MXPA99003983A - Method and system for increasing fold to streamer length ratio - Google Patents

Abstract

A method and system are provided for use in marine seismic data surveys to increase fold and offset without increasing streamer length or drag on the streamer boat. Generally the method comprises the use of a second source boat positioned in the streamer path and firing the second source (S2) at a time before the recording of information from the first source (S1) is finished. By positioning the second source (S2) about one streamer length in front of the closest hydrophone (R1), the fold is increased by two for the same length streamer.

Description

METHOD AND SYSTEM TO INCREASE THE DGL JOINT SET OF EBOTES TO THE PROBE LENGTH BACKGROUND OF THE INVENTION This invention is related to the field of the acquisition of marine seismic data and more particularly to the field of marine data acquisition of the Common Medium Point (ie 'CMP') In the field of marine seismic data acquisition the sources of seismic signal (v gr, air pistols) are towed behind a boat that also tow a set of probes The probes include signal receivers (v gr, hydrophones) that are sensitive to reflections, refractions and other information that come from impulses of sound emitted by the sources In many modern arrangements vain probes and vain sources are used, requiring very large tensile forces to handle the drag associated with the towed arrangements It has been known for a long time that to obtain high quality data, it is necessary to add vanes of information from the same layer. The associated noise in each piece of information is random, the addition of multiple signals from the same reflection point. of surface results in an increase in the information signal with noise cancellation. This procedure is commonly referred to as the Common Medium Point method.

As is known in the art, the number of reflections that come from the same reflector is commonly called the "rebound set" of the survey. The increase in the set of rebounds results in an increase in the signal to noise ratio, and , therefore, the increase in the set of bounces is desirable. Traditionally, to increase the set of bounces, the number of hydrophones in the probe is increased, making the probe longer. It is also desirable to tow vanes probes behind the seismic vessel, being the distance between probes as small as possible to increase the resolution of the survey Unfortunately, as the number of probes increases, so do the operational restrictions, resulting in a limit above the length of the probe. distance between probes, the natural movement of warping or vibrating of the probe in the water increases the chances of algae mapna in the The ends of the probes, especially during the turns In this way, the length of the probe is again limited It has also been discovered that it is desirable to increase the long distance (ie, the distance between the source and the farthest receiver) in many prospects Such an increase gives benefits that are well known in the art (v gr, increases the set of rebounds, better defines the data of deep halocline and generally improves the signal-to-noise ratios). However, to increase the distance, the probe must be lengthened The length of the increased probe increases the drag and limits the number of probes that can be towed, which results in an increase in the separation of the probes. Moreover, the strength of the information signal received over long distances is significantly lower than in the near distance. As the length of the probe increases, the strength of the signal decreases, resulting in the need for a larger source. However, larger sources increase the problems of port handling and entrainment, again limiting the size and / or density of the removable arrangement. Consequently, there is a need for a method and system to increase the set of bounces in one. marine prospecting, as well as distance, without (1) increasing the length of the probe, (2) decreasing the number of probes or (3) increasing the distance between the probes The object of the present invention is to meet the needs described above BRIEF DESCRIPTION OF THE INVENTION According to the present invention, the needs described above are solved by a 'seismic vessel' ("SEV"), towing probes and sources, used with a source vessel ("SOV") according to one embodiment, assuming that the length of the probes of the SEV was L and that the separation between the source (over the SEV) and the head of the intermeane probe outside X the source of the SOV is placed either L in front of the source position of the SOV, or L + X behind the last active probe section of the SEV The combined coverage of the distance between source and receiver will be from X to X + 2L In addition, the seismic source of the SOV will be triggered with a delay in relation to the firing time of the source of the SEV. The delay in the firing is optimized so that the seismic information generated by the source of the the SEV is not influenced by the seismic information generated by the source of the SOV. Both shots are recorded in the same record. The total record length is kept as short as possible, but long enough so that the generated seismic information is included. By the source of the SOV By this, the cycle time between shots is minimized so that the maximum coverage of the bounce set is maintained For some modalities in deep water, the Seismic record is delayed in relation to source trigger time over SEV, to reduce total cycle time and record subsurface data over a longer period Cycle time and bounce set is changed for vain water depths In some embodiments, the invention is used with individual sources on the SEV, while in others vain sources are used. In additional embodiments, the SOV places the same number of sources as the SEV, and in other modalities different numbers of sources are used between the SEV and the SOV. In other additional embodiments, the source on the SOV has a different amplitude (e.g., in an airgun arrangement, either volume, pressure or both) than the source of the SEV. For alternative modalities, the source of the SOV has the same amplitude as that of the SEV. Furthermore, in other embodiments, additional probe vessels placed behind the SEV are used. In more additional embodiments, more than one SOV is used. For example, the position of the SOV number J, in one mode, is JL in front of the source position of the SEV, or JL + X behind the last active probe section on the SEV. The combined coverage of the distance between source and receiver will be from X to X + (J + L). Different sources are triggered sequentially and recorded in the same record as described by arpba. In summary, by the use of the present invention, It increases the seismic distance without increasing the length of the probe, thus reducing the aquatic equipment, and, at the same time, maintaining and improving a high coverage of the set of bounces.

DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and for further advantages thereof, reference will be made to the following detailed description taken in conjunction with the accompanying drawings, in which: Figure 1 is a side view showing the locations of the receiver and the source in relation to reflectors. Figure 2 is a representative graph showing the order of recording the information that comes from the reflectors. Figure 3 is a top view of one embodiment of the invention. Figure 4 is a top view of an alternative embodiment of the invention. Figure 5 is a timing diagram of a source triggering method in accordance with a fashion of the invention. Figures 6A, 6B and 6C are top views of alternative embodiments of the invention. However, it should be noted that the appended drawings illustrate only typical embodiments of this invention, and that therefore they should not be considered as limiting their scope, since the invention can admit other equally effective modalities.

DETAILED DESCRIPTION OF THE INVENTION Referring now to Figure 3, the exemplary embodiment of the invention of a system for the acquisition of seismic data at along a survey line 1 comprising: a boat vessel 12a towing hydrophone probes 10 having hydrophones 14 housed therein, including a nearby hydrophone 14n and a far hydrophone 14f. The boat 12a also towed a first seismic source 16a. The distance between the first seismic source 16a and the near hydrophone 14n defines the near distance N O., and the distance between the seismic source pomera 16a and the far hydrophone 14f defines the far distance F O. A second vessel 12b is also shown, towing a second seismic source 16b by the bow of the first vessel 12a. The distance between the second source 16b and the near hydrophone 14n is approximately the far distance F.O. of the first vessel or less.

Although the present invention is useful in a single probe system, in intended embodiments, the system comprises several probes 10 (three are shown here, although the number is not limited by the present invention) being towed by the 12th boat. . Similarly, vain sources 16a are towed by the first vessel 12a, and vain sources 16b are towed behind the second vessel 12b, according to another embodiment. Referring now to Figure 4, a specific embodiment is shown with several source elements 16a1 and 16a2 constituting the source behind the vessel 12a and source elements 16b1 and 16b2 constituting the source behind the vessel 12b. According to this embodiment, the source elements 16a1 and 16a2 are laterally separated approximately 50 meters, like the source elements -6b1 and 16b2. The probes 10 are separated one from the other approximately 100 meters. As the vessels 12a and 12b move along the survey line, the source 16a1 fires and the rebounds 20a1 of the CMP are recorded (representing information that comes from the reflectors behind the surface, as explained in more detail below). Before the end of the record of rebounds 20a1 of the CMP that come from the deepest depth of interest (which can take several seconds) source 16b1 triggers, and is regulated in time so that the most recent information of interest comes from the triggering of the source element 16b1 (observed in Figure 4 as rebounds 20b1 of the CMP) is recorded in the probes 10 just after the last information of interest is recorded from the triggering of the source element 16a1. Subsequently, after recording the information of the deepest interest that comes from the firing of the source element 16b2, the source element 16a2 fires, the rebounds 20a2 of the CMP are recorded, and before the rebounds of the CMP are recorded the information of the deeper interest, the source element 16b2 triggers. The rebounds 20b2 of the CMP are recorded from the firing of the source element 16b2, preferably in the same register as the rebounds 20a2. Through the careful timing of the firing of the different source elements, the following is achieved: long distance, marine data of high set of bounces and separation between dense probes. A practical configuration would be to use twelve probes with a length of approximately 4 km, a separation between probes of 100 meters, a distance between the source elements 16a (2 elements, with a separation of approximately 50 meters) and the vessel 12a of between approximately 200 and 350 meters, and a distance between the source elements 16a and the hydrophone ppmer in the probes 10 of between approximately 200 and 350 meters. The second vessel 12b is observed towing source elements 16b (2 elements, with a spacing of approximately 50 meters), the distance between the source elements 16a and 16b is approximately the length of the probes (approximately 4 km). According to another aspect of the invention, referring again to Figure 3, there is provided a method for recording marine seismic data in a data survey comprising: towing a plurality of probes 10 behind a first vessel 12a, wherein the probes comprise a set of seismic signal receivers 14 positioned along the probes 10 to receive seismic signals and transmit the signals to the first vessel 12a, and where the outermost probes 10a and 10c define a probe path 15 substantially parallel to the survey line 1; 20 towing a first seismic signal source 16a behind the first vessel 12a, wherein the receiver closest to the source 16a defines a near distance receiver 14n and the distance between the near distance receiver 14n and the source 16a defines the distance near NO, and in where the receiver furthest from the source defines a far distance receiver 14f and the distance between the far distance receiver 14f and the source 16a defines the far distance FO of the first vessel, and tow a second source of seismic signal 16b behind a second vessel 12b, wherein the source 16b behind the second vessel 12b is towed along the probe path 15, wherein the distance between the second source 16b and the near distance receiver 14n is optimally the length of the probes 14 Referring now to Figures 1, 2 and 5, the timing of a useful method with the embodiment of Figure 3 will be described. Figure 1 shows an idealized graph of sources S1 and S2 and receivers R1 and R2, and the rays of the sources S1 and S2 to the reflectors a1-3, b1-3 and d-3, below the surface of the earth 50 For reasons of simplification, not all rays are shown in Figure 1 Figure 5 shows a diag time regulation branch of the triggering of the sources S1 and S2 and the information recorded in the hydrophones R1 and R2, and figure 2 shows the records made from the hydrophones R1 and R2, with the identification of the reflectors represented in the In reference now to Figure 5, according to this aspect of the invention, the method comprises firing the source S1 at a time ppmer t, whereby a first source trigger event is defined, registering at a time t + x, through the receivers 14 in the probes 10, in a first register (R1 of figure 2), the information that comes from the reflectors a2. b2, c2 to the first source trigger event for a time equal to the travel time from the source S1 to a maximum depth of interest. In the same way, the information that comes from the reaction of the reflectors a1, b1 and d is registered in the first register through the receiver R2. This time is represented as tdmaxl of time in Figure 5. Next, the method further comprises triggering the other source S2 at a second time t + y (Figure 5), whereby a second source trigger event is defined and in where the second source trigger event occurs before the end of the record of the information of the first source trigger event: The result is the recording of the information coming from the reflectors a3, b3 and c3 (in the receiver R1) a2 , b2 and c2 (in the receiver R2), during a time tdmax equal to the travel time from the source S2 to the maximum depth of interest and to the furthest receiver, R2. Referring now to Figure 2, a record of information signals in the first receiver R1 is recorded for both the first source S1 and the second source S2, resulting in the register R1 of figure 2, in which the reflectors a2, b2 and c2 are recorded as a result of the source 51, and reflectors a3, b3 and c3 are recorded as a result of the source 52. Further, with reference to Figure 2, a record of information signals on the second receiver R2 is recorded for both the first source S1 and the second source S2, resulting in the register R2 of figure 2, in which the reflectors a1, b1 and d are recorded as a result of the S1 source and a2 reflectors, b2 and c2 are recorded as a result of the source S2. The recording of the information that results from the firing of the second source in the same record as the record that results from the firing of the first source provides efficiencies of time regulation and computational power. However, in alternative modes, the information from the second source is recorded in a separate record. If the results from different sources are recorded in the same registry, the data need not be separated into information collected from each source and processed according to traditional methods, for example as collected from CMP. Those skilled in the art will recognize that while the survey continues, there will be many data sets of all the reflectors that will have to be collected, some recorded from the hydrophones between R1 and R2, and the invention is not limited to the example shown. Referring now to Figures 6A-6C, several alternative embodiments are shown. As shown in Figure 6A, the simple tow boat mode in which the length of the probes is L is shown, and the separation between the source S1 of the boat 12a and the head of the intermediate probe is X, the source S2 is placed L in front of the source S1, or, as shown in Figure 6C, L + X behind the last active probe. Referring now to Figure 6B, according to an alternative embodiment, a third source 16c is towed behind a third source vessel. 12c, also along the probe path, wherein the distance between the third source 16c and the far distance receiver is approximately 2L + X The third source 16c is triggered in a third instant, whereby a third source trigger event is defined, and the information coming from the third source trigger event is recorded, through the receivers 14 in the probes 10, preferably in the same register as the information coming from the firing of the sources S1 and S2 for a time equal to the travel time of the third source to the maximum depth of interest and to the far distance receiver. The modalities described above are given by way of example only. Other modalities will be available to those skilled in the art, which will not depart from the spirit of the invention.

Claims (5)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A method to record map seismic data in a data prospecting, the survey has a line of investigation, and the method comprises: towing a plurality of probes behind a vessel ship; further characterized in that the probes comprise a set of seismic signal receivers placed along the probe to receive seismic signals and transmit the signals to the first vessel, and where the outermost probes define a probe path substantially parallel to the line research; tow a ppmera source of seismic signal behind the vessel, where the receiver closest to the seismic source defines a near distance receiver, where the distance between the near distance receiver and the seismic source ppmera defines the near distance , where the furthest receiver of the seismic source ppmera defines a distant distance receiver, and where the distance between the distant distance receiver and the seismic source ppmera defines the distance distant from the ship's vessel; towing a second source of seismic signal behind a second vessel, wherein the source behind the second vessel is towed along the probe path, where the distance between the second source and the nearest receiver is approximately L or less; shoot one of the sources at first, with which a ppmer source trigger event is defined; receiving, through the receivers in the probes, the information of the first source trigger event for a time equal to the travel time from one of the sources to a maximum depth of interest to the far distance receiver; triggering the other source in a second instant, thereby defining a second source trigger event; receiving, through the same receivers in the probes, the information of the second source trigger event for a time equal to the travel time of the other source up to the maximum depth of interest to the far distance receiver; and where the second source trigger event occurs before the end of the recording of the ppmer information source trigger event.
2. 2. A method according to claim 1, further characterized in that the information received from the second source trigger event is recorded in the same register as the information received from the first source trigger event.
3. 3. A method according to claim 1, further characterized in that the information received from the second source trigger event is recorded in a register different from the record of the first source trigger event.
4. 4. A method according to claim 1, further comprising: towing a third source behind a third vessel, wherein the source behind the third vessel is towed along the probe path, wherein the distance between the third source and the nearest probe is approximately 2L or less; firing the third source in a third instant, whereby a third source trigger event is defined; recording, through the receivers in the probes in a third register, the information of the third source trigger event for a time equal to the travel time of the third source to the maximum depth of interest and to the far distance receiver; wherein the third source trigger event occurs before the end of the record of the information of the third source trigger event.
5. 5. A method according to claim 4, characterized in that the third record is appended to the second record. 6. - A method according to claim 1, further comprising: towing a third probe vessel substantially parallel to the probe vessel, where the distance between the two probes closest to the probe and second probe vessels is approximately equal to the distance between the probes of the first probe vessel; and towing a third probe vessel substantially parallel to the first probe vessel, wherein the distance between the two probes closest to the first and third probe vessels is almost equal to the distance between the probes of the probe vessel; record the information that comes from the first and second firing events in the second probe vessel; Y Record the information that comes from the first and second shooting events on the third probe vessel. 7. A method according to claim 1, further characterized in that the second source is fired with an amplitude greater than that of the firing of the first source. 8. A method according to claim 7, further characterized in that the second source is fired with at least about twice the amplitude of the first source. 9. A method according to claim 1, further characterized in that: said source pomera comprises a first source arrangement having a first source element and a second source element separated on a line substantially normal to the survey line; said second source comprises a second source arrangement having a third source element and a fourth source element separated on a line substantively normal to the survey line at about the same distance as the separation between the ppomer and second source elements; the first source element is triggered at the first instant of time and the third source element is triggered before the end of the recording of the trigger information of the ppmer source element; after recording the information of the third source element trigger, the second source element is triggered; and the fourth source item fires before the end of the record of the information that comes from the firing of the second source element. 10. A method according to claim 9, further characterized in that the second source is fired with an amplitude greater than that of the firing of the first source. 11. A method according to claim 10, further characterized in that the second source is fired with at least about twice the amplitude of the first source. 12. A method according to claim 1, further comprising: towing a third source behind a third source vessel, wherein the third source behind the third vessel is towed along the probe path, at where the distance between the third source and the nearest receiver is approximately twice the distance away from the first vessel, plus the near distance, or less. 13. A method for recording marine seismic data in a data survey, the survey has a line of investigation, and the method comprises: towing a plurality of probes behind a first vessel; further characterized in that the probes comprise a set of seismic signal receivers placed along the probe to receive seismic signals and transmit the signals to the first vessel, and where the outermost probes define a probe path substantially parallel to the line research; tow a first source of seismic signaling behind the first vessel, where the receiver closest to the first seismic source defines a near distance receiver, where the distance between the near distance receiver and the first seismic source defines the near distance, where The furthest receiver of the seismic source ppmera defines a distant distance receiver, and where the distance between the distant distance receiver and the first seismic source defines the distance away from the first vessel; towing a second source of seismic signal behind a second vessel, where the source behind the second vessel is towed along the probe path, wherein the distance between the second source and the nearest receiver is approximately the distance distant from the boat, or less; shoot one of the sources at first, which defines a ppmer source trigger event; receive, through the receivers in the probes, information from the source trigger event for a time equal to the travel time from one of the sources to a maximum depth of interest to the far distance receiver; triggering the other source in a second instant, thereby defining a second source trigger event; receiving, through the same receivers in the probes, the information of the second source trigger event for a time equal to the travel time of the other source up to the maximum depth of interest to the far distance receiver; and wherein the second source trigger event occurs before the end of the record of the information of the first source trigger event. 14 -. 14 - A method according to claim 13, further characterized in that the information received from the second source trigger event is recorded in the same register as the information received from the source trig trigger event 15 - A method in accordance with the claim 13, further characterized in that the information received from the second source trigger event is recorded in a register other than the record of the source trigger event pnmer 16 - A method according to claim 13, further comprising towing a second probe vessel substantially parallel to the first probe vessel, where the distance between the two probes closest to the probe and second probe vessels is approximately equal to the distance between the probes of the probe vessel, and towing a third probe vessel substantially parallel to the probe boat, where the distance in The two closest probes of the first and third probe vessels is approximately equal to the distance between the probes of the probe vessel, record the information that comes from the meter and second trigger events on the second probe vessel, and record the information that comes from the ppmero and second shooting events in the third probe vessel 17. - A method according to claim 13, further characterized in that the second source is fired with an amplitude greater than that of the firing of the first source. 18. A method according to claim 17, further characterized in that the second source is triggered with at least about twice the amplitude of the source digit. 19. A method according to claim 17, further characterized in that: said source poem comprises a first source arrangement having a first source element and a second source element separated on a line substantially normal to the survey line. said second source comprises a second source arrangement having a third source element and a fourth source element separated on a line substantially normal to the survey line at about the same distance as the separation between the first and second elements of fountain; The ppmer source element is triggered in the ppmer instant of time and the third source element is triggered before the end of the record of the information of the first trigger of source element; after recording the Information of the third trigger of the source element, it triggers the second source element; and the fourth source element fires before the end of the recording of the trigger information of the second source element. 20. - A method according to claim 19, further characterized in that the second source is fired with an amplitude greater than that of the firing of the first source. 21. A method according to claim 20, further characterized in that the second source is fired with at least about twice the amplitude of the first source.