Well-head gas

Ethane prices are generally determined by local circumstances. The floor price for ethane is set often priced according to the price of gas on an energy basis. For example in the US for flexible fuel cracking operations can use both ethane and naphtha if demand falls then ethane can be left in the gas stream and sold as gas. The US Energy Information Administration collates data for the well-head gas price. The data is shown in Figure 3.7. 

This graph shows collated data from across the US. Prior to about 2000, apart from a few spikes, the prices ranged typically in the range 1 to 2/Mcf. Since 2000, gas prices have been very volatile and as with the rise in energy prices over the period 2003 onwards there has been a dramatic rise in the price of well head gas with some extreme peaks over 10/Mcf. 

Within a relatively short period after their commercialization, membranes for gas separation have been utilized in a wide variety of applications. Among these applications are recovery of hydrogen from purge streams such as encountered in ammonia plants, retrofit chemical plants and from hydroprocessors in refineries. Membrane systems have been introduced into oil fields for C02 recovery from well-head gas in enhanced oil recovery, and they have been used to separate oxygen from nitrogen in air. Also, they have been utilized in combination with other recovery systems, such as cryogenic and adsorption, to both reduce cost and increase efficiency. 

Methanol can be quite efficiently produced from almost any hydrocarbon fuel. Natural gas is very suitable, as is the well-head gas that is often just burnt off if an oil well is at all remote. The first stage is the simple and well-established process of reacting with steam - a process covered in some depth in Chapter 8 that follows. This produces a mixture of hydrogen, carbon monoxide, and carbon dioxide, the proportions depending on the fuel feedstock, temperature, and pressure. These gases then react to form methanol using either of the reactions... 

There are numerous, large turboexpanders operating in the pressure range of 130-200 bar, most of them in well-head natural gas serviee. 

A blowout, which is the continuous flow of oil or gas to the surface through the annulus, is the result of a lack of sufficient bottomhole pressure from the column of circulating fluid and proper well head equipment. 

The rate of flow of a gas well unrestricted by any pressure at the well head other than that of the atmosphere. It is measured in m per day at standard conditions or in standard cu.ft. per day. 

A levy by the owner of the subsoil or by the state on the value of gas produced, frequently expressed as a percentage of well-head value. 

Some of the important features of the flow of two-phase mixtures composed of a liquid together with a gas or vapour are discussed in this section. There are many applications in the chemical and process industries, ranging from the flow of mixtures of oil and gas from well heads to flow of vapour-liquid mixtures in boilers and evaporators. 

The optimal routing of a two-phase flow pipeline was investigated by Shamir (SI). Such pipelines are commonly used to convey both oil and gas from producing wells to collecting facilities and plants. They obviate the necessity for oil-gas separation facilities at the well head, which are sometimes uneconomical or impractical. In this context it is reasonable to assume that the pipeline will operate under the pressure differential naturally available between the source (well) and the point of delivery (refinery) and that the desired flow rate is specified. Hence one constraint on the optimal route is given by... 

Reciprocating compressors are also favored over centrifugal machines for temporary installations such as gas and field-well head service. Also, when low initial capital investment is favored over longterm maintenance costs, reciprocating compressors are used. 

Figure 7.40 Mallik 5L-38 process flow diagram for well-head handling of gases and recirculating brine during thermal test. (From Hancock, S.H., et al., in Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada, Geological Survey of Canada Bulletin 585, including CD (2005b). With permission.)...

Reservoir-foam applications may involve slug injection, in which foaming surfactant solution is injected into the gas stream at the well-head over a period of a few hours, semi-continuous injection, in which surfactant solution is injected at intervals over a period of a day or so, and continuous injection, in which surfactant solution is injected continuously for months or even years. Recently, much attention has been paid to near-well applications of foams [345,726-728],... 

Gas at well head including gathering-system costs ... 

There may be other reasons why the temperature at the well head should be kept low. Often it is desirable to inject the acid gas in the liquid phase (more on injection pressure is presented in chapter 8). 

The typical US well head cost in 2007 was around 6.37/GJ and this has been used as the basis for the input cost in this case study. The fixed costs are the non feed operating costs which for a relatively simple turbo-expander gas plant would be about 5% per annum of the fixed capital and the capital recovery charge which is placed at 14.3% per annum of the capital (see Appendix for derivation of this value). 

Parameters and variables that determine the system dynamic changes, such as ambient temperature, flow rate of well-head injected gas are measurable or a priori known as opening of production choke. Therefore, using these values, model can be adapted to the plant. 

To evaluate the proposed adaptive control performance, opening of production choke and flow rate of injected gas at the well-head are random pulses as command signals, as shown in figure 5. The opening value of the production choke Upc also is the manipulated variable of the control strategy. Figure 6 shows noisy measurements and filtering outputs of closed-loop system, where variable variances of measurement noises are apparent. Note that Wpc illustrated the stabilized behavior of closed-loop system. 

Most natural gas at the well head contains almost no carbon dioxide although some wells yield gas with up to 10% carbon dioxide and a few much more [26]. Carbon dioxide in the presence of moisture or other proton source is also acidic in nature. If present, it is also collected by the monoethanolamine with about the same efficiency as hydrogen sulfide, although it reacts more slowly (Eqs. 9.11-9.14 Table 9.3). 

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