CN113109870B - High-precision shallow stratum speed acquisition method - Google Patents
High-precision shallow stratum speed acquisition method Download PDFInfo
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- CN113109870B CN113109870B CN202110376637.0A CN202110376637A CN113109870B CN 113109870 B CN113109870 B CN 113109870B CN 202110376637 A CN202110376637 A CN 202110376637A CN 113109870 B CN113109870 B CN 113109870B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/28—Processing seismic data, e.g. analysis, for interpretation, for correction
- G01V1/30—Analysis
- G01V1/303—Analysis for determining velocity profiles or travel times
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V2210/00—Details of seismic processing or analysis
- G01V2210/60—Analysis
- G01V2210/62—Physical property of subsurface
- G01V2210/622—Velocity, density or impedance
- G01V2210/6222—Velocity; travel time
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/30—Assessment of water resources
Abstract
The invention discloses a high-precision shallow stratum velocity acquisition method, which is applied to the field of acquisition and processing of seismic data in wells in geophysical exploration, and aims at solving the problem that the accurate velocity of 20-300m shallow stratum is difficult to obtain in the prior art.
Description
Technical Field
The invention belongs to the field of seismic data acquisition and processing in wells in geophysical exploration, and particularly relates to a high-precision seismic velocity acquisition technology aiming at 20-300m shallow stratum.
Background
With the continuous development of high-precision seismic exploration and development technology, the precision requirement of the seismic velocity is increasingly improved, the VSP velocity becomes an indispensable velocity 'scale' in high-precision seismic processing, however, the shallow stratum velocity near the wellhead is difficult to obtain accurately, and a method for effectively improving the VSP velocity precision of the shallow stratum is urgently needed, so that reliable velocity support is provided for high-precision seismic processing.
At present, a controlled seismic source of 28t-34t or an explosive source of 1-3kg is used in most VSP data acquisition, so that good well seismic information can be recorded. However, under the influence of the volume, weight, excitation energy and wellhead safety factors of a seismic source, the conventional seismic source cannot be excited near a wellhead, and the observation offset is usually larger than 50m, so that refraction of shallow seismic waves occurs, and the accuracy of calculation of the shallow seismic velocity is greatly influenced; meanwhile, the acquisition density of most of interstage cables of the conventional borehole geophone is 5-20m, the calculation accuracy of the shallow stratum velocity is very unfavorable only by a slowly-lifting mode, no special acquisition equipment, no matched technology and no method exist at home and abroad at present, the requirement of increasingly developed high-precision seismic exploration is met, research on a high-precision velocity acquisition method of the shallow stratum VSP is urgently needed, a method and preparation equipment for effectively improving the VSP velocity accuracy of the shallow stratum are formed, and reliable velocity support is provided for high-precision seismic processing.
Disclosure of Invention
Aiming at the problem that the accurate speed of 20-300m shallow stratum is difficult to obtain by a conventional geophysical method, the invention provides a high-precision shallow stratum speed obtaining method, and a reliable speed parameter is provided for the exploration and development of high-precision oil and gas reservoirs.
The invention adopts the technical scheme that: a high-precision shallow stratum velocity acquisition method comprises the following steps:
s1, selecting an acquisition operation well;
s2, determining the optimal observation azimuth of the acquisition operation well selected in the step S1;
s3, acquiring well seismic data by utilizing a light weight seismic source and high-density distributed optical fiber equipment based on the acquisition operation well selected in the step S1 and the optimal observation azimuth determined in the step S1;
s4, processing the well seismic data acquired in the step S3;
s5, acquiring first arrival time according to the well seismic data processed in the step S4, measuring and calculating well source distance and vertical distance, and calculating shallow stratum speed by using the first arrival time, the well source distance and the vertical distance.
The step S2 specifically comprises the following steps: and S1, setting down high-density distributed optical fibers in the operation well selected in the step S1, setting multi-azimuth near-well head excitation test points at the periphery of the well, and selecting a test azimuth corresponding to the minimum average first arrival time data of the same recording depth as an optimal observation azimuth through a light source excitation test.
Step S3 also includes time sampling intervals of less than or equal to 0.5ms for the borehole seismic data.
The processing in step S4 specifically includes: noise suppression and wavelet consistency processing.
The noise suppression is particularly used for suppressing random noise, wellbore wave noise, casing wave noise and optical cable noise.
The wavelet consistency processing specifically adopts a cross-correlation processing method to correct the wavelet amplitude, the wavelet morphology and the like of the multi-excitation data.
The vertical distance in step S5 is calculated by using a straight ray or by using a curved ray.
The invention has the beneficial effects that: the invention relies on the existing well drilling, utilizes a high-frequency near-wellhead seismic source and high-density well receiving equipment to collect high-precision shallow stratum well seismic data, further calculates and obtains 20-300m shallow stratum velocity which is difficult to obtain by other geophysical methods, and provides a reliable technical method for obtaining the shallow stratum velocity.
Drawings
FIG. 1 is a block flow diagram of the method of the present invention.
Fig. 2 is an acquisition observation system in the present embodiment.
Fig. 3 is a schematic diagram of calculation in the present embodiment.
Detailed Description
The present invention will be further explained below with reference to the drawings in order to facilitate understanding of technical contents of the present invention to those skilled in the art.
The invention relies on the existing drilling, utilizes a high-frequency near-wellhead seismic source and high-density well receiving equipment to acquire and obtain seismic data in a shallow stratum well, and further calculates and obtains 20-300m shallow stratum velocity which is difficult to obtain by other geophysical methods, as shown in figure 1, the invention comprises the following steps:
1) Collecting operation well selection: and in a detection zone where the shallow stratum speed is required to be accurately calculated, well drilling with good well conditions is selected as a supported acquisition operation well.
The well condition refers to well cementation quality of drilling well, no bridge plug blocking of a collecting section, no oil and gas collecting operation and the like.
Alternatively, the depending well may be one well or a plurality of wells, as determined by the geological requirements of the zone of investigation and the condition of the job site. Such as: when a plurality of drilling wells are arranged in the detection area, the plurality of drilling wells are selected as supporting wells, and the acquisition density is not higher than 1 well per square kilometer.
2) Determination of the observation orientation: and (3) lowering the high-density distributed optical fibers in the operation well selected in the step 1), arranging multi-azimuth near-well head excitation test points at the periphery of the well, and determining the optimal observation azimuth through a light source excitation test.
The light seismic source is light and can be moved to near-wellhead excitation, and the excitation frequency can be higher than 200 Hz. Because the invention is based on oil and gas drilling, explosive, air gun vibration source and the like which possibly damage a wellhead cannot be selected, and the small controllable vibration source has low acquisition frequency output and is not applicable to the implementation of the invention, so that a light weight vibration source is preferred.
The high-density distributed optical fiber refers to distributed optical fiber equipment with vertical recording resolution less than 1m, which meets the requirements of the invention. The common receiving equipment comprises a wave detector, a hydrophone and the like which adopt a node recording mode with a 5-20m interval, so that the implementation of the high-precision data acquisition is not facilitated.
As shown in FIG. 2, the near-wellhead excitation test refers to that after an optical fiber in a well is pushed against or adsorbed stably, a plurality of test positions in different directions around the wellhead are excited by a light seismic source and recorded to obtain a seismic wave field for comparison as test data, wherein the number of orientations of the test positions is not less than 4, and the recording depth of test points in each orientation is not less than 3.
The determination of the optimal observation azimuth refers to that in the comparison of test data, the test azimuth corresponding to the minimum average first arrival time data with the same recording depth is selected, and because the optical fiber in the well is close to the well wall but the azimuth is uncertain, the nearest distance between the optical fiber and the excitation point can be determined through the test, and the method is very important for obtaining a high-precision shallow velocity calculation result.
The method for determining the optimal observation azimuth by using the near-wellhead light seismic source and distributed optical fiber combination observation mode and the multipoint near-wellhead test is the key innovation point of the invention.
3) Acquiring well seismic data: based on the collecting operation well selected in the step 1) and the observation azimuth determined in the step 2), the light weight seismic source and the high-density distributed optical fiber equipment are used for collecting and obtaining the well seismic data.
The well seismic data refers to seismic wave information recorded by receiving equipment, including first arrival time information, wave field information and the like, and single-component data recorded by an optical fiber instrument can completely meet the implementation of the invention because multi-component information is not required by the invention.
And acquiring the seismic data in the well, namely acquiring the seismic data of all detection depths corresponding to the azimuth once after the azimuth is selected, wherein the detection depth is 20-300m or more than the range.
In particular, the time sampling interval of the well seismic data is not more than 0.5ms to ensure the recording requirement of the later high-precision speed.
4) Processing the seismic data in the well: and (3) performing noise suppression and wavelet consistency processing on the well seismic data acquired in the step (3) to obtain processed well seismic data.
The noise suppression processing means that random noise, shaft wave noise, casing wave noise and optical cable noise are suppressed by the existing processing means. In particular, when the quality of cementing is extremely poor, resulting in a casing that is noisy and not effective to compress, the practice of the present invention will be disadvantageous and the need to avoid such wellbores as much as possible.
The wavelet consistency processing means that the wavelet amplitude, the wavelet shape and the like of the multi-excitation data are corrected by adopting a cross-correlation processing method, thereby being beneficial to high-precision first arrival pickup.
5) Calculation of shallow formation velocity: and 4) acquiring first arrival time by using the seismic data in the well processed in the step 4), measuring and calculating a well source distance, and calculating shallow stratum speed by using the first arrival time, the well source distance and the vertical distance, as shown in fig. 3.
The data first arrival time refers to time t corresponding to each recording depth N obtained by picking up at the first arrival wave jump position N 。
The measurement and calculation of the well source distance means that the distance L from the well center of the minimum azimuth to the excitation test point is measured first, and the well head inner diameter R is subtracted and recorded as L'.
L′＝L-R
The vertical distance refers to the oblique propagation distance D of the seismic wave with the Nth recording depth by utilizing a trigonometric function 1N Corrected to vertical propagation distance D 2N To reduce the influence of the calculation accuracy caused by the offset distance L'. Because the invention innovatively provides an observation mode of a near wellhead, the method for calculating the propagation distance by adopting the straight rays can also accurately obtain the shallow stratum speed, and can also be realized by using the tracking method of the existing commercial software finite element simulation and other curved rays.
The speed calculation means using the vertical propagation distance D 2N Divided by the propagation time t N Recorded as velocity V N 。
O in FIG. 3 represents the center point of the well, O min 、S min For representing the point at which the offset is the smallest.
Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (6)
1. The high-precision shallow stratum speed acquisition method is characterized by comprising the following steps of:
s1, selecting an acquisition operation well;
s2, determining the optimal observation azimuth of the acquisition operation well selected in the step S1; the method comprises the steps that a high-density distributed optical fiber is placed in an operation well selected in the step S1, multi-azimuth near-well head excitation test points are arranged on the periphery of the well, and test orientations corresponding to minimum average first arrival time data of the same recording depth are selected as optimal observation orientations through a light source excitation test; the number of the positions and the directions of the test positions is not less than 4, and the recording depth of the test points in each position is not less than 3;
s3, acquiring well seismic data by utilizing a light weight seismic source and high-density distributed optical fiber equipment based on the acquisition operation well selected in the step S1 and the optimal observation azimuth determined in the step S1;
s4, processing the well seismic data acquired in the step S3;
s5, acquiring first arrival time according to the seismic data in the well processed in the step S4, measuring and calculating well source distance and vertical distance, and calculating shallow stratum speed by using the first arrival time, the well source distance and the vertical distance; shallow formation velocity is denoted as V N The calculation formula is as follows:
wherein D is 2N Represents the vertical propagation distance, t N Represent propagation time, D 1N Seismic wave oblique propagation distance representing Nth recording depth, L representing minimum azimuthThe distance from the well center to the excitation test point, R, represents the wellhead inside diameter.
2. The method of claim 1, wherein step S3 further comprises the step of time sampling intervals of the borehole seismic data being less than or equal to 0.5ms.
3. The method for obtaining high-precision shallow formation velocity according to claim 1, wherein the processing in step S4 specifically comprises: noise suppression and wavelet consistency processing.
4. A method of obtaining a high accuracy shallow formation velocity according to claim 3, wherein the noise suppression is specifically used for suppressing random noise, wellbore wave noise, casing wave noise, and cable noise.
5. A method for obtaining shallow stratum velocity with high precision according to claim 3, wherein the wavelet consistency process specifically adopts a cross-correlation process method to correct the wavelet amplitude and morphology of the multi-shot data.
6. The method according to claim 1, wherein the vertical distance in step S5 is calculated by using a straight ray or by using a curved ray.
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