A NEW MODEL FOR STEAM CIRCULATION PREHEATING STAGE OF SAGD PRODUCTION

摘要

The whole steam assisted gravity drainage (SAGD) production can be divided into two stages: the pre-heating stage and the production stage. Earlier researchers focused more on the production stage of SAGD, ignoring the importance of the pre-heating stage. Although several investigations have been carried out with the help of commercial reservoir simulator to probe the influences of reservoir properties, wellbore configurations and injection parameters, the simulation process takes too much computational time and the simulation results are greatly affected by the mesh size of the numerical model. In this paper, we build a new model to calculate the instantaneous heat loss rate and reservoir temperature distribution during the pre-heating stage. In the pre-heating stage, steam is injected through both the production well and injection well. Unlike SAGD production stage, heat is mainly transferred by thermal conduction. Therefore, the problem can be expressed as a transient conductive heat transfer equation with constant temperature inner boundary condition and well interference. First, Duhamel 's principle is used to convert the constant temperature inner boundary into variable heat flow rates inner boundary to deal with the well interference effects. By applying Laplace transformation to the basic function system, the analytical solutions for instantaneous heat loss rate and temperature distribution in Laplace space can be obtained. Then, with Stephest numerical inverse transformation method, the heat loss rate and temperature distribution can be calculated numerically. At last, we compare the results of our new model with that of two commercial simulators, and great agreement is observed. The quick and accurate solution for heat loss rate and temperature distribution can help people determine a proper steam injection rate and reasonable pre-heating days.