Giving oil a lift
When a section of a well has been drilled, casing and tubing are inserted. Ideally, during the first stage in the life cycle of a field, the oil finds its way to the production wells and rises to the surface of its own accord, due to the natural reservoir pressure. When the pressure falls it is necessary to use techniques such as gas lift, which involves injecting pressurised gas via the production string. The gas reduces the weight of the column of liquid, meaning that the well can continue to produce under its own steam. After this stage (known as the eruptive phase), a range of pumping technologies can be used, depending on the properties of the crude, its gas content and the pressure conditions. Where the gas content is low and the reservoir pressure is falling, the oil is brought to the surface by deep well pumps. Only the pumps’ drive mechanisms – the characteristic pumpjacks – are visible on the surface. Electric rotary submersible pumps can be used to achieve higher flow rates.
Treatment – separation of gas, oil and water
In its produced state, crude oil is not yet suitable for transportation and refining, and it must first undergo a number of processes. Given favourable circumstances, in the shape of a strong inherent drive mechanism and good reservoir conditions, primary recovery of over 50 percent of the reserves in place is possible. However, if the reservoir pressure is weak or the crude is highly viscous, the primary recovery rate may only be between five and 15 percent. After the crude has been produced the formation water and sand in it must be removed by treatment systems (separators and tanks). The associated gas goes straight into the grid as soon as it has been dried, but the crude is collected in tanks before being transported to a refinery by rail or pipeline. The separated water is pumped back into the reservoirs it has come from.
At present over 60 percent of the oil reserves in place stay in the ground. RAG Exploration & Production is carrying out research into methods of raising the recovery rate so as to ensure that Austrian oil remains available as a feedstock for domestic industry for many years to come. As there will be no “post-petroleum age” when oil is no longer needed, good stewardship of this invaluable resource is vital.