Where is oil found?
The oil and natural gas that power our homes, transportation, and businesses are produced in more than 100 countries around the world. Most of those countries produce both oil and natural gas; a few produce only natural gas. Many factors can affect the level of a county’s oil production, such as civil unrest, national or international politics, adherence to quotas, oil prices, oil demand, new discoveries, and technology development or application.
The oil reservoir is typically composed of layers of sandstone, limestone, or dolomite. The reservoir rock has tiny pores, and, in many cases, cracks or fissures, that are filled with oil, gas, and water. The pores and cracks are connected, so that when a well is drilled into the reservoir, the fluids in the pores can drain into the well. Above an oil reservoir is a layer of shale or other fine-grained rock through which water or oil cannot pass. This layer acts like a seal or cap over the actual reservoir. Some Illinois reservoirs are found in dolomite. This rock is similar to limestone but has been chemically altered. The limestone has been recrystalized to form fine-grained dolomite, a process that may dissolve fossils and limestone to form large and small holes (pores) that can hold oil.
where there was a sedimentry rocks, which were rich in organic matter, and then buried at depths where the tempertaure and pressure are enough to transform the organic matter into oil, mostly oil migrates because of the pressure from the area of formation (source rock) through permeable and porous rocks till it is trapped in permeable and porous rocks surrounded by impermeable rocks (trap rocks) ..
