METHODS AND SYSTEMS FOR CONCURRENT LAND VIBROSEIS ACQUISITION WITH SIMULTANEOUS ACTIVATION

Abstract

Land seismic survey including providing at least two vibrators in a first group, wherein each vibrator in the first group is assigned to a respective source line, where the source lines of the first group run substantially parallel to one another; providing at least two vibrators in a second group, wherein each vibrator in the second group is assigned to a respective source line that is different than the source lines assigned to vibrators from the first group; actuating the vibrators in the first group simultaneously using different frequency bandwidth sweeps and different phase encodings; actuating the vibrators in the second group at the same time as those in the first group, and simultaneously using different frequency bandwidth sweeps and different phase encodings; and detecting the resulting seismic signals with a plurality of seismic sensors that are placed in contact with the earth and as part of a seismic spread.

Claims

1. A method for performing a land seismic vibroseis survey, comprising: providing at least two vibrators in a first group, wherein each vibrator in the first group is assigned to a respective source line, where the source lines of the first group run substantially parallel to one another; providing at least two vibrators in a second group, wherein each vibrator in the second group is assigned to a respective source line that is different than the source lines assigned to vibrators from the first group; actuating the vibrators in the first group simultaneously using different frequency bandwidth sweeps and different phase encodings; actuating the vibrators in the second group at the same time as those in the first group, using different frequency bandwidth sweeps and different phase encodings; and detecting the resulting seismic signals with a plurality of seismic sensors that are placed in contact with the earth and as part of a seismic spread.

2. The method of claim 1, comprising at least two vibrators in a third group, wherein each vibrator in the third group is assigned to a respective source line, where the source lines of the third group run substantially parallel to one another.

3. The method of claim 2, comprising at least two vibrators in a fourth group, wherein each vibrator in the third group is assigned to a respective source line, where the source lines of the fourth group run substantially parallel to one another.

4. The method of claim 1, wherein the source lines of the first group are not shared with the source lines of the second group.

5. The method of claim 2, wherein the source lines of the first group and the source lines of the third group are shared.

6. A method of seismic vibroseis surveying, comprising: a first vibrator group comprising four vibrators, V1, V2, V3 and V4, wherein each of the four vibrators are located on a different source line, the source lines running parallel to one another, the V1 being actuated for a shot 1 between 2-27 Hz and at a phase of 0 degrees, V2 being actuated for a shot 1 between 24-48 Hz and at a phase of 90 degrees, V3 being actuated for a shot 1 between 45-69 Hz and at a phase of 180 degrees, and V4 being actuated for a shot 1 between 66-90 Hz and at a phase of 270 degrees.

7. The method of claim 6, wherein: the V1 being actuated for a shot 2 between 24-48 Hz and at a phase of 90 degrees, V2 being actuated for a shot 2 between 49-69 Hz and at a phase of 180 degrees, V3 being actuated for a shot 2 between 66-90 Hz and at a phase of 270 degrees, and V4 being actuated for a shot 2 between 2-27 Hz and at a phase of 0 degrees.

8. The method of claim 7, wherein: the V1 being actuated for a shot 3 between 46-69 Hz and at a phase of 180 degrees, V2 being actuated for a shot 3 between 66-90 Hz and at a phase of 270 degrees, V3 being actuated for a shot 3 between 2-27 Hz and at a phase of 0 degrees, and V4 being actuated for a shot 3 between 24-48 Hz and at a phase of 90 degrees.

9. The method of claim 8, wherein: the V1 being actuated for a shot 4 between 66-90 Hz and at a phase of 270 degrees, V2 being actuated for a shot 4 between 2-27 Hz and at a phase of 0 degrees, V3 being actuated for a shot 4 between 24-48 Hz and at a phase of 90 degrees, and V4 being actuated for a shot 4 between 45-90 Hz and at a phase of 180 degrees.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The following brief description of the drawings is meant to aid the understanding of one skilled in the art when reviewing this document and any associated claims, and is not meant in any way to unduly limit those or any future related claims.

[0013] FIG. 1: shows features relating to a simultaneous vibroseis surveys with two vibrators shooting.

[0014] FIG. 2: shows vibroseis concurrent acquisition with 2 groups of vibroseis units separated by a predefined distance; in each group the vibrators sweep simultaneously using split bandwidth sweeps; each vibrator group is independent of each other.

[0015] FIG. 3: is a Composite amplitude spectrum of 4 split bandwidth sweeps listed in Table 1.

[0016] FIG. 4: shows two ways to acquire encoded sweeps with 4 split_bandwidth and phase encoded: sweep1-listen_time, sweep2_listen_time, sweep3_listen_time, sweep4_lisyen time ((ex: for 5 sec sweep and 6 sec listen_time total time=44 sec); sweep1,sweep2,sweep3,sweep4,listen_time (ex: for 5 sec sweep and 6 sec listen_time total time=26 sec).

[0017] FIG. 5: shows examples of shot records for conventional acquisition (20 sec sweep, 6 listening) (left) vs. embodiments of the method described herein with encoded sweeps (right).

[0018] FIG. 6: shows vibroseis concurrent acquisition with four groups of vibroseis units separated by a predefined distance; in each group the vibrators sweep simultaneously using encoded sweeps; each vibrator group is independent of each other.

DETAILED DESCRIPTION

[0019] The following detailed description is meant to aid the understanding of one skilled in the art regarding the various combinations of embodied features described herein and in the claims, as well as future related claims. It is in no way meant to unduly limit those present or future claims.

[0020] A challenge to the noted issue of survey speed is the ability to activate vibrators at the same time (or very near thereto) at different locations around a seismic sensor spread (receiver patch). If many shot points can be acquired at the same time or nearly the same time, the receiver patch can be moved quickly to the new location and the total duration of the survey can be reduced. Unfortunately, when vibrators are actuated too close to one another and at the same time or nearly the same time, the signals can interfere with one another when detected by a sensor, thereby degrading the detected data.

[0021] The present application describes embodiments relating to new and novel method(s) of actuating land seismic vibrators and performing a seismic survey that provides improved efficiencies to dramatically improve commercial results in the areas of cost, time and efficiency in connection with a land seismic survey.

[0022] The present application relates to methods for conducting a land seismic survey using a plurality of land seismic sensors in connection with a plurality of land seismic vibroseis units.

[0023] In land seismic vibroseis surveying, and according to embodiments herein, a large number of seismic survey sensors are distributed in connection with the earth. It is possible to use at any one time 10,000, 20,000, 50,000, 100,000 and even up to and more than 200,000 individual land sensors in a survey. Further, it is possible to move a land survey spread involving those numbers of sensors from one area to an adjacent area to eventually complete survey of a total area.

[0024] As part of a seismic survey, a vibratory impulse is imputed into the earth. In a simple manner, an impulse can be actuated at any one time. However, using that simple method ensures that the survey will take a very long time and will be commercially less efficient and successful. To improve efficiencies, it is desirable to operate multiple vibrators at the same time. However, complications can arise in that scenario if the signals interfere with one another when detected by a sensor. There are a number of ways to address that issue, such as encoding the signals, and or other separation techniques.

[0025] Processing of the data acquired with current land simultaneous shooting treat the seismic interference as noise and noise attenuation methods are applied for active source separation. To achieve successful results, the vibrator units that are firing at the same time need to be separated by a large distance and thus creates a need to use a large receiver spread.

[0026] In the present application various embodiments are disclosed that allow closer intervals between vibrator units and also deployment of a smaller receiver spread

[0027] According to various embodiments, efficiency of a vibroseis survey can be increased if one or more groups of vibrators shoot concurrently over a receiver (sensor) spread. Each group of vibrators may include at least 2, 3 or 4 vibroseis units and each vibroseis unit in a group may sweep at a different frequency bandwidth sweep. In each vibroseis unit could be 1, 2 or more vibrators. There are various mechanical configurations for a vibroseis unit.

[0028] As shown in FIG. 1, various features of a simultaneous shooting survey are shown as used for vibroseis land surveys, where the sources (vibroseis units identified as V1 and V2) actuate simultaneously and are separated by a distance in space or can be separated by a firing time interval. If either time separation (slip sweep) or distance separation are employed properly a signal in the defined target area will not undesirably interfere with one another.

[0029] FIG. 2 shows a group of four vibroseis units (V1, V2, V3, V4) operating as and in a group. The four vibroseis units (V1, V2, V3, V4) are placed on four adjacent and substantially parallel source lines 1. A source line is a track (imaginary line) that the vibroseis unit is to move along and occasionally activate at predetermined locations and in a predetermined way. Receiver lines 2 are perpendicular to the source lines 1. As shown in FIG. 2, one of the vibroseis devices (V1, V2, V3, V4) is a single vibroseis unit (in some cases a truck). In each group, a vibroseis unit is placed in a respective track as shown, and each vibroseis unit activates simultaneously producing a different frequency bandwidth sweep with a different phase encoding. If for conventional vibroseis acquisition the sweep frequency is 2-90 Hz and the sweep length is 20 sec., with a single sweep per shot point, one implementation is to split 2-90 Hz sweep in four parts, each part having a different bandwidth and different phase. The length of each sweep can then be 5 seconds. Such an embodiment may be: V1: 2-27 Hz, phase=0; V2=24-48 Hz, phase=90; V3=45-69 Hz, phase=180, V4=66-90 Hz, phase=270. In that case, each vibroseis device stays on the same shot point and sweeps four times, each time with a different bandwidth. This scenario is outlined and described in Table 1. In Table 1, split bandwidth sweeps for a group of four vibroseis devices are placed on four different source lines 1, where each vibroseis device sweeps four times at a same location.

TABLE-US-00001 TABLE 1 Shot Sweep Listening SP-11(line-1) SP-21(line-2) SP-31(line-3) SP-41(line-4) number length time V.sub.1: 2-27 Hz V.sub.2 = 24-48 Hz V.sub.3 = 45-69 Hz V.sub.4 = 66-90 Hz Shot-1 5 sec. 6 sec. Phase = 0 Phase = 90 Phase = 180 Phase = 270 V.sub.1 = 24-48 Hz V.sub.2 = 45-69 Hz V.sub.3 = 66-90 Hz V.sub.4 = 2-27 Hz Shot-2 5 sec. 6 sec. Phase = 90 Phase = 180 Phase = 270 Phase = 0 V.sub.1 = 45-69 Hz V.sub.2 = 66-90 Hz V.sub.3 = 2-27 Hz V.sub.4 = 24-48 Hz Shot-3 5 sec. 6 sec. Phase = 180 Phase = 270 Phase = 0 Phase = 90 V.sub.1 = 66-90 Hz V.sub.2 = 2-27 Hz V.sub.3 = 24-48 Hz V.sub.4 = 45-90 Hz Shot-4 5 sec. 6 sec. Phase = 270 Phase = 0 Phase = 90 Phase = 180

[0030] According to embodiments shown in FIG. 1 and described in Table 1, to recover a full bandwidth of 2-90 Hz, each shot can be correlated with a proper sweep for each vibroseis device and a vertical sum of the four shots on the same location are performed after correlation. The resulting small overlap between the consecutive frequency bandwidth and the taper applied for each sweep are designed to provide a continuous composite spectrum as shown in FIG. 3.

[0031] According to a combination of various embodied features, vibroseis units can be placed at certain distances from one another and can generate sweeps as those described in Table 1. In that scenario, the phase for each sweep in group-2 can be encoded, such as: 45, 135, 225 and 315. In that scenario, the distance between the groups can be based on a survey design and modeling study to assure that the effect of seismic interference in the target zone is minimized to an acceptable level. The second group of vibroseis units may shoot independently of the first group of vibroseis units.

[0032] In the scenarios described herein, the number of vibroseis unit groups can be more than two, depending on the survey size. Each vibrator group can have a different number of vibroseis units, and can be 2, 3, 4 or more. A comparison between the sweeping time with an embodied method versus a conventional shooting (no simultaneous shooting) is presented in Table 2 below. Table 2 is a comparison between sweeping time for conventional acquisition (no simultaneous shooting) and split bandwidth simultaneous shooting with one group and two groups of four vibroseis units.

TABLE-US-00002 TABLE 2 Split bandwidth simultaneous Conventional shooting with 4 vibroseis Split bandwidth simultaneous shooting with a units on 4 source lines shooting with 8 vibroseis single sweep and a s + l + s + l + s + l + s + l units on 8 source lines Acquisition vibroseis unit on 1 s = sweep time s + s + s + l + s + l + s + s + parameters source line l = listening time s + s + l s + l + s + l s + s + l Sweep length 20 sec. 5 sec. 5 sec. 5 sec. 5 sec. Listening time 6 sec. 6 sec. 6 sec. 6 sec. 6 sec. Number of active 1 4 4 8 8 shot lines Number of 1 4 4 4 4 sweeps per vibroseis point Total time per 26 sec. 11 sec. 6.5 sec. 11 sec. 6.5 sec. vibroseis point for a source line Total time per 26*4 = 104 sec. 44 sec. 26 sec. 44 sec. 26 sec. vibroseis point for 4 source lines Total time per 26*8 = 208 sec. 44 sec. 26 sec. 44 sec. 26 sec. vibroseis point for 8 source lines

[0033] According to embodiments herein, in order to reduce the total line time per vibroseis source points the four sweeps, V1, V2, V3, V4 can be concatenated to eliminate the listening time for V1, V2, and V3. In that scenario, the total time for sweeping at four source locations is 26 seconds instead of 44 seconds. This is illustrated in FIG. 4. It should be appreciated that a savings of 16 second per shot location, in the context of a large land seismic survey is multiplied many thousands of times and produces a significant improvement in time efficiency, commercial viability, and success of a land seismic vibroseis survey.

[0034] Another group of 4 vibroseis units can be placed at a certain distance and will generate the same sweeps as is described in Table 1. The phase for each sweep in group-2 will be also encoded, for example: 45, 135, 225 and 315. The distance between groups can be based on survey design and modeling study to assure that the effect of seismic interference in the target zone is minimized. The second group of vibroseis units will shot independently of the first group of vibroseis units.

[0035] The number of the vibroseis unit groups may be more than two, depending on the survey size. FIG. 6 shows four vibrator groups, each group with four vibrator (units and each vibrator group working independently.

[0036] FIG. 6 shows vibroseis concurrent acquisition with four groups of vibroseis units separated by a predefined distance where in each group the vibrators sweep simultaneously using encoded sweeps, and each vibrator group is independent of each other

[0037] Each vibrator group could have a different number of vibroseis units, typically, 2, 3, or 4.

[0038] During operations the number of units per group could be changed to accommodate the operational conditions. Changes can be included in the shooting plan prepared during survey planning.

[0039] As shown in FIG. 6, two groups of vibrator units (V1, V2, V3, V4) may share source lines wherein the source lines of each group are collinear, or the same, as those of another group.

[0040] If one or more vibrator units are not at the required locations due to different field conditions (ex. obstructions) the vibrators could sweep the same sequence of sweeps at the current locations, provided the x,y,z coordinates are recorded based on Global Positioning System (GPS) and altimetry measurements. That actuation method gives flexibility in operations and could minimize the non-productive time.

[0041] According to present embodiments, new methods and systems for performing land seismic vibroseis surveys are disclosed. However, no matter how efficient such a method is and what commercial improvements are realized, it is all for not if the actual seismic data results are inadequate. According to the present disclosure and according to experimentation it has been shown that survey results using the present embodiments are similar to, if not better than, conventional more inefficient methods. This is shown in FIG. 5. A comparison of data acquired with conventional acquisition (20 second length and 6 second listening time, one shot point at each time) vs shooting with four vibrators placed on four different lines, simultaneously, each vibrator shooting a different split bandwidth sweep (5 second length and 6 second listening time) is shown in FIG. 5.

[0042] While the present disclosure relates to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate that numerous modifications and variations therefrom are possible while staying within the scope of the disclosure herein. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the disclosure recited herein.