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  Interpreting Sequence Stratigraphy Data

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- but we're looking at world-wide effects. And so how does thisimpact how we interpret what our sands and shales look like? If we use the chronostratigraphic concepts we look for maximum flooding surfaces. So if you're using logging, or seismic, whatever you're using, you start looking for maximum flooding surfaces. It may just be a twitch on your well logs. It could be a velocity changein your seismic patterns. And you find those, andthen you start looking for variations along those. In this case we have coastal plain, a very low sea level system here. Flooding surface comes in. That flooding surface can also be a seal. The sediment package moves far inland. And here we have the coastalplain sandstone and shales, and here we have the shale,shallow marine system. And then we have dropping of sea level, so these transgress outacross the earlier sediments, and then a major flooding again, another major flooding surface, and so on. So, we have this package of sequences, and if we have unconformities, then we'll call the whole thing a sequence in each one of these parasequences. And you can see this helps you identify which sands occurred. You can use paleontological or palynology to help you define these as ages, and you can see how thesecorrelate from well to well. If you use lithostratigraphic concepts, and just look at the type ofsediment but not the ages, you might make a correlation like this where you correlate this sand three, with this sand two withsand one and sand one. And these sands look like they correlate, and if you were to produce this field that this would all bea connected reservoir. Through production testingand production history you might quickly find outthat they're not correlated and you'd have to start thinking about "How can I re-map the field?". Well, think about chronostratigraphic concepts and sequence stratigraphy. And as you're doing that, either locally with one field or regionally, think about the sea level curves. When you had major rising sea levels you'd tend to form some greatmaximum flooding surfaces. When you had falling sea level systems, lots of reservoirs formedand within these sequences you have parasequencesthat you can identify to help you map your systems either regionally, or within fields.