Relative isochronous logging and earthquake calibration method

Abstract

The invention relates to the technical field of petroleum and natural gas exploration and development, and discloses a relative isochronous logging and earthquake calibration method, which is characterized in that a multi-well average velocity unified calibration method is adopted for calibration of the top and the bottom of a marker bed, and trend correction is carried out on a velocity body according to errors and layer space distribution characteristics; and finally, the calibration error of the above-well layering and the seismic interpretation layer is very small, and the result is in normal distribution. In the calibration process, the single well curve is not stretched or compressed, it is guaranteed that the speed trend is reasonable, no distortion section exists, and the speed model is closer to the real speed. The method mainly aims at calibration of thin sand layers which are thin in thickness, rapid in transverse change and unstable in distribution in continental clastic rock deposition in China, and particularly has a good effect on connectivity research such as development area small layer comparison and water injection.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploration and development, in particular to the technical field of intelligent processing and interpretation, and specifically to a relative isochronous logging and seismic calibration method. Background Art

[0002] Stratum calibration or well-seismic combination is to combine the logging information in the depth domain with the seismic information in the time domain to determine the correspondence between the seismic reflection event axis and the formation interface and reservoir development characteristics. In addition to being affected by factors such as the frequency and type of the wavelet, it is also affected by the density of the formation, the speed of seismic wave propagation in the formation, and the law of formation development. The calibration of geological bodies with large thickness, obvious characteristics, and relatively stable distribution in the study area is relatively simple and generally does not have deviations. However, the calibration of thin sand layers with thin thickness, rapid lateral changes, and unstable distribution in my country's continental clastic rock deposits is sometimes difficult in actual work.

[0003] At present, the industry uses three well-seismic calibration methods for marker layers and thicker reservoirs: average velocity calibration, VSP (vertical seismic profile) calibration, and acoustic wave synthetic seismic record calibration. There is no method for accurate calibration of laterally homogeneous and thin interlayer reservoirs. Summary of the invention

[0004] In order to make up for the shortcomings of the prior art, the present invention solves the problems of large calibration error for thin interlayer reservoirs with strong lateral homogeneity and poor well-seismic correspondence between interlayer small layers. On the one hand, the calibration accuracy of thin interlayer reservoirs is achieved, and on the other hand, the calibration is free of artificial stretching and compression, and the velocity model is free of distortion, which can be directly used for variable velocity mapping.

[0005] The purpose of the present invention is achieved through the following technical solutions and steps:

[0006] A relative isochronous logging and seismic calibration method comprises the following steps:

[0007] (1) Generally, a set of strata located at or near the top of the reservoir is selected as the top marker layer for well seismic calibration, and calibration is performed from top to bottom;

[0008] (2) By using the two-way travel time corresponding to the well geological layer depth and the top marker layer interpretation, the average velocity of multiple wells at the marker layer position is obtained, and the time-depth relationship of the top marker layer of the target layer is converted using this average velocity. Then, the top marker layer is preliminarily calibrated using this time-depth relationship and the error between each well logging layer and the seismic marker layer is calculated. According to the error, the velocity body is trend-corrected according to the spatial distribution characteristics of the layer, and finally the calibration error of the well layer and the seismic interpretation layer is very small and the result is normally distributed, completing the calibration of the top marker layer;

[0009] (3) After the top marker layer is calibrated and leveled along the layer, the average layer velocity between the top marker layer and the next marker layer is obtained using the acoustic logging curve. The next marker layer is calibrated based on the time-depth relationship obtained from the average velocity. The calibration error is still corrected using the error trend surface. This is repeated layer by layer to achieve the calibration of multiple marker layers.

[0010] (4) After completing the calibration of the marker layer, we obtain multiple sets of time-depth relationships at the top and bottom of the reservoir or inside the reservoir. Based on this time-depth relationship, we make synthetic seismic records and complete the calibration of the thin sand layer inside the reservoir.

[0011] (5) In actual production research, the acoustic velocity logging curve and the density logging curve are multiplied to obtain the wave impedance curve, which is then converted into a reflection coefficient and then convolved with the seismic wavelet to obtain the wellside synthetic record. By comparing the wave group with the original seismic trace near the well, the final well-seismic calibration in the time domain and depth domain is completed.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The calibration of the top and bottom of the marker layer adopts the method of unified calibration of the average velocity of multiple wells. According to the error, the velocity body is trend-corrected according to the spatial distribution characteristics of the layer, so that the calibration error of the well stratification and seismic interpretation layer is very small and the results are normally distributed.

[0014] During the calibration process, no stretching or compression is performed on the single well curve, which ensures that the velocity trend is reasonable, there is no distortion segment, and the velocity model is closer to the actual velocity.

[0015] It has a good effect in the calibration of thin sand layers with thin thickness, rapid lateral changes and unstable distribution in my country's continental clastic rock deposits, especially in the comparison of small layers in development areas, and connectivity studies such as water injection. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. 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 work.

[0017] Figure 1 It is a flow chart of the relative isochronous logging and seismic calibration technology provided by an embodiment of the present invention;

[0018] Figure 2It is an average velocity map of the strata above the marker layer calculated by using well stratification and seismic interpretation horizons. H1 is the marker layer selected on the seismic data volume, t is the two-way travel time corresponding to each well on the H1 horizon, D is the stratification depth corresponding to the H1 horizon of each well, and the average velocity of the strata above the H1 horizon is:

[0019] Va=,i=1,2,3,···,n. (3)

[0020] Va is the average velocity of the upper strata of the H1 horizon;

[0021] Figure 3 The top marker layer of each well is initially calibrated by replacing the interlayer velocity of the overlying strata with Va. The calibration result has some errors.

[0022] Figure 4 The error is corrected once or multiple times according to the spatial distribution characteristics of the formation, and then the top layer is calibrated. If the calibration error is small and presents a normal distribution, the calibration work of the reservoir top marker layer is basically completed. Finally, the logging layer and the seismic interpretation layer are manually aligned to eliminate the subtle differences caused by the deformation of the logging instrument and the seismic imaging datum surface.

[0023] Figure 5 After the top marker layer is calibrated, the stratification and interpretation layers are leveled. The purpose is to unify the marker layer onto a standard surface to facilitate the calibration of the next marker layer.

[0024] Figure 6 It uses the acoustic wave curve to calculate and replace the average velocity map between layers;

[0025] Figure 7 It is the acoustic logging curve, using the comprehensive wavelet synthesis record to make the final fine adjustment of the calibration;

[0026] Figure 8 is the top error plane distribution diagram of the top average velocity calibration;

[0027] Fig. 9 is the average speed calibration top level error profile;

[0028] Fig.10 This is a comparison chart of the trend speed grid calculated by four methods;

[0029] Fig.11 This is the T1 calibration error diagram after the least squares trend correction speed;

[0030] Fig.12 It is the restoration of the sedimentary paleo-geomorphology of the first section of Qing and the amplitude attribute map of the top and edge layers of Qing;

[0031] Fig.13 It is the reflection characteristic map of the upper and lower profiles of the target layer on the seismic profile.

[0032] Specific implementation methods

[0033] In order to make the technical means and objectives of the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments. The experimental methods used in the following examples are all conventional methods unless otherwise specified. Example 1

[0034] The Qianshaokou Formation and Quantou Formation in the southern Songliao Basin are fine clastic sandstone interlayer deposits mainly in river-lake and delta phases. The Yaojia Formation and the Nenjiang Formation have a sudden change from mud to sand on the lithological interface, which is manifested as a jump interface from high value to low value on the well logging curve, and a stable wave impedance reflection interface (T1) on the seismic, and can be traced and compared in the whole area. Therefore, T1 is used as the top marker layer for this well-seismic calibration. During the research process, if the overall thickness distribution of the target layer is relatively stable, only two marker layers - one at the top and one at the bottom - are selected to control and complete the calibration of the internal thin sand layer. On the contrary, as many marker layers as possible are selected. The Qingshankou Formation, the target layer of the present invention, is relatively stable in distribution in the study area, with an overall thickness of about 600 meters. Therefore, on the basis of selecting the top marker layer, the present invention selects T2*, which is relatively close to the low interface of the target layer, as the transition layer of the calibration bottom. T2 is the bottom of the Qingshankou Formation, but the response characteristics of the T2 layer are not obvious in the seismic profile, while T2* is similar to T1 in geology, logging and seismicity, and both have stable interfaces.

[0035] Firstly, based on the detailed interpretation of T1, the average velocity of the overlying formations of multiple wells is calculated by using the two-way travel time at the well points and the depth corresponding to the logging layer. Then, this average velocity is used to calibrate all the wells in the work area. The calibration results show that the error is large and has a certain trend.

[0036] We use the four methods described above, namely least squares, Laplace iteration, distance weighting, and spline interpolation, to perform error trend fitting correction. The results are as follows: Fig. 9 As shown in the figure, we can see that the spline interpolation method has more mutation points and the interpolation effect is the worst; the Laplace iteration method and the distance weighted method are abrupt for interpolation of individual large value points, and the effect is not good; while the quadratic surface method has a smooth transition between error points and the interpolation effect is the best. According to the effect, we finally use the least squares method to correct the error trend layer velocity ( Fig.10 ) and then calibrate T1. The calibration result has a small error and a normal distribution ( Fig.11 ), the calibration quality control of the top marker layer of the target layer was qualified, and finally the T1 layer on the well logging and the T1 layer on the seismic were manually aligned to eliminate the slight differences caused by the deformation of the logging instrument and the seismic imaging datum surface.

[0037] From the seismic profile, it can be seen that the target layer in the study area is bounded by T2*, and there are two sets of reflections with different characteristics above and below, so the average velocity of the calibration well needs to be obtained in two sections; and because there are two sets of material sources distributed in the east and west of the study area, and their directions are different, the study area is divided by the central fault zone in the middle, and the average inter-layer velocity difference between the east and west areas is large, so the study area is divided into two parts along this fault zone and calibrated separately. ( Fig.12 , 13 )

[0038] After completing T1 calibration and leveling along the layer, the sonic logging curves of the calibration wells (see Figure 6 ) Obtain the average inter-layer velocity between T1 and T2*, use the average velocity to further obtain the time-depth relationship and repeat the T1 calibration process to calibrate T2* in sections. After the bottom layer T2 is calibrated, the calibration results are quality controlled, and the error is basically controlled within 5 meters.

[0039] After T1 and T2* are calibrated, we need to make synthetic records and compare them with the waveforms of the seismic traces in the well side channels to complete the calibration of the thin sand layers between the marker layers. For the main target layer, the well and seismic are combined to obtain the comprehensive sub-wave, and the time-depth relationship obtained above is used to calibrate the synthetic records of each well separately. According to the correspondence between the synthetic records and the waveforms of the original seismic traces, slight adjustments are made, and the synthetic records and seismic traces of each well are adjusted to the most reasonable positions, and then the error quality control is performed on the calibration positions of the top, bottom and middle thin layers. If the error is about 2 meters, the quality control conditions are met and this calibration work is completed.

[0040] 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 make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A relative isochronous logging and seismic calibration method, characterized in that: The following steps are involved: (1) Select a set of strata located at or near the top of the reservoir as the top marker layer for well seismic calibration and calibrate from top to bottom; (2) By using the two-way travel time corresponding to the well geological layer depth and the top marker layer interpretation, the average velocity of multiple wells at the marker layer position is obtained, and the time-depth relationship of the top marker layer of the target layer is converted using this average velocity. Then, the top marker layer is preliminarily calibrated using this time-depth relationship and the error between each well logging layer and the seismic marker layer is calculated. According to the error, the velocity body is trend-corrected according to the spatial distribution characteristics of the layer, and finally the calibration error of the well layer and the seismic interpretation layer is very small and the result is normally distributed, completing the calibration of the top marker layer; (3) After the top marker layer is calibrated and leveled along the layer, the average layer velocity between the top marker layer and the next marker layer is obtained using the acoustic logging curve. The next marker layer is calibrated based on the time-depth relationship obtained from the average velocity. The calibration error is still corrected using the error trend surface. This is repeated layer by layer to achieve the calibration of multiple marker layers. (4) After the marker layer is calibrated, multiple sets of time-depth relationships between the top and bottom of the reservoir or inside the reservoir are obtained. Based on this time-depth relationship, synthetic seismic records are produced to complete the calibration of the thin sand layer inside the reservoir; (5) In actual production research, the acoustic velocity logging curve and the density logging curve are multiplied to obtain the wave impedance curve, which is then converted into a reflection coefficient and then convolved with the seismic wavelet to obtain a synthetic well track. By comparing the wave group with the original seismic track near the well, the final well-seismic calibration in the time domain and depth domain is completed.

2. The relative isochronous logging and seismic calibration method according to claim 1, characterized in that: The top marker layer in step (1) is selected as a jump interface from high value to low value on the well logging curve, and as a stable wave impedance reflection interface T1 on the seismic.

3. The relative isochronous logging and seismic calibration method according to claim 1, characterized in that: In step (1), on the basis of selecting the top marker layer, T2* which is relatively close to the low interface of the target layer segment can also be selected as the transition layer for calibrating the bottom.

4. The relative isochronous logging and seismic calibration method according to claim 1, characterized in that: The trend correction methods described in step (3) are least squares, Laplace iteration, distance weighting, and spline interpolation.

5. The relative isochronous logging and seismic calibration method according to claim 1, characterized in that: The specific calculation method of the time-depth relationship described in step (4) is as follows: after completing the calibration of T1 and leveling along the layer, the average interlayer velocity between T1 and T2* is obtained using the acoustic logging curve of the calibration well, and the time-depth relationship is further obtained using the average velocity and the T1 calibration process is repeated to calibrate T2* in sections. After the bottom layer T2 is calibrated, the calibration results are quality controlled and the error is basically controlled within 5 meters.

6. The relative isochronous logging and seismic calibration method according to claim 1, characterized in that: The error of the final well-seismic calibration in step (5) is within 2 meters.

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