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Using Gas Chimney Detection to Asess Hydrocarbon Charge and Top Seal Effectivness - Offshore, Namibia
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 76th EAGE Conference and Exhibition 2014, Jun 2014, Volume 2014, p.1 - 5
Abstract
Gas chimney processing was performed on a 3D seismic data in deep water of Namibia. The purpose of the study was to prioritize identified prospects and understand the petroleum system better. The study area is unexplored, but recent offset drilling has identified mature, oil-prone source rocks underlying Upper Cretaceous clastic reservoirs. Gas chimneys were observed below shallow amplitude anomalies attributed to gas in the 3D seismic data. The primary question was whether these disturbed zones represent valid hydrocarbon migration or are due to degradation of the seismic signal below the shallow gas anomaly. Second, if valid then from what interval are the chimneys originating, how are they involved in the charging of the identified prospects, and do they provide clues to the character of leakage from the traps?
Results demonstrate that shallow disturbances represent valid gas chimneys. In a typical slope canyon prospect, Middle Cretaceous source rock is providing hydrocarbon charge to the prospective Upper Cretaceous reservoir objectives. Up dip a broad gas cloud overlies the reservoir, indicating the reservoirs are fully saturated with hydrocarbons and the lighter components are leaking. This implies, that if the migrating hydrocarbons are mixed phase, the objective reservoirs may be oil prone.