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Hydrocarbon Leakage through Fine-grained Series - Focused vs. Distributed
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 79th EAGE Conference and Exhibition 2017, Jun 2017, Volume 2017, p.1 - 5
Abstract
The study compares two modes of hydrocarbon leakage through fine-grained series: focused and distributed. It is based on two types of datasets, a 3-D seismic volume and a set of outcropping seep carbonate bodies. Seismic images of leakage-related features on a 3-D block from West Africa show two contrasting types of anomalies: narrow stacks of amplitude anomalies (“pipes”) on the one hand and km-wide zones of disrupted reflections (“chimneys”) on the other. Pipes are interpreted to reflect hydraulic fracturing above local high points, while km-wide chimneys record capillary leakage from one accumulation. Field observations of fossil seep carbonate bodies indicate that they consist in many cases of a local enrichment in methane-derived carbonate concretions rather than continuous carbonate bodies. Two examples are presented and illustrate the same contrast as previously mentioned about seismic data: the first one, a pinpoint mound at the tip of a hydrofracture fossilized by a sand dyke, records extreme focusing; the second is a 10-m thick interval containing a few percent of concretions that can be followed over several kilometers; it indicates laterally distributed migration. These examples show that geometric analysis can help approach fluid migration processes, on outcrops as well as on seismic data.