Method for predicting top surface burial depth of ancient submerged mountain while drilling

Abstract

The invention belongs to the technical field of seismic exploration, and discloses a method for predicting the burial depth of the top surface of a palaeosubmerged mountain while drilling, which comprises the following steps: selecting a first seismic marker bed and a second seismic marker bed on the top surface of the palaeosubmerged mountain, and determining a third seismic marker bed on the top surface of the palaeosubmerged mountain; and calibrating the first seismic marker bed and the second seismic marker bed by using the acoustic logging data while drilling, and solving the velocity of the acoustic layer. Seismic reflection time distance curves of well passing points of the first seismic marker layer and the second seismic marker layer are obtained, and the first seismic layer velocity is solved. And calculating a velocity correction value according to the sound wave layer velocity and the first seismic layer velocity. And obtaining a seismic reflection time distance curve of well passing points of the third seismic marker layer and the second seismic marker layer, and solving the velocity of the second seismic layer. And correcting the second seismic horizon velocity by using the velocity correction value to obtain a third seismic horizon velocity, and predicting the top surface burial depth of the ancient diving mountain. According to the method, the speed correction value is obtained through acoustic logging while drilling to correct the layer speed, and the top surface burial depth of the ancient diving mountain can be accurately predicted.

Description

Technical Field

[0001] The present invention belongs to the technical field of seismic exploration. Specifically, the present invention relates to a method for predicting the buried depth of the paleo-buried hill top while drilling. Background Art

[0002] During the drilling construction process, in order to optimize the wellbore structure design, timely adjust the mud density design, ensure the smooth implementation of the drilling and completion project, improve the drilling efficiency, and reduce the drilling engineering risk, it is necessary to know in real time the distance between the bit buried depth point and the paleo-buried hill top, so as to modify the drilling operation plan and adjust the wellbore structure accordingly.

[0003] In the prior art, the prediction of the buried depth of the paleo-buried hill top before drilling mainly adopts the average velocity prediction method, that is, the buried depth of the paleo-buried hill top is calculated according to the regional average velocity or the time-depth conversion relationship and the two-way travel time of the seismic reflection event of the paleo-buried hill top. Due to the heterogeneity of the underground formation, the regional average velocity or the time-depth conversion relationship is applicable to the statistical data of the corresponding area. Using it for the average velocity or time-depth conversion relationship of a certain point underground has certain errors.

[0004] In addition, in the prior art, the seismic layer velocity method is usually used to calculate the distance between the bit buried depth point and the paleo-buried hill top. Specifically, it includes: determining the two-way travel time corresponding to the bit buried depth point and the two-way travel time corresponding to the paleo-buried hill top on the seismic section, then picking up the corresponding stacking velocities on the seismic stacking velocity spectrum according to the two two-way travel times, respectively performing dip correction and then converting the two stacking velocities into two root-mean-square velocities, using the Dix formula to calculate the layer velocity between the bit buried depth point and the paleo-buried hill top, and finally calculating the distance between the bit buried depth point and the paleo-buried hill top according to the layer velocity and the travel time difference between the bit buried depth point and the paleo-buried hill top. In this process, the root-mean-square velocity obtained through the seismic velocity spectrum itself has certain errors. Further, due to the error amplification effect of the Dix formula itself, the calculation error is amplified in the process from the root-mean-square velocity to the layer velocity, resulting in a further increase in the deviation of the buried depth of the paleo-buried hill top.

[0005] It can be seen that whether using the regional average velocity method or the method of calculating the seismic layer velocity by the Dix formula, there is a certain error between the predicted buried depth of the paleo-buried hill top and the actual buried depth of the paleo-buried hill top. If referring to the data with large errors, the drilling speed, mud density and other drilling plans cannot be adjusted in time, which may bring systematic hazards to the drilling engineering operation.

[0006] In view of this, there is an urgent need to provide a method for accurately predicting the buried depth of the paleo-buried hill top while drilling, so as to improve the prediction accuracy of the buried depth of the paleo-buried hill top and provide data guarantee for the drilling construction. Summary of the Invention

[0007] In order to solve at least one or more of the above-mentioned technical problems, the present invention provides a method for predicting the buried depth of the paleo-buried hill top while drilling, including: the first step, obtaining a post-stack seismic profile, selecting a first seismic marker bed and a second seismic marker bed penetrated by a well above the paleo-buried hill top, and determining a third seismic marker bed of the paleo-buried hill top; the second step, calibrating the first seismic marker bed and the second seismic marker bed by using the while-drilling acoustic logging data, determining the distance and time difference between the first seismic marker bed and the second seismic marker bed, and obtaining the acoustic layer velocity; the third step, obtaining the seismic reflection travel-time curve of the well points passing through the first seismic marker bed and the second seismic marker bed, and obtaining the first seismic layer velocity between the first seismic marker bed and the second seismic marker bed; the fourth step, obtaining a velocity correction value according to the acoustic layer velocity and the first seismic layer velocity; the fifth step, obtaining the seismic reflection travel-time curve of the well points passing through the third seismic marker bed and the second seismic marker bed, and obtaining the second seismic layer velocity between the third seismic marker bed and the second seismic marker bed; the sixth step, correcting the second seismic layer velocity by using the velocity correction value to obtain the third seismic layer velocity, and predicting the buried depth of the paleo-buried hill top by using the third seismic layer velocity.

[0008] According to an embodiment of the present invention, the first seismic marker bed and the second seismic marker bed are located above the bit buried depth point.

[0009] According to an embodiment of the present invention, in the second step, the time difference is determined by using the acoustic logging data or read on the post-stack seismic profile.

[0010] According to an embodiment of the present invention, in the third step, multiple points of the seismic reflection travel-time curve are taken, and the first seismic layer velocity is calculated by using the travel-time curve equation and Dix formula.

[0011] According to an embodiment of the present invention, in the fourth step, the velocity correction amount is the difference between the acoustic layer velocity and the first seismic layer velocity.

[0012] According to an embodiment of the present invention, in the third step, the velocity correction amount is the ratio of the acoustic layer velocity to the first seismic layer velocity.

[0013] According to an embodiment of the present invention, the paleo-buried hill top is identified on the post-stack seismic profile through seismic reflection unconformity interfaces and seismic reflection characteristics.

[0014] According to an embodiment of the present invention, the first step to the fourth step are repeated to obtain multiple velocity correction values; the mean value of the multiple velocity correction values is taken as the final velocity correction value; and the second seismic layer velocity is corrected by using the final velocity correction value.

[0015] According to an embodiment of the present invention, the seismic reflection travel-time curve of the well point is taken from the common receiver gather constrained by the dip angle of the well point.

[0016] According to an embodiment of the present invention, the second seismic marker bed is closer to the third seismic marker bed than the first seismic marker bed.

[0017] In the present invention, by selecting two seismic marker beds penetrated by wells above the top surface of the buried hill, and calculating the interval velocity between the two seismic marker beds using seismic data and logging data respectively, the interval velocity error obtained from the seismic data can be accurately obtained as the velocity correction value. By correcting the interval velocity between the second seismic marker bed and the top surface of the buried hill with the velocity correction value, a relatively accurate third seismic interval velocity can be obtained, so that the burial depth of the top surface of the buried hill can be accurately predicted using the third seismic interval velocity. By calculating the root-mean-square velocity at multiple points on the seismic reflection travel-time curve, the stability of the root-mean-square velocity can be improved. By repeatedly selecting different first seismic marker beds and second seismic marker beds to obtain the velocity correction value, a relatively accurate velocity correction value can be obtained, so as to accurately predict the burial depth of the top surface of the buried hill. By selecting the first seismic marker bed and the second seismic marker bed closest to the third seismic marker bed, the error of the second seismic interval velocity can be reduced, and the accuracy of predicting the burial depth of the top surface of the buried hill can be further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood. In the drawings, several embodiments of the present invention are shown by way of illustration and not limitation, and like or corresponding reference numerals indicate like or corresponding parts, wherein:

[0019] Figure 1 shows a schematic diagram of a 3D seismic exploration system;

[0020] Figure 2 shows a schematic diagram of the steps of a method for predicting the burial depth of the top surface of the buried hill while drilling;

[0021] Figure 3 shows a schematic diagram of a post-stack seismic profile;

[0022] Figure 4 shows a schematic diagram of calibrating a post-stack seismic profile using a logging curve;

[0023] Figure 5 shows a schematic diagram of a gather passing through a well point. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] It should be understood that the terms "comprising" and "including" used in the specification and claims of the present invention indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0026] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification and claims of the present invention, unless otherwise clearly specified in the context, the singular forms "a", "an", and "the" are intended to include the plural forms. It should be further understood that the term "and / or" used in the specification and claims of the present invention refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0027] Figure 1 A schematic diagram of a three-dimensional seismic exploration system is shown.

[0028] As Figure 1 shown, in the system 100, a plurality of mutually spaced geophones 110 for detecting seismic waves are arranged on the surface 101 of the exploration target area, forming a geophone array that covers the target area in a plane. These geophones 110 are connected to the seismic information processing device by wired or wireless means, and a plurality of seismic sources 120 are also provided. The seismic information processing device can perform preliminary processing on seismic data. The working process of the three-dimensional seismic exploration system is as follows: The seismic sources 120 located at multiple positions are artificially excited to generate seismic waves. The seismic waves are reflected from the boundary of the formation 102 and received by the geophone array, forming seismic information collected in a plane and varying with time. The seismic information received by the geophone array represents certain measures of the seismic wave energy as a function of time, such as displacement, velocity, wave impedance, pressure, etc. These information can be grouped in different ways, such as traces, gathers, etc., and then processed or format-converted according to the corresponding relationship of time and space to form a three-dimensional seismic data volume in the form of a three-dimensional array. It can also be said that this three-dimensional seismic data volume is formed by stacking interface points in space. The interpretation of the three-dimensional seismic data volume can observe the morphology of the geological interface from different directions and study the changes of the geological body in three-dimensional space by cutting transverse sections, longitudinal sections, and horizontal slices.

[0029] Figure 2 The schematic diagram of the steps of the method for predicting the buried depth of the paleo-buried hill top while drilling is shown.

[0030] Figure 3 The schematic diagram of the post-stack seismic profile is shown.

[0031] As Figure 2 shown, a method for predicting the buried depth of the paleo-buried hill top while drilling includes: the first step S201, obtaining a post-stack seismic profile, selecting a first seismic marker bed and a second seismic marker bed above the paleo-buried hill top, and determining a third seismic marker bed of the paleo-buried hill top; the second step S202, calibrating the first seismic marker bed and the second seismic marker bed by using the while-drilling acoustic logging data, determining the distance and time difference between the first seismic marker bed and the second seismic marker bed, and obtaining the acoustic layer velocity; the third step S203, obtaining the seismic reflection travel-time curve of the well points passing through the first seismic marker bed and the second seismic marker bed, and obtaining the first seismic layer velocity between the first seismic marker bed and the second seismic marker bed; the fourth step S204, obtaining the velocity correction value according to the acoustic layer velocity and the first seismic layer velocity; the fifth step S205, obtaining the seismic reflection travel-time curve of the well points passing through the third seismic marker bed and the second seismic marker bed, and obtaining the second seismic layer velocity between the third seismic marker bed and the second seismic marker bed; the sixth step S206, correcting the second seismic layer velocity by using the velocity correction value to obtain the third seismic layer velocity, and predicting the buried depth of the paleo-buried hill top by using the third seismic layer velocity.

[0032] The while-drilling seismic technology is a technology that combines the information related to drilling such as the formation depth and velocity updated in real time during the drilling process, updates the velocity and geological model to realize the prediction in front of the drill bit, and thus guides the drilling process. The solution of the present invention belongs to the application of the seismic data analysis method in the while-drilling seismic technology.

[0033] The post-stack seismic profile refers to the seismic profile formed after processing the seismic profile of the drilling area that has been obtained by denoising, gain adjustment, waveform extraction, etc., to further improve the data quality, and the post-stack processing can be carried out by using the existing technology.

[0034] In the first step, as Figure 3As shown in the figure, on the seismic profile 300, with the well 301 as a reference, two seismic marker horizons passing through the well are arbitrarily selected, namely the first seismic marker horizon 311 and the second seismic marker horizon 312. A seismic marker horizon refers to a rock layer with obvious and stable waveform characteristics that can be continuously traced in most areas within the region and has obvious characteristics that can be used as a formation correlation marker. Among them, both the first seismic marker horizon 311 and the second seismic marker horizon 312 are penetrated by the well 301, and the first seismic marker horizon 311 and the second seismic marker horizon 312 are located above the bit depth point. The top surface of the buried hill is used as the third seismic marker horizon 313, which is the target horizon whose buried depth needs to be predicted. The top surface of the buried hill is identified on the post-stack seismic profile through the seismic reflection unconformity interface and seismic reflection characteristics, that is, the onlap surface is determined through the break point of the seismic reflection event in the seismic reflection characteristics, and the position and scope of the top surface of the buried hill are determined using the seismic reflection unconformity interface.

[0035] Figure 4 The figure shows a schematic diagram of calibrating a post-stack seismic profile using well logging curves.

[0036] In the second step, the acoustic logging-while-drilling data refers to the well logging curves obtained by acoustic logging. By corresponding the well logging data with the first seismic marker horizon and the second seismic marker horizon on the seismic profile, the depth of the first seismic marker horizon and the depth of the second marker horizon, as well as the acoustic time difference between the two, are determined. In addition, the time difference between the first seismic marker horizon and the second seismic marker horizon can also be directly read on the seismic profile, that is, the time difference is determined using the acoustic logging data or read on the post-stack seismic profile. When used to calculate the acoustic layer velocity between two seismic marker horizons, the time difference obtained by acoustic logging is more accurate than the time difference read from the seismic profile. When the difference between the two time differences is small, the two can also be used interchangeably. The acoustic layer velocity is the quotient of the distance between the first seismic marker horizon and the second seismic marker horizon and the time difference.

[0037] As Figure 4 shown, in the calibrated seismic profile 400, the well 301 is the theoretical drilling trajectory, and the oblique line deviating from the theoretical drilling trajectory on its side is the actual well 302. The well logging curve 410 of the actual well 302 is used to calibrate the actual well and the seismic profile, so that the first seismic marker horizon 311 and the second seismic marker horizon 312 correspond to the mutations in the well logging curve 410, so that the distance and time difference between the two can be accurately read.

[0038] In the third step, the seismic reflection traveltime curves of the first seismic marker horizon and the second seismic marker horizon at the well penetration points are taken from the gather data at the well penetration points, that is, the seismic reflection traveltime curves at the well penetration points are taken from the common receiver gather constrained by the dip angle at the well penetration points. For example, the super gather data (CRP) constrained by the dip angle at the well penetration points, and the super gather refers to the gather formed by acquiring seismic traces in multiple azimuths.

[0039] Figure 5 A schematic diagram showing a gather of cross-well points is presented.

[0040] As Figure 5 shown, the two-way travel time 511 of the first seismic marker bed is 1070 ms, the two-way travel time 512 of the second seismic marker bed is 1350 ms, and the two-way travel time 513 of the third seismic marker bed is 2550 ms. Seismic reflection travel-time curves with vertices located at the two-way travel time 511 of the first seismic marker bed and the two-way travel time 512 of the second seismic marker bed are obtained from the gather data 500 respectively. Two root-mean-square velocities are obtained according to the travel-time curve equation, and then the first seismic layer velocity between the first seismic marker bed and the second seismic marker bed is calculated using Dix formula.

[0041] Specifically, using the travel-time curve equation: where t represents time, x represents offset, and v represents velocity. Multiple points are taken on the seismic reflection travel-time curve, and multiple root-mean-square velocity values corresponding to the first seismic marker bed and the second seismic marker bed are calculated using the travel-time curve equation. The mean value of the multiple root-mean-square velocity values is obtained to get the seismic root-mean-square velocities of the first seismic marker bed and the second seismic marker bed respectively.

[0042] The Dix formula is: Also known as the Dix formula. That is, the layer velocity of the nth layer is equal to the two-way travel time of the nth layer multiplied by the square of the root-mean-square velocity of the nth layer and then subtract the two-way travel time of the (n - 1)th layer multiplied by the square of the root-mean-square velocity of the (n - 1)th layer and finally divide by the difference between the two-way travel times of the nth layer and the (n - 1)th layer.

[0043] Through the above formula, the layer velocity between the first seismic marker bed and the second seismic marker bed, that is, the first seismic layer velocity, can be calculated.

[0044] In the fourth step, a velocity correction value is obtained according to the acoustic wave layer velocity and the first seismic layer velocity. Specifically, the difference between the two can be obtained, or the ratio of the two can be calculated, or the mean square error of the two can be calculated, etc. to obtain the correction value. Preferably, the velocity correction amount is the difference between the acoustic wave layer velocity and the first seismic layer velocity. Preferably, the velocity correction amount is the ratio of the acoustic wave layer velocity to the first seismic layer velocity.

[0045] In the fifth step, seismic reflection travel-time curves of the well points where the third seismic marker horizon and the second seismic marker horizon cross are respectively obtained from the gather data 500. That is, a seismic reflection travel-time curve with the two-way travel time 513 of the vertex located at the third seismic marker horizon is obtained on the seismic gather 500. Since the drilling has not extended to the third seismic marker horizon, the well point where the third seismic marker horizon crosses refers to the intersection point of the extension line of the third marker horizon and the well. Similarly, the interval velocity between the second seismic marker horizon and the third seismic marker horizon, i.e., the second seismic interval velocity, is calculated using the Dix formula.

[0046] Optionally, in this step, the interval velocity between the third seismic marker horizon and the first seismic marker horizon can be selected for calculation. When the second seismic marker horizon is closer to the third seismic marker horizon than the first seismic marker horizon, it is preferred to calculate the interval velocity between the third seismic marker horizon and the second seismic marker horizon, because the distance between them is relatively close, which can further reduce the velocity error.

[0047] In the sixth step, the second seismic interval velocity is corrected using the velocity correction value. When the velocity correction value is the difference between the acoustic interval velocity and the first seismic interval velocity, the second seismic interval velocity is summed with the velocity correction value to obtain the third seismic interval velocity. When the velocity correction value is the ratio of the acoustic interval velocity to the first seismic interval velocity, the second seismic interval velocity is multiplied by the velocity correction value to obtain the third seismic interval velocity. And so on, the second seismic interval velocity can be corrected to a more accurate value.

[0048] By multiplying the third seismic interval velocity by the time difference between the third seismic marker horizon and the second seismic marker horizon, the interval between them can be obtained. Summing this interval with the depth of the second seismic marker horizon gives the burial depth of the buried hill. Further, by taking the difference between the burial depth of the buried hill and the depth point of the drill bit, the distance from the drill bit to the top surface of the buried hill can be obtained.

[0049] Preferably, in order to further determine the velocity correction value, the first step to the fourth step can be repeated to obtain multiple velocity correction values; the mean value of the multiple velocity correction values is taken as the final velocity correction value; and the second seismic interval velocity is corrected using the final velocity correction value.

[0050] When repeating the first step to the fourth step, different first seismic marker horizons and second seismic marker horizons are respectively selected for the calculation of the velocity correction value. Preferably, the first seismic marker horizon and the second seismic marker horizon closest to the third seismic marker horizon are selected.

[0051] In the present invention, two seismic marker beds penetrated by wells are selected above the top surface of the buried hill. The interval velocity is calculated between the two seismic marker beds by using seismic data and logging data respectively, and the interval velocity error obtained from the seismic data can be accurately obtained as the velocity correction value. By correcting the interval velocity between the first seismic marker bed and the top surface of the buried hill with the velocity correction value, a relatively accurate third seismic interval velocity can be obtained, and thus the burial depth of the top surface of the buried hill can be accurately predicted by using the third seismic interval velocity. By calculating the root-mean-square velocity at multiple points on the seismic reflection travel-time curve, the stability of the root-mean-square velocity can be improved. By repeatedly selecting different first seismic marker beds and second seismic marker beds to obtain the velocity correction value, a relatively accurate velocity correction value can be obtained, and thus the burial depth of the top surface of the buried hill can be accurately predicted. By selecting the first seismic marker bed and the second seismic marker bed closest to the third seismic marker bed, the error of the second seismic interval velocity can be reduced, and the accuracy of predicting the burial depth of the top surface of the buried hill can be further improved.

[0052] Although several embodiments of the present invention have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many variations, changes, and alternative approaches may occur to those skilled in the art without departing from the spirit and scope of the present invention. It should be understood that various alternatives to the embodiments of the present invention described herein may be employed in practicing the present invention. The appended claims are intended to define the scope of the present invention and thus cover equivalents or alternatives within the scope of these claims.

Claims

1. A method for predicting the depth of the top of an ancient buried mountain while drilling, characterized in that: include: The first step is to obtain a post-stack seismic profile, select the first seismic marker layer and the second seismic marker layer penetrated by the well above the top of the ancient buried mountain, and determine the third seismic marker layer on the top of the ancient buried mountain; The second step is to calibrate the first seismic marker layer and the second seismic marker layer using the while drilling sonic logging data, determine the distance and time difference between the first seismic marker layer and the second seismic marker layer, and obtain the sonic layer velocity; The third step is to obtain the seismic reflection time-distance curve of the first seismic marker layer and the second seismic marker layer passing through the well point, and obtain the velocity of the first seismic layer between the first seismic marker layer and the second seismic marker layer; The fourth step is to obtain a velocity correction value according to the acoustic layer velocity and the first seismic layer velocity; The fifth step is to obtain the seismic reflection time-distance curve of the third seismic marker layer and the second seismic marker layer passing through the well point, and obtain the velocity of the second seismic layer between the third seismic marker layer and the second seismic marker layer; The sixth step is to use the velocity correction value to correct the second seismic layer velocity to obtain a third seismic layer velocity, and use the third seismic layer velocity to predict the burial depth of the ancient buried mountain top.

2. The method according to claim 1, characterized in that The first seismic marker layer and the second seismic marker layer are located above the drill bit burial depth point.

3. The method according to claim 1, characterized in that: In the second step, the time difference is determined using sonic logging data or read on a post-stack seismic section.

4. The method according to claim 1, characterized in that: In the third step, multiple points of the seismic reflection time-distance curve are taken, and the first seismic layer velocity is calculated using the time-distance curve equation and Dick's formula.

5. The method according to claim 1, characterized in that In the fourth step, the velocity correction amount is the difference between the acoustic layer velocity and the first seismic layer velocity.

6. The method according to claim 1, characterized in that In the third step, the velocity correction amount is the ratio of the acoustic layer velocity to the first seismic layer velocity.

7. The method according to claim 1, characterized in that In the first step, the top of the ancient buried mountain is identified by the seismic reflection discontinuity interface and seismic reflection characteristics on the post-stack seismic section.

8. The method according to claim 1, characterized in that Also includes: Repeat the first step to the fourth step to obtain multiple speed correction values; Taking the average of multiple speed correction values ​​as the final speed correction value; The second seismic layer velocity is corrected using the final velocity correction value.

9. The method according to claim 1, characterized in that: The seismic reflection time-distance curve passing through the well point is taken from the common receiving point gather constrained by the inclination angle of the well point.

10. The method according to claim 1, characterized in that The second seismic marker layer is closer to the third seismic marker layer than the first seismic marker layer.

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