3-D structural inversion applied to seismic data from the Northeast China
The fourth 3-D structural inversion case study is from the onshore northeast China; it involves a 3-D survey that covers an area of nearly 150 km2. The surface area is roughly a rectangle with dimensions of approximately 13 km in the inline direction and 12 km in the crossline direction. Survey statistics include more than 1.8 million traces recorded and nearly 120 000 stacked traces. The average fold of coverage is 30, the inline trace spacing is 25 m, and the crossline trace spacing is 50 m.
The fold of coverage is fairly uniform over the survey area as seen from the map in Figure 10.9-1. There are 19 swaths of data recorded using four cables that are 100-m apart, each with 60 receiver groups at 50-m interval. The shots were placed in the direction perpendicular to the swaths. A sketch of the receiver cable layout is also shown in Figure 10.9-1.
Shown in Figure 10.9-2 are selected shot records from each of the 19 swaths with a display gain applied. Each shot record contains 240 traces that correspond to the four 60-channel receiver cables. Examine the shot records and note that the quality of the recorded data is remarkably good, except for some coherent, dispersive, low-frequency and high-amplitude noise at near offsets that may be associated with the ground-roll energy.
With this case study, we shall develop a comprehensive, time-and-depth workflow for processing, inversion and interpretation of 3-D seismic data. This workflow is applicable to many of the oil and gas provinces with low-relief structures and complex structures that involve folding and faulting caused by extensional or compressional tectonism, and moderate-to-strong lateral velocity variations. The workflow, however, is not suitable for imaging beneath complex overburden structures associated with salt tectonism or overthrust tectonism, and strong-to-severe lateral velocity variations (2-D poststack depth migration).
- 3-D DMO processing
- 3-D prestack time migration
- From RMS to interval velocities
- Structural inversion
- Structural and stratigraphic interpretation