Combination D-loop/splice for seismic leader wire

#This invention relates generally to devices for storing and transporting geophone leader wires used in seismic exploration, and particularly to a molded D-loop on a leader wire that includes an electrical conductor splice by which the leader wire is joined to a connector assembly which allows sections of leader wire and geophones to be connected end-to-end.

#In land seismic exploration work, geophones are mounted at spaced points along a length of leader wire and are connected to a multi-conductor cable that leads to a multi-channel recording device. For example, an individual section of leader wire might be about 150 feet long and have 12 geophones spaced therealong and electrically connected to its pair of insulated conductors. Each geophone includes a sensor that is contained in a housing which can be anchored to the ground by a spike on the lower end thereof. After the geophones are properly positioned and the leader wires connected up to the main cable, a suitable seismic source such as a charge of dynamite is exploded to generate acoustic waves which travel down through the earth and are reflected back upward when they encounter boundaries between rock strata having impendence differences. The arrivals at the surface of the reflected waves are detected by the geophones, which sends signals over the leader wire and the multi-conductor cable and to the recorder. The signals are used to construct a map of the underground rock layers, which is highly useful in the discovery of structures which might contain oil or gas.

#To facilitate the collection and storage of the leader wires and geophones, so-called "D-Loops" have been used. Instead of coiling or rolling up a string of phones on leader wire which can result in a twisted tangle of equipment, D-Loops which are molded onto the leader wire about every four feet are hung on a hasp structure which resembles a large safety pin. In order to redeploy the geophones along a survey line, the hasp is unhooked and the field person while walking along the survey line permits the D-Loops to slide off of the hasp as the wire and phones are strung out.

#The present invention has the above as well as other objects, features and advantages which will become more clearly apparent in connection with the following detailed description of a preferred embodiment, taken in conjunction with the appended drawings in which:

#FIG. 1 is a side elevational view showing a length of leader wire having D-Loops thereon and stored on a hasp;

#FIG. 2 is a side view, partly in section, of a combination D-Loop and splice in accordance with the invention;

#Referring initially to FIG. 1, a length of geophone leader wire 10 having a plurality of D-Loops 11 thereon is shown stored on a hasp 12 in a manner such that sections 9 of the wire hang between adjacent D-Loops. The D-Loops 11 are positioned at spaced points along the leader wire 10, for example at about ever four (4) feet. The wire 10 can be about 150 ft. long and have about a dozen geophones 8 mounted thereon at spaced points, for example about every twelve feet. In this manner three D-Loops 11 are found between each pair of geophones 9. The hasp 12 can be made of spring wire and has a top arm 13 and a lower arm 18 connected at their inner ends by a vertical leg 16 and several wire coils 17. The outer end of the upper arm 13 is bent downward to provide a vertical leg 14 that terminates in a hook 15. The hook 15 can be engaged with the outer portion 21 of the lower arm 18 in order to trap the D-Loops 11 and the leader wire 10 on the hasp 12 for ease of transportation and storage. One D-Loop 19 is shown as having been removed from the lower arm 18, and is located adjacent to a multi-pin electrical connector 22 by which the end of the leader cable 10 is connected to the main seismic cable (not shown). As will be described in detail below, the D-Loop 19 is combined with a splice in accordance with the present invention. Each of the other D-Loops 11 has a U-shaped upper portion 20 whose lower ends are joined to a tubular body 25 in a manner such that a short length of the leader wire passes axially therethrough. Typically each of the D-Loops 11 is molded onto the leader wire 10 in a single operation as an aid to handling, storage and transportation.

#As shown in FIG. 2, the D-Loop 19 also has an inverted, U-shaped upper portion 20 which is received on the hasp arm 18 during transport and storage. The lower ends 23, 24 of each side leg 7, 8 of the portion 20 are joined to a molded cylindrical body 26 having an outer diameter that is somewhat larger than the outer diameter of the leader wire 10. The opposite end portions 27, 28 of the body 26 extend well beyond the outer sides of the legs 7, 8 and then taper inward to the diameter of the leader wire 10. The extension of the portions 27, 28 provides strain relief due to bending of the wire 10. The respective end portions 30, 31 of the wire 10 extend into the body portions 27, 28 and are bonded thereto. The inner ends of the wire portions 30, 31 are terminated generally just inside the leg ends 23, 24 of the D-Loop 19.

#A length of insulation is stripped from each of the conductor wires 32, 33 (FIG. 4) which are inside the respective leader cable ends, and the bare wires 34, 35 are soldered to terminals 36, 37 near the outer ends of a splice member 38 in the form of a printed circuit board card. The card 38 can be generally rectangular in shape, and the terminals 36, 37 are electrically connected by strips 40, 41 of a conductive foil or solder. The card 38, which is made of a nonconductive or dielectric material, is commercially available from Circuit Boards Of America. Reference may be had to U.S. Pat. No. 4,710,593 for further details of the PCB card construction, which is incorporated herein by express reference. The pair of conductor wires 32, 33 can be connected as shown, or two pairs of conductor wires can be connected with strips and terminals as shown in FIG. 4 on both sides of the card 38. Once the conductors 32 and 33 are connected to the splice card 38 as shown, the body 26 is molded thereover to provide a protected and moisture-proof assembly.