Abstract

The Phetchabun Basin, located within the central Loei Foldbelt, is one of over thirty significant Tertiary Basins in Thailand. The Basin contains numerous, small but complexly faulted structures from which Fletcher Challenge and its Joint Venture partners have produced hydrocarbons. Wichian Buri-1 flowed 500 BOPD on initial tests. Two appraisal wells failed to find hydrocarbons. Reinterpretation with additional infill 2D seismic data did not identify structural closure. Fletcher Challenge then decided to record a 3D seismic survey.

The 14.68 sq. km. survey used 1024 channel Sign Bit technology and a Vibroseis source which was a first for Southeast Asia. Source lines were placed perpendicular to receiver lines to provide sufficient raypaths of varying azimuth and offset in each reconstruction bin. The final bin size was 15 meters in the receiver direction by 22.5 meters in the source direction.

A conventional 3D processing sequence was applied to the data. 3D refraction statics resulted in significant improvement of shallow data when compared with data processed with elevation statics only. Comparisons were made between 1 pass and 2 pass 3D migration.

Line and trace displays and time slices reveal a complexly faulted SE dipping structural nose. The main fault trends run NE to SW and have a frequency of 500 meters or less. A NW to SE trending wrench fault system which was not identifiable with the existing 2D grid cuts across the survey area. Intrusives dated as Mid Miocene are visible on time slices.