Drilling-while-drilling depth migration method based on horizontal well track

Abstract

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. The method comprises the following specific steps: determining two control points, namely a first control point and a second control point, on a well trajectory; loading well information of the first control point and the second control point; calculating the well seismic difference at each control point, and solving an anisotropy parameter delta; interpolating and extrapolating the delta values of the first control point and the second control point to the whole target area; setting an anisotropic parameter epsilon; calculating a vertical velocity Van; updating the depth of the model according to a principle of keeping travel time unchanged; generating an anisotropic field; delta, epsilon and Van are input into GeoEast software for anisotropic pre-stack depth migration processing; and checking whether the anisotropic pre-stack depth migration profile meets the actual drilling requirements of the horizontal well or not. The problem of low imaging precision at the boundary of the earthquake work area is solved, and the well earthquake coincidence rate at the boundary is greatly improved.

Description

Technical Field

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

[0002] Migration is the last step in seismic data processing, and it is also the most important and critical process, especially for complex underground media. Migration processing methods are divided into two categories: one is based on stacking, called post-stack migration; the other is performed before stacking, called pre-stack migration. In the seismic imaging stage, in order to obtain more underground wave field information, the migration aperture is often above 5,000 meters; however, the data collected at the boundary of the seismic work area is limited and cannot meet the input data requirements of the migration aperture, resulting in a significant decrease in the accuracy of migration imaging at the boundary of the work area, and a significant decrease in the well-seismic coincidence 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 the 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, and the specific steps are as follows:

[0005] Step 1: Investigate the boundary range of the work area and the coincidence of 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 range of the survey area in step 1 to all sides according to the horizontal well drilling situation to form the target area for while-drilling depth migration processing; calculate the well-seismic difference at each control point to obtain the anisotropy parameter δ; interpolate and extrapolate the δ values ​​of the first control point and the second control point 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 the vertical velocity (anisotropic velocity) V an , where V0 is the isotropic velocity;

[0010] Step 6: Update the model depth according to the "travel time remains unchanged" principle: Where D is When the profile is isotropic, D an is the profile depth when it is anisotropic; the model refers to: picking up the layers of the 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 model for short;

[0011] Step 7: Generate anisotropy field, including δ, ε and V an Three types of anisotropy 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 well-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 depth of the seismic event axis.

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

[0017] Furthermore, the distance expanded in step 3 is 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 The thickness of the well layer.

[0019] Furthermore, in step 9, the actual drilling requirement is that the maximum value of the 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 trajectory, which has the beneficial effect of using horizontal well trajectory information to perform while-drilling depth migration processing, solving the problem of low imaging accuracy at the boundary of the seismic work area, and greatly improving the well-seismic consistency rate at the boundary. The while-drilling depth migration based on the horizontal well trajectory eliminates the stubborn problem of insufficient data volume for the boundary migration of the work area, and the well-seismic consistency of the last section of the horizontal well is significantly improved. The invention can apply drilling information in a timely manner, obtain a small range of while-drilling migration results, and has high efficiency. 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative labor.

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

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

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

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

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

[0027] Figure 6 The seismic profile and error statistics along the z-well trajectory before the present invention is applied are shown;

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

[0029] Specific implementation methods

[0030] 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 by no means 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 creative work are within the scope of protection of the present invention.

[0031] In order to further understand the content of the present invention, the present invention is further described below in conjunction with specific implementation methods. Embodiment 1:

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

[0033] Preparation work before implementation; perform isotropic depth migration processing according to the depth domain velocity modeling, model optimization and data volume pre-stack depth migration sequence; select the existing known wells in the work area, perform anisotropic pre-stack depth migration processing, and form the first-stage results to provide to the drilling frontline; conduct statistics on well trajectory and well-seismic coincidence rate information on the horizontal well site, and feed it back to the back-line processing center;

[0034] Step 1: The processing center promptly conducts seismic work area boundary analysis and well-seismic consistency analysis based on the feedback, and determines two control points on the well trajectory, namely the first control point k1 (i.e., point 4 in the figure, whose well sounding is 5736) and the second control point k2 (i.e., point 5 in the figure, whose well sounding 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 axis 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, the vertical depth TVD and the vertical depth TVDSS above sea level;

[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 while drilling depth migration processing; 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 distribution of δ is shown in the figure. 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 The thickness of the well layer.

[0037] Step 4: Set the anisotropy parameter ε: ε = k*δ, where k is the proportional 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 attribute correction model. The model here refers to: the three-dimensional figure formed by interpolating and extrapolating the layers of strong reflection strata picked up on the profile in three-dimensional space 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 "travel time remains unchanged" principle: Where D is When the profile is isotropic, D an is the profile depth when it is anisotropic; the model refers to: picking up the layers of the 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 model for short;

[0040] Step 7: Generate anisotropy field, including δ, ε and V an Three types of anisotropy 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 requirements. The actual drilling requirement is that the maximum difference between the seismic depth and the well trajectory depth is no more than 10 meters. If the requirement is met, output the results; otherwise, return to step (3) to recalculate the well-seismic difference and complete the subsequent processing until the horizontal well drilling requirements are 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-k2 are different, the well-seismic consistency is better, and the imaging accuracy is improved. Figure 6 , Figure 7 They 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 was -13.8 meters; Figure 7The maximum absolute error of the well-seismic difference was -4 meters. After comparison, it was found that the invention significantly improved the well-seismic coincidence rate of the z well; the results of the second phase were used to guide the horizontal well drilling of other branch wells. Since the branches of the platform wells are close to each other, the invention results can quickly support the successful drilling of other branches, which is an important embodiment of the integration of the front and back lines, 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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 range of the work area and the coincidence of 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 range of the survey area in step 1 to all sides according to the horizontal well drilling situation to form the target area for while-drilling depth migration processing; calculate the well-seismic difference at each control point to obtain the anisotropy parameter δ; interpolate and extrapolate the δ values ​​of the first control point and the second control point to the entire target area; 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; 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: Where D is When the profile is isotropic, D an is the profile depth when it is anisotropic; the model refers to: picking up the layers of the 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 model for short; 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 well-seismic difference and complete subsequent processing until the requirements for horizontal well drilling are met.

2. A 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, 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.

3. A 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 wellhead 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 The thickness of the well layer.

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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