WO1999031760A1

WO1999031760A1 - Seismic data acquisition radio antenna

Info

Publication number: WO1999031760A1
Application number: PCT/IB1998/002043
Authority: WO
Inventors: Larry George Slay; William Terry Mcdavid
Original assignee: Schlumberger Holdings Limited; Schlumberger Canada Limited; Services Petroliers Schlumberger
Priority date: 1997-12-17
Filing date: 1998-12-15
Publication date: 1999-06-24
Also published as: AU1443099A

Abstract

A radio antenna for use during seismic data acquisition having first and second antenna elements (12) lying in offset approximately vertical planes, and electrical contacts that allow the first and second antenna elements to transmit seismic data in an omni-directional horizontally polarized manner. The antenna elements are moveable between deployed positions and stowed positions and a transformer (24) positioned at the top of the antenna mast (14) is protected by shock absorbing material. The antenna elements are preferably collapsible against the mast and may be locked in the collapsed position and the deployed position by fasteners. A method of acquiring seismic data using the radio antenna is also disclosed.

Description

SEISMIC DATA ACQUISITION RADIO ANTENNA

The present invention relates to radio antennas and more particularly to a radio antenna adapted for use during seismic data acquisition.

Seismic data is acquired to analyze the subsurface of the Earth, particularly in connection with hydrocarbon exploration and production activities. To acquire seismic data during a seismic survey, an acoustic source is used which may comprise explosives or a seismic vibrator on land or an impulse of compressed air at sea. The acoustic signals produced by the acoustic source are reflected by the various geologic layers beneath the surface of the Earth and are sensed by a large number (typically hundreds or thousands) of sensors such as geophones on land and hydrophones at sea. The seismic data is recorded and analyzed to derive an indication of the geology in the subsurface. Maps produced by processing the seismic data are used to assess the likelihood and location of potential hydrocarbon deposits.

Seismic surveys are typically conducted using one or more receiver lines, each receiver line having a plurality of receiver station locations spaced evenly along its length. A plurality of sensors are typically placed in an areal pattem about each receiver station location. In some types of environments, seismic data is relayed from the sensors to centralized recording equipment using transmission cables. In other types of environments, particularly in what are referred to as transition zones (deltas, swamps, marshes, etc.), it is very difficult to deploy transmission cables between the receiver station locations and the centralized recording equipment and radio transmission equipment is used to relay the seismic data from the sensors to a radio receiver and its associated seismic data recording and processing equipment. A device that receives seismic data from sensors located at between 1 and 4 receiver station locations and transmits the seismic data to a radio receiver is referred to as a seismic data acquisition unit. The inventive radio antenna is typically used in conjunction with such a seismic data acquisition unit or similar types of seismic data acquisition equipment. The seismic data acquisition unit typically comprises a sealed buoyant container that is connected to sealed seismic sensors (hydrophones and/or geophones) and contains analog to digital conversion circuitry for converting the seismic signals picked up by the sensors into digital data and a radio transmitter for transmitting the digital data to a radio receiver connected to processing equipment for processing the digital data. The seismic data acquisition unit also typically incorporates a memory device that stores the seismic data until an acknowledgment has been received from the radio receiver that the seismic data has been properly transmitted and received. Information is exchanged in both directions between the radio receiver and each seismic data acquisition unit as seismic data is being acquired by the seismic data acquisition system, and each seismic data acquisition unit (and its associated radio antenna) is involved with both transmitting and receiving information while the seismic survey is being conducted.

The antennas most commonly used with seismic data acquisition units are lightweight vertically polarized omni-directional dipole whip antennas. A significant advantage of this type of antenna is that it does not need to be aligned toward a particular radio receiver location. This is particularly important for seismic surveys because the position of the radio receiver may need to be moved during a seismic survey and it often cost prohibitive to reorient a large number of deployed antennas during a seismic survey. It is significantly more cost effective to deploy the seismic data acquisition unit (and its associated radio antenna) and then to revisit the location only once to collect the equipment when seismic data from the vicinity of that particular station location is no longer required. The omnidirectional nature of these whip antennas also reduces the possibility that radio contact with the seismic data acquisition unit will be lost due to the accidental reorientation of the antenna while the seismic survey is being conducted.

Whip antennas used with seismic data acquisition units are typically enclosed within a hollow tapered epoxy-fiberglass antenna housing that provide the antenna with mechanical support as well as protection from environmental forces. Because these antennas are shaped like pool cues, they are easily handled and transported. The antennas may be bundled together and manually carried by the seismic survey crew members or by transportation equipment such as trucks or helicopters. This is particularly important because seismic surveys are often conducted in very difficult to access areas, and the cost of transporting seismic data acquisition equipment into and out of a survey area is often a significant component in the cost of conducting a seismic survey. Another advantage of these antennas is that they are very durable. Seismic surveys are often conducted in extremely difficult operational areas, and the equipment used must be extremely rugged to withstand environmental forces such as wind and rain, saltwater corrosion, contamination by dirt and mud, and rough handling.

A significant problem with the conventional whip antennas, however, is that their transmission/reception range is significantly restricted in areas having dense vegetation. Steps that have been taken in the past to address this limitation of conventional whip antennas have included increasing the power of the transmitter unit, raising the antenna until it projects above the vegetation, and using directional antennas. The use of more powerful transmitters both increases the cost and decreases the battery life of the seismic data acquisition equipment. It may take a team of two seismic crew members twenty minutes to mount a conventional whip antenna on to a sixty foot extension pole. The additional time required can significantly increase the cost of conducting a seismic survey, particularly when large numbers of extension poles are required. While directional antennas have better transmission and reception ranges in densely vegetated areas than conventional whip antennas, they suffer from numerous drawbacks, including being relatively expensive, cumbersome, and lacking the durability of conventional whip antennas. Even more significant is the fact that directional antennas can effectively transmit and receive information from only a limited range of directions. If a change in location of the radio receiver is required, this often requires the directional antennas to be reoriented. Because the cost of reorienting a directional antenna can be roughly equivalent to the cost of placing the seismic acquisition equipment at the station location in the first place, in practice it eliminates the option of moving the radio receiver while the seismic survey is being conducted, thus effectively limiting the spread size that can be used during the seismic survey.

It is an object of the present invention to provide an improved radio antenna that is particularly adapted for use during seismic data acquisition.

An advantage of the present invention is that the antenna operates in an omnidirectional horizontally polarized manner and possesses an enhanced transmission range through dense vegetation.

A further advantage of the present invention is that under certain circumstances the antenna will not need to be moved or reoriented if the radio receiver is moved during a seismic survey.

According to the present invention there is provided a radio antenna for use during seismic data acquisition having first antenna elements, second antenna elements connected to the first antenna elements, these first and second antenna elements lying in offset approximately vertical planes, and electrical contacts that allow the first and second antenna elements to transmit seismic data in a omni^¬ directional horizontally polarized manner to a radio receiver. Preferred features of the inventive radio antenna include mounting the antenna elements for easy movement between deployed positions and stowed positions and mounting the antenna elements so they lie in orthogonal vertical planes when deployed.

Additional preferred features include driving the antenna elements using a 90 degree Hybrid Matching transformer and driving the first antenna elements at +45 degrees and the second antenna elements at -45 degrees, balanced to ground. The antenna elements may also be DC grounded through the transformer to the shield return of the RF coaxial unbalanced antenna transmission line for DC static drain.

The antenna elements are preferably mounted to a mast that is deployed in a substantially vertical manner. The transformer that drives the antenna elements is preferably located at the top of the mast and is protected by shock absorbing material. The antenna elements are preferably collapsible against the mast and may be locked in the stowed position or in the deployed position by a spring loaded fastener.

An inventive method of acquiring seismic data using the radio antenna is also disclosed that involves the steps of deploying a radio receiver, and deploying a omni-directional horizontally polarized radio antenna to transmit seismic data to said radio receiver.

A preferred embodiment of the method involves deploying the omni-directional horizontally polarized radio antennas at station locations where dense vegetation is present between the radio receiver and the station locations and deploying whip antennas at other station locations. Further preferred features of the present invention are set out in the dependent claims.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of a radio antenna for use during seismic data acquisition in accordance with the invention;

Figure 2 shows an enlarged external view of the top of the radio antenna from Figure 1;

Figure 3 shows a vertical cross sectional view through the top of the radio antenna from Figure 1 ;

Figure 4 shows a horizontal cross sectional view through the top of the radio antenna from Figure 1 taken along line 4-4 in Figure 3;

Figure 5 shows a side view of an alternative embodiment of the inventive radio antenna;

Figure 6 shows a top down view of the radio antenna from Figure 5;

Figure 7 shows an enlarged view of portions of the radio antenna from Figure 5; and

Figure 8 shows a schematic view of a seismic survey being conducted using the inventive radio antenna. A perspective view of a radio antenna in accordance with the present invention is shown in Figure 1 and is generally designated as reference number 10. Radio antenna 10 has four arms 12 that are pivotally mounted to a mast 14. The arms 12 may be moved between a deployed position perpendicular to the mast 14 and a collapsed position generally parallel to the mast. In Figure 1 , three arms 12 have been placed in the deployed position and one arm has been placed in the collapsed position for illustration purposes. At the end of the arms 12 are safety tips 16 that reduce the chance of eye injuries to seismic crew members handling or coming into contact with the radio antenna 10. Large protective balls or loops could also be used at the ends of the arms 12 instead of the safety tips 16. A retention cup 18 is slidingly mounted about the mast 14 and is biased in an upward position by spring 20. To place the radio antenna 10 in the stowed or collapsed position, each of the arms 12 are pivoted into a position parallel to the mast 14. The retention cup 18 is then manually slid toward the bottom of the mast 14 and the safety tips 16 are placed adjacent to the mast. The retention cup 18 is then released and the spring 20 moves the cup upward toward the top of the mast 14, thereby surrounding and restraining the arms 12 and allowing the radio antenna 10 to be transported in the stowed or collapsed position. In this way, the retention cup 18 acts as a spring loaded fastener. Other types of fasteners could also used, such as a piece of hook and loop tape attached to one of the arms 12 that is wrapped around the other arms 12 and then fastened, much in the way the ribs of some umbrellas are restrained in their collapsed position. At the bottom of the radio antenna 10 is an electrical connector 22 that allows the radio antenna to be connected to a seismic data acquisition unit. At the top of the mast 14 is a rubber bumper 24 that helps to protect the electronics used to drive the antenna arms 12. Many of the components of the antenna 10 are manufactured from stainless steel to prevent component corrosion in the field. This embodiment is referred to by Applicants as the "turnstile" antenna. The inventive radio antenna 10 has a transmission range in dense vegetation approximately 50% greater than the transmission range of a conventional whip antenna. In this embodiment, the pairs of arms 12 located on opposite sides of the mast 14 act as first and second antenna elements which are driven by an internal transformer (discussed below) and which transmit seismic data in an omnidirectional horizontally polarized manner to a radio receiver. The mast is intended to be mounted approximately vertically and the pairs of arms 12 are therefore located in 90 degree offset (orthogonal) approximately vertical planes when deployed.

Figure 2 shows an external enlarged view of the top of the radio antenna 10. It can be seen in Figure 2 that each arm 12 is rigidly attached by small pins to a support bracket 26. The support bracket 26 is attached by a spring biased pin 28 that pulls the bracket toward a pair of recesses that hold the sleeve in two alternative positions. In the collapsed position, a portion of the support sleeve rests within a first recess 30 and in the deployed position, this portion of the support sleeve rests within a second recess 32. The spring biased pins 28 act as fasteners to lock the support brackets 26 and associated arms 12 into place in these positions. The bumper 24 is typically made of rubber or a similar shock absorbing elastomeric material that helps to protect the internal electrical components from damage. A pair of wires 34, connected to the support bracket 26, are used as electrical contacts that allow the arms 12 to transmit seismic data in an omni-dimensional horizontally polarized manner to a radio receiver.

A cross sectional view of the top of the radio antenna 10 is shown in Figure 3. A transformer 36 located at the top of the mast 14 is connected by a length of coaxial cable 38 that passes through the center of the mast 14 to the electrical connector 22. The transformer 36 is preferably a 90 degree Hybrid transformer with dual balanced terminal outputs and an unbalanced input terminal. In the preferred embodiment, the transformer 36 is a broadband 90 degree Hybrid Matching transformer (having 50 ohm antenna input and two balanced 75 ohm output ports). This transformer drives the first antenna elements at +45 degrees and the second antenna elements at -45 degrees, balanced to ground, using two power splitters, in the 16 MHz band. A Trafo Signal Transformer sold by IF Engineering may be used for instance as the transformer 36. During assembly of the radio antenna 10, the transformer 36 is covered by potting compound and the lid 40 is secured to the primary housing 42 using an adhesive. The transformer 36 is preferably located at the top of the mast 14 to limit the chances of moisture intruding into and shorting out the electrical circuitry. The antenna elements may be DC grounded through the transformer 36 to the shield return of the coaxial cable 38, which is also referred to as RF coaxial unbalanced antenna transmission line, for DC static drain.

Figure 4 shows how the transformer 36 may be electrically connected to the arms 12 through the use of the wires 34. Crimp terminals may be used to attach the wires 34 to the output studs of the transformer 36.

It can be seen in Figure 4 that opposite (rather than adjacent) arms 12 are paired up. The support bracket 26 and connected arm 12 located on the top-left of Figure 4 is paired up with the support bracket 26 and connected arm 12 located on the lower-right of Figure 4. These components act as first antenna elements in radio antenna 10. Similarly, the support bracket 26 and connected arm 12 located on the lower-left of Figure 4 is paired up with the support bracket and connected arm located in the upper-right corner. These elements are depicted in the stowed position and are therefore not visible in the plan view shown in Figure 4. These components act as second antenna elements in radio antenna 10. The first antenna elements and second antenna elements are physically connected, in this case by being pivotally fixed to the primary housing 42, but the first antenna elements and the second antenna elements are electrically connected only through a transformer winding interface within the transformer 36. Figure 5 shows a side view of an alternative embodiment of the inventive radio antenna which is generally designated as reference number 50. Alternative radio antenna embodiment 50 utilizes four metal spring loaded flat bladed antenna loops 52 instead of the arms 12 shown in Figure 1. The antenna loops 52 are supported by a mast 54, made of a suitable material such as fiberglass or aluminum, and is shown attached to a conventional seismic data acquisition unit 56. Located on the top of the mast 54 is a fixed support 58 and located between the top and bottom of the mast is a sliding guide 60. When the sliding guide 60 is locked in its uppermost position (shown), the antenna loops 52 are locked in their deployed positions. When the sliding guide 60 is locked in its lowermost position, the antenna loops collapse against the mast 54 and are locked in their collapsed positions. In this position, the alternative embodiment is stowed and may be easily transported. A single 50 ohm coax cable runs through the center of the mast 54.

Figure 6 shows a top down view of the alternative embodiment 50. It can be seen in this view that the ribbon-like antenna loops 52 lie in orthogonal approximately vertical planes when deployed.

Figure 7 shows a close up view of the fixed support structure 58 and the sliding guide 60. The sliding guide 60 incorporates a pair of spring loaded pins 62 which are biased inwardly toward the mast 54. These spring loaded pins 62 match up with sets of corresponding holes in the mast 54 and allow the radio antenna 50 to be placed in the deployed position or the collapsed position simply by retracting the pins, sliding the sliding guide 60 into the appropriate position, releasing the pins, and allowing the ends of the pins to seat into the appropriate positioning holes. When the sliding guide 60 has been locked in the lowermost stowed position, the antenna loops 52 will be located near the mast 54. The lower ends of antenna loops 52 are connected to the sliding guide 60 by lower pivot pins 64. Similarly the upper ends of the antenna loops 52 are connected to the fixed support structure 58 by upper pivot pins 66. A transformer 68 is connected to the antenna loops 52 by four jumper wires 70 (only two of which are shown in Figure 7). Sufficient freeplay is incorporated into the length of the jumper wires 70 to allow a connector 72, which joins jumper wire 70 and antenna loop 52, to freely pivot about upper pivot pins 66 when the antenna loops are moved between their deployed and the collapsed positions. Opposing antenna loops 52 are electrically connected together within the sliding guide 60, such as through the use of a jumper strap.

Similarly to the previous embodiment, the antenna loop 52 located on the top of Figure 6 is paired up with the opposite antenna loop 52 located on the bottom of Figure 6 and these components act as first antenna elements in radio antenna 50. Similarly, the antenna loop 52 located on the left of Figure 6 is paired up with the opposite antenna loop 52 located on the right of Figure 6 and these elements act as second antenna elements in radio antenna 50. The first antenna elements and second antenna elements are physically connected, in this case by being pivotally connected to the support structure 58 and the sliding guide 60, but the first antenna elements and the second antenna elements are electrically connected only through a transformer winding interface within the transformer 68. The antenna elements may be DC grounded through the transformer 68 to the shield return of the coax cable for DC static drain.

The radio antennas 10 and 50 provide broadband frequency response and greater RF operating range in dense vegetation than conventional vertically polarized whip antennas.

To maintain the essentially vertical orientation of the masts 14 or 54, the antennas 10 or 50 may be mounted directly on the seismic data acquisition unit or may, alternatively, be directly mounted on the ground using a suitable support, such as being lashed to a tree. The radio antenna 50 has an operating frequency range of between 66 and 82 MHz and can accept up to 5 watt of power (which could be higher with a higher powered transformer). The Dual Loop antenna gain is - 3 dBd (Horizontal Polarization) for Omni-Directional use. The Single Loop antenna gain is 0 dBd (Horizontal Polarization) for Bi-Directional use. The matching network drives the loops 90 degrees out of phase, balanced to ground. The antenna matching network uses a 90 degree quad hybrid transformer having 50 ohm antenna input and 2 balanced 200 ohm output ports. The network and feedline remain stationary in transport or in operational mode.

Figure 8 is a schematic view of a seismic survey showing a method of acquiring seismic data using the inventive radio antenna. In Figure 8, an area having dense vegetation is denoted as heavily vegetated area 74 and an area lacking dense vegetation is denoted as remaining area 76. A radio receiver 78 is located in the middle of a number of receiver lines 80, each of which typically has a number of station locations spaced evenly along their lengths. The radio receiver 78 may use, for instance, an omni-directional dipole antenna or a large directional log-periodic dual beam antenna. The radio receiver antenna may be mounted on a large commercial antenna mast that could be between 90 and 120 feet in height. Positioned at station locations inside the heavily vegetated area 74 are omni-directional horizontally polarized antennas 82 and positioned at station locations in the remaining area 76 are omni-directional vertically polarized antennas 84. Using this type of layout, it is possible to move the position of the radio receiver 78 without requiring the reorientation of the antennas 82 and 84, due to the omni-directional nature of the antennas.

In some circumstances, it may also be necessary or desirable to use the omnidirectional horizontally polarized antennas 82 in areas lacking heavy vegetation. It may be desirable, for instance, to use the antennas in lightly vegetated areas when heavily vegetated areas are present between the antenna location and the radio receiver 78.

In an actual seismic survey, over five hundred seismic data acquisition unit antennas may be used and these antennas may be positioned along a number of receiver lines.

In addition, it is possible that the length of the receiver lines 80 may exceed the operating range of the antennas 82 and 84 and their associated transmission and reception equipment. The receiver lines 80 may for instance be between 12 and 14 miles in length while the operating range of the antennas 82 and 84 may be limited to 7 or 8 miles. In this case, it is possible to divide the seismic survey area into two or more regions and to use a different radio receiver 78 in each of these regions.

The present invention includes any novel feature or novel combination of features disclosed herein, either explicitly or implicitly.

Claims

CLAIMS:

1. A radio antenna for use during seismic data acquisition, said radio antenna comprising: first antenna elements, second antenna elements, connected to said first antenna elements, and electrical contacts allowing said first and second antenna elements to transmit seismic data in an omni-directional horizontally polarized manner to a radio receiver.

2. A radio antenna as claimed in Claim 1 , in which said first and second antenna elements lie in orthogonal approximately vertical planes.

3. A radio antenna as claimed in either Claim 1 or 2, in which said antenna elements are mounted for movement between deployed positions and stowed positions.

4. A radio antenna as claimed in any one of the preceding claims, in which said antenna elements may be fastened in said stowed positions and in said deployed positions.

5. A radio antenna as claimed in any one of the preceding claims, in which said first antenna elements comprise a pair of arms and said second antenna elements comprise a pair of arms.

6. A radio antenna as claimed in Claim 5, in which said arms are pivotally mounted on pins and are spring biased toward pairs of recesses that alternatively hold said arms in deployed positions or in collapsed positions.

7. A radio antenna as claimed in any one of the preceding claims, in which said antenna elements are driven by a transformer.

8. A radio antenna as claimed in Claim 7, in which said transformer is connected to a RF coaxial unbalanced antenna transmission line having a shield return and said antenna elements are DC grounded through said transformer to said shield return for DC static drain.

9. A radio antenna as claimed in either Claim 7 or 8, in which said first antenna elements are driven at +45 degrees and said second antenna elements are driven at -45 degrees, balanced to ground.

10. A radio antenna as claimed in any one of Claims 7 to 9, in which said transformer is a 90 degree Hybrid Matching transformer.

11. A radio antenna as claimed in Claim 7, in which said antenna elements are mounted on to a mast having a top and a bottom.

12. A radio antenna as claimed in Claim 11 , in which said mast is deployed in a substantially vertically manner.

13. A radio antenna as claimed in either Claim 11 or 12, in which said antenna elements are collapsible against said mast.

14. A radio antenna as claimed in any one of Claims 11 to 13, in which said transformer is located at or near said top of said mast.

15. A radio antenna as claimed in any one of Claims 11 to 14, in which said transformer is protected by a shock absorbing material.

16. A method of acquiring seismic data, said method comprising the steps of: deploying a radio receiver, and deploying a radio antenna at a station location to transmit seismic data to said radio receiver, said radio antenna having first antenna elements, second antenna elements connected to said first antenna elements, and electrical contacts allowing said first and second antenna elements to transmit seismic data in an omni-directional horizontally polarized manner to said radio receiver.

17. A method of acquiring seismic data as claimed in Claim 16, further comprising the step of deploying a whip antenna to transmit seismic data to said radio receiver at a station location different from the station location at which said omni-directional horizontally polarized radio antenna is deployed.

18. A method of acquiring seismic data as claimed in Claim 17, in which said omni-directional horizontally polarized radio antenna is deployed at a station location where dense vegetation is present between said radio receiver and said station location and said whip antenna is deployed at a station location where dense vegetation is not present between said radio receiver and said station location.

19. A method of acquiring seismic data as claimed in any one of Claims 15 to 18, in which said first and second antenna elements are mounted for movement between deployed positions and stowed positions.

20. A method of acquiring seismic data as claimed in any one of Claims 15 to 19, in which said first and second antenna elements are connected to a seismic data acquisition unit.

21. Seismic data acquisition equipment including a radio antenna as claimed in any one of Claims 1 to 15 and further including a seismic data acquisition unit connected to said radio antenna.