Azimuth Preservation in Pre-Stack Time Migration using Offset Vector Tiles

Abstract

Abstract Wide azimuth (WAZ) land 3D seismic recording geometry typically generates data that is spatially well sampled with a wide range of azimuths and a regular distribution of offsets at those azimuths. Unfortunately, the azimuth information is lost in the pre-stack time migration (PSTM) using traditional processing techniques. Preserving azimuth (the angle measured clockwise from north of a geometric ray that starts at the source point and passes through the receiver point) and offset (the distance between a trace's source and receiver points) information in image gathers is desirable so that the attributes can be used in the detection of horizontal transverse isotropy (HTI), which can provide insight into reservoir fracture orientation. This paper describes the Offset Vector Tile (OVT) processing approach, a new industry trend in seismic data processing to preserve shot-receiver azimuth on image gathers. OVT, also commonly refered to as Common Offset Vector (COV) gathers, are minimal data sets that are linked to patch dimensions and repeat patterns observed in WAZ 3D recording geometry. The OVT method is used to produce single fold pre-stack data volumes that cover the full 3D survey area. All of the traces in a single OVT volume share similar offset and azimuth attributes. Additionally, they provide new opportunities for noise attenuation, trace interpolation, and data regularization. These signal enhancements lead to less migration noise and an overall image improvement. Migration is performed on all of the OVT volumes resulting in an equivalent number of pre-stack migrated data sets, each with their respective azimuth and offset preserved. Traces from each common image point of the numerous migrated OVT volumes are grouped to form image gathers, which can then be analyzed for azimuthal anisotriopy. The OVT method is demonstrated as a case history on a WAZ land 3D survey in the Eastern Province of Saudi Arabia.