Associated gas

Knowledge of a crude oil s overall physical and chemical characteristics will determine what kind of initial treatment —associated gas separation and stabilization at the fi ld of production— transport, storage, and of course, price. 

The resulting vapor phase is called associated gas and the liquid phase is said to be the crude oil. The production of gas is generally considered to be unavoidable because only a small portion is economically recoverable for sale, and yet the quantity produced is relatively high. The reservoirs in the Middle East are estimated to produce 0.14 ton of associated gas per ton of crude. 

Sulfur comes mainly from the decomposition of organic matter, and one observes that with the passage of time and of gradual settling of material into strata, the crude oils lose their sulfur in the form of H2S that appears in the associated gas, a small portion stays with the liquid. Another possible origin of H2S is the reduction of sulfates by hydrogen by bacterial action of the type desulforibrio desulfuricans (Equation 8.1) ... 

To prepare gas for evacuation it is necessary to separate the gas and liquid phases and extract or inhibit any components in the gas which are likely to cause pipeline corrosion or blockage. Components which can cause difficulties are water vapour (corrosion, hydrates), heavy hydrocarbons (2-phase flow or wax deposition in pipelines), and contaminants such as carbon dioxide (corrosion) and hydrogen sulphide (corrosion, toxicity). In the case of associated gas, if there is no gas market, gas may have to be flared or re-injected. If significant volumes of associated gas are available it may be worthwhile to extract natural gas liquids (NGLs) before flaring or reinjection. Gas may also have to be treated for gas lifting or for use as a fuel. 

The composition of natural gas varies oonsiderably from lean non-associated gas which is predominantly methane to rich associated gas containing significant proportion of natural gas liquids. Natural gas liquids (NGLs) are those components remaining once methane and all non-hydrocarbon components have been removed, i.e. (Cg-C ). 

Associated gas free natural gas in immediate contact, but not in solution, with cmde oil in the reservoir. 

The main commercial source of methane, ethane, and propane is natural gas, which is found ia many areas of the world ia porous reservoirs they are associated either with cmde oil (associated gas) or ia gas reservoirs ia which no oil is present (nonassociated gas). These gases are basic raw materials for the organic chemical industry as well as sources of energy. The composition of natural gas varies widely but the principal hydrocarbon usually is methane (see Gas, natural). Compositions of typical natural gases are Hsted ia Table 2. 

In the 1980s, however, the prices of oil and natural gas reversed their upward trends. Natural gas discoveries, both on-shore and off-shore, have considerably iacreased the world s energy supply and oil discoveries, many with associated gas, contributed more feedstock potential for ammonia production. 

Based on these developments, the foreseeable future sources of ammonia synthesis gas are expected to be mainly from steam reforming of natural gas, supplemented by associated gas from oil production, and hydrogen rich off-gases (especially from methanol plants). 

American Gas Association, Gas Engineers Handbook, Industrial Press, New York, 1978. 

Natural gas is a naturally occurring mixture of light hydrocarbons accompanied by some non-hydrocarbon compounds. Non-associated natural gas is found in reservoirs containing no oil (dry wells). Associated gas, on the other hand, is present in contact with and/or dissolved in crude oil and is coproduced with it. The principal component of most... 

Natural gas liquids (condensable hydrocarbons) are those hydrocarbons heavier than methane that are recovered from natural gas. The amount of NGL depends mainly on the percentage of the heavier hydrocarbons present in the gas and on the efficiency of the process used to recover them. (A high percentage is normally expected from associated gas.)... 

Naphtha is also a major feedstock to steam cracking units for the production of olefins. This route to olefins is especially important in places such as Europe, where ethane is not readily available as a feedstock because most gas reservoirs produce non-associated gas with a low ethane content. 

As mentioned in Chapter 4, synthesis gas may be produced from a variety of feedstocks. Natural gas is the preferred feedstock when it is available from gas fields (nonassociated gas) or from oil wells (associated gas). 

Polyethylene is the most extensively used thermoplastic. The ever-increasing demand for polyethylene is partly due to the availability of the monomer from abundant raw materials (associated gas, LPG, naphtha). Other factors are its relatively low cost, ease of processing the polymer, resistance to chemicals, and its flexibility. World production of all polyethylene grades, approximately 100 billion pounds in 1997, is predicted... 

Methane is the major constituent of both associated and unassociated gas at source. There will be higher (heavier) hydrocarbons in varying amounts present in the gas, associated gas having more than unassociated gas. 

Non-associated gas containing less than 3 gallons of condensable hydrocarbons per 1,000 cu.ft. of gas. 

Associated gas is natural gas found in contact with oil accumulations in the same reservoir. This gas may be dissolved in the oil under reservoir temperatures and pressure (solution gas) or may form a cap of free gas above the oil in the reservoir (gas cap gas). 

Non-associated gas is natural gas, not in contact with or dissolved in crude oil in a reservoir. 

Plant condensate, recovered in a plant in a natural gas gathering, compression and associated gas treating system. 

Free petroleum associated gas accumulated in the structurally highest part of a reservoir and in contact with oil. Secondary gas caps can be formed during the production development. 

A water-continuous emulsion, suitable for use as an antifoam additive, contains 85% to 98% by weight of a fluorosilicone oil and 2% to 15% by weight of an aqueous surfactant solution [1722]. The additive is suitable for use in separation of crude oil that contains associated gas. The additive may be used in both aqueous and nonaqueous systems and allows fluorosilicone oils to be used without the need for environmentally damaging chlorofluorocarbons. 

Features common to all CVD reactors include source evaporators with an associated gas handling system to control input gases and gas-phase precursor concentrations, a reactor cell with a susceptor heated by either radio frequency or infrared radiation, and an exhaust system to remove waste products (which may include a vacuum pump for low-pressure operations). Substrate temperatures can vary from less than 200 °C to temperatures in excess of 1000 °C, depending on the nature of the material layer and precursor used. Schematic diagrams of some simple CVD reactors are shown in Figure 4. 

The South African government initiated the Mossgas project in the mid-1980s to investigate the conversion of gas and associated natural gas liquids into transportation fuel. This eventually led to the construction of the Mossgas gas-to-liquids plant (presently known as PetroSA) in Mossel Bay, South Africa. It was designed as a 33,000 barrels per day oil equivalent facility, with two thirds of the production being derived from Fischer-Tropsch synthesis and the remainder from associated gas liquids. This facility reached full commercial production in 1993 and was aimed at the production of transportation fuel only.50... 

ABSTRACT The Mallik gas hydrate field represents an onshore permafrost-associated gas hydrate accumulation in the Mackenzie Delta on the coast of the Beaufort Sea, Northwest Territories, Canada. This deposit contains a high concentration of natural gas hydrate with an underlying aquifer or free-gas zone at the base of the hydrate stability field. The physical and chemical properties of CH4 and C02 hydrates indicate the possibility of coincident C02 sequestration and CH4 production from the Mallik gas hydrate bearing zones. This study presents a numerical assessment of C02 sequestration and the recovery of CH4 from the gas hydrates at the Mallik site, Mackenzie Delta, Canada. 

Just as oil, natural gas is also categorised as conventional and unconventional. Unlike crude oil, however, natural gas deposits are normally classified according to the economic or technical approach, i.e., all occurrences that are currently extract-able under economic conditions are considered conventional, whereas the rest are termed unconventional. Conventional natural gas includes non-associated gas from gas reservoirs in which there is little or no crude oil, as well as associated gas , which is produced from oil wells the latter can exist separately from oil in the formation (free gas, also known as cap gas, as it lies above the oil), or dissolved in the crude oil (dissolved gas). Unconventional gas is the same substance as conventional natural gas, and only the reservoir characteristics are different and make it usually more difficult to produce. Unconventional gas comprises natural gas from coal (also known as coal-bed methane), tight gas, gas in aquifers and gas hydrates (see Fig. 3.17). It is important to mention in this context so-called stranded gas , a term which is applied to occurrences whose extraction would be technically feasible, but which are located in remote areas that at the moment cannot (yet) be economically developed (see Section 3.4.3.1). 

The monetization of remote natural gas has been a key economic driver for catalysis research over the past 20 years. Significant reserves of natural gas exist in remote locations, distant from available gas pipehnes, which cannot be readily brought to market. The conversion of these resources to higher-valued, transportable products, such as methanol or polyolefins can allow the economical utilization of these stranded assets. Other low-valued natural gas streams, such as associated gas from oil production, could also provide feedstocks to such a technology. The conversion of remote gas, typically valued at US 0.50-1.50 per MMBTU, into polyolefins, valued at more than US 1000/t, via methanol has sparked the development of several MTO technologies. 

The development of new syngas-based processes is one of the objectives for the near future, despite the current low price of oil. Syngas can be produced from various carbonaceous sources, including coal, heavy residue, biomass and gas, the latter being the most economical and abundant feedstock. Chemical valorization of natural or associated gas is a priority objective, since liquefaction of remote gas via alcohol synthesis permits convenient shipping to markets not directly connected to the gas source by pipeline. 

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