A depth domain velocity modeling method for four-dimensional seismic monitoring of oil sand reservoir development

Abstract

The application discloses a kind of oil sand reservoir exploitation four-dimensional seismic monitoring depth domain velocity modeling method, comprising the following steps: step S101: to reference seismic, according to time domain velocity model conversion smoothness obtains initial velocity model;Step S102: to reference seismic, using initial velocity model, carry out prestack depth migration, obtain initial depth domain seismic profile and gather;Step S103: to reference seismic, pick up residual delay on initial depth domain seismic gather, residual delay is converted into residual migration equation set by ray tracing.The application truly reflects the change of underground depth domain velocity information in the process of steam assisted gravity drainage, and the change of this velocity information is used for the oil sand reservoir exploitation monitoring of steam assisted gravity drainage, which can obtain the depth domain velocity change and corresponding depth domain seismic profile between reference seismic and monitoring seismic, so that we can observe the influence of steam and the change rule of reservoir.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil sand reservoir exploitation monitoring, in particular to a depth domain velocity modeling method for four-dimensional seismic monitoring of oil sand reservoir exploitation. BACKGROUND

[0002] Steam Assisted Gravity Drainage (SAGD): a method of injecting steam into an oil reservoir from a straight well or a horizontal well above a horizontal production well near the bottom of the reservoir, and producing heated crude oil and steam condensate from the horizontal well at the bottom of the reservoir.

[0003] Four-dimensional seismic refers to the process of monitoring oil and gas reservoir dynamics by repeatedly acquiring differential seismic information of the same work area at different times.

[0004] Before or at the beginning of steam assisted gravity drainage, three-dimensional seismic observation is performed on the work area to obtain corresponding baseline seismic information. Thereafter, steam is continuously injected for a certain period of time (e.g., within six months), and then three-dimensional seismic observation is performed again on the work area to obtain corresponding monitoring seismic information. The difference between the monitoring seismic information and the baseline seismic information is used to monitor the oil sand oil and gas reservoir exploitation.

[0005] The commonly used monitoring information based on four-dimensional seismic is the time delay and amplitude change obtained on the time migration seismic profile. Due to steam injection, the spatial velocity of the reservoir will decrease. Reasonable depth domain velocity model difference information can not only truly reflect the change of underground velocity information, but also be used for monitoring the process of steam assisted gravity drainage reservoir exploitation. The existing technology uses four-dimensional attributes such as time delay and amplitude change obtained on the pre-stack time migration data profile for monitoring, but it is difficult to obtain reliable depth domain velocity model through time migration velocity calculation method, and further difficult to obtain reasonable depth domain velocity difference information.

[0006] Therefore, the present application provides a depth domain velocity modeling method for four-dimensional seismic monitoring of oil sand reservoir exploitation, which aims to truly reflect the change of underground depth domain velocity information in the process of steam assisted gravity drainage. This change of velocity information is used for monitoring the oil sand reservoir exploitation of steam assisted gravity drainage, and can obtain the depth domain velocity change and corresponding depth domain seismic profile between the baseline seismic and the monitoring seismic, so that we can observe the influence of steam and the change rule of the reservoir. SUMMARY

[0007] The present application provides a depth domain velocity modeling method for four-dimensional seismic monitoring of oil sand reservoir exploitation to solve the problems raised in the background.

[0008] In order to achieve the above object, the present application provides the following technical scheme: a depth domain velocity modeling method for oil sand reservoir four-dimensional seismic monitoring, comprising the following steps:

[0009] Step S101: converting and smoothing the reference seismic according to the time domain velocity model to obtain an initial velocity model;

[0010] Step S102: using the initial velocity model to perform pre-stack depth migration on the reference seismic to obtain initial depth domain seismic profile and gather;

[0011] Step S103: picking up residual delay on the initial depth domain seismic gather of the reference seismic, converting the residual delay into a residual migration equation set through ray tracing, converting the residual migration equation set into a residual velocity field by using reflection tomography inversion to obtain a velocity update amount, and further obtaining an updated depth domain velocity model;

[0012] Step S104: using the updated depth domain velocity model to perform pre-stack depth migration on the reference seismic to obtain updated depth domain velocity profile and gather data;

[0013] Step S105: judging whether the residual delay of the depth domain seismic gather output by S104 is less than an allowable error or not;

[0014] Step S106: if yes, stopping the update, taking the velocity model used in S104 as the final depth domain velocity model of the reference seismic, and taking the seismic profile output by S104 as the final depth domain seismic profile of the reference seismic;

[0015] Step S107: if no, repeating steps S103-S104 to continue the update until the residual delay of the output depth domain seismic gather is less than the allowable error, at this time, taking the velocity model as the final depth domain velocity model of the reference seismic, and taking the output seismic profile as the final depth domain seismic profile of the reference seismic;

[0016] Step S108: using the final depth domain velocity model of the reference seismic as the initial velocity model of the monitoring data to perform pre-stack depth migration on the monitoring seismic to obtain initial depth domain seismic profile and gather data of the monitoring seismic data;

[0017] Step S109: picking up residual delay on the initial depth domain seismic gather of the monitoring seismic, converting the residual delay into a residual migration equation set through ray tracing, converting the residual migration equation set into a residual velocity field by using reflection tomography inversion to obtain a velocity update amount, and further obtaining an updated depth domain velocity model;

[0018] Step S110: using the updated depth domain velocity model, pre-stack depth migration is performed on the monitoring seismic to obtain updated depth domain velocity profile and gather data;

[0019] Step S111: judging whether the residual delay of the depth domain seismic gather outputted by S110 is less than the allowed error;

[0020] Step S112: if yes, stopping updating, taking the velocity model used in S110 as the final depth domain velocity model of the monitoring seismic, and taking the seismic profile outputted by S110 as the final depth domain seismic profile of the monitoring seismic;

[0021] Step S113: if no, repeating steps S109-S110 to continue updating until the residual delay of the outputted depth domain seismic gather is less than the allowed error, at this time, the velocity model is taken as the final depth domain velocity model of the monitoring seismic, and the outputted seismic profile is taken as the final depth domain seismic profile of the monitoring seismic.

[0022] Preferably, the method further comprises the following steps:

[0023] Step S114: subtracting the final depth domain velocity model of the reference model from the final depth domain velocity model of the monitoring seismic to obtain the absolute variation of the depth domain velocity.

[0024] Preferably, the method further comprises the following steps:

[0025] Step S115: dividing the variation obtained by S114 by the final depth domain velocity model of the reference model to obtain the relative variation of the depth domain velocity.

[0026] Preferably, the method further comprises the following steps:

[0027] Step S116: using the absolute variation and the relative variation of the depth domain velocity to monitor the variation law of the oil sand reservoir of the steam assisted gravity drainage.

[0028] The present application provides a depth domain velocity modeling method for four-dimensional seismic monitoring of oil sand reservoir exploitation. The method has the following advantages:

[0029] (1), the present application can realize the accurate homing of seismic data by comparing with prestack time migration profile, the velocity analysis method only relying on time domain migration imaging method, often difficult to obtain reliable depth domain velocity model, may cause the illusion of underground structure, the existing technology uses the four-dimensional attribute such as time delay and amplitude change obtained on prestack time migration section to monitor the change rule of oil sand oil and gas reservoir, through the technical scheme of the present application, the respective reasonable depth domain velocity model of reference seismic and monitoring seismic can be obtained, and then the depth domain velocity change and corresponding depth domain seismic profile between reference seismic and monitoring seismic are obtained, so that we can more reasonably obtain the influence of steam injection on oil sand oil and gas reservoir and the corresponding change rule, and the more accurate velocity change information can be used for steam assisted gravity drainage oil sand reservoir exploitation monitoring.

[0030] (2), the present application can reflect the change of underground depth domain velocity information in the process of steam assisted gravity drainage, and the change of velocity information is used for steam assisted gravity drainage oil sand reservoir exploitation monitoring, so that the depth domain velocity change and corresponding depth domain seismic profile between reference seismic and monitoring seismic can be obtained, and we can observe the influence of steam and the change rule of reservoir. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0032] A preferred embodiment of a depth domain velocity modeling method for oil sand reservoir exploitation four-dimensional seismic monitoring provided by the present application is as follows:

[0033] Step S101: converting and smoothing the initial velocity model according to the time domain velocity model for the reference seismic.

[0034] Step S102: using the initial velocity model to perform prestack depth migration for the reference seismic to obtain the initial depth domain seismic profile and gather.

[0035] Step S103: picking up the residual delay on the initial depth domain seismic gather for the reference seismic, converting the residual delay into residual migration equation set through ray tracing, converting the residual migration equation set into residual velocity field by using reflection tomography inversion to obtain the velocity update, and then obtaining the updated depth domain velocity model.

[0036] Step S104: using the updated depth domain velocity model, prestack depth migration is performed on the reference seismic to obtain updated depth domain velocity profile and gather data;

[0037] Step S105: for the reference seismic, it is judged whether the residual delay of the depth domain seismic gather output by S104 is less than the allowable error;

[0038] Step S106: if yes, stop updating, take the velocity model used in S104 as the final depth domain velocity model of the reference seismic, and take the seismic profile output by S104 as the final depth domain seismic profile of the reference seismic;

[0039] Step S107: if no, repeat steps S103-S104 to continue updating until the residual delay of the output depth domain seismic gather is less than the allowable error, and the velocity model at this time is taken as the final depth domain velocity model of the reference seismic, and the seismic profile output at this time is taken as the final depth domain seismic profile of the reference seismic;

[0040] Step S108: for the monitoring seismic, the final depth domain velocity model of the reference seismic is used as the initial velocity model of the monitoring data to perform prestack depth migration to obtain the initial depth domain seismic profile and gather data of the monitoring seismic data;

[0041] Step S109: for the monitoring seismic, residual delay is picked up on the initial depth domain seismic gather, the residual delay is converted into a residual migration equation set through ray tracing, the residual migration equation set is converted into a residual velocity field through reflection tomography inversion to obtain a velocity update amount, and then an updated depth domain velocity model is obtained;

[0042] Step S110: using the updated depth domain velocity model, prestack depth migration is performed on the monitoring seismic to obtain updated depth domain velocity profile and gather data;

[0043] Step S111: for the monitoring seismic, it is judged whether the residual delay of the depth domain seismic gather output by S110 is less than the allowable error;

[0044] Step S112: if yes, stop updating, take the velocity model used in S110 as the final depth domain velocity model of the monitoring seismic, and take the seismic profile output by S110 as the final depth domain seismic profile of the monitoring seismic;

[0045] Step S113: if no, repeat steps S109-S110 to continue updating until the residual delay of the output depth domain seismic gather is less than the allowable error, and the velocity model at this time is taken as the final depth domain velocity model of the monitoring seismic, and the seismic profile output at this time is taken as the final depth domain seismic profile of the monitoring seismic;

[0046] Step S114: subtracting the final depth domain velocity model of the reference model from the final depth domain velocity model of the monitored earthquake to obtain the absolute variation of the depth domain velocity;

[0047] Step S115: dividing the variation obtained in S114 by the final depth domain velocity model of the reference model to obtain the relative variation of the depth domain velocity;

[0048] Step S116: the absolute variation and the relative variation of the depth domain velocity can be used to monitor the variation law of the oil sand reservoir of the steam assisted gravity drainage.

[0049] Although the embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A depth-domain velocity modeling method for four-dimensional seismic monitoring of oil sands reservoir development, characterized in that, Includes the following steps: Step S101: For the reference earthquake, the initial velocity model is obtained by smoothing the time-domain velocity model. Step S102: For the reference earthquake, use the initial velocity model to perform pre-stack depth migration to obtain the initial depth domain seismic profile and gathers; Step S103: For the reference earthquake, the residual delay is picked on the initial depth domain seismic gather. The residual delay is converted into the residual migration equations by ray tracing. The residual migration equations are converted into the residual velocity field by reflection wave tomography inversion to obtain the velocity update, and then the updated depth domain velocity model is obtained. Step S104: For the reference earthquake, use the updated depth domain velocity model to perform pre-stack depth migration to obtain the updated depth domain velocity profile and gather data; Step S105: For the reference earthquake, determine whether the residual delay of the depth domain seismic gather output in S104 is less than the allowable error; Step S106: If yes, stop updating, use the velocity model used in S104 as the final depth domain velocity model of the reference earthquake, and use the seismic profile output in S104 as the final depth domain seismic profile of the reference earthquake. Step S107: If not, repeat steps S103-S104 to continue updating until the remaining delay of the output depth domain seismic gather is less than the allowable error. The velocity model at this time is used as the final depth domain velocity model of the reference earthquake, and the output seismic profile at this time is used as the final depth domain seismic profile of the reference earthquake. Step S108: For the monitored earthquake, the final depth domain velocity model of the reference earthquake is used as the initial velocity model of the monitored data, and pre-stack depth migration is performed to obtain the initial depth domain seismic profile and gather data of the monitored earthquake data. Step S109: For the monitored earthquake, the residual delay is picked on the initial depth domain seismic gather, and the residual delay is converted into the residual migration equations by ray tracing. The residual migration equations are then converted into the residual velocity field by reflection wave tomography inversion to obtain the velocity update, and thus the updated depth domain velocity model is obtained. Step S110: For the monitored earthquakes, use the updated depth domain velocity model to perform pre-stack depth migration to obtain the updated depth domain velocity profile and gather data; Step S111: For the monitored earthquake, determine whether the residual delay of the depth domain seismic gather output in S110 is less than the allowable error; Step S112: If yes, stop updating, use the velocity model used in S110 as the final depth domain velocity model for monitoring earthquakes, and use the seismic profile output in S110 as the final depth domain seismic profile for monitoring earthquakes. Step S113: If not, repeat steps S109-S110 to continue updating until the remaining delay of the output depth domain seismic gather is less than the allowable error. The velocity model at this point is used as the final depth domain velocity model for the monitored earthquake, and the output seismic profile at this point is used as the final depth domain seismic profile for the monitored earthquake.

2. The depth domain velocity modeling method for four-dimensional seismic monitoring of oil sands reservoir development according to claim 1, characterized in that: It also includes the following steps: Step S114: Subtract the final depth domain velocity model of the baseline model from the final depth domain velocity model of the monitored earthquake to obtain the absolute change in depth domain velocity.

3. The depth domain velocity modeling method for four-dimensional seismic monitoring of oil sands reservoir development according to claim 2, characterized in that: It also includes the following steps: Step S115: Divide the change obtained in S114 by the final depth domain velocity model of the baseline model to obtain the relative change of depth domain velocity.

4. The depth domain velocity modeling method for four-dimensional seismic monitoring of oil sands reservoir development according to claims 2 and 3, characterized in that: It also includes the following steps: Step S116: The absolute and relative changes in depth domain velocity can be used to monitor the variation patterns of oil sand reservoirs in steam-assisted gravity flooding.