f Cross-equalization and pre-stack seismic inversion of timelaps land seismic data, Thrace Basin, Turkey

This study aims to map undrained gas zones by crossequalization and pre-stack seismic inversion of the base and monitor surveys for sweet spot mapping and discriminating pore fill and pressure changes. 4D land seismic data acquired and used in this study is reasonably in good quality but the repeatability is very poor. Spurious 4D anomalies are present in the data even after parallel processing including deconvolution and pre-stack migration. For land seismic data, this is usually expected but it should be noted that amplitude difference between 4D data is not acceptable, and timelapse difference amplitudes seem not to be reasonable (Figure 1, top panel). As a result, a cross-equalization is required before any attempt of time-lapse data analysis and interpretation. The seismic and inverted acoustic impedance (AI) difference maps of crossequalized time-lapse data showed good agreement with the production data at the producing wells assuming that the changes are due to changes in pore fill only. Possible changes and its effect from pressure decrease due to production need further investigation. The gas production is free of water. It is expected to have no water drive, when the gas in the reservoir is produced the gas-water contact stays at the same level.