Natural gas and petroleum serve as primary energy sources that power much of modern society. These substances are hydrocarbons, organic compounds made primarily of hydrogen and carbon atoms. They are formed from the remains of ancient organisms and are extracted from beneath the Earth’s surface to fuel transportation, generate electricity, and heat homes.
From Ancient Life to Underground Reserves
The formation of the Earth’s hydrocarbon reserves began millions of years ago with the accumulation of organic matter. This organic material included microscopic marine organisms and terrestrial plants. These organisms settled on the bottom of ancient seas and lakes or accumulated in vast swamps after their death.
As layers of sediment covered these organic deposits, the material became buried deeper underground. This burial process created an anaerobic environment, preventing rapid decomposition of the organic matter by bacteria. Over vast stretches of geological time, the increasing weight of the overlying sediments exerted immense pressure on the buried organic layers.
Meanwhile, as the organic matter was driven deeper into the Earth’s crust, it was subjected to rising temperatures due to geothermal heat. The pressure and temperature transformed the organic material through a process known as catagenesis. During catagenesis, the complex organic molecules broke down into simpler hydrocarbon compounds.
Temperature, pressure, and organic matter type determined whether crude oil or natural gas formed. Generally, oil forms at temperatures between 60 and 150 degrees Celsius, while natural gas, a simpler hydrocarbon, requires higher temperatures exceeding 150 degrees Celsius, or longer heating. These newly formed hydrocarbons then migrated through porous rock formations, accumulating in permeable reservoir rocks capped by impermeable layers, creating underground traps.
Finding and Tapping the Earth’s Deposits
Locating these hydrocarbon reserves requires advanced geological and geophysical techniques. Geologists first conduct regional studies, analyzing surface and historical geological data to identify areas with potential source rocks, reservoir rocks, and trapping structures. This initial assessment helps narrow down vast areas to promising exploration targets.
Seismic surveys are then employed to create detailed images of subsurface rock layers. This method involves generating sound waves using specialized trucks or air guns, and recording the echoes that bounce back from different rock interfaces. Analyzing the travel times and patterns of these reflected waves allows geophysicists to map the underground geological structures and identify potential hydrocarbon traps.
Once a promising deposit is identified, drilling operations begin to access the hydrocarbons. Conventional drilling involves sinking a vertical wellbore directly into the reservoir rock to extract oil or natural gas. This method is effective for reservoirs that are relatively shallow and directly beneath the drilling rig.
For complex or spread-out reservoirs, directional drilling and horizontal drilling techniques are utilized. Directional drilling allows the wellbore to be steered at an angle from the vertical, accessing reserves beneath inaccessible areas or multiple reservoirs from a single drilling pad. Horizontal drilling extends a wellbore horizontally through a reservoir rock layer, maximizing exposure to the hydrocarbon-bearing formation and increasing extraction efficiency.
Hydraulic fracturing, or fracking, is a specialized technique used to extract natural gas and oil from low-permeability shale formations. This process involves pumping a high-pressure mixture of water, sand, and chemicals into a horizontally drilled wellbore. The pressure creates tiny fractures in the shale rock, propped open by sand, allowing the trapped natural gas or oil to flow into the well and to the surface.
Transforming Raw Material for Use
After extraction, crude oil or natural gas undergoes several processing steps to make it usable. Natural gas contains impurities like water vapor, hydrogen sulfide, carbon dioxide, and heavier hydrocarbons. These “wet” gases are sent to gas processing plants where these impurities are removed.
The removal of water prevents pipeline corrosion and hydrate formation, while hydrogen sulfide and carbon dioxide are acid gases, corrosive and reduce energy content. Heavier hydrocarbons like propane and butane are separated out as natural gas liquids (NGLs) with commercial uses. The remaining “dry” natural gas, primarily methane, is then compressed and transported.
Crude oil, a complex hydrocarbon mixture, requires refining to be transformed into products like gasoline, diesel, jet fuel, and lubricants. At a refinery, crude oil is heated and sent to a distillation tower, where different hydrocarbon components separate based on their boiling points. Lighter, more volatile components rise to the top of the tower, while heavier components remain at the bottom.
To transport natural gas over long distances where pipelines are not feasible, it can be cooled to -162 degrees Celsius (-260 degrees Fahrenheit), converting it into liquefied natural gas (LNG). This liquefaction process reduces its volume, allowing economic transport by specialized LNG tankers across oceans. Pipelines serve as the primary method for transporting raw and processed natural gas and crude oil from production sites to processing plants, refineries, and distribution networks.