Natural Gas Production
Exploration of Natural Gas
Natural gas production begins with its exploration. This is actually a fairly involved process. Technologies used in the exploration of oil and gas have changed drastically over the last 20 years. Natural gas exploration and production is quite different today than it was in the early days. The only way to locate underground petroleum and natural gas in those days was to search for evidence on the surface of the ground. Those looking for it had to go around searching for seepages of oil or gas being emitted from the underground before they had any idea where deposits of these substances were. Since so few petroleum or natural gas deposits actually seep to the surface, their efforts were very inefficient and the exploration process was extremely difficult.
Due to the advancement of technology, geologists and geophysicists have gained knowledge about the properties of underground natural gas deposits. By gathering certain data which can be interpreted, they can make educated guesses as to where natural gas deposits may be. Since most of these deposits are thousands of feet below the surface of the earth, this exploration is still uncertain.
The first step in the exploration for natural gas is a geological survey. In this process, geologists examine the surface structure of the earth. It’s interesting, but in the mid 18oos, it was discovered that “anticlinal slopes” (slopes where the earth folds upward upon itself) had a particularly high chance of containing petroleum or natural gas deposits. These anticlinal slopes form a dome shaped area. This is the case for a large number of petroleum reservoirs. The geologist can first survey and map out the surface and the sup surface features of a specific area. They can then extrapolate the areas that are most apt to contain one of these reservoirs of petroleum or natural gas.
Geologists use a number of useful tools in gathering all of their data. They gather clues from such things as the outcroppings of rocks that are found in valleys or gorges. They gather other information from samples that are dug up during the digging of other oil or gas wells along with water wells. These samples can tell the geologist a lot about the formation of rocks that are underneath the surface of any particular area. If you would like more information on petroleum geology, you can visit the American Association of Petroleum Geologists (AAPG).
Once the geologist has located areas that have a good possibility of containing reservoirs of natural gas, their findings are given to a geophysicist, who then uses their specific technology in finding and mapping underground rock formations. The tests they run allow for a lot more accurate mapping of these underground formations. What they are looking for are formations that are commonly associated with these reservoirs.
Seismology is probably the greatest breakthrough for the exploration of natural gas and petroleum. Seismology is the study of seismic energy waves, and how they move through the Earth’s crust. Through this technology, they can determine the makeup of various formations far beneath the earth’s surface. The concept of seismology is fairly simple. The Earth’s crust is composed of many different layers. The makeup and density of each formation affects how these seismic waves travel.
It was Luigi Palmieri who designed the first mercury seismometer in 1855. This was designed to record the time, intensity, and duration of an earthquake. It was 1921 when this technology was first introduced to the petroleum industry in locating underground fossil fuel formations.
Through seismology, the geophysicists can create vibrations on the surface and then record the vibrations that are reflected back to the surface on very sensitive geophones, that are embedded in the ground. Different rock formations will reflect those waves back differently. Thus, they are able to confirm the rock formations. The more dense the rock, the more solid the vibrations will be that return. Rock that is extremely porous will absorb the vibrations.
The data that is picked up by these geophones is collected by a seismic recording truck. This data is then reviewed and analyzed by the geophysicists and engineers. At times, they set off an underground explosive and measure the seismic waves. These underground explosions have been pretty much curtailed due to environmental concerns. Currently, instead of using underground explosions, newer technology involves the use of a very large wheeled or tracked vehicle that carries special equipment that is designed to create a large impact or a series of vibrations. This truck uses a large piston in the middle to create the vibrations on the surface. The seismic waves are sent downward and reflected back where they are recorded.
For offshore seismic exploration, the process is a little different. Since the exploration is being done under the surface of water a ship is used instead of a truck. Instead of geophones, hydrophones are used. These hydrophones are towed behind the ship. The other part that is different is the ship used a large air gun to release bursts of compressed air under the water. This then creates the seismic waves which are capable of traveling through the Earth’s crust. As a result, the seismic reflections necessary to get the proper readings are also generated.
There are two other devices used by geophysicists for determining the composition of formations below the Earth’s surface. These two devices are the magnetometer and the gravimeter. The magnetometer is designed to measure small differences in the Earth’s magnetic field, which are generated as a result of various underground formations. The magnetic properties of various underground formations provide valuable geological and geophysical data. The gravimeter is a device that measures gravitational force. Various underground formations and rock types all have a different effect on the gravitational field that surrounds the Earth. This device is extremely sensitive and measures very minute differences in gravitational force. Through those measurements, geophysicists can analyze those formations and determine their makeup. They can determine whether the formations have the potential for containing hydrocarbons like natural gas.
The best, and most accurate method for determining the geology of the subsurface, is to drill an exploratory well. Exploratory wells consist of digging into the Earth to allow geologists to study the composition of the various rock layers in detail. The problem with exploratory wells is they are expensive and time consuming. The only time they drill an exploratory well is when there is already an indication there is a high probability of petroleum formations.
The legal process has to be completed before drilling can begin. Next comes negotiating a legal arrangement to allow the natural gas company to extract and sell the resources under a specific area of land. This contract is established between the gas company and the legal owner of the mineral rights and land. Sometimes, the owner of the land doesn’t own the mineral rights. Once this is completed, the drilling company accesses the proper drilling permits.
Processes to Extract Natural Gas
Once potential natural gas deposits have been located and the geophysical team identifies the optimal location for the well, the baton is handed off to the drilling experts. Each time a new well is dug, there is an inherent chance that no gas will be found. There has been some advancement in this technology which has increased the efficiency, as well as the success rate, in drilling natural gas wells. This is true for onshore as well as offshore gas wells. Exploration and production companies spend a large sum of money before any drilling takes place.
There are a number of factors that determine the exact placement of the drill site. With the new technology of horizontal drilling, the rig doesn’t have to be set up directly above the potential formation.
If the well is a success and comes in contact with natural gas deposits, it is termed a “development” well. Now the well may be completed, which will bring about the production of natural gas. But, if they were wrong and there isn’t potential for a marketable amount of natural gas, the well is termed a “dry well.” At that point, it’s back to the drawing board.
Once the well has been verified that quantities are sufficient to extract, the well still must be completed. A casing is used to strengthen the well hole. Once they evaluate the temperature and pressure of the product, the proper equipment is put in place to ensure adequate flow of natural gas from the well.
There are actually two different kinds of conventional natural gas wells. There are “natural gas wells” and “natural gas condensate wells.” Often, oil wells also contain rich supplies of natural gas, which can be harvested. The natural gas is often used to add pressure to the well which enhances the extraction of the oil.
Condensate wells are wells that contain both natural gas and a liquid condensate, which is a liquid hydrocarbon mixture. This liquid is either separated from the natural gas at the wellhead or during the processing stage. Since natural gas is actually lighter than air, it naturally rises to the surface of a well.
Extracting Through Gasification
Gasification is a procedure where natural gas is extracted from coal. The diagram above is provided by Conoco Philips, which shows the gasification process, which utilizes a gasifier. Coal is fed into the gasifier and exposed to intense heat, oxygen and steam. The oxygen level is as high as 99% (room air is 21%). Instead of burning, the coal is broken apart into what is called syngas. The portion of coal that doesn’t become syngas includes carbon monoxide, hydrogen, and other gases. These become a slag material that resembles glass. Other byproducts are sulfur and ammonia. Any ash that is formed is removed in a later process.
The syngas that is produced by the gasifier goes through significant processing. In this processing, pollutants are stripped out and the resulting product is methanol. Other chemicals are stripped out and used for a variety of purposes. Hydrogen is used in fertilizer production and in the production of fuel cells.
Extracting Through Fracking
Fracking is short for hydraulic fracturing. Fracking is used to extract natural gas from shale rock that is deep below the Earth’s surface. Hydraulic involves a fluid. In this case, it is water. This water is mixed with sand and certain chemicals and pressurized. This pressurized mix is pumped into the shale rock, which causes fractures in the rock. Since the natural gas is pressurized, when fractures and cracks occur in the shale rock, the gas is released. There has recently been a lot of controversy over fracking and ground water quality.
One thing to keep in mind is that shale natural gas is typically one to two miles below the surface of the ground, while ground water is several hundred feet down at the most. Fracking wells contain multiple barriers of steal casing and cement that reach well below the water table, which protect the water from contamination. Much of the fracking water is now recycled and it is kept away from drinking water.
Future Production of Natural Gas
Notice the chart below that is provided by U.S. Energy Information Administration (EIA). Shale gas had grown to approximately 14% of all natural gas supplied in 2009. It is projected to contribute close to half of our total supply by the year 2035. Natural gas production is just getting ready to take off.