A method of depth migration while drilling based on horizontal well trajectory

Abstract

The present invention relates to a method for depth migration while drilling based on a horizontal well trajectory, belonging to the field of seismic velocity modeling and imaging technology. The specific steps are as follows: determining two control points on the well trajectory, namely the first control point and the second control point; loading the well information of the first control point and the second control point; calculating the well-seismic difference at each control point and obtaining the anisotropy parameter δ; interpolating and extrapolating the δ values ​​of the first control point and the second control point to the entire target area; setting the anisotropy parameter ε; and calculating the vertical velocity V. an ; Update the model depth according to the "travel time remains unchanged" principle; Generate anisotropy field; Input δ, ε and V into GeoEast software an Perform anisotropic prestack depth migration processing and check whether the anisotropic prestack depth migration profile meets the requirements of horizontal well drilling. This solves the problem of low imaging accuracy at the boundaries of the seismic work area and significantly improves the well-seismic consistency rate at the boundaries.

Description

Technical Field

[0001] The invention relates to a while-drilling depth migration method based on a horizontal well trajectory, and belongs to the technical field of seismic velocity modeling and imaging. Background Art

[0002] Migration is the final step in seismic data processing and is also the most important and critical process, especially for complex subsurface media. Migration processing methods are divided into two categories: one is performed on the basis of stacking, known as post-stack migration; the other is performed before stacking, known as pre-stack migration. During the seismic imaging stage, to obtain more subsurface wavefield information, the migration aperture is often larger than 5000 meters. However, the data collected at the boundaries of the seismic work area is limited and cannot meet the input data requirements of the migration aperture. This leads to a significant decrease in the accuracy of migration imaging at the boundaries of the work area and a significant reduction in the well-seismic agreement rate. Summary of the Invention

[0003] In order to solve the above-mentioned problems existing in the prior art, the present invention discloses a method for while-drilling depth migration based on horizontal well trajectory, which uses horizontal well trajectory information to perform while-drilling depth migration processing, solves the problem of low imaging accuracy at the boundary of the seismic work area, and can provide reliable seismic data for on-site horizontal well drilling.

[0004] The technical solution adopted by the present invention is: a method for depth migration while drilling based on horizontal well trajectory, the specific steps are as follows:

[0005] Step 1: Investigate the boundary of the work area and the consistency between well and seismic data, and determine two control points on the well trajectory, namely the first control point and the second control point;

[0006] Step 2: Load the well information of the first control point and the second control point;

[0007] Step 3: Expand the boundary of the survey area in step 1 based on the horizontal well drilling situation to form the target area for depth-while-drilling migration processing. Calculate the wellbore-seismic difference at each control point to obtain the anisotropy parameter δ. Interpolate and extrapolate the δ values ​​of the first and second control points to the entire target area.

[0008] Step 4: Set the anisotropy parameter ε: ε = k * δ, where k is the scale factor and the value range of k is 0.6 to 1.4. The specific value needs to be tested according to the imaging effect;

[0009] Step 5: Calculate vertical velocity: According to the formula Calculate vertical velocity (anisotropic velocity) V an , where V0 is the isotropic velocity;

[0010] Step 6: Update the model depth according to the principle of "travel time remains unchanged": Among them D is The profile depth when isotropic, D an The depth of the section when it is anisotropic; the model refers to: picking up the layers of the strong reflection strata on the section, and forming a three-dimensional figure by interpolation and extrapolation in three-dimensional space, which is called a geological model, or simply a model;

[0011] Step 7: Generate anisotropy field, including δ, ε and V an Three types of anisotropic fields.

[0012] Step 8: Input δ, ε and V into GeoEast software an Perform anisotropic prestack depth migration processing;

[0013] Step 9: Check whether the anisotropic prestack depth migration profile meets the requirements for horizontal well drilling. If so, output the results. Otherwise, return to step 3 to recalculate the wellbore-seismic difference and complete subsequent processing until the requirements for horizontal well drilling are met.

[0014] Furthermore, in step 1, the first control point and the second control point are k1 and k2 respectively, wherein k1 is the point with the smallest absolute value of the well-seismic difference in the well trajectory direction, and k2 is the point with the largest absolute value of the well-seismic difference in the well trajectory direction.

[0015] Furthermore, the well-seismic difference is the difference between the depth in the well trajectory direction and the seismic event depth.

[0016] Furthermore, in step 2, the loaded data includes well head information, well layer data and well depth data.

[0017] Furthermore, the distance in step 3 is expanded to 5000 meters.

[0018] Furthermore, in step 3, the anisotropy parameter δ is given by the formula Calculated, where H t is the earthquake thickness, H w is the well layer thickness.

[0019] Furthermore, in step 9, the actual drilling requirement is that the maximum difference between the seismic depth and the well trajectory depth is no more than 10 meters.

[0020] The present invention discloses a method for while-drilling depth migration based on horizontal well trajectories. Its beneficial effect is that it utilizes horizontal well trajectory information for while-drilling depth migration processing, resolving the issue of low imaging accuracy at seismic work area boundaries and significantly improving the well-to-seismic consistency at these boundaries. While-drilling depth migration based on horizontal well trajectories eliminates the persistent problem of insufficient data for work area boundary migration, significantly improving the well-to-seismic consistency at the end of the horizontal well. This invention enables the timely application of drilling information, enabling the efficient acquisition of small-scale while-drilling migration results. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Figure 1 Shown is a flow chart of the present invention;

[0023] Figure 2 Shown is a diagram of drilling information data in an embodiment of the present invention;

[0024] Figure 3 Shown is a distribution diagram of δ values ​​according to an embodiment of the present invention;

[0025] Figure 4 The figure shows a seismic profile along the trajectory of the H1-2 well before the present invention is applied;

[0026] Figure 5 Shown is a seismic profile along the H1-2 well trajectory after applying the present invention;

[0027] Figure 6 The figure shows the seismic profile and error statistics along the Z well trajectory before the present invention is applied;

[0028] Figure 7 Shown is the seismic profile along the z-well trajectory and the error statistics diagram after applying the present invention. Specific implementation methods

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0030] In order to further understand the content of the present invention, the present invention is further described below in conjunction with specific implementation methods.

[0031] Example 1:

[0032] like Figures 1 to 7 As shown in FIG, a method for depth migration while drilling based on horizontal well trajectory is shown, and the specific steps are as follows:

[0033] Preparatory work before implementation: Perform isotropic depth migration according to depth-domain velocity modeling, model optimization, and pre-stack depth migration sequence of the data volume; Select existing known wells in the work area and perform anisotropic pre-stack depth migration, generating first-phase results and providing them to the drilling frontline; Statistical analysis of well trajectory and well-seismic coincidence rate of horizontal wells is conducted on site and fed back to the back-end processing center;

[0034] Step 1: Based on the feedback, the processing center promptly analyzes the boundary of the seismic work area and the well-seismic consistency rate, and determines two control points on the well trajectory: the first control point k1 (point 4 in the figure, whose well depth is 5736) and the second control point k2 (point 5 in the figure, whose well depth is 6320). The first control point k1 is the point with the smallest absolute value of the well-seismic difference in the direction of the well trajectory, and the second control point k2 is the point with the largest absolute value of the well-seismic difference in the direction of the well trajectory. The well-seismic difference is the difference between the well depth and the seismic event depth.

[0035] Step 2: If Figure 2 As shown, the well information of the first control point and the second control point is loaded, including the well measurement information MD, vertical depth TVD and vertical depth above sea level TVDSS;

[0036] Step 3: Expand the boundary of the survey area in step 1 by 5000 meters in all directions according to the horizontal well drilling situation to obtain more underground wave field information and form the target area for depth migration while drilling. Calculate the well-seismic difference at each control point and obtain the anisotropy parameter δ. Interpolate and extrapolate the δ values ​​of the first and second control points to the δ values ​​of the entire target area. The δ distribution is shown in the figure below. Figure 3 As shown in the figure, the physical meaning and calculation method of δ are explained as follows: δ is one of the anisotropy parameters, which describes the error between the depth of the event axis in the stacked section and the depth of the well. From the performance of the seismic stacked section and the CIP gather, the role of δ is to adjust the depth of the event axis to correct the well-seismic difference. The anisotropy parameter δ is given by the formula Calculated, where H t is the earthquake thickness, H w is the well layer thickness.

[0037] Step 4: Set the anisotropy parameter ε: ε = k * δ, where k is the scale factor and the value of k is 1; ε is one of the anisotropy parameters, which describes the anisotropic characteristics of the formation and is used to correct the curvature of the CIP gather event axis and improve the focusing and continuity of the event axis.

[0038] Step 5: Calculate vertical velocity: Calculate vertical velocity according to the layer velocity of the new anisotropic property correction model. The model here refers to: picking up the layers of strong reflection strata on the profile, and forming a three-dimensional figure by interpolation and extrapolation in three-dimensional space, which is called a geological model, or simply model. The model formed by picking up layers in the time domain is defined as a time domain model; the model formed by picking up layers in the depth domain is defined as a depth domain model. The present invention uses a time domain model. Assume that the initial velocity (isotropic velocity) is V0 and the anisotropic velocity is V an , the relationship between the two is:

[0039] Step 6: Update the model depth according to the principle of "travel time remains unchanged": Among them D is The profile depth when isotropic, D an The depth of the section when it is anisotropic; the model refers to: picking up the layers of the strong reflection strata on the section, and forming a three-dimensional figure by interpolation and extrapolation in three-dimensional space, which is called a geological model, or simply a model;

[0040] Step 7: Generate anisotropy field, including δ, ε and V an Three types of anisotropic fields.

[0041] Step 8: Input δ, ε and V into GeoEast software an Perform anisotropic prestack depth migration processing;

[0042] Step 9: Check whether the anisotropic prestack depth migration profile meets the horizontal well drilling requirement. The drilling requirement is that the maximum difference between the seismic depth and the well trajectory depth is no more than 10 meters. If it meets the requirement, output the result; otherwise, return to step (3) to recalculate the well-seismic difference and complete the subsequent processing until the horizontal well drilling requirement is met.

[0043] The present invention is used to quickly carry out a small-scale while-drilling migration process, which generally takes about 3 days to obtain the second-stage while-drilling depth migration results. Figure 4 and 5 By comparison, it can be seen that the seismic tilt directions between control points k1 and k2 are different, the well-seismic agreement is better, and the imaging accuracy is improved. Figure 6 、 Figure 7 The following are the profiles along the z-well trajectory and the error statistics before and after the application of the present invention, Figure 6 The maximum absolute error of the well-seismic difference is -13.8 meters; Figure 7The maximum absolute error of the well-seismic difference was -4 meters. Comparison revealed that the present invention significantly improved the well-seismic agreement rate for Well Z. The results of the second phase were applied to guide horizontal well drilling in other lateral wells. Because the laterals of the platform wells are closely spaced, the present invention can rapidly support the successful drilling of other laterals, demonstrating the integration of frontline and backline exploration, geophysical exploration, and engineering.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for depth migration while drilling based on horizontal well trajectory, comprising the following steps: Step 1: Investigate the boundary of the work area and the consistency between well and seismic data, and determine two control points on the well trajectory, namely the first control point and the second control point; Step 2: Load the well information of the first control point and the second control point; Step 3: Expand the boundary of the survey area in step 1 based on the horizontal well drilling situation to form the target area for depth-while-drilling migration processing. Calculate the wellbore-seismic difference at each control point to obtain the anisotropy parameter δ. Interpolate and extrapolate the δ values ​​of the first and second control points to the entire target area. Step 4: Set the anisotropy parameter ε: ε = k * δ, where k is the scaling factor and the value range of k is 0.6 to 1.4; Step 5: Calculate vertical velocity: According to the formula Calculate the vertical velocity V an , where V0 is the isotropic velocity; Step 6: Update the model depth according to the "travel time remains unchanged" principle: Among them D is The profile depth when isotropic, D an The depth of the section when it is anisotropic; the model refers to: picking up the layers of the strong reflection strata on the section, and forming a three-dimensional figure by interpolation and extrapolation in three-dimensional space, which is called a geological model, or simply a model; Step 7: Generate anisotropy field, including δ, ε and V an Three types of anisotropy fields; Step 8: Input δ, ε and V into GeoEast software an Perform anisotropic prestack depth migration processing; Step 9: Check whether the anisotropic prestack depth migration profile meets the requirements for horizontal well drilling. If so, output the results. Otherwise, return to step 3 to recalculate the wellbore-seismic difference and complete subsequent processing until the requirements for horizontal well drilling are met.

2. The method for depth migration while drilling based on horizontal well trajectory according to claim 1, characterized in that: In step 1, the first control point and the second control point are k1 and k2 respectively, where k1 is the point with the smallest absolute value of the well-seismic difference in the well trajectory direction, and k2 is the point with the largest absolute value of the well-seismic difference in the well trajectory direction.

3. The method for depth migration while drilling based on horizontal well trajectory according to claim 2, characterized in that: The well-seismic difference is the difference between the well depth and the seismic event depth.

4. The method for depth migration while drilling based on horizontal well trajectory according to claim 1, characterized in that: In step 2, the loaded data includes well head information, well layer data and well depth data.

5. The method for depth migration while drilling based on horizontal well trajectory according to claim 1, characterized in that: In step 3, the distance is expanded to 5000 meters.

6. The method for depth migration while drilling based on horizontal well trajectory according to claim 1, characterized in that: In step 3, the anisotropy parameter δ is given by the formula Calculated, where H t is the earthquake thickness, H w is the well layer thickness.

7. The method for depth migration while drilling based on horizontal well trajectory according to claim 1, characterized in that: In step 9, the actual drilling requirement is that the maximum difference between the seismic depth and the well trajectory depth is no more than 10 meters.

8. The method for depth migration while drilling based on horizontal well trajectory according to claim 1, characterized in that: In step 4, the value range of k is 1.

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