ABSTRACT
Convective heat flow involving flowing rock, magma, or groundwater is an efficient way to move heat and has concentrated heat in some places to create significant energy resources. A major distinction between different kinds of energy sources is the energy return on energy investment, sometimes called energy return on investment, or the useful energy yield. Growing world population and economic development mean that the demand for energy will almost certainly increase. Petroleum trapped in the subsurface is an important source of energy, but deposits vary in volume, in productivity, and in quality. Petroleum companies sometimes use other production technologies, collectively called tertiary recovery, or enhanced oil recovery, to supplement primary and secondary production. Once a promising petroleum deposit is found, focus shifts from exploration to production. Oil companies extracted petroleum using primary recovery technology. When primary production wanes and is no longer profitable, secondary recovery techniques may be employed.
