The simple steamflood model is qualitatively supported by empirical observations. In well-to-well pressure transient tests, it takes on the order of hours to days for a pressure pulse at one well to propagate to an adjacent well. Pressure is transmitted through the fluid in the connected pore space at a relatively fast rate because it does not require fluid transport to propagate diffusively. Temperature observation wells show that thermal fronts take on the order of weeks to months to propagate similar well-to-well distances. This is because heat transfer occurs through a combination of conduction and convective transport of heated fluids through the permeable pore space, both of which tend to be relatively slow processes. Finally, a desaturated steam zone propagates even slower than a thermal front, because of the additional work required to drive fluid out of pore space. Hence, a steam zone propagates at the speed that heat is conducted through the rock matrix, which is much slower than either convective thermal transport, or pressure diffusion.

To first approximation, according to empirical observations, a steam-induced pressure front should travel at least one order of magnitude faster than the associated thermal or steam fronts. This implies that a distant observer in the reservoir will first notice an increase in pressure but not temperature. The next zone to arrive will be high-pressure heated oil as the thermal effects propagate outward from the steam injector. A hot water zone of condensed steam follows and heats the oil ahead of it. Finally, closest to the injector, a hot steam zone with negligible fluid saturation exists as the heat source that drives the total fluid-flow process.

11/12/1997