Natural Gas Lecture 1 PDF

Basra Engineering Technical College Instructor: Iltifat Hameed Department of fuel and energy Gas Technology Lecture 1 Class – 3rd 1.0 INTRODUCTION Th...

Basra Engineering Technical College Instructor: Iltifat Hameed Department of fuel and energy Gas Technology Lecture 1 Class – 3rd 1.0 INTRODUCTION The Basics of Natural Gas Natural gas is a subcategory of petroleum that is a naturally occurring, complex mixture of hydrocarbons, with a minor number of inorganic compounds. Is a fossil energy source are made from plants and animals which accumulate in deep beneath the earth's surface. Is considered as an environmentally friendly clean fuel, offering important environmental benefits when compared to other fossil fuels. The superior environmental qualities over coal or crude oil are that emissions of sulfur dioxide are negligible or that the levels of nitrous oxide and carbon dioxide emissions are lower. This helps to reduce problems of acid rain, ozone layer, or greenhouse gases. Natural gas is also a very safe source of energy when transported, stored, and used. Natural gas contains many different compounds. Table 1 shows composition of a typical natural gas. The largest component of natural gas is methane, a compound with one carbon atom and four hydrogen atoms (CH4). Natural gas also contains smaller amounts of hydrocarbon gas liquids, and nonhydrocarbon gases, such as carbon dioxide and water vapor. Table 1: Composition of a Typical Natural Gas 1 Raw natural gas comes primarily from any one of three types of gas wells: 1) crude oil wells 2) gas wells 3) condensate wells. Natural gas wells average 6000 feet deep. Almost 1828.800m. Raw Natural Gas Raw natural gas can be processed into different fractions: – Natural Gas – methane content of 90%, processed to specific composition and energy content – Natural Gas Liquids (NGL) – mixture of ethane, propane, butane and pentane – Liquefied Petroleum Gas (LPG) – mixture of propane and butane compressed to liquid at room temperature – Liquefied Natural Gas (LNG) – natural gas liquefied by refrigeration at -162⁰C and atmospheric pressure, volume 1/600 of natural gas at room temperature – Compressed Natural Gas (CNG) – natural gas compressed to less than 1% of volume at atmospheric pressure Formation of natural gas Millions to hundreds of millions of years ago and over long periods of time, the remains of plants and animals (such as diatoms) built up in thick layers on the earth’s surface and ocean floors, sometimes mixed with sand, silt, and calcium carbonate. Over time, these layers were buried under sand, silt, and rock. Pressure and heat changed some of this carbon and hydrogen-rich material into coal, some into oil (petroleum), and some into natural gas. 2 Basic Definition 1. Migration: Migration is the movement of oil from a mother rock to a reservoir rock. There are three types of hydrocarbon migration Primary Migration Primary migration is the process by which hydrocarbons are expelled from the source rock into an adjacent permeable carrier bed. i. Secondary Migration Secondary migration is the movement of hydrocarbons along a "carrier bed" from the source area to the trap. ii. Tertiary migration It is a migration that occurs when petroleum moves from one trap to 3  another or to a seep. 2. Mother Rock: Mother rocks are any rocks in which sufficient organic matter to form Petroleum has been accumulated & preserved. 3. Reservoir Rock: Other porous, permeable rock formations in which petroleum has accumulated. 4. Trap: A geometric configuration of structure in which permeable rock types are surrounded and confined by impermeable rock types. 5. Pores are open spaces between the particles of a rock. Pores may contain air, gas, or liquid (water or oil). The more pore space, the higher the porosity. The more “connected” the pores, the higher the permeability. Pore fluids will flow more easily in rocks that are more permeable. ‫فديو توضيحي لعملية الهجرة البترولية وكيفية حدوثها‬ https://www.youtube.com/watch?v=iCTDSuDcyPw Parameters Controlling Oil and Gas Occurrence 1. Source Rocks (Mother Rocks) ▪ Source rock refers to rocks from which hydrocarbons have been generated or are capable of being generated. ▪ They are organic-rich fine-grained sediments that may have been deposited in a variety of environments including deep water marine, lacustrine and deltaic, and under low energy, reducing conditions. ▪ The most important factor in the generation of petroleum in source rock is temperature: 225o to 350oF (107o and 176oC) - the “hydrocarbon window”. 4 ▪ The action of heat on the insoluble organic matter (kerogen) contained in source rocks leads to the formation of oil and gas. 2. Reservoir Rocks ▪ A petroleum reservoir is a porous and permeable rock in communication with a mature source bed. ▪ Sandstones and carbonate rocks form the overwhelming majority of reservoirs world-wide. ▪ Under special circumstances, igneous and metamorphic rocks can also act as petroleum reservoirs. 3. Traps ▪ A trap is an arrangement of rock layers that contains an accumulation of hydrocarbons, yet prevents 5  them from rising to the surface. ▪ The trap consists of an impermeable layer of rock above a porous, permeable layer containing the hydrocarbons. It can be structural traps or stratigraphic traps or combination of these factors. I. Structural traps occur when the reservoir formation deforms, the three basic forms of structural traps are the anticline trap, the fault trap and the salt dome trap. a. Anticlinal (fold) Trap An anticline is an area of the subsurface where the strata have been pushed into forming a domed shape. If there is a layer of impermeable rock present in this dome shape, then hydrocarbons can accumulate at the crest until the anticline is filled, the highest point where hydrocarbons can escape the anticline. This type of trap is by far the most significant to the hydrocarbon industry. 6  b. Fault Trap This trap is formed by the movement of permeable and impermeable layers of rock along a fault line. The permeable reservoir rock faults such that it is now adjacent to an impermeable rock, preventing hydrocarbons from further migration. c. Salt dome Trap Masses of salt are pushed up through clastic rocks due to their greater buoyancy, eventually breaking through and rising towards the surface (see salt dome). This salt is impermeable and when it crosses a layer of permeable rock, in which hydrocarbons are migrating, it blocks the pathway in much the same manner as a fault trap. II. Stratigraphic traps are formed as a result of lateral and vertical variations in the thickness, texture, porosity or lithology of the reservoir rock. Examples of this type of trap are an unconformity trap, a lens trap and a reef trap. 7  a. unconformity trap A stratigraphic trap formed by folding, uplift, and erosion of porous strata, followed by the deposition of later beds which can act as a seal for oil, gas, or water. Although common structures, these traps contain only 4% of the world's oil, perhaps because of losses that occur during uplift and erosion. b. reef trap Stratigraphic oil or gas trap produced by porous reef limestones (reservoir rock) covered by impermeable strata. Porosity of limestones depends on post-depositional diagenetic changes. Natural Gas Resources As illustrate in figure 1.1, in some places, natural gas moved into large cracks and spaces between layers of overlying rock. The natural gas found in these types of formations is sometimes called conventional natural gas. In other places, natural gas occurs in the tiny pores (spaces) within some formations of shale, sandstone, and other types of sedimentary rock. This natural gas is referred to as shale gas or tight gas, and it is sometimes called unconventional natural gas. Of the unconventional gas sources, the one most source for industry is coal bed methane (CBM) which is natural gas that has been formed along with the geological processes that formed coal. Natural gas also occurs with deposits of crude oil, and this natural gas is called associated natural gas. Natural gas deposits are found on land, and some are offshore and deep under the ocean floor. 8  I. Conventional Resources are concentrations of oil or gas that occur in discrete accumulations or pools. Rock formations hosting these pools traditionally have high porosity and permeability and are found below impermeable rock formations. These impervious layers form barriers to hydrocarbon migration resulting in oil and gas being trapped below them. Conventional oil and gas pools are developed using vertical well bores and using minimal stimulation. II. Unconventional Resources are oil or gas-bearing units where the permeability and porosity are so low that the resource cannot be extracted economically through a vertical well bore and instead requires a horizontal well bore followed by multistage hydraulic fracturing to achieve economic production. III. Coal bed methane (CBM) is a form of natural gas extracted from coal beds, is released or produced when the pressure of water inside the buried coal decreases by pumping either vertically or tilting into horizontal surface holes. In recent decades it has become an important source of energy in United States, Canada, Australia, and other countries. Utilization of Natural Gas Natural gas is one of the major fossil energy sources. When one standard cubic feet of natural gas is combusted, it generates 700 Btu to 1,600 Btu of heat, depending upon gas composition. Natural gas provided efficient quantity of energy around the world, the main uses of NG include: 9  1. Power generation 2. Hydrogen production 3. Vehicles 4. Residential domestic use 5. Fertilizer 6. Aviation 7. Natural gas is also used in the manufacture of fabrics, glass, steel, plastics, paint, and other products Exercise Natural gas from the Gazprom County, Russia, is the world's largest natural gas company has a heating value of 1,598 Btu/scf. If this gas is combusted to generate power of 1,000 kW, what is the required gas flow rate in Mscf/day? Assume that the overall efficiency is 50 percent (1 kW= 3412 Btu/h). 10 Figure 8: expectation the amount of Iraqi gas production and consumption. 11