Oil and Gas Exploration
Oil and natural gas are a crucial part of the world economy.
Oil, natural gas, and their byproducts like propane and butane are collectively called hydrocarbons. Differences in carbon atoms and in the bonds between atoms give the various hydrocarbons their distinct qualities.
Hydrocarbons are found largely beneath the surface of the earth. They were formed by the decomposition of organic matter over a long period of time and collect within layers of rock. As it collects, pressure rises, the hydrocarbons are expelled and then move through the interconnected pore space within the rock. Rock that is more permeable allows the hydrocarbons to move more easily through it. When the hydrocarbons come up against a layer of rock that is impermeable, they become trapped there and create an oil and/or gas reservoir. Wells drilled into these reservoirs enable the hydrocarbons to be extracted.
Before drilling a well, companies need to identify where the reservoirs are located. In the early days of oil and gas exploration, companies and prospectors would find seeps and drill around them in the hope that large reservoirs would be near. The success rate has greatly improved since then due to the availability of improved exploration methods and the development of technology for improved hydrocarbon recovery. Identifying and defining the reservoir rock, trap, structural elements, and hydrocarbon presence are key to drilling a successful well. Many tools such as well and sample logs, seismic sections, and other surveys can be used to help determine the best location for a well to be drilled.Once a potential location is identified, and leases and right-of-way agreements with landowners are secured, a well can be drilled. Land may need to be cleared and access roads may need to be built in order to get to the future well site. A source of water is necessary and pits are dug to contain the drilling mud.
Once preparations are complete, all equipment is on site, and a drilling permit and other necessary paperwork have been obtained, the next step is to drill the well. Drilling rig with all of its related equipment (drill pipe, drill collars, generators, mud pumps, transfer pumps, motors, bits, steel circulating pits, water storage tanks, etc.) is moved to the well site and is erected. After rigging up, the drilling operation begins. The drill bit cuts through the rock layers beneath the surface and, as it goes deeper, pipe is continually added to give it additional length and reach. Drilling rigs have circulation systems that use pumps and drilling mud to remove the rock fragments created by the drill bit, and it also serves to reduce the friction on the drill bit. The rock fragments and drilling mud that return to the surface are usually examined to determine at what depths various rock layers have been penetrated. The rock layer’s visible porosity and any hydrocarbon indicators are also observed.
Once the drilled hole reaches its final depth and the presence of hydrocarbons is further evaluated by running a suite of electrical logs. Oil company geologists and petroleum engineers review the entire well’s data and recommend completion of the well based on their assessment that the well is deemed likely to produce hydrocarbons. The completion of the well involves running casing to the bottom of the well bore and cementing the casing in the hole by pumping liquid cement that fills up the annular space between the casing and the hole. After waiting on the cement to set, the drilling rig is rigged down and moved off the well site. A completion rig is then moved in and rigged on the well. The completion process usually involves running of depth correlation and cement bond logs. The wellhead is then set up to control the pressure of the well. The well’s casing is then perforated in the prospective hydrocarbon bearing zone. After running a tubing string in the hole, the well is brought in by swabbing the wellbore fluid out of the hole. The wells that penetrate in highly porous rocks generally do not require fracture stimulation for enhanced daily production. The wells that penetrate tight rocks are fractured to enhance porosity and permeability. The wells that do not flow because of lack of pressure or permeability are placed on a pumping system in order to “lift” oil to surface. New gas wells normally do not require any lift system.
The crude oil and natural gas recovered from wells are not the final products. These hydrocarbons must be refined and processed before they reach consumers in the form of many valuable, necessary, and useful everyday products. Fortunately, the byproducts created during the refining of crude oil and natural gas also have many commercial uses and add to its value.
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