Oil and natural gas form within organic-rich rocks that are buried and heated by natural geologic processes. These are referred to as source rocks and are typically organic rich black shales, but can also include coal beds which generate natural gas. Organic-rich shales form when organic matter, primarily in the form of algae living and dying in shallow seas, is deposited and buried with sediments on the seafloor. Over time, the sediment is compressed and undergoes chemical changes, resulting in consolidation of the sediments into rock. With deeper burial, the organic matter is heated and transformed into oil and natural gas. In Ohio, these rocks formed within the Appalachian Basin during the Paleozoic Era, which occurred from 541 to 252 million years ago. The source rocks in Ohio have been identified as the Point Pleasant Formation, the Olentangy and Ohio Shales, the Sunbury Shale, and Pennsylvanian-age coal beds.
Conventional oil and gas reservoirs typically are sandstones, limestones, and dolomites that trap oil and gas in pore space of the rock. Oil and natural gas are lighter than water and will migrate out of a source rock and buoyantly move upwards until it is trapped within the pores of a reservoir rock. A trap for oil and natural gas could include impermeable layers next to the permeable rocks, or it could be related to a geologic structure, such as folds or faults in the rock units. In Ohio, oil and natural gas is produced from conventional reservoirs, such as the Rose Run sandstone, the Trenton Limestone, the “Clinton” sandstone, the Oriskany Sandstone, the Berea Sandstone, and Pennsylvanian-age sandstones.
Ohio has been commercially producing oil and natural gas continuously since 1860. For the first 150 years of oil and natural gas production in Ohio, companies drilled vertical wells to reach conventional reservoirs. Recently, new technologies have been applied to the production of oil and natural gas. Horizontal drilling into organic-rich black shales has opened up new opportunities for oil and natural gas production. Previously, oil and natural gas were explored by drilling into reservoir rocks. The current paradigm is to drill into the source rocks, such as a black shale; hydraulically fracture the shales to produce larger-scale permeability; and allow the oil, natural gas, and natural gas liquids to flow into the horizontal well bore. This methodology currently is being used in the exploration and production of oil, natural gas, and natural gas liquids of the Point Pleasant Formation of Ohio.
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