| Mineral oil production | ||
| The oil deposits that can be worked economically using known technology
are being recovered today from onshore wells as deep as 8,000 m and to an increasing
extent from offshore wells, too. Offshore facilities consist of jack-up drilling platforms
(in water depths of around 100 m), floating drilling platforms (in depths down to around
1,000 m) and drilling ships (in greater depths). Primary recovery: Natural pressure, i.e. the pressure of rock or gas, forces the oil out of the drilled well. Secondary recovery: If the pressure is too low from the outset or drops too far in the course of primary recovery, water is injected through small and often widely branching bore holes at the periphery of the oil field. These injection pumps have delivery rates of up to 4,000 m3/h, delivery heads of up to 2,100 m, and maximum shaft outputs of 19 MW at the working point. They inject either ground water from nearby reserves (in onshore fields) or sea water (in offshore and coastal onshore fields), or – on rare occasions – the water or gas produced with the recovered oil. Gas is also reinjected for intermediate storage. When brine (sea water) or saline ground water is used, the water is treated chemically and mechanically, sterilized and deoxydated prior to injection. With just around 30 % of the oil recovered by the primary and secondary methods, tertiary recovery (enhanced oil recovery, EOR) is becoming increasingly significant. EOR consists of heat flooding (heating of the oil bearing rock), solvent flooding (forcing in of organic solvents, liquefied gases or CO2) and chemical flooding (injection of surfactants or polymer solutions).
|
The composition of natural oils differs, with over 500 components having been found to date. As equally diverse are the technical terms for crude oil. Examples: wet crude (contains water), dry crude (contains no water), unstable crude (contains gas), stable or stabilized crude (contains no gas), sweet crude (with low sulphur contact), sour crude (with high sulphur content > 1%) etc. The water emulsified in or carried by the oil has up to 30% TDS (total dissolved solids, i.e. salts and other minerals). It is normal practice to pretreat the drilled oil immediately it leaves the well (removing the water and volatile constituents), after which it is put into intermediate storage or pumped – often over great distances – to storage tanks at the shipping facilities or refineries. The diversity of pumped media and the diversity of operating conditions call for the use of various – often highly specialized – pumps, whose seals have to fulfill extreme demands. Requirements on mechanical seals are particularly high in pipeline pumps, injection pumps and drill head mud pumps. Demands on operational safety are in any case very high, but on offshore platforms they are even more stringent and supplemented by greater requirements on assembly and maintenance convenience. It goes without saying that the solids and high proportions of corrosive constituents in the pumped media necessitate materials with high wear and corrosion resistance (materials for...). Correct selection of the mechanical seal and its safety and auxiliary devices can only result from close collaboration between the planner, the pump builder and a manufacturer of mechanical seals with experience in these fields. |
| As an example of the host of implemented designs, the pictures show an
injection pump, the cross section of the installed mechanical seal, a diagram of the buffer fluid circuit, and the attendant pressure retaining and refill unit.
|
