Virtual vsp well logging calibration for turning wave velocity depth migration method

Abstract

The present application provides a kind of virtual VSP logging calibration rotary wave velocity depth migration method, which comprises the following steps: step 1, isotropic rotary wave ray TOMO inversion is carried out;Step 2, establish the initial velocity model of depth migration;Step 3, iterative update of migration velocity is carried out;Step 4, select one or more control points in the work area of virtual VSP velocity curve;Step 5, calculate the reasonable calibration coefficient according to the geological conditions of work area;Step 6, the original shallow TOMO velocity is calibrated as a whole by calibration coefficient;Step 7, establish a new overall migration velocity model.The virtual VSP logging calibration rotary wave velocity depth migration method is more stable than VSP constrained TOMO inversion, and in the area without VSP well, the velocity curve updated by depth migration reflection wave velocity analysis is used instead of VSP curve, and the TOMO velocity can still be calibrated by using these virtual VSP curves.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oilfield development, and particularly relates to a virtual VSP logging calibration turning wave velocity depth migration method. BACKGROUND

[0002] In the complex piedmont zone of the western region, the surface relief and surface structure change greatly. Due to the influence of the surface, near-surface and complex underground geological conditions, various interference waves develop in the low signal-to-noise ratio area, especially in the mountainous area. The quality of the seismic data is poor, and in particular, the shallow seismic reflection events are missing or unclear, which seriously affects the shallow velocity modeling and updating of the next depth migration.

[0003] The current feasible method is to use the turning wave ray tomography of the first arrival walk time of the big gun to obtain the shallow velocity required by the depth migration, and combine the velocity converted from the root mean square (RMS) velocity of the deep layer to form an overall depth migration velocity model. However, due to the factors such as near-surface anisotropy, stratum absorption Q value and error of the tomography numerical algorithm, the velocity obtained by the isotropic shallow tomographic inversion algorithm is often higher than the true velocity of the stratum. The inaccurate shallow velocity not only affects the shallow migration imaging effect, but also has a direct impact on the imaging of the middle and deep layers.

[0004] The inaccurate shallow turning wave tomographic inversion velocity can be constrained by the VSP or micro-logging velocity curve to perform tomographic inversion, but the well-constrained inversion is easy to form a "bull's eye" phenomenon with a significant difference from the surrounding velocity near the well. In addition, in some areas, there is no VSP well data, and the micro-logging (or small refraction) record is often very shallow, usually tens to hundreds of meters, which can only control the very shallow layer of the TOMO inversion, and has little improvement on the overall TOMO velocity, and is easy to appear the phenomenon of inversion of the controlled shallow layer and the lower layer velocity.

[0005] The current more feasible method is to directly calibrate the unconstrained inversion TOMO result by using the VSP velocity, refer to the VSP velocity curve and the corresponding TOMO velocity at the same point, set different calibration coefficients for the shallow low velocity drop zone and the deep layer, so that the calibrated TOMO velocity at this point is as close as possible to the real VSP stratum velocity, and then apply the same calibration coefficient to the TOMO velocity below the surface. If there are multiple VSP wells in the work area, the lateral variation of the calibration can also be considered. In this way, the calibrated TOMO velocity is closer to the real stratum velocity as a whole.

[0006] In the complex piedmont zone of western region, the signal-to-noise ratio of seismic data is low, and the shallow seismic events are missing or unclear. For the shallow velocity modeling of depth migration, the turning wave ray tomography of the first arrival of the big gun is generally used to provide, but due to the anisotropy of the near-surface, the absorption Q value of the stratum and the error of the tomography numerical algorithm, the velocity obtained by the isotropic shallow tomographic inversion algorithm is often higher than the true velocity of the stratum.

[0007] The inaccurate velocity can be calibrated by the VSP velocity curve to improve the tomography, so that the overall high TOMO velocity is corrected to be closer to the true stratum velocity, which has achieved good results in practical application. However, in some areas, there is no VSP record, and the micro-logging or small refraction record is too shallow.

[0008] In the Chinese patent application with the application number: CN202010502973.0, a method and device for establishing a horizontal variable velocity layer velocity model by zero offset VSP are involved, the method comprises the following steps: S1. Based on the input data, a zero offset VSP corridor fine calibration overwell seismic section is realized; S2. The best calibrated time difference is used to shift the overwell seismic section, and several main seismic reflection time horizons are picked up from shallow to deep, and the time horizon array is saved; S3. The seismic reflection time horizon is refined into a thin layer by linear interpolation, and the time domain layer velocity model is obtained by filling the zero offset VSP layer velocity along the thin layer; S4. The time-depth relationship of each trace of the time domain layer velocity model is calculated, the time domain is converted to the depth domain, and the depth domain velocity model is obtained after gridding.

[0009] In the Chinese patent application with the application number: CN201410085309.5, a sonic logging curve correction method based on VSP data is involved, the method comprises: correcting the sonic logging curve to the same reference surface according to the time-depth relationship of the first arrival of the VSP data; correcting the time-depth relationship of the sonic logging curve for each layer in the target layer section by using the VSP data, calculating the time difference between the time-depth relationship point of the VSP data and the time-depth relationship point of the sonic logging curve; calculating the average value of the time difference of the time-depth relationship point of each layer of the VSP data and the sonic logging curve; stretching the sonic logging curve by the average value of the time difference; adjusting the sonic velocity value, and obtaining the corrected sonic logging curve when the average layer velocity of the sonic logging curve is consistent with the average layer velocity of the VSP data.

[0010] In the Chinese patent application with the application number CN201310585459.8, a seismic horizon calibration method using vertical seismic profile and well logging is related. The longitudinal wave time-depth relationship and corridor stack profile are obtained according to zero well source distance data, the sonic logging and density logging data are obtained, the time difference is calculated by sonic time-depth relationship and VSP time-depth relationship, the sonic curve is corrected, the corrected well logging curve is convolved with seismic wavelet to obtain a synthetic record, the time shift amount of VSP corridor and correct polarity are determined, and the horizon calibration map is made, and the horizon calibration is performed on the surface seismic profile according to the known drilling geological layering.

[0011] The above prior art is quite different from the present application, and cannot solve the technical problems we want to solve. Therefore, we have invented a new virtual VSP logging calibration turning wave velocity depth migration method. SUMMARY

[0012] The purpose of the present application is to provide a virtual VSP logging calibration turning wave velocity depth migration method using virtual VSP velocity curve to recalibrate the TOMO velocity of shallow layer.

[0013] The purpose of the present application can be achieved by the following technical measures: the virtual VSP logging calibration turning wave velocity depth migration method comprises:

[0014] Step 1, isotropic turning wave ray TOMO inversion is performed;

[0015] Step 2, an initial velocity model for depth migration is established;

[0016] Step 3, iterative updating of migration velocity is performed;

[0017] Step 4, the virtual VSP velocity curve of one or more control points in the work area is selected;

[0018] Step 5, a reasonable calibration coefficient is calculated according to the geological conditions of the work area;

[0019] Step 6, the original shallow layer TOMO velocity is calibrated as a whole by the calibration coefficient;

[0020] Step 7, a new overall migration velocity model is established.

[0021] The purpose of the present application can also be achieved by the following technical measures:

[0022] In step 1, isotropic turning wave ray TOMO inversion is performed by using the picked up shot first arrival time.

[0023] In step 2, the shallow TOMO velocity and the layer velocity converted from the time-processed RMS velocity are combined into an overall depth migration initial velocity model.

[0024] In step 3, select areas with good in-phase shaft quality and use reflected waves to iteratively update the offset velocity only in these areas.

[0025] In step 4, the velocity curves in these areas are optimized by checking the quality of shallow layer stacking and whether the common imaging point gather is flattened. Furthermore, good velocity curves are selected to ensure that the velocity curves are as close as possible to the actual formation velocity. These selected velocity curves are used as virtual VSP curves.

[0026] In step 4, based on the lateral variation of shallow velocity, virtual VSP velocity curves of one or more control points within the work area are flexibly selected to calibrate laterally constant or variable velocities. The number of control points should be minimized to keep the calibrated TOMO velocities as simple as possible, which is beneficial for subsequent velocity updates.

[0027] In step 5, before calibration, the virtual VSP record and the TOMO velocity elevation must be kept consistent. At each control point, a reasonable calibration coefficient is calculated using the relationship between the virtual VSP velocity curve and the corresponding TOMO chromatography velocity, so that the calibrated TOMO chromatography velocity is as close as possible to the virtual VSP velocity curve at that point.

[0028] In step 5, two calibration coefficients are used for the shallow low-velocity zone and the deep zone (below 300 meters), which can also be adjusted as needed; the weight of the calibration coefficients is determined according to the different lithologies of the work area.

[0029] In step 5, if both non-conglomerate and conglomerate areas exist, the non-conglomerate area will dominate.

[0030] In step 5, when the lateral speed variation in a region is significant, multiple control points are set to ensure that the calibration coefficient also varies laterally, thus adapting to the lateral speed variation.

[0031] In step 6, the calibration coefficients calculated in step 5 are used to calibrate the original shallow TOMO velocity volume, and the virtual VSP velocity curves at the control points are used to make the calibrated overall shallow TOMO velocity volume close to the actual formation velocity.

[0032] In step 7, the calibrated shallow rotating wave TOMO velocity model is combined with the deep time-processed RMS conversion layer velocity to form a new overall migration velocity model, which is then provided for the next round of depth migration and reflection wave velocity updates.

[0033] The innovative aspect of the virtual VSP logging calibration rotary wave velocity-depth offset method in this invention lies in:

[0034] (1) Using (virtual) VSP velocity curve to calibrate the turning wave TOMO result directly, it is usually more stable than VSP constrained TOMO inversion, and the "bull's eye" phenomenon of constrained inversion does not appear.

[0035] (2) In the area without VSP logging data, in one or more control points with good quality seismic data and clear reflection event, the virtual VSP velocity curve is obtained by using the depth migration reflection velocity update, and the shallow layer TOMO velocity is recalibrated by using the virtual VSP velocity curve.

[0036] (3) According to the trend of the lateral variation of the shallow layer velocity, one or more control points can be selected to adjust the lateral invariability or variation of the calibration coefficient. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The flow chart of a specific embodiment of the virtual VSP logging calibration turning wave velocity depth migration method of the present application;

[0038] Figure 2 The schematic diagram of common imaging point gathers used in the depth migration reflection velocity analysis of a specific embodiment of the present application;

[0039] Figure 3 The schematic diagram of the position of the finally selected virtual VSP on the plane elevation map of the working area in a specific embodiment of the present application;

[0040] Figure 4 The schematic diagram of the initial TOMO velocity curve, the virtual logging curve and the calibrated TOMO velocity curve at the position of the virtual logging in a specific embodiment of the present application;

[0041] Figure 5 The calibration coefficient curve diagram at the position of the virtual VSP well in a specific embodiment of the present application. DETAILED DESCRIPTION

[0042] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0043] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments consistent with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, and / or groups thereof.

[0044] In some locations of depth migration velocity analysis, the reflection event quality is good, and after the reflection wave velocity is updated, the common imaging point gathers are relatively flat and the stack quality is good. The depth migration reflection wave updated velocity curve of these location points is taken as a virtual VSP velocity curve to recalibrate the turning wave TOMO velocity, so as to provide the depth migration to do velocity analysis and migration imaging again. The TOMO velocity calibrated by the virtual VSP velocity curve is closer to the real formation velocity than the uncalibrated TOMO velocity, and the effect is obvious especially for the place where the shallow reflection event is unclear and the depth migration reflection velocity updating cannot be carried out.

[0045] The present application is aimed at the double complex seismic work area without VSP well, and the virtual VSP record obtained by the migration reflection wave velocity analysis is used to recalibrate the turning wave TOMO velocity, comprising the following steps:

[0046] (1) The isotropic turning wave ray TOMO inversion of the shallow layer is carried out by using the picked up shot first arrival time.

[0047] (2) The shallow turning wave TOMO velocity is combined with the depth migration initial velocity model of the whole layer velocity converted from the deep time processing root mean square (RMS) velocity.

[0048] (3) The seismic data quality of the double complex area is poor, and the reflection event of the shallow layer position is missing or unclear in many places, so it is difficult to update the whole migration velocity iteratively by using the reflection wave. We can select some places with good event quality to update the migration velocity of these places iteratively by using the reflection wave.

[0049] (4) The velocity curve of these places is optimized by the quality inspection of the shallow stack and whether the common imaging point gathers are flattened or not, and the good velocity curve is further selected to ensure that the velocity curve is as close to the real formation velocity as possible. The selected velocity curve can be taken as a virtual VSP curve, and the virtual VSP velocity curve of one or more control points in the work area can be selected flexibly according to the lateral variation of the shallow velocity to carry out the lateral constant or variable velocity calibration. In principle, the control points are as few as possible to make the calibrated TOMO velocity as simple as possible, which is beneficial to the further velocity updating.

[0050] (5) Before calibration, keep the virtual VSP record consistent with the TOMO velocity elevation, and calculate a reasonable calibration coefficient at each control point by using the relationship between the virtual VSP velocity curve and the corresponding TOMO tomographic velocity, so that the TOMO tomographic velocity after calibration is as close as possible to the virtual VSP velocity curve at the point. Generally, two calibration coefficients are used for the shallow low velocity zone and the deep layer (300 meters below), and they can also be adjusted according to the situation. According to the different lithology of the work area, the weight of the calibration coefficient is determined, for example, in the non-gravel area and the gravel area, the non-gravel area is given priority. This is because the gravel area usually has the phenomenon of velocity inversion, which is not consistent with the trend of the TOMO inversion velocity of the turning wave which is roughly linear from shallow to deep. In addition, if the velocity changes obviously in the lateral direction of a region, multiple control points can be set to make the calibration coefficient also have a lateral change to adapt to the situation of the lateral change of the velocity.

[0051] (6) The original shallow turning wave TOMO velocity body is calibrated by using the calibration coefficient calculated in the previous step, and the virtual VSP velocity curve at the control point is used to make the overall shallow TOMO velocity body after calibration close to the real velocity of the stratum.

[0052] (7) The calibrated shallow turning wave TOMO velocity model is combined with the RMS converted layer velocity of the deep time processing (or the updated migration deep velocity model in the previous step) to form a new overall velocity model which is provided to the next round of depth migration and reflection wave velocity update.

[0053] The following are several specific embodiments of the application.

[0054] Embodiment 1:

[0055] In a specific embodiment 1 of the application, as shown in Figure 1 , Figure 1 is a flow chart of the virtual VSP logging calibration turning wave velocity depth migration method of the application. The virtual VSP logging calibration turning wave velocity depth migration method includes the following steps:

[0056] Step 1, use the picked up big gun first arrival time to perform isotropic turning wave ray TOMO inversion in the shallow layer.

[0057] Step 2, combine the turning wave TOMO velocity in the shallow layer with the layer velocity converted from the RMS velocity of the time processing in the deep layer to form an initial depth migration velocity model.

[0058] Step 3, select some places with good reflection wave events, and use reflection wave only to iteratively update the migration velocity of these places. As shown in Figure 3 is a work area elevation plan, the south is a mountainous area and the north is a plain, and we select some reflection wave events, especially the points with good quality in the shallow layer The reflection tomography velocity is updated, and only the relatively best one is selected from the points As the virtual VSP control point. This is because in principle the control point is as few as possible so that the calibrated TOMO velocity is as simple as possible, which is conducive to further velocity updating.

[0059] Step 4, optimize the velocity curve in these places by checking the quality of the shallow layer stack and whether the common imaging point gathers are flattened, and further select the good velocity curve to ensure that the velocity curve is as close to the real formation velocity as possible. These selected velocity curves can be used as virtual VSP curves. As shown in Figure 2 The reflection velocity analysis and update of the common imaging point are performed on the initial depth migration velocity model (the overall velocity body combined with the shallow layer turning wave TOMO velocity and the deep layer time processing root mean square (RMS) velocity), and the quality of the migration stack and whether the common imaging point gathers are flattened are used to determine the quality of the updated velocity, and as the determination standard for selecting the virtual VSP velocity curve.

[0060] Step 5, before calibration, keep the virtual VSP record consistent with the TOMO velocity elevation, and calculate the reasonable calibration coefficient of the virtual VSP velocity curve and the corresponding TOMO tomographic velocity at each control point, so that the calibrated TOMO tomographic velocity is as close to the virtual VSP velocity curve as possible. As shown in Figure 5 The calibration coefficient curve obtained, since the shallow low velocity zone (more than 200 meters) and the deep layer velocity change law are different, we use different calibration coefficients for the two sections to conform to the actual velocity change law.

[0061] Step 6, use the calibration coefficient calculated in the previous step to calibrate the original shallow layer turning wave TOMO velocity body, and use the virtual VSP velocity curve at the control point to make the calibrated overall shallow layer TOMO velocity body close to the real formation velocity. As shown in Figure 4 The initial TOMO velocity, the virtual VSP curve at this point, and the calibrated TOMO velocity can be seen, and the overall calibrated TOMO velocity is closer to the virtual VSP curve.

[0062] Step 7, the calibrated shallow layer turning wave TOMO velocity model is combined with the deep layer time processing RMS converted layer velocity (or the previously updated migration deep layer velocity model) to form a new overall velocity model, which is provided to the next round of depth migration and reflection velocity update.

[0063] As shown in Figure 2As shown, the reflection wave velocity of common imaging points is analyzed and updated on the initial depth migration velocity model (the overall velocity volume formed by combining the shallow layer's TOMO velocity and the layer velocity converted from the time-processed root mean square (RMS) velocity). The quality of the migration superposition and whether the common imaging point gather is flattened are used to determine the quality of the update velocity, and these are used as the criteria for selecting the virtual VSP velocity curve.

[0064] like Figure 3 As shown, since the south is mountainous and the north is a plain, the phase axis of the offset common imaging point gather is relatively clear in many places in the south, and updating with reflected wave velocity is more effective. Here, we only select the relatively ideal point as the virtual VSP control point. This is because, in principle, the number of control points should be minimized to keep the calibrated TOMO velocity as simple as possible, which is beneficial for subsequent velocity updates.

[0065] like Figure 4 and Figure 5 The initial TOMO velocity volume was calibrated by multiplying all velocity points below the specified elevation by a calibration factor at the same depth. This calibration used only one high-quality virtual VSP control point in the southern region and did not consider lateral variations in the calibration factors. For areas with significant lateral variations in shallow velocities, calibration factors with lateral variations controlled by multiple virtual VSP wells could be considered.

[0066] Example 2:

[0067] In the Kelasu Mountain foreland area of ​​the Tarim Basin, the surface conditions and subsurface structures are complex, resulting in significant lateral velocity variations. Some areas have actual VSP velocity curves, while others do not. In areas lacking actual VSP velocity curves, we obtained virtual VSP curves through combined tomographic inversion. These virtual curves were then combined with actual VSP curves to calibrate the shallow TOMO velocities with a more gradual and variable lateral velocity, making the overall shallow velocity more consistent with actual velocity variation patterns.

[0068] Example 3:

[0069] In the Yubei work area of ​​Xinjiang, the surface is covered by desert, with only one measured VSP well. To further verify the reliability of the VSP velocity curve of this well, we extracted virtual VSP velocity curves from several other shallow reflection phase axis good points. By comparing them with the measured VSP well, we extracted a calibration coefficient curve that is more consistent with the whole area and calibrated the overall shallow velocity of the whole area, achieving ideal results.

[0070] Compared with existing VSP logging-constrained TOMO inversion, this invention has two main advantages:

[0071] (1) Using (virtual) VSP velocity curve to calibrate the turning wave TOMO result is usually more stable than VSP constrained TOMO inversion, and the "bull's eye" phenomenon of constrained inversion does not appear.

[0072] (2) In the area without VSP well, the control point with good quality of seismic reflection wave event is selected, the velocity curve updated by depth migration reflection wave velocity analysis is used to replace the VSP curve, and the virtual VSP curve can still be used to calibrate the TOMO velocity.

[0073] Finally, it should be noted that the above only for the preferred embodiments of the present application, and is not intended to limit the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement of the technical solutions recorded in the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included within the scope of the present application.

[0074] In addition to the technical features described in the specification, they are known to those skilled in the art.

Claims

1. A virtual VSP well tie depth migration method for turning wave velocities, characterized in that, The virtual VSP logging calibration turning wave depth migration method comprises: Step 1, isotropic turning wave ray TOMO inversion is carried out; Step 2, an initial velocity model for depth migration is established; Step 3, iterative updating of migration velocity is carried out; Step 4, a virtual VSP velocity curve of one or more control points in the working area is selected; Step 5, a reasonable calibration coefficient is calculated according to the geological conditions of the working area; Step 6, the original shallow layer TOMO velocity is calibrated as a whole by using the calibration coefficient; Step 7, a new overall migration velocity model is established; In step 2, the shallow layer turning wave TOMO velocity is combined with the layer velocity converted from the RMS velocity of the deep layer time processing to form an initial overall depth migration velocity model; In step 3, the migration velocity of the places with good phase axis quality is iteratively updated by using reflection waves; In step 4, the velocity curve of these places is optimized by checking the quality of the shallow layer stack and whether the common imaging point gathers are flattened, and further good velocity curves are selected to ensure that the velocity curve is as close to the real formation velocity as possible, and these selected velocity curves are used as the virtual VSP velocity curve; In step 4, according to the lateral variation of the shallow layer velocity, one or more virtual VSP velocity curves of the control points in the working area are flexibly selected for lateral constant or variable velocity calibration, and the number of control points is as small as possible to make the calibrated TOMO velocity as simple as possible, which is beneficial to further velocity updating.

2. The virtual VSP logging monochromatic wave velocity depth migration method according to claim 1, characterized in that, In step 1, the isotropic turning wave ray TOMO inversion of the shallow layer is carried out by using the picked up shot first arrival time.

3. The virtual VSP log calibration turning wave velocity depth migration method according to claim 1, wherein, In step 5, the virtual VSP record is kept consistent with the TOMO velocity elevation before calibration, and a reasonable calibration coefficient is calculated at each control point by using the relationship between the virtual VSP velocity curve and the corresponding TOMO tomographic velocity, so that the calibrated TOMO tomographic velocity is as close to the virtual VSP velocity curve as possible.

4. The virtual VSP log calibration turning wave velocity depth migration method according to claim 3, characterized in that, In step 5, two calibration coefficients are used for the shallow layer low velocity drop zone and the deep layer (below 300 meters) respectively, which can also be adjusted according to the situation; the weight of the calibration coefficient is determined according to the different lithology of the working area.

5. The virtual VSP log calibration turning wave velocity depth migration method according to claim 4, wherein, In step 5, the non-gravel area is given priority in the presence of both non-gravel and gravel areas.

6. The virtual VSP log calibration turning wave velocity depth migration method of claim 4, wherein, In step 5, when the velocity changes obviously in a certain area, multiple control points are set to make the calibration coefficient also have lateral variation to adapt to the lateral variation of the velocity.

7. The virtual VSP log calibration turning wave velocity depth migration method of claim 1, wherein, In step 6, the original shallow layer turning wave TOMO velocity body is calibrated by using the calibration coefficient calculated in step 5, and the virtual VSP velocity curve at the control point is used to make the calibrated overall shallow layer TOMO velocity body close to the real formation velocity.

8. The virtual VSP log calibration turning wave velocity depth migration method of claim 1, wherein, In step 7, the calibrated shallow layer turning wave TOMO velocity model and the RMS converted layer velocity of the deep layer time processing are combined to form a new overall migration velocity model, which is provided for the next round of depth migration and reflection wave velocity updating.

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