Previous 3D visualization studies in seismic data have largely been focused on visualizing reservoir geometry. However, there has been less effort to visualize the vertical hydrocarbon migration pathways, which may provide charge to these reservoirs. Vertical hydrocarbon migration was recognized in normally processed seismic data as vertically aligned zones of chaotic low-amplitude seismic response called gas chimneys, blowout pipes, gas clouds, mud volcanoes, or hydrocarbon-related diagenetic zones based on their morphology, rock properties, and flow mechanism. Because of their diffuse character, they were often difficult to visualize in three dimensions. Thus, a method has been developed to detect these features using a supervised neural network. The result is a “chimney” probability volume. However, not all chimneys detected by this method will represent true hydrocarbon migration. Therefore, the neural network results must be validated by a set of criteria that include (1) pockmarked morphology, (2) tie to shallow direct hydrocarbon indicators, (3) origination from known or suspected source rock interval, (4) correlation with surface geochemical data, and (5) support by basin modeling or well data. Based on these criteria, reliable chimneys can be extracted from the seismic data as 3D geobodies. These chimney geobodies, which represent vertical hydrocarbon migration pathways, can then be superimposed on detected reservoir geobodies, which indicate possible lateral migration pathways and traps. The results can be used to assess hydrocarbon charge efficiency or risk, and top seal risk for identified traps. We investigated a case study from the Dutch North Sea in which chimney processing results exhibited vertical hydrocarbon pathways, originating in the Carboniferous age, which provided the charge to shallow Miocene gas sands and deep Triassic prospects.
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. For this evaluation four examples of hydrocarbon accumulations with effective seals, one example of a breached seal, and one untested prospect are evaluated. From these examples, we have developed criteria to quantify the seal risk and charge capacity by differentiating different types of chimneys 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 and rank prospects. For the intact seals, three of the examples studied had minor chimneys above the accumulation and clear evidence of chimneys providing vertical migration into 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.
SummaryIn this paper we describe how seismically derived gas chimneys can be used to determine hydrocarbon migration paths. The emphasis will be on how to interpret chimney cubes. Through several case history examples, we will show chimney cubes can reveal vertical hydrocarbon migration paths that can be interpreted from their source into reservoir traps all the way to the surface. We will highlight distinguishing features of chimneys for oil-prone versus gas-prone prospects, and those related to separating active fault migration pathways. Further, we will show chimneys can support charging of shallow reservoirs. Our understanding of the petroleum system can improve by combining gas chimney data with other information. As such a chimney cube can be seen as a new exploration tool.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.