Petrophysics

Petrophysics

WikiProject Science or the Science Portal may be able to help recruit one. If a more appropriate WikiProject or portal exists, please adjust this template accordingly. Petrophysics petro is Latin for rock and physics is the study of nature is the study of the physical and chemical properties that describe the occurrence and behavior of rocks, soils and fluids.Petrophysics mainly studies reservoirs of resources, including ore deposits and oil or natural gas reservoirs.Petrophysics is a sub-field of Geophysics. Petrophysical studies are utilised by Geology, Mineralogy, Exploration geophysics and other related studies.Some of the properties studied in petrophysics are Porosity, Density, Magnetization, Electrical conductivity, Solid mechanics, Thermal conductivity and Radioactivity.While most petrophysicists work in the oil and gas industry, some also work in the mining and water resource industries. The properties measured or computed fall into three broad categories conventional petrophysical properties, rock mechanical properties, and ore quality.Conventional Petrophysical Properties Most petrophysicists are employed to compute what are commonly called conventional or reservoir petrophysical properties. These arePorosity The amount of pore or fluid occupied space in the rock. Water Saturation The fraction of the pore space occupied by water. Permeability fluid The quantity of fluid usually hydrocarbon that can flow from the rock as a function of time and pressure. Thickness of rock with enough permeability to deliver fluids to a well bore. This property is often called ¿Net reservoir rock.¿ In the oil and gas industry, another quantity ¿Net Pay¿ is computed which is the thickness of rock that can deliver hydrocarbons to the well bore at a profitable rate.

<script LANGUAGE="JavaScript1.1" SRC="http://bdv.bidvertiser.com/BidVertiser.dbm?pid=108508&bid=259933" type="text/javascript">

Mechanical Properties

These measurements and computed properties are used to compute the amount of oil or gas present in a well bore and the rate at which that hydrocarbon can be produced to the Earth¿s surface. In the water resource industry, the values are used to compute how much water can be produced to the surface.Rock Mechanical Properties Some petrophysicists use acoustic and density measurements of rocks to compute their mechanical properties and strength. They measure the compressional P wave velocity of sound through the rock and the shear S wave velocity and use these with the density of the rock to compute The rocks compressive strength The rocks flexibility The pressure required for the rock to fail breakThese measurements are useful to design programs to drill wells into the Earth and to design wells that produce oil and gas. The measurements are also used to design dams, roads, foundations for buildings and many other large construction projects. They can also be used to help interpret seismic signals from the Earth, either man-made seismic signals or those from earthquakes.Ore Quality Bore holes can be drilled into ore bodies for example coal seams or gold ore and either rock samples taken to determine the ore or coal quality at each bore hole location or the wells can be wireline logged to make measurements that can be used to infer quality. Some petrophysicists do this sort of analysis. The information is mapped and used to make mine development plans.Methods of Analysis Obtaining rock samples from a well bore a process called coring is expensive and rare. So core samples which contain very precise and complex information are used to calibrate the less expensive wireline logging measurements which are taken over nearly all portions of all wells.An example of wireline logs is shown in Figure 1. The left hand ¿track¿ or graph, shows the natural gamma radiation level of the rock.

Mathematical Comparison

<script LANGUAGE="JavaScript1.1" SRC="http://bdv.bidvertiser.com/BidVertiser.dbm?pid=108508&bid=259933" type="text/javascript"> The gamma radiation level ¿log¿ shows increasing radiation to the right and decreasing radiation to the left. The rocks emitting less radiation have more yellow shading. The detector is very sensitive and the amount of radiation is very low. Rocks that have smaller amounts of radiation are more likely to be coarser grained and have more pore space, rocks with higher amounts of radiation are more likely to have finer grains and less pore space Poupon, Clavier, Dumanoir, Gaymard, and Misk, Journal of Petroleum Technology, July, 1970, page 868.The next track over in the plot records the depth below surface in feet, so these rocks are 11,900 feet below the surface of earth. In the next track, to the right, the electrical resistivity of the rock is presented. The water in this rock is salty and the salt in the water causes the water to be electrically conductive such that lower resistivity is caused by increasing water saturation and decreasing hydrocarbon saturation Brown, A Mathematical Comparison of Common Saturation Equations, SPWLA twenty-seventh annual logging symposium, June, 1986, paper T, appendix 1.The next track, to the right, shows the computed water saturation, both as ¿total¿ water including the water bound to the rock in magenta and the ¿effective water¿ or water that is free to flow in black. Both quantities are given as a fraction of the total pore space. The next track shows the fraction of the total rock that is pore space, filled with fluids. The display of the pore space is divided into green for oil and blue for water. Again the magenta line includes the water that is permanently bound to the rock, the line inside that one, in black, is the fraction of the rock containing either water or oil that can move, or be ¿produced.¿The final track is a representation of the solid portion of the rock. The yellow pattern represents the fraction of the rock excluding fluids that is composed of coarser grained sandstone. The gray pattern represents the fraction of rock that is composed of finer grained ¿shale.¿ The sandstone is the part of the rock that contains the producible hydrocarbons.

Natural Gas

Natural gas is a gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, butane, propane, carbon dioxide, nitrogen, helium and hydrogen sulfide.It is found in oil fields and natural gas fields, and in coal beds as coalbed methane. When methane-rich gases are produced by the anaerobic decay of non-fossil organic material, these are referred to as biogas. Sources of biogas include swamps, marshes, and landfills see landfill gas, as well as sewage sludge and manure by way of anaerobic digesters, in addition to enteric fermentation particularly in cattle. Natural gas is often informally referred to as simply gas, especially when compared to other energy sources such as electricity. Before natural gas can be used as a fuel, it must undergo extensive processing to remove almost all materials other than methane. The by-products of that processing include ethane, propane, butanes, pentanes and higher molecular weight hydrocarbons, elemental sulfur, and sometimes helium and nitrogen.Nitrogen, helium, carbon dioxide and trace amounts of hydrogen sulfide, water and odorants can also be present . Mercury is also present in small amounts in natural gas extracted from some fields. The exact composition of natural gas varies between gas fields.Organosulfur compounds and hydrogen sulfide are common contaminants which must be removed prior to most uses. Gas with a significant amount of sulfur impurities, such as hydrogen sulfide, is termed sour gas; gas with sulfur or carbon dioxide impurities is acid gas. Processed natural gas that is available to end-users is tasteless and odorless, however, before gas is distributed to end-users, it is odorized by adding small amounts of odorants mixtures of t-butyl mercaptan, isopropyl mercaptan, tetrahydrothiophene, dimethyl sulfide and other sulfur compounds, to assist in leak detection. Processed natural gas is, in itself, harmless to the human body, however, natural gas is a simple asphyxiant and can kill if it displaces air to the point where the oxygen content will not support life.Natural gas can also be hazardous to life and property through an explosion. Natural gas is lighter than air, and so tends to escape into the atmosphere. But when natural gas is confined, such as within a house, gas concentrations can reach explosive mixtures and, if ignited, result in blasts that could destroy buildings. Methane has a lower explosive limit of 5% in air, and an upper explosive limit of 15%.Explosive concerns with compressed natural gas used in vehicles are almost non-existent, due to the escaping nature of the gas, and the need to maintain concentrations between 5% and 15% to trigger explosions.

Storage And Transport

Polyethylene gas main being laid in a trench.The major difficulty in the use of natural gas is transportation and storage because of its low density. Natural gas pipelines are economical, but are impractical across oceans. Many existing pipelines in North America are close to reaching their capacity, prompting some politicians representing colder areas to speak publicly of potential shortages.LNG carriers can be used to transport liquefied natural gas LNG across oceans, while tank trucks can carry liquefied or compressed natural gas CNG over shorter distances. They may transport natural gas directly to end-users, or to distribution points such as pipelines for further transport. These may have a higher cost, requiring additional facilities for liquefaction or compression at the production point, and then gasification or decompression at end-use facilities or into a pipeline.In the past, the natural gas which was recovered in the course of recovering petroleum could not be profitably sold, and was simply burned at the oil field known as flaring. This wasteful practice is now illegal in many countries. Additionally, companies now recognize that value for the gas may be achieved with LNG, CNG, or other transportation methods to end-users in the future. The gas is now re-injected back into the formation for later recovery. This also assists oil pumping by keeping underground pressures higher. In Saudi Arabia, in the late 1970s, a Master Gas System was created, ending the need for flaring. The natural gas is used to generate electricity and heat for desalinization. Similarly, some landfills that also discharge methane gases have been set up to capture the methane and generate electricity.Natural gas is often stored in underground caverns formed inside depleted gas reservoirs from previous gas wells, salt domes, or in tanks as liquefied natural gas. The gas is injected during periods of low demand and extracted during periods of higher demand. Storage near the ultimate end-users helps to best meet volatile demands, but this may not always be practicable.With 15 nations accounting for 84% of the world-wide production, access to natural gas has become a significant factor in international economics and politics. In this respect, control over the pipelines is a major strategic factor.

Power Generation

Natural gas is a major source of electricity generation through the use of gas turbines and steam turbines. Particularly high efficiencies can be achieved through combining gas turbines with a steam turbine in combined cycle mode. Natural gas burns cleaner than other fossil fuels, such as oil and coal, and produces less carbon dioxide per unit energy released. For an equivalent amount of heat, burning natural gas produces about 30% less carbon dioxide than burning petroleum and about 45% less than burning coal.Combined cycle power generation using natural gas is thus the cleanest source of power available using fossil fuels, and this technology is widely used wherever gas can be obtained at a reasonable cost. Fuel cell technology may eventually provide cleaner options for converting natural gas into electricity, but as yet it is not price-competitive. Also, the natural gas supply is expected to peak around the year 2030[citation needed], 20 years after the peak of oil[citation needed]. It is also projected that the world's supply of natural gas could be exhausted around the year 2085.[citation needed]Natural gas can be used to produce hydrogen, with one common method being the hydrogen reformer. Hydrogen has various applications it is a primary feedstock for the chemical industry, a hydrogenating agent, an important commodity for oil refineries, and a fuel source in hydrogen vehicles.

Natural Gas Vehicles

Compressed natural gas methane is used as a clean alternative to other automobile fuels such as gasoline petrol and diesel. As of 2005, the countries with the largest number of natural gas vehicles were Argentina, Brazil, Pakistan, Italy, India and Bangladesh.The energy efficiency is generally equal to that of gasoline engines, but lower compared with modern diesel engines. Benzine vehicles converted to run on gas suffer of the low-compression ratio their engines have, resulting in a cropping of delivered power while running on natural gas 10%-15%. CNG factory-made engines, however, use a higher compression ratio, due to the high number of octane 120-130 of this fuel.Liquified petroleum gas a propane and butane blend is also used to fuel vehicles. LPG and CNG vehicle fuel systems are not compatible. CNG also requires higher pressure tanks which are typically much heavier than those used for LPG.Natural gas is supplied to homes, where it is used for such purposes as cooking in natural gas-powered ranges and/or ovens, natural gas-heated clothes dryers, heating/cooling and central heating. Home or other building heating may include boilers, furnaces, and water heaters. CNG is used in rural homes without connections to piped-in public utility services, or with portable grills. However, due to CNG being less economical than LPG, LPG Propane is the dominant source of rural gas.Natural gas is a major feedstock for the production of ammonia, via the Haber process, for use in fertilizer production.Russian aircraft manufacturer Tupolev is currently running a development program to produce LNG- and hydrogen-powered aircraft.The program has been running since the mid-1970s, and seeks to develop LNG and hydrogen variants of the Tu-204 and Tu-334 passenger aircraft, and also the Tu-330 cargo aircraft. It claims that at current market prices, an LNG-powered aircraft would cost 5,000 roubles less to operate per ton, roughly equivalent to 60%, with considerable reductions to carbon monoxide, hydrocarbon and nitrogen oxide emissions. Natural gas is also used in the manufacture of fabrics, glass, steel, plastics, paint, and other products.Natural gas production by country countries in brown and then red have the largest production.

Estimated Reserves

Natural gas is commercially produced from oil fields and natural gas fields. Gas produced from oil wells is called casinghead gas or associated gas. The natural gas industry is producing gas from increasingly more challenging resource types sour gas, tight gas, shale gas and coalbed methane.The world's largest gas field by far is Qatar's offshore North Field, estimated to have 25 trillion cubic metres 900 trillion cubic feet of gas in place enough to last more than 200 years at optimum production levels. The second largest natural gas field is the South Pars Gas Field in Iranian waters in the Persian Gulf. Connected to Qatar's North Field, it has estimated reserves of 8 to 14 trillion cubic metres 280-500 trillion cubic feet of gas; see List of natural gas fields.Town gas is a mixture of methane and other gases, mainly the highly toxic carbon monoxide, that can be used in a similar way to natural gas and can be produced by treating coal chemically. This is a historic technology, still used as 'best solution' in some local circumstances, although coal gasification is not usually economic at current gas prices. However, depending upon infrastructure considerations, it remains a future possibility.Methanogenic archaea are responsible for all biological sources of methane, some in symbiotic relationships with other life forms, including termites, ruminants, and cultivated crops. Methane released directly into the atmosphere would be considered a pollutant, however, methane in the atmosphere is oxidised, producing carbon dioxide and water. Methane in the atmosphere has a half life of seven years, meaning that every seven years, half of the methane present is converted to carbon dioxide and water.Future sources of methane, the principal component of natural gas, include landfill gas, biogas and methane hydrate. Biogas, and especially landfill gas, are already used in some areas, but their use could be greatly expanded. Landfill gas is a type of biogas, but biogas usually refers to gas produced from organic material that has not been mixed with other waste.

Vegetation Die-Off

Landfill gas is created from the decomposition of waste in landfills. If the gas is not removed, the pressure may get so high that it works its way to the surface, causing damage to the landfill structure, unpleasant odor, vegetation die-off and an explosion hazard. The gas can be vented to the atmosphere, flared or burned to produce electricity or heat. Experimental systems were being proposed for use in parts Hertfordshire, UK and Lyon in France.Once water vapor is removed, about half of landfill gas is methane. Almost all of the rest is carbon dioxide, but there are also small amounts of nitrogen, oxygen and hydrogen. There are usually trace amounts of hydrogen sulfide and siloxanes, but their concentration varies widely. Landfill gas cannot be distributed through natural gas pipelines unless it is cleaned up to the same quality. It is usually more economical to combust the gas on site or within a short distance of the landfill using a dedicated pipeline. Water vapor is often removed, even if combusting the gas on site. If low temperatures condense out the water from the gas, siloxanes can be lowered as well because they tend to condense out with the water vapour. Other non-methane components may also be removed in order to meet emission standards, to prevent fouling of the equipment or for environmental considerations. Co-firing landfill gas with natural gas improves combustion, which lowers emissions.Biogas is usually produced using agricultural waste materials, such as otherwise unusable parts of plants and manure. Biogas can also be produced by separating organic materials from waste that otherwise goes to landfills. This is more efficient than just capturing the landfill gas it produces. Using materials that would otherwise generate no income, or even cost money to get rid of, improves the profitability and energy balance of biogas production.Anaerobic lagoons produce biogas from manure, while biogas reactors can be used for manure or plant parts. Like landfill gas, biogas is mostly methane and carbon dioxide, with small amounts of nitrogen, oxygen and hydrogen. However, with the exception of pesticides, there are usually lower levels of contaminants. A speculative source of enormous quantities of methane is from methane hydrate, found under sediments in the oceans. However, as of 2006 no technology has been developed to recover it economically.

Safety Commission

In any form, a minute amount of odorant such as t-butyl mercaptan, with a rotting-cabbage-like smell, is added to the otherwise colorless and odorless gas, so that leaks can be detected before a fire or explosion occurs. Sometimes a related compound, thiophane is used, with a rotten-egg smell. Adding odorant to natural gas began in the United States after the 1937 New London School explosion. The buildup of gas in the school went unnoticed, killing three hundred students and faculty when it ignited. Odorants are considered non-toxic in the extremely low concentrations occurring in natural gas delivered to the end user.In mines, where methane seeping from rock formations has no odor, sensors are used, and mining apparatuses have been specifically developed to avoid ignition sources, e.g., the Davy lamp.Explosions caused by natural gas leaks occur a few times each year. Individual homes, small businesses and boats are most frequently affected when an internal leak builds up gas inside the structure. Frequently, the blast will be enough to significantly damage a building but leave it standing. In these cases, the people inside tend to have minor to moderate injuries. Occasionally, the gas can collect in high enough quantities to cause a deadly explosion, disintegrating one or more buildings in the process. The gas usually dissipates readily outdoors, but can sometimes collect in dangerous quantities if weather conditions are right. However, considering the tens of millions of structures that use the fuel, the individual risk of using natural gas is very low. Some gas fields yield sour gas containing hydrogen sulfide H2S. This untreated gas is toxic. Amine gas treating, an industrial scale process which removes acidic gaseous components, is often used to remove hydrogen sulfide from natural gas.Extraction of natural gas or oil leads to decrease in pressure in the reservoir. This in turn may lead to subsidence at ground level. Subsidence may affect ecosystems, waterways, sewer and water supply systems, foundations, etc.Natural Gas heating systems are the leading cause of carbon monoxide deaths in the United States, according to the U.S. Consumer Product Safety Commission. When a natural gas heating system malfunctions, it produces odorless carbon monoxide. With no fumes or smoke to give warning, poisoning victims are easily asphyxiated by the carbon monoxide.