rules for identifying the drill string state based on the discrete cosine transform decomposition signal are as follows: For a continuous segmented signal, if the first characteristic coefficient of its discrete cosine transform decomposed signal is negative and the second characteristic coefficient is positive, then the state of the drill string under this state is determined to be the state dominated by inertia in the vertical well section. In the subsequent process, if the first two characteristic coefficients of the discrete cosine transform decomposed signal are completely reversed relative to the previous state, that is, the first characteristic coefficient is positive and the second characteristic coefficient is negative, then the state of the drill string in this state is determined to be the horizontal section friction dissipation state. In the subsequent process, if the first two characteristic coefficients of the discrete cosine transform decomposed signal are completely reversed again compared to the previous state, that is, the first characteristic coefficient is negative and the second characteristic coefficient is positive, then the state of the drill string in this state is determined to be the horizontal segment inertia-dominated state.

2. The method for identifying the state of a torsional drilling string based on wellhead impedance according to claim 1, characterized in that, The measuring section is equipped with a torque measuring unit and a speed measuring unit.

3. The method for identifying the state of a torsional drilling string based on wellhead impedance according to claim 1, characterized in that, The periodic torque load is obtained by superimposing a constant load and a periodic load, and the waveform of the periodic load is one of sine wave, cosine wave, triangular wave, and trapezoidal wave.

4. The method for identifying the state of a torsional drilling string based on wellhead impedance according to claim 1, characterized in that, The measurement frequency for speed and torque is not less than 500Hz.

5. The method for identifying the state of a torsional drilling string based on wellhead impedance according to claim 1, characterized in that, The speed and torque signals are segmented using a Hanning sliding window, with a window length of 10-20s and a step size of 0.5s.

6. The method for identifying the state of a torsional drilling string based on wellhead impedance according to claim 1, characterized in that, The Fourier transform is either the Fast Fourier Transform or the Short-Time Fourier Transform.

7. The method for identifying the state of a torsional drilling string based on wellhead impedance according to claim 1, characterized in that, The equivalent torsional resistance function is: In the formula, Characterizes the dynamic response characteristics of the drill string system to torsional excitation, that is, the torque response capability corresponding to a unit angular velocity input; This represents the complex frequency domain expression of the torque time-domain signal T(t) after Fourier transform; The complex frequency domain representation of the rotational speed time-domain signal ω(t) after Fourier transform; the amplitude-frequency characteristic and phase-frequency characteristic are: , In the formula, Indicates amplitude-frequency response; Indicates phase frequency characteristics; express The real part; express The imaginary part; This represents the arctangent function in the four quadrants.

8. The method for identifying the state of a torsional drilling string based on wellhead impedance according to claim 1, characterized in that, Amplitude-frequency characteristics are used to generate amplitude-frequency curves, and these curves are then used to assist in the identification of drill string conditions. When it is initially determined that the drill string is in a state dominated by inertia in the vertical section or the horizontal section, the low-frequency energy proportion is high and the harmonic distortion coefficient shows an upward trend in the amplitude-frequency curve. When it is initially determined that the drill string is in a horizontal section of frictional dissipation state, the concentration of the main peak in the amplitude-frequency curve increases and the harmonic distortion coefficient is low. If the preliminary judgment result is inconsistent with the amplitude-frequency curve result, the signal segment is marked as an uncertain state, and it is corrected by combining the results of the adjacent signal segments: if the state of the drill string is the same in two adjacent signal segments, the state of the drill string represented by the signal segment is adjusted to the state of the drill string in the adjacent signal segment; if the state of the drill string is different in two adjacent signal segments, the state of the drill string is kept as the preliminary judgment state.

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