Abstract

A series of experiments were performed in physical models saturated with heavy oils of 0.6 to 12.7 Pa.s. The oil was displaced by gravity drainage at constant pressure and it was produced using horizontal wells. The pressure was maintained either using a vacuum pump or by injection of an inert gas at low injection pressures. Computer Assisted Tomography was used for the visualization of the displacement front. Additional gravity drainage tests were performed in long vertical columns and in two dimensional glass micromodels. In this paper a detailed description of the performed experiments is presented. Production characteristics are shown and images of the gravity drainage process are a/so included. The recoveries varied from 20 % to 50 % recovery of the original oil in place. The pressure difference was maintained between 10 and 30 kPa. In the cases where sand parting was not observed, a uniform displacement front was formed. In the cases where parting was observed the experiment was temporarily shut in. Substantial amounts of oil were produced following the shut in period. Temporary shut in was also implemented at gas breakthrough with considerable increase in the oil recovery.

Introduction

In the Lloydminster area of west central Saskatchewan and east central Alberta, large reserves of heavy oil exist which can be mobilized at reservoir conditions. Conventional primary production of these reservoirs has utilized mainly vertical wells on relatively large spacings, resulting in recoveries of 5–10 % OOIP. Recent applications of horizontal wells in these reservoirs hold some promise of increasing recoveries, but thin pay intervals, low reservoir pressures and low GOR's limit the effectiveness of recovery mechanisms based on gravity, natural pressure depletion and solution gas drive.

The work described in this paper considers the enhancement of gravity drainage in LIoydminster reservoirs through injection of immiscible gas and production via horizontal wells. In addition to presenting results of lab experiments in various physical models, an extensive review of relevant literature is included.

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