Under the expected operating conditions of a Steam Assisted Gravity Drainage (SAGD) pilot project, it is anticipated that both the injection and the production wells will be able to flow unassisted to surface should a loss of well control incident occur. Industry practice regarding the design of such flowing wells dictates that the well completion include double barriers in the production tubing string and the production casing annulus. Unfortunately, downhole equipment suitable for such a high temperature application does not currently exist. To help evaluate the comparative risk between a double and single barrier completion, a reservoir modeling study was conducted to investigate the flowing potential (flow rates, durations and composition of the fluids) of the SAGD pilot wells under various blowout scenarios.
This paper presents the results of this reservoir modeling study in terms of the coupled wellbore/reservoir behavior during the blowout condition. A commercial coupled wellbore/reservoir simulator was used along with a "custom?? code developed to include a critical choke velocity constraint into the reservoir simulation considerations.
The various blowout scenarios investigated include flow through both the injection and the production wells, at three different points during the production life of the well pair (beginning of the steam injection phase, middle of the steam chamber development and end of the steam injection phase) and through three possible flow paths (through the tubing, through the tubing-casing annulus and through both the tubing and the annulus).
The reservoir modeling confirmed that both the injection and the production wells in this SAGD application have the potential for a blowout lasting for significant periods of times should a loss of well control occur, and with liquid rates that can be over 50 times the normal production liquid rates.
The availability of successfully tested technology to exploit the huge bitumen and heavy oil reserves worldwide, along with the high oil price scenario are boosting the feasibility of bitumen and heavy oil production projects. In this context, Steam Assisted Gravity Drainage (SAGD) has emerged as one of the most efficient thermal recovery technologies to produce those resources.
The usual way to predict the production performance of SAGD processes is by using reservoir thermal simulation. When long term production predictions are made, a classical sink/source formulation to describe the wellbore in the reservoir model is commonly used, under the assumption that localized transient phenomena within the wellbore doesn't affect the final SAGD oil recovery. That formulation assumes that the production/injection constraints, which normally include constant pressure or constant flow rate, will be independently applied at each point within the gridblocks where the wellbore is placed, in the reservoir simulation model, without any consideration of the fluids flow through the wellbore.
Author: Vanegas, J. W. P., Cunha, L. B., Worth, D. J., & Crepin, S.
Publisher: International Thermal Operations and Heavy Oil Symposium, 20-23 October, Calgary, Alberta, Canada
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