Acquiring bottom cable 3D seismic data in environmentally sensitive shallow-water areas greatly increases the need for planning and project management to ensure a safe and efficient program. Addressing these challenges on such a program in offshore Qatar Block 13 demonstrated the value of regular and proactive project team coordination and flexibility; and the skill set and knowledge base of a diverse multidisciplinary team.
In fall 2003, a 250 km2 ocean bottom cable (OBC) 3D seismic program wassuccessfullycompletedinBlock13,offshoreQatar(Figure 1).Seismic acquisition, even a shallow-water 3D program, is not in and of itself a unique operation. Several issues made this program more challenging:
the presence of a 39km2 coral reef, in part, tidally emergent;
water depths in the survey area generally less than 10 meters with the average depth closer to 5 meters; and
the western limit of the survey area corresponding with an international boundary.
Regular and proactive project team communication, operational coordination and flexibility; and a skilled diverse multidisciplinary team were critical to the success of this operation.
Because of the shallow water depths, the Block 13 survey used ocean Bottom cables and a small air gun source. The bottom cables were deployed in a patch of four 3-1/2 km long cables set 400m apart(Figure 2). The source boatshot perpendicular to the cables while an adjacent cable patch is being placed in the next area to be shot. The cable patches are leapfrogged to cover the survey area. An OBC program is equipment-intensive - several tens of kms of cables (Figure 3) and 23 vessels were utilized for this program, while 132 crew members were in the to conduct the operations (Figure 4). Acquisition activities were only conducted during daylight hours for safety reasons, and wind, waves, current, and tides affected the program schedule requiring significant logistical creativity and flexibility (Figure 5).