1. What does the modern-day search for oil begin with?
2. What is the basic concept of seismic-reflection profiling?
3. What drilling equipment and techniques are used in the modern-day oil exploration?
Task 3. Using Fig.9 and 10, demonstrate that the modern-day search for oil is a complex procedure with many steps.
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ALTERNATIVE RESERVES OF HYDROCARBONS
Task1.
Tar Sands (Oil Sands)
So far, we’ve focused our discussion on hydrocarbon reserves that can be pumped from the subsurface in the form of a liquid or a gas. But in several locations around the world, most notably Alberta (in western Canada) and Venezuela, vast reserves of very viscous, tarlike “heavy oil” exist. This heavy oil, known also known as bitumen, has the consistency of heavy molasses, and thus cannot be pumped directly from the ground; it can fill the pore spaces of sand or of poorly cemented sandstone, constituting up to 12% of the sediment or rock volume. Sand or sandstone containing such high concentrations of bitumen is known as tar sand or oil sand.
The hydrocarbon system that leads to the generation of tar sands begins with the production and burial of a source rock in a large sedimentary basin (specifically, a type of basin called a foreland basin, which forms along the continent side of a mountain belt). When subjected to temperatures of the oil window, the source rock yields oil and gas, which migrate into sandstone layers and then up the dip of tilted layers to the edge of the basin, where they become caught in stratigraphic traps. Initially, these hydrocarbons have relatively low viscosity; in the geologic past, they could have been pumped easily. But over time, microbes (bacteria) attacked the oil reserve underground, digested lighter, smaller hydrocarbon molecules, and left behind only the larger molecules, whose presence makes the remaining oil so viscous. Geologists refer to such a transformation process as biodegradation. Generation of tar sand by biodegradation is yet another example of the interaction between physical and biological components of the Earth System.
Production of usable oil from tar sand is difficult and expensive, but not impossible. It takes about 2 tons of tar sand to produce one barrel of oil. Oil companies mine near-surface deposits in open-pit mines, then heat the tar sand in a furnace to extract the oil. Producers then crack the heavy oil molecules to produce smaller, more usable molecules. Trucks dump the drained sand back into the mine pit. To extract oil from deeper deposits of tar sand, oil companies drill wells and pump steam or solvents down into the sand to liquefy the oil enough so that it can be pumped out.
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