Publications

Dip or strike? During the decision making process for a new marine towed streamer seismic survey, the shooting direction depends not only on geophysical factors such as, expected frequency content, structural dip, fault orientation, but also surface logistics such as, survey dimensions and obstructions to the movement of the vessel and it’s spread. Generally, data is acquired in the geologic dip direction to enable finer inline sampling in the dominant dip direction and perpendicular orientation to the faults. However, in many cases, economic and logistical factors override the geophysical issues and a survey is acquired in the most efficient direction. This case study describes a survey adjacent to a surface no-access zone, and the subsurface structural dip of interest is not aligned to the most efficient survey direction. Prior to acquisition, extensive 3D kinematic ray tracing analysis and 3D illumination studies were performed to estimate the illumination and sampling requirements for a steeply dipping fault zone and thereby determine the optimum practical direction. The need for optimal sampling in the dip direction whilst maintaining efficiency, led to data acquisition using multi-measurement streamers. This technology allows for reconstruction of the wavefield sampled equally in both inline and crossline directions, thereby achieving both operational efficiency and geophysical sampling requirements. To further validate the integrity of the shooting direction decision, a swath of data was also acquired in the dip direction and compared to the reconstructed data acquired in the strike direction.