Heat and Mass Transport in Steam-Drive Processes

Abstract

Abstract Steam-injection tests in the field have shown that heat transport into theoil/water region, ahead of the steam zone, may have a significant effect on theproduction process. Earlier theoretical work on reservoir heating by hot-fluidinjection can be used to describe the growth of the steam zone, but only ifheat transport from steam zone into oil/water region is neglected. It thereforebecame necessary to re-examine and extend the earlier theory. It was found that this theory ceases to be consistent with the physicalmodel of the process at a certain critical time, which depends on reservoirthickness, temperature, and quality of the steam. The critical time marks animportant change in the heat flow across the condensation front: (Equation) On the basis of the new equation, an approximate description for the steam-zonegrowth is developed by making use of upper and lower bounds for the exactsolution of the problem. The boundary conditions for heat and mass flow insidethe oil/water region are established, and a simple method of determining thesaturation at the downstream side of the condensation front is presented. Experimental results show that the theory gives an accurate description ofsteam-zone expansion before the critical time. At times near critical time, andalso after critical time, experimental data show theoretical steam-zone volumesto be high, Even so, the accuracy of the calculated steam-zone volumes issufficient for practical purposes. Theory of Steam-Zone Growth Introduction The engineering evaluation of steam-drive processes is based mainly on amathematical description of reservoir heating by hot fluid injection presentedseveral years ago by Marx and Langenheim. This theory can be used to determinethe growth of the steam zone, provided the flow of heat from the steam zoneinto the liquid zone ahead of the condensation front (Fig. 1) is neglected. Since we must expect, however, that heat transport into and inside theliquid region (the region between condensation front and production wells) willaffect both the water/oil flow and the growth of the steam zone, it isnecessary to re-examine and to generalize the Marx and Langenheim theory asapplied to steam drive, which will hereafter be termed the "old"theory. Observations made in several field tests emphasize the need to studythe heat flow across the condensation front (CF). On several occasions it wasdiscovered that heat was transported in the liquid zone far ahead of theadvancing CF, resulting in an early breakthrough of warm water.