A New Lumped Parameter (Tank) Model for Reservoirs Containing Carbon Dioxide

Abstract

Two of the common characteristics of Turkey’s geothermal fields are that they are initially all liquid dominated and almost all contain some amounts of carbon dioxide. However, such small quantities of carbon dioxide have profound effects on the reservoir pressure behavior. Carbon dioxide has the tendency to shift the flashing point of the reservoir fluid to a considerably higher value. This causes a gas phase to form in the reservoir. Due to the gas phase formed during production, reservoir pressure can be maintained better. When modeling such a reservoir, it is crucial that the effects of carbon dioxide be included in the model. In this study we present a new lumped parameter (tank) model capable of considering the effects of carbon dioxide. The model is based on three conservation equations; mass balances on water and carbon dioxide and an overall energy balance. By doing so, we are able to keep track of average reservoir pressure, average reservoir temperature and the amount of carbon dioxide. A Synthetic field example is given to illustrate the affects of CO2 on reservoir behavior. It can be utilized to better understand the behavior of hot water systems that contain carbon dioxide and to forecast future performance.