Analytical modeling of oil production rate during the entire steam-assisted gravity drainage process in heavy oil reservoirs

Abstract

The steam-assisted gravity drainage (SAGD) process is a widely used thermal recovery technique for heavy oil reservoirs worldwide. In addition to numerical simulation methods, analytical models are alternative tools for the prediction and evaluation of heavy oil recovery by SAGD. In this study, a new analytical oil production rate prediction model for the entire SAGD process, including the rising, transition, expanding and depletion stages, is derived based on the movement rules of the steam chamber interface. The main improvements compared with existing analytical models in this work involve the introducing of a transition stage which is between the rising and the expansion stages, the modification of the depletion stage, the consideration of homogeneity with anisotropy, and the modification of the initial slope angle and shape factors which vary with reservoir parameters and steam injection parameters. Furthermore, the new analytical model is validated against with a relatively complete analytical model and numerical simulation models under field conditions. The results show that the new analytical model can predict the oil rate during the entire SAGD process more accurately than other available analytical models and with high agreement with numerical simulation results and field data. The results also show that the continuity of oil rate is improved by introducing the transition stage. The anisotropy of the permeability cannot be ignored, because it affects the peak oil rate and plateau time of the SAGD process. Moreover, the new model can quickly diagnose the phase of the steam chamber development, which provides guidance for the follow-up adjustment in heavy oil field application.