A method for predicting pore pressure of a formation ahead of a drill bit while drilling

Abstract

The application discloses a method for predicting formation pore pressure in front of a drill bit while drilling, which comprises collecting measured formation P-wave velocity and formation pore pressure data of adjacent wells, establishing a formation pore pressure calculation model, collecting while-drilling measurement P-wave velocity data and lithology data of a drilling well and setting a depth step length Δd, then identifying mudstone of a drilled well section of the drilling well, and segmenting along the depth at the depth step length Δd interval, fitting the relationship between mudstone P-wave velocity V i and depth d i of the Δd depth section where the drill bit is located, and further predicting mudstone velocity and formation pore pressure of the Δd depth section in front of the drill bit. The method disclosed by the application has a short implementation period and high efficiency, can realize continuous approximation and accurate prediction, and can iteratively realize continuous prediction of the formation pore pressure in front of the drill bit.

Description

Technical Field

[0001] The present invention relates to the technical field of formation pressure pre-monitoring, and more particularly to a method for predicting formation pore pressure ahead of a drill bit while drilling. Background Art

[0002] Formation pore pressure refers to the pressure exerted by the fluid in the porous medium of a formation. Under normal circumstances, formations are normally compacted, with pressure close to hydrostatic pressure. In Cenozoic basins, where sedimentation is rapid, the drainage efficiency of fine-grained sediments decreases with increasing depth, causing formation fluids to become trapped in the pores and partially bear the load of the overlying strata, resulting in abnormally high pressure. During oil and gas exploration in abnormally high-pressure formations, it is necessary to accurately predict the variation of formation pressure with depth to provide fundamental data for casing programming and mud performance optimization in drilling projects.

[0003] During the drilling process, the pressure of the drilled formation can be monitored in real time using logging while drilling, mud logging and drilling engineering parameters. At the same time, the pressure of the undrilled formation ahead of the drill bit needs to be predicted to prevent engineering risks caused by potential high pressure ahead of the drill bit.

[0004] Currently, the most common methods for predicting formation pressure ahead of the drill bit include mid-course VSP technology and pre-stack depth migration while drilling (PSDM). Mid-course VSP uses upgoing wavefield inversion from zero-bias VSP recordings to determine the formation velocity below the drill bit. PSDDM uses iterative processing of seismic pre-stack depth migration while drilling to determine the formation velocity below the drill bit. The formation pressure below the drill bit is then calculated based on the velocity-pressure relationship. However, both mid-course VSP and PSDDM suffer from long analysis cycles, low velocity accuracy, and low efficiency, making them unable to meet the requirements for efficient and safe drilling operations. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the existing mid-course VSP technology and pre-stack depth migration while drilling technology, which have long implementation cycle and low efficiency, and to provide a method for predicting the pore pressure of the formation ahead of the drill bit while drilling. The method can carry out continuous pore pressure prediction of the undrilled formation ahead of the drill bit during the drilling process, so as to achieve the purpose of continuously approximating and accurately predicting the pore pressure of the formation ahead of the drill bit.

[0006] The technical solution adopted in the present invention is:

[0007] A method for predicting the pore pressure of the formation ahead of the drill bit while drilling comprises the following steps:

[0008] Step S1: collecting formation compressional wave velocity and formation pore pressure data measured in adjacent wells and establishing a formation pore pressure calculation model;

[0009] Step S2, collecting the P-wave velocity data and lithology data of the well being drilled;

[0010] Step S3, setting the depth step Δd;

[0011] Step S4: Mudstone identification is performed on the drilled section of the well being drilled, and the section is segmented along the depth with the depth step Δd, and the longitudinal wave velocity V of the mudstone in the Δd depth section where the drill bit is located is fitted. i and depth d i relationship;

[0012] Step S5: The mudstone longitudinal wave velocity V fitted in step S4 is i and depth d i The relationship between the two is used to predict the mudstone velocity in the depth section Δd ahead of the drill bit.

[0013] Step S6: predicting the formation pore pressure at a depth of Δd ahead of the drill bit based on the formation pore pressure calculation model established in step S1;

[0014] Step S7: The well being drilled continues to be drilled to a new depth, and steps S2-S6 are iterated until the formation pore pressure while drilling prediction work is completed.

[0015] Furthermore, in step S1, the formation compressional wave velocity includes well logging compressional wave velocity.

[0016] Furthermore, in step S1, the formation compressional wave velocity may also include vertical seismic profile velocity.

[0017] Furthermore, in step S1, the formation pore pressure data includes formation pore pressure data directly measured by cable measurement or drill stem testing.

[0018] Furthermore, in step S1, the formation pore pressure calculation model is a functional relationship between formation velocity and formation pore pressure, and its expression is:

[0019]

[0020] Where P is the formation pore pressure,

[0021] V n is the P-wave velocity of the normally compacted formation,

[0022] V i is the actual measured formation P-wave velocity,

[0023] f is the regional experience coefficient.

[0024] Furthermore, in step S3, the depth step Δd is 5m-200m.

[0025] Furthermore, in step S4, mudstone in the drilled well section is identified based on the lithologic data collected in step S2.

[0026] Furthermore, as one of the solutions, in step S4, the mudstone longitudinal wave velocity V at the depth section Δd where the drill bit is located is i and depth d i The fitting relationship is expressed by a linear function, and its expression is:

[0027] V i =a×d i +b

[0028] Where a and b are fitting coefficients.

[0029] Furthermore, as another solution, in step S4, the mudstone longitudinal wave velocity V at the depth section Δd where the drill bit is located is i and depth d i The fitting relationship is expressed by a constant function, and its expression is:

[0030] V i =V c

[0031] Where V c is the average velocity of the mudstone P-wave velocity in the corresponding depth segment, which is a constant and has nothing to do with the depth.

[0032] Furthermore, in step S7, during the drilling process, the iteration may start from any new depth.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] Compared with existing mid-course VSP or pre-stack depth migration while drilling (PWD) techniques, the method disclosed in this invention offers a shorter implementation cycle, higher efficiency, and the ability to continuously approximate and accurately predict the pore pressure of the formation ahead of the drill bit. This method iteratively predicts the pore pressure of the formation ahead of the drill bit, enabling continuous pore pressure prediction of undrilled formations ahead of the drill bit during drilling. This allows for the timely detection of potential abnormally high pressures in the formation ahead of the drill bit, reducing drilling operation risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to the present invention;

[0036] Figure 2 A comparison chart of speed and pressure while drilling and before drilling in Example 1;

[0037] Figure 3 This is a schematic diagram of picking up the P-wave velocity of mudstone formation in Example 1;

[0038] Figure 4 Schematic diagram of the fitting of the longitudinal wave velocity of mudstone at a depth of 2300-2400 m above the drill bit in Example 1;

[0039] Figure 5 Schematic diagram of prediction of mudstone P-wave velocity and pore pressure at a depth of 2400-2500 m in Example 1;

[0040] Figure 6 Schematic diagram comparing the prediction scheme of formation pore pressure ahead of the drill bit based on mid-course VSP inversion and the one described in Example 1;

[0041] Figure 7 This is a schematic diagram of the prediction of mudstone P-wave velocity and pore pressure in the 2400-2450m depth section in Example 3. DETAILED DESCRIPTION

[0042] The present invention is further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only and are not to be construed as limiting this patent. Certain components in the accompanying drawings may be omitted, enlarged, or reduced in size to better illustrate the embodiments, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that certain well-known structures and their descriptions may be omitted from the accompanying drawings.

[0043] The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "front", "rear", "left", "right", etc. indicating an orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances. In addition, in the present invention, descriptions such as "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" or "second" can explicitly or implicitly include at least one such feature.

[0044] Example 1

[0045] This embodiment provides a method for predicting the formation pore pressure ahead of the drill bit while drilling. This embodiment is applied to Well No. 1, which is currently being drilled in the South China Sea. Well No. 1 is equipped with a while-drilling acoustic measurement tool starting from the 12-1 / 4" well section. Due to the deviation between the measured formation compressional wave velocity and the pre-drilling prediction result, the while-drilling monitoring formation pore pressure in the drilling section deviates from the pre-drilling designed formation pore pressure. Therefore, the method for predicting the formation pore pressure ahead of the drill bit while drilling described in this embodiment is applied.

[0046] See Figure 1 The method for predicting the pore pressure of the formation ahead of the drill bit while drilling comprises the following steps:

[0047] Step S1: Collect the measured formation compressional wave velocity and formation pore pressure data of adjacent wells and establish a formation pore pressure calculation model. Specifically, select wells with similar geological characteristics (i.e., adjacent wells) in the area where Well No. 1 is located and collect the logging compressional wave velocity V of these wells. j (i.e., the measured formation compressional wave velocity) and cable pressure data P M (i.e. the formation pore pressure data), select the well logging P-wave velocity V corresponding to the mudstone section in the normal pressure section of the drilled well j The polynomial regression method is used to calculate the P-wave velocity V of the normally compacted formation in the area where Well No. 1 is located. N ;

[0048] Calculate the logging compressional wave velocity V j The longitudinal wave velocity V of the normal compacted layer in the region N The speed difference, that is (V N -V j );

[0049] The cable pressure measurement data P M The speed difference (V N -V j ) is fitted to obtain the formation pore pressure calculation model of the area where Well No. 1 is located. The formation pore pressure calculation model is a functional relationship between formation velocity and formation pore pressure, and its expression is:

[0050]

[0051] Where P is the formation pore pressure,

[0052] V n is the longitudinal wave velocity of the normal compacted formation, i.e., V in this embodiment N ,

[0053] V i is the actual measured formation compressional wave velocity, i.e., V in this embodiment. j ,

[0054] f is the regional empirical coefficient. In the South China Sea region where Well No. 1 is located, the value of f ranges from 1000 to 2500.

[0055] Step S2: collecting the longitudinal wave velocity data and lithology data of the well being drilled. Specifically, the lithology data is the gamma curve data of Well No. 1;

[0056] See Figure 2 as well as Figure 3 At a drilling depth of 2400 m, the measured P-wave velocity deviated from the pre-drilling prediction. The formation pore pressure monitored while drilling also deviated from the pre-drilling prediction. It was necessary to predict the pore pressure of the undrilled formation ahead of the drill bit. The following steps were then performed to guide the optimization of the drilling mud density:

[0057] Step S3, set the depth step Δd to 100m; at the same time, according to the gamma curve data, obtain the following Figure 3 The curve of the longitudinal wave velocity of mudstone in the drilled section changes with depth is shown;

[0058] Step S4: Figure 4 As shown in the figure, the drilled section of the well being drilled is segmented along the depth with the depth step Δd, that is, the depth section of 2300-2400m above the drill bit is selected, and the mudstone longitudinal wave velocity V in the depth section Δd where the drill bit is located is fitted. i and depth d i relationship,

[0059] The fitting results are:

[0060] a=1 / 4.63, b=13156 / 4.63,

[0061] Right now

[0062] Step S5, refer to Figure 5 , according to the mudstone longitudinal wave velocity V fitted in step S4 i and depth d i The relationship between the velocity and the velocity of the mudstone in the Δd depth section ahead of the drill bit (i.e., the depth section of 2400-2500 m) is predicted;

[0063] Step S6: predicting the formation pore pressure in the depth section Δd ahead of the drill bit (i.e., the depth section of 2400-2500 m) based on the formation pore pressure calculation model established in step S1;

[0064] Step S7: Continue drilling to 2500 m and iterate steps S2-S6 to continuously predict the P-wave velocity and pore pressure of the mudstone formation at a depth of 100 m ahead of the drill bit until the pore pressure while drilling prediction is completed.

[0065] Comparative Example

[0066] In the No. 1 well, the existing mid-course VSP inversion technology was also applied, such as Figure 6 As shown in the figure, mid-course VSP inversion was used to obtain the formation P-wave velocity at depths of 2400-3000 m ahead of the drill bit and to predict the formation pore pressure at the corresponding depths. It can be seen that mid-course VSP inversion is limited by engineering conditions and can only be measured a limited number of times. Furthermore, VSP inversion is affected by the quality of seismic data, resulting in large fluctuations in the inverted formation P-wave velocity and the corresponding predicted formation pore pressure.

[0067] The method for predicting the formation pore pressure ahead of the drill bit while drilling disclosed in this embodiment is not restricted by engineering conditions. As the drill bit depth increases, the amount of formation compressional wave velocity data measured while drilling increases, allowing for continuous iteration of the implementation process, continuously predicting the formation compressional wave velocity ahead of the drill bit and the corresponding formation pore pressure. The predicted velocity and pressure are close to the actual measured formation compressional wave velocity and monitored formation pore pressure after drilling through the formation.

[0068] Example 2

[0069] The method for predicting the formation pore pressure ahead of the drill bit while drilling provided in this embodiment is applied to Well No. 2 currently being drilled in the South China Sea. Well No. 2 is equipped with a while drilling acoustic wave measurement tool starting from the 12-1 / 4" well section.

[0070] The difference between this embodiment and the first embodiment is that the measured formation compressional wave velocity and formation pore pressure data of the adjacent wells collected in step S1 are different. That is, when one specific formation data (such as well logging compressional wave velocity) cannot be obtained, this method can also establish the formation pore pressure calculation model by obtaining another type of formation data (such as vertical seismic profile velocity).

[0071] Specifically, in this embodiment, the method for predicting the pore pressure of the formation ahead of the drill bit while drilling includes the following steps:

[0072] Step S1: Collect the measured formation compressional wave velocity and formation pore pressure data of adjacent wells and establish a formation pore pressure calculation model. Specifically, select wells with similar geological characteristics (i.e., adjacent wells) in the area where Well No. 2 is located and collect the vertical seismic profile velocity V of these wells. k (i.e. the measured formation compressional wave velocity) and the formation pore pressure data P directly measured by drill stem testing N (i.e., drill pipe pressure measurement data), select the vertical seismic profile velocity V corresponding to the mudstone section in the normal pressure section of the drilled well k The polynomial regression method is used to calculate the P-wave velocity V of the normally compacted formation in the area where Well No. 2 is located. N ;

[0073] Calculate the vertical seismic profile velocity V k The longitudinal wave velocity V of the normal compacted layer in the region N The speed difference, that is (V N -V k );

[0074] The drill pipe pressure data P N The speed difference (V N -V k ) is fitted to obtain the formation pore pressure calculation model of the area where Well No. 2 is located. The formation pore pressure calculation model is a functional relationship between formation velocity and formation pore pressure, and its expression is:

[0075]

[0076] Where P is the formation pore pressure,

[0077] V n is the longitudinal wave velocity of the normal compacted formation, i.e., V in this embodiment N ,

[0078] V i is the actual measured formation compressional wave velocity, i.e., V in this embodiment. k ,

[0079] f is the regional empirical coefficient. In the South China Sea region where Well No. 2 is located, the value of f ranges from 1000 to 2500.

[0080] Step S2: collecting the P-wave velocity data and lithology data of the well being drilled. Specifically, the lithology data is the gamma curve data of Well No. 2.

[0081] At a drilling depth of 2400 m, the measured P-wave velocity deviated from the pre-drilling prediction. The formation pore pressure monitored while drilling also deviated from the pre-drilling prediction. The pore pressure of the undrilled formation ahead of the drill bit needed to be predicted. The following steps were then performed to guide the optimization of the drilling mud density:

[0082] Step S3: setting the depth step length Δd to 100 m; and obtaining a curve of the longitudinal wave velocity of the mudstone in the drilled section varying with depth based on the gamma curve data;

[0083] Step S4: Mudstone identification is performed on the drilled section of the well being drilled. The mudstone identification of the drilled section is based on the lithologic data collected in step S2 and is segmented along the depth with the depth step Δd, that is, the depth section of 2300-2400m above the drill bit is selected, and the longitudinal wave velocity V of the mudstone in the depth section Δd where the drill bit is located is fitted. i and depth d i relationship,

[0084] Fitting

[0085] Step S5: The mudstone longitudinal wave velocity V fitted in step S4 is i and depth d i The relationship between the velocity and the velocity of the mudstone in the Δd depth section ahead of the drill bit (i.e., the depth section of 2400-2500 m) is predicted;

[0086] Step S6: predicting the formation pore pressure in the depth section Δd ahead of the drill bit (i.e., the depth section of 2400-2500 m) based on the formation pore pressure calculation model established in step S1;

[0087] Step S7: The wellbore continues drilling to 2500 m, and steps S2-S6 are iterated to continuously predict the P-wave velocity and formation pore pressure of the mudstone formation at a depth of 100 m ahead of the drill bit until the formation pore pressure while drilling prediction is completed. Of course, it should be noted that during continued drilling of the wellbore, the iterations can be started from any new depth, not limited to 2300 m, 2400 m, or 2500 m disclosed in this embodiment.

[0088] Example 3

[0089] The method for predicting the formation pore pressure ahead of the drill bit while drilling provided in this embodiment is applied to Well No. 3 currently being drilled in the South China Sea. Well No. 3 is equipped with a while drilling acoustic wave measurement tool starting from the 12-1 / 4" well section.

[0090] The method for predicting the pore pressure of the formation ahead of the drill bit while drilling comprises the following steps:

[0091] Step S1: Collect the measured formation compressional wave velocity and formation pore pressure data of adjacent wells and establish a formation pore pressure calculation model. Specifically, select wells with similar geological characteristics (i.e., adjacent wells) in the area where Well No. 3 is located and collect the vertical seismic profile velocity V of these wells. k (i.e. the measured formation compressional wave velocity) and the formation pore pressure data P directly measured by drill stem testing N (i.e., drill pipe pressure measurement data), select the vertical seismic profile velocity V corresponding to the mudstone section in the normal pressure section of the drilled well k The polynomial regression method is used to calculate the P-wave velocity V of the normally compacted formation in the area where Well No. 3 is located. N ;

[0092] Calculate the vertical seismic profile velocity V k The longitudinal wave velocity V of the normal compacted layer in the region N The speed difference, that is (V N -V k );

[0093] The drill pipe pressure data P N The speed difference (V N -V k ) is fitted to obtain the formation pore pressure calculation model of the area where Well No. 3 is located. The formation pore pressure calculation model is a functional relationship between formation velocity and formation pore pressure, and its expression is:

[0094]

[0095] Where P is the formation pore pressure,

[0096] V n is the longitudinal wave velocity of the normal compacted formation, i.e., V in this embodiment N ,

[0097] V i is the actual measured formation compressional wave velocity, i.e., V in this embodiment. k ,

[0098] f is the regional empirical coefficient. In the South China Sea region where Well No. 3 is located, the value of f ranges from 1000 to 2500.

[0099] Step S2: collecting the P-wave velocity data and lithology data of the well being drilled. Specifically, the lithology data is the gamma curve data of Well No. 3.

[0100] At a drilling depth of 2400 m, the measured P-wave velocity deviated from the pre-drilling prediction. The formation pore pressure monitored while drilling also deviated from the pre-drilling prediction. The pore pressure of the undrilled formation ahead of the drill bit needed to be predicted. The following steps were then performed to guide the optimization of the drilling mud density:

[0101] Step S3: setting the depth step length Δd to 50 m; and at the same time, obtaining a curve of the longitudinal wave velocity of the mudstone in the drilled section varying with depth based on the gamma curve data;

[0102] Step S4: Mudstone identification is performed on the drilled section of the well being drilled. The mudstone identification of the drilled section is based on the lithologic data collected in step S2 and is segmented along the depth with the depth step Δd interval. That is, the depth section of 2350-2400m above the drill bit is selected, and the average longitudinal wave velocity of the mudstone in this section is 3350m / s, that is, V c =3350m / s,

[0103] The average value of the mudstone P-wave velocity is assigned to the depth section of 2400-2450 m to obtain V i =V c =3350m / s;

[0104] Step S5, according to the mudstone P-wave velocity V fitted in step S4 i The mudstone velocity in the depth section Δd ahead of the drill bit (i.e. the depth section 2400-2450m) is constant, i.e. 3350m / s;

[0105] Step S6, referring to Figure 7 According to the formation pore pressure calculation model established in step S1, the formation pore pressure in the depth section Δd ahead of the drill bit (i.e. the depth section 2400-2450m) is predicted.

[0106] Step S7, the well drilling continues to drill to 2450m, and the steps S2-S6 are iterated to realize the continuous prediction of the mudstone formation P-wave velocity and the formation pore pressure in the depth section 50m ahead of the drill bit until the work of the formation pore pressure prediction while drilling is finished.

[0107] Of course, in some other embodiments, the set depth step Δd can also be any value in 5m, 10m, 20m, 50m, 100m, 150m or 200m, or any value in the range of 5-200m.

[0108] In the specific content of the above specific embodiments, any technical features can be combined without contradiction, and in order to make the description brief, all possible combinations of the above technical features are not described, however, as long as the combination of the technical features does not exist contradiction, it should be considered as the scope of the present disclosure.

[0109] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made. Here, it is not necessary and also impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for predicting the pore pressure of the formation ahead of the drill bit while drilling, characterized in that: The following steps are involved: Step S1: Collect the measured formation compressional wave velocity and formation pore pressure data of adjacent wells and establish a formation pore pressure calculation model. The formation pore pressure calculation model is a functional relationship between the measured formation compressional wave velocity and the formation pore pressure, and its expression is: Where, P is the formation pore pressure, V n is the P-wave velocity of the normally compacted formation, V i To measure the formation compressional wave velocity, is the regional experience coefficient; Step S2, collecting the P-wave velocity data and lithology data of the well being drilled; Step S3, setting the depth step Δd; Step S4: identify the mudstone in the drilled section of the well being drilled, and segment it along the depth with the depth step Δd, and fit the mudstone longitudinal wave velocity in the Δd depth section where the drill bit is located. V is and depth d i relationship; Step S5: The longitudinal wave velocity of the mudstone fitted in step S4 V is and depth d i The relationship between the two is used to predict the mudstone velocity in the depth section Δd ahead of the drill bit. Step S6: predicting the formation pore pressure at a depth of Δd ahead of the drill bit based on the formation pore pressure calculation model established in step S1; Step S7: The well being drilled continues to be drilled to a new depth, and steps S2-S6 are iterated until the formation pore pressure while drilling prediction work is completed.

2. The method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to claim 1, characterized in that: In step S1, the formation compressional wave velocity includes well logging compressional wave velocity.

3. The method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to claim 1, characterized in that: In step S1, the formation compressional wave velocity includes vertical seismic profile velocity.

4. The method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to claim 1, characterized in that: In step S1, the formation pore pressure data includes formation pore pressure data measured by cable measurement or directly measured by drill stem testing.

5. The method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to claim 1, characterized in that: In step S3, the depth step Δd is 5m-200m.

6. The method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to claim 1, characterized in that: In step S4, mudstone in the drilled well section is identified based on the lithologic data collected in step S2.

7. The method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to claim 1, characterized in that: In step S4, the longitudinal wave velocity of the mudstone in the Δd depth section where the drill bit is located is V is and depth d i The fitting relationship is expressed by a linear function, and its expression is: Where a and b are fitting coefficients.

8. The method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to claim 1, characterized in that: In step S4, the longitudinal wave velocity of the mudstone in the Δd depth section where the drill bit is located is V is and depth d i The fitting relationship is expressed by a constant function, and its expression is: Where, V c is the average velocity of the mudstone P-wave velocity in the corresponding depth segment, which is a constant and has nothing to do with the depth.

9. The method for predicting the pore pressure of the formation ahead of the drill bit while drilling according to claim 1, characterized in that: In step S7, while the well is being drilled, the iteration may be started from any new depth.

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