Effect of Drainage Height and Grain Size on Production Rates in the Vapex Process: Experimental Study

Abstract

Summary Interest in the vapor-extraction (Vapex) process for heavy-oil and bitumen recovery has grown considerably as a viable and environmentally friendly alternative to the currently used thermal methods. The potential for the success of the Vapex process is even more attractive in some scenarios that preclude the thermal methods. The presence of an overlying gas cap and/or bottomwater aquifer, thin pay zones, low thermal conductivity, high water saturation, and unacceptable heat losses to overburden and underbur-den formations are some of the limitations with the thermal techniques, which potentially can be overcome by Vapex implementation. However, predicted low production rates by previous researchers for field application of the Vapex technique remain a serious barrier to commercial applications of the process. The scaleup methods that have been used by previous workers for translating the laboratory results to field predictions were based primarily on the reservoir transmissibility. An analytical model developed by Butler and Mokrys1 showed that the oil rate should be proportional to the square root of reservoir transmissibility. The effect of convective dispersion between solvent and virgin heavy oil in porous media was ignored in developing this model. The main objective of this work is to develop an improved scaleup method for the Vapex process using physical-model experiments carried out in models of different sizes. In this paper, we report the results of a new series of experiments that extend the previously reported results of Karmaker and Maini2 to a significantly wider range of model heights. These new experiments used a new design of slice-type physical models that places the sandpack in the annulus formed by two cylindrical pipes. Combining the new results with the previous data of Karmaker and Maini,2 we show that the transmissibility-based scaling-up method seriously underpredicts the results at larger scales. This observation suggests that much higher rates can be expected in the field implementation of the Vapex process. A new correlation also has been proposed for scaling up the experimental data to the real field cases. It indicates the height dependency of the convective-dispersion contribution, which can be the dominant mass-transfer mechanism for the process, to be a higher order than previously postulated. Experimental results from this work show that the stabilized rate is a function of drainage height to the power of 1.1 to 1.3, instead of the square-root functionality of the Butler and Mokrys1 model.