A method of transient electromagnetic logging while drilling

Abstract

The application provides a while-drilling transient electromagnetic logging method, and relates to the technical field of while-drilling logging transient electromagnetic measurement of oil and natural gas. The application is applied to a while-drilling transient electromagnetic logging instrument comprising a transmitting coil, a first receiving coil and a second receiving coil. Air layer observation signals of the two receiving coils are synchronously collected, a compensation coefficient changing with time is calculated, double-receiving compensation is performed on the formation observation signals in the process of while-drilling drilling, and a compensated signal of the formation is obtained. On this basis, full-period apparent resistivity is inversed by using dichotomy search, and the distance of the formation boundary is determined according to the bifurcation time of the curve changing with time, so that stable long-distance formation detection under the condition of short instrument is realized.

Description

Technical Field

[0001] This invention relates to the field of transient electromagnetic measurement technology for logging while drilling in the oil and gas industry, and in particular to a transient electromagnetic logging while drilling method. Background Technology

[0002] Electromagnetic logging-while-drilling (EMLDR) instruments use electromagnetic waves of 1kHz-4MHz to perform real-time detection during the drilling process. This is used to detect the properties of the formation around the well and in front of the drill bit (parameters such as formation resistivity, resistivity anisotropy, and formation dip). This allows for early identification of the target formation, ensuring the drill collar lands in the target formation, maintaining drilling within the reservoir, mapping the reservoir, and identifying potential hazards in front of the drill bit. It also guides the drill bit to remain within the reservoir and adjusts the drilling trajectory in a timely manner to avoid drilling risks, thus achieving safe, economical, and efficient drilling.

[0003] As the requirements for long-distance formation detection around the well and in front of the drill bit continue to increase, the frequency of existing drilling electromagnetic wave instruments is constantly decreasing and the length of the instruments is constantly increasing to meet the requirements of longer detection distances. However, with the increase in instrument length, the longest currently reaching 40m, it has caused many inconveniences in the use of the instruments and affected their widespread adoption. Furthermore, the current instruments have high operating costs and complex structures, and their detection capabilities cannot adequately meet the needs of long-distance (30m) detection. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a transient electromagnetic logging method while drilling, which obtains the formation-compensated signal through dual receiver compensation driven by the air layer compensation coefficient and stably outputs the apparent resistivity throughout the entire period.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A transient electromagnetic logging-while-drilling method is applied to a transient electromagnetic logging-while-drilling instrument, which includes a transmitting coil, a first receiving coil, and a second receiving coil. A first source distance is set between the transmitting coil and the first receiving coil, and a second source distance is set between the transmitting coil and the second receiving coil. The method includes:

[0007] The air layer observation signals of the first receiving coil and the second receiving coil are synchronously acquired in the air layer through the first receiving coil and the second receiving coil;

[0008] A compensation coefficient that varies with time is calculated based on the ratio of the air layer observation signal of the second receiving coil to the air layer observation signal of the first receiving coil, so that the air layer compensation signal obtained by performing compensation operation on the air layer observation signal of the second receiving coil and the air layer observation signal of the first receiving coil based on the compensation coefficient is zero.

[0009] During drilling, the formation observation signal of the first receiving coil and the formation observation signal of the second receiving coil are collected and synchronized through the first receiving coil and the second receiving coil, respectively.

[0010] The formation-compensated signal is obtained by subtracting the compensation coefficient from the formation observation signal of the second receiving coil and multiplying it by the formation observation signal of the first receiving coil.

[0011] A binary search is used to iterate within a preset apparent resistivity range. The calculated value of induced electromotive force is calculated based on the median apparent resistivity of the range and compared with the observed electromotive force corresponding to the formation compensation signal. If the accuracy condition is met, the apparent resistivity for the whole period is output. If the accuracy condition is not met, the apparent resistivity range is updated and iterated according to the monotonically decreasing characteristic of induced electromotive force.

[0012] The formation resistivity is determined based on the change of apparent resistivity over time throughout the entire period, and the distance between the drilling transient electromagnetic logging instrument and the formation boundary is determined based on the moment when the curve of apparent resistivity over time begins to bifurcate.

[0013] Preferably, calculating a compensation coefficient that varies with time based on the ratio of the second receiving coil air layer observation signal to the first receiving coil air layer observation signal, so that the air layer compensation signal obtained by performing compensation operation on the second receiving coil air layer observation signal and the first receiving coil air layer observation signal based on the compensation coefficient is zero, includes:

[0014] Acquire the air layer observation signal of the second receiving coil and the air layer observation signal of the first receiving coil;

[0015] An air layer compensation signal is constructed for air layer compensation calculation; the air layer compensation signal is equal to the second receiving coil air layer observation signal minus the compensation coefficient multiplied by the first receiving coil air layer observation signal;

[0016] With the air layer compensation signal being zero as a constraint, the compensation coefficient is determined to be equal to the ratio of the air layer observation signal of the second receiving coil to the air layer observation signal of the first receiving coil;

[0017] The process of determining the compensation coefficient is repeated at different time points to obtain the compensation coefficient that changes over time.

[0018] Preferably, the formation-compensated signal is obtained by subtracting the compensation coefficient from the formation observation signal of the second receiving coil and multiplying it by the formation observation signal of the first receiving coil, including:

[0019] Acquire the formation observation signal from the second receiving coil and the formation observation signal from the first receiving coil;

[0020] The compensation coefficient calculated in the air layer is invoked, and the compensation coefficient is made to correspond in time with the formation observation signal;

[0021] Perform formation compensation calculation, wherein the formation compensation calculation is: subtract the compensation coefficient from the formation observation signal of the second receiving coil and multiply it by the formation observation signal of the first receiving coil;

[0022] The result of the formation compensation calculation is output as the formation compensation signal.

[0023] Preferably, after obtaining the formation-compensated signal, the method further includes:

[0024] Identify the influence components of the drill collar of the drilling transient electromagnetic logging instrument on the formation observation signals of the first receiving coil and the second receiving coil;

[0025] The influencing components are suppressed or eliminated based on the formation-compensated signal.

[0026] The output signal, after eliminating the influencing components, corresponds to the field excited by the magnetic dipole.

[0027] Preferably, a binary search is used to iterate within a preset apparent resistivity range. The calculated induced electromotive force (EMF) value is calculated based on the median apparent resistivity of the range and compared with the observed EMF corresponding to the formation-compensated signal. When the accuracy condition is met, the apparent resistivity for the entire period is output, including:

[0028] Set the minimum value and the maximum value of the preset apparent resistivity range;

[0029] The preset apparent resistivity interval is divided into two equal parts to obtain the median apparent resistivity of the interval;

[0030] The calculated value of the induced electromotive force is calculated based on the median apparent resistivity of the interval;

[0031] The observed electromotive force is determined from the formation-compensated signal, and the calculated value of the induced electromotive force is compared with the observed electromotive force.

[0032] When the calculated value of the induced electromotive force and the observed electromotive force satisfy the accuracy condition, the median apparent resistivity of the interval is output as the apparent resistivity for the entire period.

[0033] Preferably, when the accuracy condition is not met, the apparent resistivity range is updated and iterated based on the monotonically decreasing characteristic of the induced electromotive force, including:

[0034] The preset apparent resistivity range is used as the initial range of the apparent resistivity range in the binary search, and the two endpoints of the apparent resistivity range are respectively used as the minimum value and the maximum value of the apparent resistivity range.

[0035] When the calculated value of the induced electromotive force is greater than the observed electromotive force corresponding to the formation compensation signal, the apparent resistivity interval is updated to an interval consisting of the median apparent resistivity of the interval to the maximum value of the apparent resistivity interval.

[0036] When the calculated value of the induced electromotive force is less than the observed electromotive force corresponding to the formation compensation signal, the apparent resistivity interval is updated to an interval consisting of the minimum value of the apparent resistivity interval to the median apparent resistivity of the interval.

[0037] The updated apparent resistivity range is used as the preset apparent resistivity range for the next iteration, and the binary search iteration is repeated until the accuracy condition is met and the full-period apparent resistivity is output.

[0038] Preferably, both the first source distance and the second source distance are no greater than 7m.

[0039] Preferably, the length of the transient electromagnetic logging-while-drilling instrument is no more than 9m; the maximum distance between the transient electromagnetic logging-while-drilling instrument and the formation boundary is 30m.

[0040] Preferably, the step "during drilling, acquiring and synchronizing the formation observation signals of the first and second receiving coils respectively to obtain the formation observation signals of the first and second receiving coils" is implemented under two formation conditions; the two formations include an upper formation and a lower formation, the resistivity of the upper formation is 50 Ω·m, and the resistivity of the lower formation is 1 Ω·m; the transient electromagnetic logging instrument is located in the upper formation; the first source distance is 5m, the second source distance is 7m; and the distance between the second receiving coil and the formation boundary is 10m, 20m, or 30m.

[0041] Preferably, the step "determining the formation resistivity based on the change of apparent resistivity over time and determining the distance between the drilling transient electromagnetic logging instrument and the formation boundary based on the moment when the curve of apparent resistivity over time begins to bifurcate" is performed under two formation conditions; the two formations include an upper formation and a lower formation, the resistivity of the upper formation is 10 Ω·m and the resistivity of the lower formation is 1 Ω·m; the resistivity of the upper formation and the resistivity of the lower formation are determined based on the change of apparent resistivity over time; when the distance between the second receiving coil and the formation boundary is different, the moment when the curve of apparent resistivity over time begins to bifurcate is different, and the moment when the bifurcation begins is used as the basis for determining the distance.

[0042] The present invention discloses the following technical effects:

[0043] This invention addresses the problem that existing electromagnetic logging while drilling tends to use lower frequencies to improve long-range detection capabilities, leading to a significant increase in instrument length, inconvenience, and high cost. It introduces synchronous observation of the air layer and calculates a compensation coefficient that varies over time. This ensures that the air layer compensation signal obtained after performing compensation calculations on the two air layer observation signals based on the compensation coefficient is zero. This suppresses the impact of tool response, drift, and common-mode interference on the observations at the source, allowing subsequent formation observations to be established on a unified and calibrable benchmark. This improves the stability and repeatability of transient electromagnetic logging while drilling in complex downhole conditions.

[0044] This invention uses formation observation signals from a first receiving coil and a second receiving coil, combined with the compensation coefficient, to form a formation-compensated signal. Based on this, a binary search is employed iteratively within a preset apparent resistivity range. Utilizing the monotonically decreasing characteristic of the induced electromotive force (EMF), the range boundary is continuously updated, allowing the calculated EMF value to gradually approximate the observed EMF corresponding to the formation-compensated signal. This results in a provably convergent apparent resistivity calculation. This process reduces reliance on manual parameter tuning, lowers the probability of misjudgments due to inversion instability, and improves computational efficiency, facilitating real-time processing during drilling.

[0045] This invention further determines formation resistivity based on the change of apparent resistivity over time throughout the entire period, and uses the moment when the curve of apparent resistivity over time begins to bifurcate as the criterion for formation boundary distance. This achieves a quantitative indication of the approach trend of the interface around the well and in front of the drill bit, supporting timely decision-making during drilling. Compared with the path of increasing instrument length to gain long-range detection capability in the prior art, this invention improves the effective information extraction capability through closed-loop processing of "compensated signal construction, full-range apparent resistivity inversion, and bifurcation time distance determination," thereby enhancing the feasibility of long-range detection applications and reducing the burden of engineering implementation without introducing additional complex structures. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A flowchart of the method provided in an embodiment of the present invention;

[0048] Figure 2 This is a schematic diagram of the instrument structure provided in an embodiment of the present invention;

[0049] Figure 3 A schematic diagram of the drilling transient electromagnetic logging instrument layout parameters in a two-layer formation model provided in an embodiment of the present invention;

[0050] Figure 4 The embodiments of the present invention are based on Figure 2 A schematic diagram of the apparent resistivity of the signal throughout the entire period after formation compensation in the formation model;

[0051] Figure 5 This is a schematic diagram of the apparent resistivity of the signal throughout the entire period after formation compensation, provided for an embodiment of the present invention, under the condition that the upper layer resistivity is 10 ohm / mm and the lower layer resistivity is 1 ohm / mm. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The purpose of this invention is to provide a transient electromagnetic logging method while drilling, which uses the bifurcation moment of the apparent resistivity curve over time to determine the formation boundary distance, thereby improving the stability of remote detection while drilling and enhancing its field usability.

[0054] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] Figure 1 The method flowchart provided in the embodiments of the present invention is as follows: Figure 1As shown, this invention provides a transient electromagnetic logging-while-drilling method, applied to a transient electromagnetic logging-while-drilling instrument. The instrument includes a transmitting coil, a first receiving coil, and a second receiving coil. A first source distance is set between the transmitting coil and the first receiving coil, and a second source distance is set between the transmitting coil and the second receiving coil. The method includes:

[0056] Step 100: Synchronously acquire the air layer observation signals of the first receiving coil and the second receiving coil through the first receiving coil and the second receiving coil in the air layer;

[0057] Step 200: Calculate the compensation coefficient that varies with time based on the ratio of the air layer observation signal of the second receiving coil to the air layer observation signal of the first receiving coil, so that the air layer compensation signal obtained by performing compensation operation on the air layer observation signal of the second receiving coil and the air layer observation signal of the first receiving coil based on the compensation coefficient is zero;

[0058] Step 300: During drilling, the formation observation signals of the first receiving coil and the second receiving coil are collected and synchronized respectively to obtain the formation observation signals of the first receiving coil and the second receiving coil.

[0059] Step 400: Subtract the compensation coefficient from the formation observation signal of the second receiving coil and multiply it by the formation observation signal of the first receiving coil to obtain the formation-compensated signal;

[0060] Step 500: Use binary search to iterate within the preset apparent resistivity range, calculate the induced electromotive force based on the median apparent resistivity of the range, and compare it with the observed electromotive force corresponding to the formation compensation signal. If the accuracy condition is met, output the apparent resistivity for the whole period. If the accuracy condition is not met, update the apparent resistivity range and iterate according to the monotonically decreasing characteristic of the induced electromotive force.

[0061] Step 600: Determine the formation resistivity based on the change of apparent resistivity over time, and determine the distance between the drilling transient electromagnetic logging instrument and the formation boundary based on the moment when the curve of apparent resistivity over time begins to bifurcate.

[0062] Specifically, such as Figure 2 As shown in the instrument structure diagram, T represents the transmitting coil, R1 and R2 are the receiving coils, and the distances between the transmitting coil and the two receiving coils are L1 and L2, respectively.

[0063] By employing signal compensation, the observed signal is processed to ultimately eliminate the influence of the drill collar on the observed signal, thus obtaining a field excited by a pure magnetic dipole.

[0064] Signal compensation: Compensation measurements are performed in the air layer. and The signals observed by receiving antennas R1 and R2 in the air layer are respectively. To obtain the compensated signal, set the compensated signal to 0, i.e.

[0065]

[0066] Where k(t) is the compensation coefficient, we can obtain

[0067]

[0068] It is a quantity that changes over time.

[0069] When the instrument drills into the formation, based on the observation signals from the two receiving antennas in the formation and the compensation coefficient k(t) obtained in the air layer, the compensated measurement value in the formation is calculated as follows:

[0070]

[0071] in, The signal after compensation in the formation. The observation signal from antenna R1 in the strata. This is the observation signal from the R2 antenna in the strata.

[0072] Based on the above method, the effectiveness of the proposed instrument structure and the compensation algorithm used in the formation was tested.

[0073] The test model is as follows Figure 3 As shown, in the two-layer model, the resistivity of the upper layer is 50 ohms / mm², and the resistivity of the lower layer is 1 ohm / mm². The instrument is located in the first layer, with the distances between the transmitting and receiving antennas being 5m and 7m, respectively. The distances (d²b) of the receiving antenna R2 from the stratum boundary are 10, 20, and 30m, respectively. The compensation coefficient k(t) in the air layer is used to compensate for the response in the stratum, and finally, the results are obtained. Figure 3 The compensated signals under different conditions in the model shown are as follows: Figure 4 As shown in section (a).

[0074] Then, the apparent resistivity over the entire period is calculated using a binary search method, with the following steps:

[0075] (i) Given an apparent resistivity range [ ] ;

[0076] (ii) Divide the interval into two equal parts, with Calculate the induced electromotive force ;

[0077] (iii) With the observed electromotive force In comparison, if the accuracy requirement is met, then output... The apparent resistivity is for the entire region; otherwise, proceed to the next step.

[0078] (iv) If Based on the monotonically decreasing characteristic of induced electromotive force, explain Update the apparent resistivity range to [ ] ;like ,illustrate Update the apparent resistivity range to [ ] ;

[0079] (v) Repeat (2) to (5) until the accuracy requirement is met.

[0080] The apparent resistivity for the entire period calculated using the steps above is as follows: Figure 4 As shown in section (b), the apparent resistivity result is 50 ohms in the early stage, while the apparent resistivity varies between 3 and 5 ohms in the later stage, accurately reflecting the resistivity changes between the upper and lower layers of the two strata. Simultaneously, the timing of the bifurcation of the blue, red, and green lines is inconsistent, reflecting the change in the distance between the instrument and the stratum boundary, thus enabling the resistivity instrument to detect the resistivity of boundaries and strata.

[0081] Figure 4 Part (a) is based on Figure 2 The model's observation signals are compensated, with blue, red, and green representing the compensated signals calculated when the distance between R2 and the boundary is 10, 20, and 30 m, respectively. Figure 4 Part (b) shows the total apparent resistivity calculated based on the relationship between the compensation signal and the apparent resistivity. Blue, red, and green represent the total apparent resistivity calculated based on the compensation signal when the distance between R2 and the boundary is 10, 20, and 30 m, respectively.

[0082] Change Figure 3 The resistivity of the two-layer model shown is 10 ohms / mm² for the upper layer and 1 ohm / mm² for the lower layer. Other parameters remain unchanged. The compensation signal is calculated following the steps described above. Figure 5 As shown in section (a), the apparent resistivity over the entire period is then calculated, as follows: Figure 5 As shown in section (b). The final inversion yields the apparent resistivity over the entire period, which reflects the resistivity changes in the two strata. The apparent resistivity of the upper stratum is 10 ohms / mm, while the apparent resistivity of the lower stratum varies between 3 and 4 ohms / mm, accurately reflecting the changes in stratum resistivity. Furthermore, when the distance between the receiving antenna R2 and the stratum boundary is different, the corresponding apparent resistivity curves begin to bifurcate at different times, which can serve as an indicator for determining the distance between the instrument and the stratum boundary.

[0083] The aforementioned instrument structure and inversion method can obtain relatively accurate resistivity of different types of formations and reflect the distance between the instrument and the formation boundary, thus possessing formation detection capabilities.

[0084] Figure 5 The instrument is located in a 100 mm formation, probing a 1 ohm formation ahead, and the obtained compensation signal ( Figure 5 (a) Part) and its corresponding total apparent resistivity ( Figure 5 (b) Part. Figure 5 (a) Partially based on Figure 2 The model's observation signals are compensated, with blue, red, and green representing the compensated signals calculated when the distance between R2 and the boundary is 10, 20, and 30 m, respectively. Figure 5 (b) The apparent resistivity for the whole period is calculated based on the relationship between the compensation signal and the apparent resistivity. Blue, red and green represent the apparent resistivity for the whole period calculated based on the compensation signal when the distance between R2 and the boundary is 10, 20 and 30 m, respectively.

[0085] The beneficial effects of this invention are as follows:

[0086] This invention enables the detection of distant stratigraphic boundaries (up to 30m) with a relatively short source distance between the transmitting and receiving antennas (no more than 7m), while also reflecting the distance between the instrument and the stratigraphic boundary.

[0087] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0088] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A transient electromagnetic logging method while drilling, characterized in that, An application is made to a transient electromagnetic logging-while-drilling (TEMP) instrument, the TEMP instrument comprising a transmitting coil, a first receiving coil, and a second receiving coil, wherein a first source distance is provided between the transmitting coil and the first receiving coil, and a second source distance is provided between the transmitting coil and the second receiving coil; the method includes: The air layer observation signals of the first receiving coil and the second receiving coil are synchronously acquired in the air layer through the first receiving coil and the second receiving coil; A compensation coefficient that varies with time is calculated based on the ratio of the air layer observation signal of the second receiving coil to the air layer observation signal of the first receiving coil, so that the air layer compensation signal obtained by performing compensation operation on the air layer observation signal of the second receiving coil and the air layer observation signal of the first receiving coil based on the compensation coefficient is zero. During drilling, the formation observation signal of the first receiving coil and the formation observation signal of the second receiving coil are collected and synchronized through the first receiving coil and the second receiving coil, respectively. The formation-compensated signal is obtained by subtracting the compensation coefficient from the formation observation signal of the second receiving coil and multiplying it by the formation observation signal of the first receiving coil. A binary search is used to iterate within a preset apparent resistivity range. The calculated value of induced electromotive force is calculated based on the median apparent resistivity of the range and compared with the observed electromotive force corresponding to the formation compensation signal. If the accuracy condition is met, the apparent resistivity for the whole period is output. If the accuracy condition is not met, the apparent resistivity range is updated and iterated according to the monotonically decreasing characteristic of induced electromotive force. The formation resistivity is determined based on the change of apparent resistivity over time throughout the entire period, and the distance between the drilling transient electromagnetic logging instrument and the formation boundary is determined based on the moment when the curve of apparent resistivity over time begins to bifurcate.

2. The transient electromagnetic logging method while drilling according to claim 1, characterized in that, A compensation coefficient is calculated based on the ratio of the second receiving coil's air layer observation signal to the first receiving coil's air layer observation signal, varying over time. This ensures that the air layer compensation signal obtained by performing compensation operations on the second receiving coil's air layer observation signal and the first receiving coil's air layer observation signal based on the compensation coefficient is zero. This includes: Acquire the air layer observation signal of the second receiving coil and the air layer observation signal of the first receiving coil; An air layer compensation signal is constructed for air layer compensation calculation; the air layer compensation signal is equal to the second receiving coil air layer observation signal minus the compensation coefficient multiplied by the first receiving coil air layer observation signal; With the air layer compensation signal being zero as a constraint, the compensation coefficient is determined to be equal to the ratio of the air layer observation signal of the second receiving coil to the air layer observation signal of the first receiving coil; The process of determining the compensation coefficient is repeated at different time points to obtain the compensation coefficient that changes over time.

3. The transient electromagnetic logging method while drilling according to claim 1, characterized in that, The formation-compensated signal is obtained by subtracting the compensation coefficient from the formation observation signal of the second receiving coil and multiplying it by the formation observation signal of the first receiving coil, including: Acquire the formation observation signal from the second receiving coil and the formation observation signal from the first receiving coil; The compensation coefficient calculated in the air layer is invoked, and the compensation coefficient is made to correspond in time with the formation observation signal; Perform formation compensation calculation, wherein the formation compensation calculation is: subtract the compensation coefficient from the formation observation signal of the second receiving coil and multiply it by the formation observation signal of the first receiving coil; The result of the formation compensation calculation is output as the formation compensation signal.

4. The transient electromagnetic logging method while drilling according to claim 3, characterized in that, After obtaining the formation-compensated signal, the following is also included: Identify the influence components of the drill collar of the drilling transient electromagnetic logging instrument on the formation observation signals of the first receiving coil and the second receiving coil; The influencing components are suppressed or eliminated based on the formation compensation signal. The output signal, after eliminating the influencing components, corresponds to the field excited by the magnetic dipole.

5. The transient electromagnetic logging method while drilling according to claim 1, characterized in that, A binary search is used to iterate within a preset apparent resistivity interval. The induced electromotive force (EMF) is calculated based on the median apparent resistivity of the interval and compared with the observed EMF corresponding to the formation-compensated signal. When the accuracy condition is met, the apparent resistivity for the entire period is output, including: Set the minimum value and the maximum value of the preset apparent resistivity range; The preset apparent resistivity interval is divided into two equal parts to obtain the median apparent resistivity of the interval; The calculated value of the induced electromotive force is calculated based on the median apparent resistivity of the interval; The observed electromotive force is determined from the formation-compensated signal, and the calculated value of the induced electromotive force is compared with the observed electromotive force. When the calculated value of the induced electromotive force and the observed electromotive force satisfy the accuracy condition, the median apparent resistivity of the interval is output as the apparent resistivity for the entire period.

6. The transient electromagnetic logging method while drilling according to claim 1, characterized in that, When the accuracy condition is not met, the apparent resistivity range is updated and iterated based on the monotonically decreasing characteristic of the induced electromotive force, including: The preset apparent resistivity range is used as the initial range of the apparent resistivity range in the binary search, and the two endpoints of the apparent resistivity range are respectively used as the minimum value and the maximum value of the apparent resistivity range. When the calculated value of the induced electromotive force is greater than the observed electromotive force corresponding to the formation compensation signal, the apparent resistivity interval is updated to an interval consisting of the median apparent resistivity of the interval to the maximum value of the apparent resistivity interval. When the calculated value of the induced electromotive force is less than the observed electromotive force corresponding to the formation compensation signal, the apparent resistivity interval is updated to an interval consisting of the minimum value of the apparent resistivity interval to the median apparent resistivity of the interval. The updated apparent resistivity range is used as the preset apparent resistivity range for the next iteration, and the binary search iteration is repeated until the accuracy condition is met and the full-period apparent resistivity is output.

7. The transient electromagnetic logging method while drilling according to claim 1, characterized in that, The first source distance and the second source distance are both no greater than 7m.

8. The transient electromagnetic logging method while drilling according to claim 1, characterized in that, The length of the transient electromagnetic logging instrument while drilling is no more than 9m; the maximum distance between the transient electromagnetic logging instrument while drilling and the formation boundary is 30m.

9. The transient electromagnetic logging method while drilling according to claim 1, characterized in that, The step "during drilling, the formation observation signals of the first receiving coil and the second receiving coil are collected and synchronized to obtain the formation observation signals of the second receiving coil" is implemented under two formation conditions; the two formations include an upper formation and a lower formation, the resistivity of the upper formation is 50 Ω·m, and the resistivity of the lower formation is 1 Ω·m; the transient electromagnetic logging instrument is located in the upper formation; the first source distance is 5m, the second source distance is 7m; the distance between the second receiving coil and the formation boundary is 10m, 20m, or 30m.

10. The transient electromagnetic logging method while drilling according to claim 1, characterized in that, The step "determining the formation resistivity based on the change of apparent resistivity over time and determining the distance between the drilling transient electromagnetic logging instrument and the formation boundary based on the moment when the curve of apparent resistivity over time begins to bifurcate" is implemented under two formation conditions; the two formations include an upper formation and a lower formation, the resistivity of the upper formation is 10 Ω·m and the resistivity of the lower formation is 1 Ω·m; the resistivity of the upper formation and the resistivity of the lower formation are determined based on the change of apparent resistivity over time; when the distance between the second receiving coil and the formation boundary is different, the moment when the curve of apparent resistivity over time begins to bifurcate is different, and the moment when the bifurcation begins is used as the basis for determining the distance.

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