| Abstract: | Material balance calculations, often referred to as “zero-dimensional” or “lumped element” reservoir evaluations, have been used extensively in petroleum and geothermal engineering. This paper presents a Havlena and Odeh-type (J. Petrol. Technol. Aug. 1963) material balance depletion model for two-phase reservoirs incorporating adsorption phenomena. A straight line, formed between groups of thermodynamic and adsorption properties of water and the cumulative production history, provides the initial fluid-in-place and the size of the vapor-dominated “steam cap”. Adsorption phenomena were found by Economides and Miller (Paper SPE 12740, California regional meeting, Soc. Petrol. Engrs, 1984) to be the controlling mechanism in the depletion of vapor-dominated geothermal reservoirs. A material balance for vapor-dominated geothermal reservoirs, demonstrating the importance of adsorption phenomena, is also presented. A straight line provides the initial fluid-in-place. |
