Christina Lake Solvent Aided Process Pilot
Authors: Gupta S.C. , Gittins S.D. 
Published: March 2010

Approximately 80% of the Canadian oil sands are too deep to be economically mined. SAGD, an in situ recovery technology, has come of age and is emerging as the technology of choice in exploitation of these resources. The current major challenge that SAGD faces is the use of expensive heat to generate steam. The authors have previously described an improvement to SAGD, Solvent Aided Process (SAP), that aims to combine the benefits of using steam with solvents. In SAP, a small amount of hydrocarbon solvent is introduced as an additive to the injected steam during SAGD. SAP holds the promise to significantly improve the energy efficiency of SAGD thus reducing the heat requirement.

This paper describes field testing of SAP at EnCana's Christina Lake SAGD Project. In addition to dwelling on some of the important parameters of a SAP test, it outlines the design considerations for the pilot and associated facility modifications. The design duration of the experiment calls for an assessment of reservoir performance on a long-term basis. However, some preliminary observations and indications are discussed. Additionally, impact of timing of solvent initiation and the well pair spacing on process performance is also explored based on modelling exercises.

Introduction

In SAGD, oil viscosity is reduced by heating with steam(1, 2). In SAP(3, 4), solvent dilution is also taken advantage of to aid this viscosity reduction. The result is an enhanced rate of oil production and recovery leading to superior economics with lower energy intensity and impact on the environment.

In the context of doing away with the heating requirement, VAPEX, a process similar to SAGD but employing only hydrocarbon vapour instead of steam, has been described in the literature(5–8). However, its development is awaiting a successful field trial. Use of solvent with steam for oil recovery is also discussed in the literature(9–12) with a focus on the enhancement of steam displacement or steam stimulation. Using solvent with steam in a SAGD context offers some practical advantages. The pressure in the vapour chamber does not need to be supported by a non-condensable gas, as would be required in some versions of VAPEX. This means that the progression of the vapour chamber in SAP does not get overwhelmed by the heat/mass transfer resistance at the vapour/oil interface. Recently, others(13, 14) have also discussed the benefits of using solvents with SAGD in a process similar to SAP. Nasr and his colleagues(13, 14) advocate the use of those solvents that match the condensation characteristics of steam at the operating conditions. Previous descriptions(3, 4) and data do not suggest such requirements for SAP.

EnCana has been developing SAP since 1996 and first piloted the process at its Senlac Thermal Project in 2002. Encouraged by the results, EnCana is presently testing SAP for in situ bitumen extraction at its Christina Lake Thermal Project.

In the Senlac SAP Pilot, some description of which has been given previously(4), solvent (butane) was co-injected in a well pair which was already in SAGD operation.