A search for seismic characteristics of vertical fluid leakage along major faults and in the overburden of fault intersections in the Mikkel area with an eye to CO2 storage
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The gas/condensate Mikkel Field is located in a structurally complex area in the Norwegian Sea, offshore Norway. The Mikkel structure is not filled to its spill point and it is possible that hydrocarbons might have leaked from the reservoir to the overburden rocks. Therefore this study was initiated to search for any possible indications of vertical hydrocarbon leakages in the area. All types of available data were utilized to analyze the seismic anomalies identified in the area. To map the possible seismic indications above the Mikkel structure, three key horizons and major and some minor faults in the overburden strata were interpreted. Seismic attribute maps were created in the interpreted intervals to highlight any possible seismic indications of leakage in the area. AVO and Petrophysical analyses were performed to determine the lithology and the type of anomalies observed in the study area. Mud gas analyses were carried out to find out any possible gasindications in the seismic deteriorated zones. After careful investigations, two zones of seismic amplitude dimming/brightening and a high amplitude anomaly were identified. The dimmed zones originated above BCU and terminated in the shallower levels. The high amplitude anomaly was observed and analyzed at the top of Tare Formation. The AVO analyses indicated similar response at the observed high amplitude anomaly and in the hydrocarbon filled Ile Formation. Seismic attribute maps were made to map these anomalies. These maps supported the earlier observations made on seismic sections. The observations showed that leakage might have occurred through the reactivated faults or fracture systems and other reason may be through pore network. The results from this study will help in focusing the discussion around suitable areas for CO2 storage.