Exporting

Having defined and gathered data adequate for an initial reserves estimation, the next step is to look at the various options to develop the field. The objective of the feasibility study is to document various technical options, of which at least one should be economically viable. The study will contain the subsurface development options, the process design, equipment sizes, the proposed locations (e.g. offshore platforms), and the crude evacuation and export system. The cases considered will be accompanied by a cost estimate and planning schedule. Such a document gives a complete overview of all the requirements, opportunities, risks and constraints. 

From the above plot, it can be seen that the recovery factor for gas reservoirs depends upon how low an abandonment pressure can be achieved. To produce at a specified delivery pressure, the reservoir pressure has to overcome a series of pressure drops the drawdown pressure (refer to Figure 9.2), and the pressure drops in the tubing, processing facility and export pipeline (refer to Figure 9.12). To improve recovery of gas, compression facilities are often provided on surface to boost the pressure to overcome the pressure drops in the export line and meet the delivery pressure specified. 

A comfortable margin is maintained between the flowing tubing head pressure (downstream of compression) and the minimum pressure required for export, since the penalties for not meeting contract quantities can be severe. The decision not to install a fourth stage of compression in the above example is dictated by economics. During the final part of the pressure decline above, the field production is of course also declining. 

Having reached the wellbore, the fluid must now flow up the tubing to the wellhead, through the choke, flowline, separator facilities and then to the export or storage point each step involves overcoming some pressure drop. 

Though the type of processing required is largely dependent upon fluid composition at the wellhead, the equipment employed is significantly influenced by location whether for example the facilities are based on land or offshore, in tropical or arctic environments. Sometimes conditions are such that a process which is difficult or expensive to perform offshore can be exported to the coast and handled much more easily on land. 

Condensable hydrocarbon components are usually removed from gas to avoid liquid drop out in pipelines, or to recover valuable natural gas liquids where there is no facility for gas export. Cooling to ambient conditions can be achieved by air or water heat exchange, or to sub zero temperatures by gas expansion or refrigeration. Many other processes such as compression and absorption also work more efficiently at low temperatures. 

Sales gas, which is typically made up of methane (CH ) and small amounts of ethane (C2Hg), can be exported by refrigerated tanker rather than by pipeline and has to be compressed by a factor of 600 (and cooled to -150°C). This is then termed Liquefied Natural Gas (LNG). 

Facilities for the treatment and compression of gas have already been described in earlier sections. However, there are a number of differences in the specifications for injected gas that differ from those of export gas. Generally there are no technical reasons for specifications on hydrocarbon dew point control (injected gas will get hotter not cooler) although it may be attractive to remove heavy hydrocarbons for economic reasons. Basic liquid separation will normally be performed, and due to the high pressures involved it will nearly always be necessary to dehydrate the gas to avoid water drop out. 

The legs of the platform can be used as settling tanks or temporary storage facilities for crude oil where oil is exported via tankers, or to allow production to continue in the event of a pipeline shut down. The Brent D platform in the North Sea weighs more than 200,000 tonnes and can store over a million barrels of oil. Topside modules are either installed offshore by lift barges, or can be positioned before the platform is floated out. 

In recent years much more attention has been given to pipeline isolation, after instances in which the contents of export pipelines fed platform fires, adding significantly to damage and loss of life. Many export and in field pipelines are now fitted with emergency shutdown valves (ESDV) close to the production platform, to isolate the pipeline in the event of an emergency. 

Metering oi the production for fiscal (taxation), tariffing and re-allocation purposes may take place as the product leaves the production platform, or as it arrives at the delivery point such as the crude oil terminal. If the export pipeline Is used by other fields (including third party users) it would be common to meter the production as it leaves the platform. 

Criticality refers to how important an equipment item is to the process. Consider the role of the export pump in following situation ... 

The above example is a simple one, and it can be seen that the individual items form part of the chain in the production system, in which the items are dependent on each other. For example, the operating pressure and temperature of the separators will determine the inlet conditions for the export pump. System modelling may be performed to determine the impact of a change of conditions in one part of the process to the overall system performance. This involves linking together the mathematical simulation of the components, e.g. the reservoir simulation, tubing performance, process simulation, and pipeline behaviour programmes. In this way the dependencies can be modelled, and sensitivities can be performed as calculations prior to implementation. 

Market forces determine the demand for a product, and the demand will be used to forecast the sales of hydrocarbons. This will be one of the factors considered by some governments when setting the production targets for the oil company. For example, much of the gas produced in the South China Sea is liquefied and exported by tanker to Japan for industrial and domestic use the contract agreed with the Japanese purchaser will drive the production levels set by the National Oil Company. 

If gas export or disposal is a problem gas re-injection into the reservoir may be an alternative, although this implies additional compression facilities. Gas production may be reduced using well intervention methods similar to those described for reducing water cut, though in this case up-dip wells would be isolated to cut back gas influx. Many of the options discussed under water treatment for multi-layered reservoirs apply equally well to the gas case. 

Whether on land or offshore, the principle of satellite development is the same. A new field is accessed with wells, and an export link is installed to the existing (host) facility. Development is not always easier on land, as environmental restrictions mean that some onshore fields have to be developed using directional drilling techniques (originally associated with offshore developments). A vertical well can be drilled offshore away from the host facility, and the well completed using a subsea wellhead. 

The role that a host facility plays in an incremental development project can vary tremendously. At one extreme all production and processing support may be provided by the host (such as gas lift and water treatment). On the other hand, the host may just become a means of accessing an export pipeline (if a production and processing facility is installed on the new field). 

Companies which own process facilities and evacuation routes, but no longer have the hydrocarbons to fill them, can continue to operate them profitably by renting the extra capacity or by charging tariffs for the use of export routes. 

With 3D-CTVicwer the export of slice-contours from parts inside the data volume is possible via the DXF-format. From these contours a two-dimensional comparison to the CAD geometry is possible if the coordinate system and the absolute scaling between both methods are well known. 

Another interesting tool is to export the samples Isosurface hull to CAD for best matehing and afterwards comparison in 3D. Therefor a polygon export in DXF and the polygon reduction is implemented. 

A larger number of features are provided by the ACDStructure Drawing Applet (ACDLabs). Both structures and reactions can be drawn, imported, and also exported. This applet supports Molfiles and has a large, integrated collection of pre-defined templates, which are extensible by the user. Additionally, gif files can be exported. It is not possible to draw or to Lmport/export chemical reactions. 

The Web-based graphical user interface permits a choice from numerous criteria and the performance of rapid searches. This service, based on the chemistry information toolkit CACTVS, provides complex Boolean searches. Flexible substructure searches have also been implemented. Users can conduct 3D pharmacophore queries in up to 25 conformations pre-calculated for each compound. Numerous output formats as well as 2D and 3D visuaHzation options are supplied. It is possible to export search results in various forms and with choices for data contents in the exported files, for structure sets ranging in size from a single compound to the entire database. Additional information and down-loadable files (in various formats) can be obtained from this service. 

To obtain more information on each reaction of the hit list, it is possible to browse through the hit list, classify it (sec Section 5.13.4), print it, and export all the references on the hit list or save the reactions in different file formats for documentation purposes. 

Zemplen helped his students in many ways. I remember an occasion in the difficult postwar period. The production of the famous Hungarian salami, interrupted by the war, was just in the process of being restarted for export. The manufacturer wanted a supportive analysis from the well-known professor. Zemplen asked for a suitable sample of some hundreds of kilograms, on which the whole institute lived for weeks. When it was gone he rightly could offer an opinion that the product was quite satisfactory. After the war, grain alcohol was for a long time the only available and widely used laboratory solvent, and, not unexpectedly, it also found other uses. Later, when it was denatured to prevent human consumption, we devised clever ways for its purification. The lab also manufactured saccharine, which was... 

Output data can be printed or exported to a spreadsheet. The rendering quality is very good. Structures can be rendered and labeled in several different ways. Molecular structures can be saved in several different formats or as image files. The presentation mode allows molecular structures to be combined with text. 

Chem3D can read a wide variety of popular chemical structure files, including Gaussian, MacroModel, MDL, MOPAC, PDB, and SYBYL. Two-dimensional structures imported from ChemDraw or ISIS/Draw are automatically converted to three-dimensional structures. The Chem3D native file format contains both the molecular structure and results of computations. Data can be exported in a variety of chemical-structure formats and graphics files. 

---