Abstract

The concept of the Vapex (vapour extraction) process has been found promising for the recovery of heavy oil and bitumen in the laboratory study using scaled physical models. In this process a vaporized hydrocarbon solvent, usually ethane, propane or butane is injected into the reservoir using a horizontal well and the diluted (and sometimes deasphalted) oil is produced through another horizontal well by gravity drainage. If a pure solvent is used, the solvent vapour chamber has to be maintained at pressures lower than the vapour pressure of the solvent to prevent the extracted region from being filled with liquid. This presents a problem because, for solvents such as propane and butane, the vapour pressures are often lower than the reservoir pressures.

In the present work the potential for injecting a noncondensible carrier gas along with the solvent to increase the operating pressure is studied. The carrier gas rflay or may /lot participate in the leaching process and in the field conditions natural gas may be used as the carrier gas. To achieve the maximum solubility of the solvent at the corresponding temperature the leaching solvent is injected as liquid which is vaporized and carried to the bitumen interface by the carrier gas. The extracted region is left filled with gas and some solvent vapour. This is the concept of the "Butex" process which has been proved to be effective from the results of experiments presented in this paper.

Introduction

Recovery of the huge reserves of highly viscous heavy oil and bitumen poses a serious challenge to the engineers. A thermal process, The Steam Assisted Gravity Drainage (SAGD) has heen applied successfully for the extraction of these crudes from relatively thicker reservoirs. In thinner reservoirs and in the low porosity carbonate rocks heat losses may prohibit the application of this process. The Vapex process[1] being nonthermal is free from this problem and can be applied to the vast majority of thin reservoirs containing mostly heavy oil in Alberta and Saskatchewan as well as to the thick bitumen reservoirs. This new process utilizes hydrocarbon solvents to reduce the crude viscosity and is highly energy efficient compared to steam processes[2].

One important advantage in the Vapex process is the in situ upgrading of the crude by deasphalting in the presence of hydrocarbon solvents, by which the metal, sulphur and nitrogen contents of the crude are reduced. It is predicted that the additions to conversion capacity in the refineries throughout the world will decrease considerably by tbe turn of this centuryl31. This and an unfavourable light heavy differential will reduce the marketability of the produced heavy crudes. Any in situ upgrading, such as in the Vapex process, may partially compensate this effect.

From the results of experiments carried out in this laboratory it could be concluded that the Vapex process can be implemented in reservoirs[2,4,5]. In these studies solvents like propane and butane were maintained at pressures close to their vapour pressures which are much lower than the usual reservoir pressures.

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