APES Energy Practice Test

Hydrocarbons originate from organic-rich sedimentary rocks that have been buried enough to heat up and mature the contained organic matter. The best source rocks are fine-grained, organic-rich sediments—think shale or mudstone—because their small particles help preserve organic material and create the right conditions for low decay and preservation of kerogen. When these rocks are buried to sufficient depths, the heat and pressure transform the organic matter into hydrocarbons, producing crude oil and natural gas. Saying the rock is fine-grained and organic-rich and buried at tens to hundreds of meters (depending on geothermal gradient) captures the essential idea of a source rock. The other options don’t fit: coarse sandstone with little organic content lacks enough organic material to generate significant hydrocarbons; an igneous rock with high silica contains little to no preserved organic matter; metamorphic rock formed under heat typically has altered or SAMPLEexpelled any original organics and isn’t a common source rock for oil and gas.