A Theoretical Comparison of Heat Transfer into Porous Media by the Injection of Steam or Hot Water

Summary A comparison of the heat-carrying capacity of hot water and steam indicatesthat hot water can impart considerably more heat to a formation than does steamat relatively low pressures. This results from the greater density of hot waterand its corresponding greater mass flow rate at a given injection pressure. Athigher pressures, this advantage of hot water becomes smaller, and itdisappears completely at the critical pressure of water. The relative heat-carrying capacities of hot water and steam are influencedby the presence of residual oil in the formation. Greater oil saturations leadto lower heat-carrying capacities of hot water relative to steam. Thesedifferences are a reflection of differences in relative permeabilities of theflowing fluids. The work reported here is considered to be preliminary in nature; severalbasic simplifying assumptions were used in it. Under conditions other thanthose assumed, the relative effectiveness of hot water and steam could besomewhat different from that reported here. Introduction When heat is imparted to a formation by hot water or steam injection, theoil recovery is increased due to thermal expansion of oil, reduction in oilviscosity and, in the case of steam drive, steam distillation of the crude (1).The degree to which oil recovery is increased is affected particularlyby the temperature dependence of the oil viscosity. In many cases, thereservoir oil viscosity can be reduced several hundred-fold by hot water orsteam heating to drastically increase the oil mobility. Figures 1 and2 show the relationship between temperature and viscosity for steam andwater (2). Note that water viscosity decreases with increasing temperature, butthat the steam viscosity increases with increasing temperature at pressuresbelow 1000 psi. When a reservoir has been selected for heal treatment, it is necessary todetermine the most economical means of transferring heat into it. At firstglance, steam may seem to be a better heat carrier than hot water because itsheat content per unit mass is higher than that of water at the sametemperature.