Christina Lake Solvent Aided Process Pilot

Abstract

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.

Design of the Injection Strategy in Expanding-Solvent Steam-Assisted Gravity Drainage

“…This could be considered as most likely the best possible value given that the reservoir simulation model is sealed at its boundaries and no losses of solvent to the far reaches of the reservoir are permitted. However, the solvent recovery is in reasonable agreement with values obtained in field pilots [5,6,8,9]. Figure 8 shows that the cost function initially rises and then falls with iteration number.…”

“…The solvent recovery was not included in the cost function because it is typically higher than 80% consistent with the data from field pilots [5,6,8,9].…”

“…Minimal solvent losses are critical especially when the injected solvent is more expensive than the produced bitumen. In 2002, EnCana (then PanCanadian) conducted the Solvent-Aided Process (SAP) pilot at their Senlac SAGD pilot in one of the Phase C wellpairs [5,6]. In this pilot, regular SAGD was implemented for the first 6.5 months.…”

“…After butane injection was stopped, the oil rate declined to the projected SAGD oil rate. The solvent recovery was reported to be over 70% [6]. EnCana has applied the SAP technology in their Christina Lake project [6].…”

“…The solvent recovery was reported to be over 70% [6]. EnCana has applied the SAP technology in their Christina Lake project [6]. So far, the results show an uplift of oil rate by over 50%.…”