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When we put together the well logs and the seismic cube, we noted a number of things about the rock layers.

• The marker beds slope up from the sides of the cube to the middle, forming a dome shape. If this dome were on the Earth’s surface it would look like a hill.
• There are some misalignments in the layers, which indicate places where the rock has shifted. This may point to faulting, because the rock layers are no longer continuous. This is common below the surface of the Earth.
• The porosity of the rock is low above the marker bed and high below it. The water saturation is high above the marker bed, low immediately below the marker bed, and then high again.

So, where are you most likely to find oil within the seismic cube? The section where the data indicates high porosity and low water saturation would indicate the greatest possibility of oil. The porosity allows fluid to accumulate, and the low water saturation suggests that something else, likely oil, has a high saturation. The rock beneath the oil reservoir would be saturated with water, which is denser than oil. Oil floats on water, so in the rock it would rise above the water.

Remember that the top of the cube represents the land surface. So the best place to drill for oil is where the two cross pieces of seismic data meet, in the middle of the cube. Drilling in this location puts you directly above the portion of the reservoir that is closest to the surface and has the greatest volume of rock with high porosity and low water saturation.