A method of detecting reservoir velocity changes using crosswell time-lapse seismic

Abstract

This invention patent proposes a method for detecting reservoir velocity changes through inter-well time-lapse seismic monitoring. The method involves conventional data processing, wavefield separation, and further processing of time-lapse seismic data. A sliding time window is designed, and the time-lapse cross-correlation coefficient is calculated for the time-lapse upwave seismic gathers within the sliding time window to obtain the delay time when the cross-correlation coefficient reaches its maximum value. The relative velocity change for each time window is calculated, and then the average velocity change is obtained. Subsequently, the wavefields of the time-lapse upwave and downwave are calculated channel by channel, and the velocity change as a function of depth is plotted. Through comprehensive comparison, the depth range of reservoir velocity changes is defined. This invention can effectively detect minute changes in underground reservoir velocity, define the depth range of velocity changes, has low investment cost and high computational efficiency, and improves the application effect of inter-well time-lapse seismic monitoring.

Description

Technical Field

[0001] This invention relates to the field of exploration geophysics, specifically a method for detecting reservoir velocity changes through inter-well time-lapse seismic detection. Background Technology

[0002] Inter-well seismic technology is one of the important technologies in the field of oil and gas exploration and development. Inter-well seismic exploration involves placing both the seismic source and the detector in a well at a certain depth above the ground, so as not to be disturbed by the surface environment, and to obtain seismic signals with high resolution and signal-to-noise ratio.

[0003] For inter-well seismic exploration, the main focus is on using imaging techniques to achieve high-precision imaging of complex structures and oil and gas reservoirs, or using tomographic imaging techniques to establish high-precision velocity models of oil and gas reservoirs. However, the wavefield of inter-well seismic data is extremely complex, posing challenges to both high-precision tomographic and migration imaging, and also making time-lapse seismic monitoring a significant challenge. Furthermore, for tomographic imaging, the workload of picking first arrivals is usually substantial, and if the wavefield is affected by noise or other conditions, it will further complicate the first arrival picking process. Imaging techniques typically require high shot density and also incur certain computational costs.

[0004] Time-lapse seismic analysis involves multiple seismic measurements of the same oil and gas reservoir. It utilizes the differences in time-lapse seismic data caused by variations in underground reservoir fluids to monitor changes in reservoir characteristics. It is the most widely used dynamic monitoring and management technology for oil and gas reservoirs. For inter-well time-lapse seismic exploration, it primarily utilizes inter-well imaging techniques and tomographic imaging methods. Through time-lapse analysis, it further monitors changes in the underground reservoir using differential imaging profiles and differential tomographic profiles. However, inter-well time-lapse monitoring also faces the same problems encountered with conventional inter-well seismic data processing methods.

[0005] Therefore, it is necessary to develop an efficient and economical inter-well time-lapse seismic monitoring technology to effectively monitor minute changes in underground reservoir velocity. This technology should have high computational efficiency while saving costs and improving the application effect of inter-well time-lapse seismic monitoring. Summary of the Invention

[0006] The purpose of this invention is to provide a method for detecting reservoir velocity changes through inter-well time-shift seismic detection, which can effectively detect minute velocity changes in underground reservoirs with low computational cost and economic investment.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for detecting reservoir velocity changes via inter-well time-lapse seismic detection includes the following steps:

[0009] 1) Perform conventional seismic data processing on the basic measurement and repeat measurement time-shift data to obtain the processed basic measurement seismic data u. b and repeated measurement seismic data u r ;

[0010] 2) For u b and u r Wavefield separation and time-shift seismic data processing are performed to obtain the up-wave field from the base measurements. and its downwave field and the repeatedly measured up-going wave field and its downwave field

[0011] 3) Design a sliding time window, the size of which is four times the period of the source wavelet;

[0012] 4) Extract the corresponding two seismic data from the up-wave field of the basic measurement and the repeated measurement, and calculate the time-shift cross-correlation coefficient and the average velocity change within the sliding time window;

[0013] 5) Perform step 4) on the uplink waves of the basic and repeated measurements one channel at a time to obtain the average velocity change at all detector depth positions, and plot the velocity change as a function of depth.

[0014] 6) Perform step 4) on the downlink waves of the basic measurement and repeated measurement one channel at a time to obtain the average velocity change at all detector depth positions, and plot the velocity change as a function of depth.

[0015] 7) Compare the average velocity variation curves of the up-wave field and the down-wave field, and define the depth range of reservoir velocity variation by the global maximum value of the curve.

[0016] Based on the above technical solutions, the present invention also provides the following optional technical solutions:

[0017] In one alternative: in step 4), the time-shift cross-correlation coefficient R(t) s The formula for calculating ) is:

[0018]

[0019] The center of the sliding time window is located at time t, and the window duration is 2t. w , t s This represents the time shift of the repeated measurement wavefield relative to the fundamental measurement wavefield.

[0020] In one alternative: when the cross-correlation coefficient R(t) is shifted... s ) in t s=τ reaches its maximum value, at which point the repeated measurement gather is equivalent to the time-shifted base measurement gather u. r (t)=u b (t-τ), that is:

[0021] t max =τ (2)

[0022] In one alternative approach: for each time window, the relative velocity change is:

[0023]

[0024] In one alternative: for local spatial variations, the average travel time variation is:

[0025]

[0026] Where <τ(t)> is the local velocity change in volume V. The mean travel time variation of the arrival time t of the multiple scattered waves caused by the scattering is given by K(r,t), which is the integral kernel.

[0027] In one alternative: average velocity change The calculation formula is:

[0028]

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] Inter-well time-lapse seismic methods for detecting reservoir velocity changes can effectively utilize the high-precision information of inter-well time-lapse seismic data to detect minute changes within subsurface reservoirs and indicate the depth location of these velocity changes. Due to its fast computation speed and small data requirement, this method can achieve rapid detection of reservoir velocity changes with relatively low computational cost and economic investment. Furthermore, it offers high accuracy in locating velocity changes, making it suitable for long-term real-time monitoring. Attached Figure Description

[0031] Figure 1 This is a geological model of the reservoir velocity before a 2% change, used in the method of detecting reservoir velocity changes through inter-well time-lapse seismic detection.

[0032] Figure 2 This is a geological model of reservoir velocity after a 2% change, used in the method of detecting reservoir velocity changes through inter-well time-lapse seismic detection.

[0033] Figure 3 Inter-well seismic shot gather data before a 2% change in reservoir velocity is used in the method of inter-well time-lapse seismic detection of reservoir velocity changes.

[0034] Figure 4Inter-well seismic shot gather data after a 2% change in reservoir velocity, as part of the method for detecting reservoir velocity changes through inter-well time-lapse seismic detection.

[0035] Figure 5 The upflow wavefield data is obtained from the inter-well shot gather data of the basic measurement system in the method of detecting reservoir velocity changes by inter-well time-lapse seismic monitoring.

[0036] Figure 6 The upflow wavefield data is obtained from repeated inter-well shot gather data in the method of detecting reservoir velocity changes through inter-well time-lapse seismic monitoring.

[0037] Figure 7 Downward wave field data obtained from inter-well shot gather data in the method of detecting reservoir velocity changes by inter-well time-lapse seismic survey.

[0038] Figure 8 Downward wave field data obtained from repeated inter-well shot gather data in a method for detecting reservoir velocity changes using inter-well time-lapse seismic monitoring.

[0039] Figure 9 The reservoir velocity change detection results are used in the method of inter-well time-lapse seismic detection of reservoir velocity changes. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0042] like Figure 1-9 As shown, an embodiment of the present invention provides a method for detecting reservoir velocity changes through inter-well time-lapse seismic detection, comprising the following steps:

[0043] 1) Perform conventional seismic data processing on the basic measurement and repeat measurement time-shift data to obtain the processed basic measurement seismic data u. b and repeated measurement seismic data u r ;

[0044] 2) For u b and u r Wavefield separation and time-shift seismic data processing are performed to obtain the up-wave field from the base measurements. and its downwave field and the repeatedly measured up-going wave field and its downwave field

[0045] 3) Design a sliding time window, the size of which is four times the period of the source wavelet;

[0046] 4) Extract the corresponding two seismic data from the upriding wavefields of the basic and repeated measurements, and calculate the time-shift cross-correlation coefficient R(t). s The formula for calculating ) is:

[0047]

[0048] The center of the sliding time window is located at time t, and the window duration is 2t. w , t s This represents the time shift of the repeated measurement wavefield relative to the fundamental measurement wavefield.

[0049] At that time, the cross-correlation coefficient R(t) s ) in t s =τ reaches its maximum value, at which point the repeated measurement gather is equivalent to the time-shifted base measurement gather u. r (t)=u b (t-τ), that is:

[0050] t max =τ (2)

[0051] For each time window, the change in relative velocity is:

[0052]

[0053] For local spatial variations, the variation in average travel time is:

[0054]

[0055] Where <τ(t)> is the local velocity change in volume V. The mean travel time variation of the arrival time t of the multiple scattered waves caused by the scattering is given by K(r,t), which is the integral kernel.

[0056] The kernel K(r,t) depends on the intensity-weighted average of all scattering paths and satisfies the following equation:

[0057] t=∫ V K(r,t)dV(r) (5)

[0058] Average velocity change The calculation formula is:

[0059]

[0060] 5) Perform step 4) on the uplink waves of the basic and repeated measurements channel by channel to obtain the average velocity change at all detector depth positions. And plot the curve of velocity change as a function of depth to indicate the depth of the top interface of the velocity-changing layer;

[0061] 6) Perform step 4) on the downlink waves of the basic and repeated measurements channel by channel to obtain the average velocity change at all detector depth positions. And plot the curve of velocity change as a function of depth to indicate the bottom interface depth of the velocity-changing layer;

[0062] 7) Compare the average velocity variation curves of the up-wave field and the down-wave field, and define the depth range of reservoir velocity variation by the global maximum value of the curve.

[0063] The above embodiments of the present invention provide a method for detecting reservoir velocity changes through inter-well time-lapse seismic detection. Figure 1-2 The geological model of reservoir change over time shown, in which Figure 1 and Figure 2 This is a geological model showing the reservoir velocity before and after a 2% change, and the recorded data... Figure 3-4 The data from the inter-well seismic shot gather, including Figure 3 and Figure 4 These are inter-well seismic shot gather data before and after a 2% change in reservoir velocity. Figure 5 and Figure 6 These are the upflow wavefield data obtained from the inter-well shot gather data of the basic measurement and repeated measurement, respectively, after wavefield separation. Figure 7 and Figure 8 These are downflow wavefield data obtained from the inter-well shot gather data of the basic measurement and repeated measurement, respectively, after wavefield separation. Figure 9 This is the result of reservoir velocity change detection. Although the reservoir velocity change is only a tiny 2%, the velocity change versus depth curve obtained from time-shifted upwave wavefield data can effectively indicate the depth of the top interface of the reservoir, while the velocity change versus depth curve obtained from time-shifted downwave wavefield data can effectively indicate the depth of the bottom interface. The combination of these two methods can accurately delineate the depth range of reservoir velocity changes. Therefore, for minute velocity changes in subsurface reservoirs, the method for detecting reservoir velocity changes through inter-well time-shifted seismic monitoring disclosed in this invention provides an effective and rapid detection method for accurately indicating the depth range of reservoir velocity changes.

[0064] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method of detecting changes in reservoir velocity using crosswell time-lapse seismic, characterized by, The method comprises the following steps: 1) performing conventional seismic data processing on the base measurement and repeat measurement time-lapse data to obtain processed base measurement seismic data and repeat measurement seismic data ; 2) to and carry out wave field separation processing and time migration seismic data processing, to obtain the upgoing wave field and the downgoing wave field of the base measurement, and the upgoing wave field and the downgoing wave field of the repeated measurement; 3) designing a sliding time window, the window size being four times the period of the source wavelet; 4) taking out corresponding two-way seismic data from the upgoing wave field of the base measurement and the repeated measurement, calculating the time-lapse cross-correlation coefficient and the average velocity variation in the sliding time window; 5) performing the calculation of step 4) on the upgoing wave of the base measurement and the repeated measurement channel by channel to obtain the average velocity variation at all depth positions of the geophone, and drawing a curve of the velocity variation varying with the depth; 6) performing the calculation of step 4) on the downgoing wave of the base measurement and the repeated measurement channel by channel to obtain the average velocity variation at all depth positions of the geophone, and drawing a curve of the velocity variation varying with the depth; 7) comprehensively comparing the average velocity variation curves of the upgoing wave field and the downgoing wave field, and demarcating the depth range of the reservoir velocity variation through the global maximum value of the curve.

2. The method of claim 1, wherein, In step 4), the time-shifted cross-correlation coefficient is calculated as follows: （1） where the center of the sliding time window is located at time with a window length of , denotes the time shift of the repeated measurement wavefield relative to the base measurement wavefield.

3. The method of claim 2, wherein, The time-shifted cross-correlation coefficient At The maximum is reached, at which point the repeat gather is equivalent to the base gather time-shifted i.e.: （2）。 4. The method of claim 3, wherein, For each time window, the relative velocity variation is: （3）。 5. The method of claim 4, wherein, For the spatial local variation, the average travel time variation is: （4） where is the body average travel time variation caused by spatial local velocity variations of the multiple scattered wave arrival time in the medium, is the integral kernel.

6. The method of claim 5, wherein, Average speed change The formula for calculating the average speed change is: （5）。

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