California State University, Long Beach
Inside CSULB Logo

Geologist to Study Where Oil-Forming Areas May Lie

Published: November 3, 2008

Geologists understand the fundamental processes of how oil is formed, but Nate Onderdonk, a CSULB assistant professor of Geological Sciences has another idea of where oil might be found.

With a $50,000 grant from the American Chemical Society’s Petroleum Research Fund, Onderdonk and student researchers will look at how the earth’s crust rotates in certain places with the hope of developing a new model of where to find oil-bearing rock as well as a greater understanding of potential seismic risks.

His research has several aspects. “The first is to evaluate how large areas of Southern California have rotated around a vertical axis. We’re situated on the edge of two massive plates, and as those plates move, you oftentimes get smaller pieces of crust that are spinning like ball bearings between those big plates. These areas can be as large as a couple hundred miles across, so we’re talking about whole mountain ranges and whole areas of Southern California,” he explained.

“Part of the grant is addressing that mechanism and how it works,” he continued. “Why do these areas spin and when they do, what kinds of faults are created at the edges and how does that affect the mountain ranges that have developed in Southern California? It’s a rather broad research question in that respect.”

He also will look at active deformation, or fault structures, in the Santa Maria Basin area just northeast of Santa Barbara. “The second aspect is evaluating what is actually happening right now,” he said. “Which faults up there are active; how are they developing over time? The area is also being squeezed and the crust is literally being folded. As you compress it, it’s like a carpet on a floor. You squeeze it and it rumples up.” As part of the study, he and his students will look at river sediment deposits in that area which will help them evaluate how that rumpling is occurring.

“The third aspect is that this is all pertinent to oil traps in that basin,” he said. “Most of the oil-bearing basins in Southern California have developed in association with this rotation. These rotating blocks are causing areas of crust to rip open and produce basins where sediments accumulate. Then, as the rotation continues, the basins are squeezed together and that causes the crust to rumple up. In the deeper parts, oil is formed when it gets into the right heat window, then that oil migrates up into the upper parts of these folds.

Nate Onderdonk

Nate Onderdonk

“People have been looking at oil-bearing basins for a long time and it’s nothing new that these things are stretched apart and organic rock gets deposited, then it gets squeezed back together and that’s where the oil gets trapped and formed. But this rotational component has been largely overlooked. Things aren’t just stretching apart perfectly orthogonally [at right angles] and coming back the same way, they’re actually being squeezed back in a rotational area. That makes it a completely different geometry to the faults and the folds that occur there. I’m evaluating how that unique geometry affects where oil is found,” he said.

“We already know that the oil is there, but to be able to understand why it occurs exactly where it does can help us find oil in other locations. My interest is more scientific, but this has applications for the oil industry, which is why they funded the project.”