Natural Gas: From Exploration to Consumption

[Dalton Tallia] [ENGL 202C] [Professor Leslie Mateer]

AUDIENCE AND SCOPE ANALYSIS The purpose of this technical document is to provide an introduction into the processes required to gather natural gas from the ground and eventually consume it. This document is suitable for introductory engineering students, personnel new to the natural gas industry, or anyone who wishes to attain a general background understanding of the process. This document will focus on providing basic information about each step in order to provide the user with a general background. This document will provide an overview of the process of gathering natural gas, which includes exploration, extraction, processing, transportation, and consumption. Natural gas has been used across the world for many years and will continue to be a primary source of energy in the future. Therefore, it is important to have a general understanding of this process of its gathering. INTRODUCTION: THE OVERALL PROCESS The gathering of natural gas, a multi-step process, consists of several stages that range from the exploration for natural gas reserves to the extraction and transportation that is necessary for it to eventually be consumed. Natural gas is found in many places around the world, but in order for it to be extracted exact locations must be found. Once a pocket of gas has been found it is necessary for drilling to occur. When the extracted natural gas has high concentrations of gases other than just methane, processing is needed so that the final gas is composed of solely methane. After it is processed, it is compressed and transported through miles of pipelines before it is finally consumed at its final location. Exploration

Extraction

Processing

Transportation

Consumption Figure 1: Process of Gathering of Natural Gas

BACKGROUND INFORMATION Natural gas is found thousands of feet in the earth in many different locations across the world. It has been extracted since as far back as 900 B.C. in China through small wells that had gas seep out of rocks and springs. In the first century, the Chinese would use metal drilling bits and hollowed-out bamboo pipes to drill deeper and extract gas. In the United States, the first use of natural gas occurred in 1821 in New York. Nearly 40 years later the first natural gas company, Fredonia Gas, Light, and Waterworks Company, was founded in the same location where it was first found. Eventually the first pipeline was created that ran 25 miles from Fredonia to Rochester in the State of New York.

As of the year 2000 there were over 600 natural gas processing plants in the United States that have gas delivered to them through over 300,000 miles of pipelines. Currently, many nations use natural gas as one of its leading sources of energy, which can be seen in Figure 2. Additionally, the United States currently uses natural gas as 13.17% of its overall electricity generation. This is a number that could increase greatly in years to come as restrictions on coal (53.42%) increase and while nuclear (20.81%) continues to be a reluctant source of energy in the publics eye.

Figure 2: World Energy Use By Fuel

When natural gas is extracted from the ground it comes out in a raw form that is made up of several gases. Typically, the primary gas that is sought after is methane, which usually makes up 70-90% of the gas that is extracted from the Earth. The natural gas that is consumed after the gathering process is finished is cleaned of other gases and has a composition that is made up almost entirely of methane. Table 1 shows the typical composition of Natural Gas when it is initially extracted from the ground, before all other gases are removed. Table 1: Typical Composition of Natural Gas Exiting The Earth Typical Composition of Natural Gas Exiting The Earth Methane Ethane Propane Butane Carbon Dioxide Oxygen Nitrogen Hydrogen sulphide Rare gases CH4 C2H6 C3H8 C4H10 CO2 O2 N2 H2S A, He, Ne, Xe 0-8% 0-0.2% 0-5% 0-5% trace 0-20% 70-90%

STEP 1: EXPLORATION The first step of the gathering of natural gas is exploration because extraction is not possible if the gas has not first been found. Across the world there are many areas that are rich in natural gas, as can be seen in Figure 3. This figure shows the areas that have high production in red. Within each red area it is still necessary to find exact locations that are guaranteed to have gas pockets.

Figure 1: Natural Gas Production The development of advanced technology over the past 20 years has revolutionized the practice of locating natural gas deposits. Previously, the location of natural gas was limited to searching for surface evidence, which was time consuming and inefficient. Even with modern day technology it can still be extremely difficult to find deposits, as they exist thousands of feet in the ground. One type of exploration is through geological surveys, through which geologists examine the earths surface for areas that resemble past deposit sources. Through this they can determine the areas that are most likely to have natural gas. One example of this is through anticlinal slopes where the earth has folded on itself, creating a dome that is typical of many reservoirs. A more technological method is through seismic exploration. Essentially, scientists found out that they can create vibrations on the surface that run through the earth and are reflected back. Based on differences in how the vibrations are returned, gas pockets can be found as they do not reflect the vibrations.

Other methods include offshore seismology and the use of magnetometers and gravimeters. In general, it is important to realize that exploration is a necessary step in the gathering of natural gas. It is extremely expensive to drill thousands of feet into the earth, which makes it essential that when drilling occurs there is actually gas below. STEP 2: EXTRACTION Natural gas can be extracted from the ground in both onshore and offshore locations. There are countless factors that go into the extraction process, including the type of rock being drilled into, the depth of the gas, and the pressure at which it is at. After drilling down, some natural gas is at a high enough pressure that it will rise to the surface on its own. Once this pressure decreases and gas ceases to rise to the surface it is necessary to use additional help. One common way to continue to gather gas is through the use of pumps. The process of gathering high pressure gas along with the use of pumps is commonly referred to as the primary recovery stage. In the secondary stage it is necessary to pump fluids down into the well to gather more gas. The gas from the primary stage commonly has water in it. When water is extracted it is at times pumped back into the well, effectively pushing gas out, while disposing of the waste water. There are other techniques that are at times used in order to maximize the amount of gas that is gathered. Regardless of the technique, it is essential that as much gas is captured as possible in order for the well to be profitable. Extraction occurs across the world, and as seen in Figure 4, water is not a limitation when it comes to the gathering of natural gas.

Figure 2: Offshore Drilling Rig STEP 3: PROCESSING When gas is extracted from the earth it comes out in its raw form. Typically, it reaches the surface with only about 70-90% of its content as methane. Therefore, it is necessary to remove the other gases that are mixed with it, as well as any water, liquid, dirt, and sand. The amount of these excess materials varies depending on the region where the natural gas is gathered, which determines the extent of processing that is needed.

Any solid materials, such as dirt and sand can first be removed through filters or traps that are located near the well. After this, it may be necessary to remove water vapor that is in the gas. This is necessary because at points in the pipeline the vapor may condense into water, which could sit in low spots in the pipeline, eventually causing corrosion problems. The water vapor is removed by passing the gas through a tower with a liquid or solid desiccant. Desiccants are objects that essentially promote drying, as the particles remove the water vapor from the natural gas. Glycol is commonly used as a liquid desiccant in dehumidifiers. The final step is to remove all other hydrocarbons, so that methane is essentially the only remaining gas. This is done in gas processing plants that receive natural gas from many wells in a certain region. Figure 5 shows a picture of a gas processing plant. These plants remove the gases through a two possible processes. The first is similar to the process that is used for the removal of water, through the use of oil that has a high affinity (or attraction) to the molecules of the heavier gases that are not methane.

Figure 3: Natural Gas Processing Plant

The second method is through cryogenic expansion. All of the gases that exit the ground have different chemical make ups, with methane being the least dense. Therefore, they all have varying freezing points. By passing all of the natural gas through a tower that has a temperature near -120 degrees it is possible to extract unwanted gases. This temperature drop causes the heavier gases that must be removed to condense while keeping methane in its gaseous form allowing it to flow out alone. All of these steps allow for the successful removal of unwanted materials, which is necessary for final consumption. STEP 4: TRANSPORTATION Now that the gas has been found, extracted, and cleaned, it is ready to be transported to its final destination. The transportation of natural gas is done through miles of pipeline systems. In order for the gas to move, it must be at a high enough pressure. Therefore, it is necessary to compress the gas, which increases the pressure to anywhere between 200 and 1500 psi (pounds per square inch). Depending on the initial pressure, it is necessary for the gas to enter a compressor station about every 100 miles in order to keeps the gas flowing. Figure 6 shows the transcontinental pipeline system.

Figure 4: Transcontinental Pipeline System

STEP 5: CONSUMPTION Once the gas reaches its final destination it is ready for consumption. The gas has been processed to be essentially methane, which can be burned for a variety of uses. In some areas, the gas is stored in underground caverns prior to use, whereas in many cities the gas is transported directly to its destination. Once the gas is ready for consumption, the pressure is once again reduced, to around 0.25 psi. Natural gas is used for a variety of purposes, as can be seen in Figure 7. This shows that the main use is for electric generation (30%). Additionally, it is used for industrial, residential, and commercial purposes.

Figure 5: Natural Gas Consumption By Sector

CONCLUSION The gathering of natural can be simplified into five steps: 1. Exploration: The first step is to find where large deposits of natural gas are located. 2. Extraction: Drilling is necessary to gather the gas from thousands of feet below the earths surface. 3. Processing: Raw natural gas must be cleaned before it can be transported and consumed. 4. Transportation: The gas must be compressed and then transported through extensive pipeline systems that span the country. 5. Consumption: Once it reaches its destination the natural gas can be used for a variety of purposes. With such a large portion of the worlds energy dependent on the use of natural gas it is important to know the overall process. It is a clean alternative to other energy sources and will be prevalent for many years to come. Every year the number of jobs in this industry increases, and you could possibly find yourself filling one of these positions in the future. Just remember, that the gathering of natural gas can be simplified into five steps, and if needed you can quickly refresh your knowledge of the process using this document.

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