Computed Tomography Study of VAPEX Process in Laboratory 3D Model
Wu, G.Q., Kantzas, A. and Salama, D.
CIM 2008-136 presented at the 59th Annual Technical Meeting of the Petroleum Society held in Calgary, June 17-19, 2008;
SPE 133204, CIPC 2008-136;
Journal of Canadian Petroleum Technology, 49(02), February 2010, Pages 40-47
The vapour extraction (VAPEX) process has been an intense research topic in recent years as an alternative technology to thermal recovery methods for heavy oil and bitumen resources. Most previous 2D transparent models had simulated the vapour chamber evolution behaviour of a vertical slice of the reservoir; however, the longitudinal vapour chamber evolution characteristic in 3D geometry could not be detected.
This paper presents the results of 3D monitoring of the VAPEX process in a laboratory model, using computed tomography (CT) technology to investigate the vapour chamber expansion behaviour in both radial and longitudinal directions.
The results show that in 3D geometry, “V?? shape vapour chamber expansion was a localized phenomenon. The dominant characteristic was that solvent gas first broke through upward to the top, progressing through the high-permeability zone by gravity segregation, forming a vapour chamber at the top. It then expanded downward from the top as the experiment progressed. From the numerical analysis of the CT images, the in-situ porous medium’s porosity, density and oil saturation profiles were obtained. The results further imply that contained gravity drainage may be the key for the success of the VAPEX process.
For the more than 400 billion m3 heavy oil and bitumen deposits in Canada, only 10% is surface minable. The major part of the deposits has to be relied on in-situ recovery processes(1). However, because of their high viscosities and low-degree API gravities in native state(2), these reservoirs can only be recovered with low recovery efficiency by conventional methods. For example, primary recovery in the best of these heavy oil reservoirs is approximately 6% of the original oil in place (OOIP). Subsequent waterflooding can improve the recovery to an extent of 1% ~ 2% incremental of OOIP(3). In order to more effectively recover these reserves, enhanced oil recovery (EOR) or improved oil recovery (IOR) methods have to be directly applied(4). The main technology challenge is to reduce the heavy oil viscosity in-situ(5). As the oil viscosity is very sensitive to temperature, thermal recovery methods seem to be very effective and have been widely researched and piloted(6), including cyclic steam simulation (CSS), in-situ combustion (ISC), steam assisted gravity drainage (SAGD) and steamflooding(7). The SAGD process has been commercially used by several oil companies in Canada. However, the SAGD process is not always applicable for all heavy oil reservoirs; some economic constraints arise if the high cost of steam generation and excessive heat losses in some thin oil reservoirs are considered(8). As alternatives, non-thermal processes such as solvent-based processes are still a logical choice to recover such heavy oil/bitumen reservoirs(9).