A Unified Model for Prediction of CSOR in Steam-Based Bitumen Recovery

Paper Number: 2007-027

Authors: Neil Edmunds, Jeff Peterson - Laricina Energy Ltd.

Source: presented at the Petroleum Society’s 8th Canadian International Petroleum Conference (58th Annual Technical Meeting), Calgary, Alberta, Canada, June 12 – 14, 2007.

Copyright: Copyright 2008, Petroleum Society of CIM

Preview
An analytical model to estimate the cumulative steam/oil ratio of SAGD or other steam-based bitumen recovery processes is presented. Model predictions are compared with both numerical and field cases. Cyclic steam processes are interpreted as unsteady-state SAGD recovery, which can be operated at effective temperatures about half that for SAGD.

Introduction
Attempts are sometimes made to correlate the cumulative steam/oil ratio (CSOR) performance of current SAGD projects against single reservoir variables, whether pay thickness, operating pressure, oil saturation, etc. In fact, all of these and more reservoir variables come into play; but the SOR is not just a property of the rocks and the process, but also of time. Due to ongoing reservoir heat loss, production or facility delays also have an impact on the field CSOR. This paper presents a simple analytical model to predict the CSOR for steam-based recovery of bitumen from high permeability reservoirs. The model is useful for screening and evaluation purposes, as well as the analysis of the economic effects of various production variables, including shut-ins or impairment. The founding assumptions are that:

  1. depletion is gravity driven, and therefore the geometry of the depleted zone (steam chamber) more or less follows from the production well geometry; and
  2. produced oil is from the steam zone, and the steam zone has been uniformly reduced to residual oil saturation (pace Butler's SAGD model1, this is equivalent to saying that drainage within the chamber is much more rapid than the rate of chamber expansion).

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