ABSTRACT

This paper describes how seismically derived 3D chimney volumes or “cubes” can be used to assess seal risk in exploration wells in the shelf and upper slope of the Gulf of Mexico. In this study, four examples of hydrocarbon accumulations with effective seals, one example of a breached seal, and one untested prospect were evaluated. From these examples, criteria were developed to quantify the seal risk and charge capacity based on chimney character, distribution and other information. Such criteria can then be applied to predict seal integrity on un-drilled prospects. The emphasis will be on how chimney cube interpretation can be used in an integrated workflow to constrain uncertainty on both seal and charge for hydrocarbon exploration. For the intact seals, three of the examples studied had minor chimneys above the accumulation and clear evidence of chimneys below the reservoir interval. These traps were also characterized by relatively low relief and inferred low strain rates. One of the intact seals was adjacent to a zone of vertical chimneys related to salt movement. However the reservoirs themselves were outside this disturbed zone and were characterized by moderate to low relief and low strain. In contrast, the trap which represented a breached accumulation was adjacent to a major chimney which vented hydrocarbons to the surface. It was also characterized by high structural relief and was within the disturbed zone, inferring higher strain rates. The Prospect evaluated was also adjacent to a zone of vertical chimney development. However, the reservoir objectives for this Prospect were outside the disturbed zone inferring lower strain rates. The trap also had moderate relief and is interpreted as a moderate to low risk for seal failure.

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