In Situ Combustion Isc Process Using Horizontal Wells
Authors: Greaves M. , Al-Shamali O. 
Published: March 2010

A series of dry in situ combustion experiments, and a single wet combustion experiment, have been carried out on heavy Wolf Lake crude oil using a rectangular 3D combustion cell measuring DAD m by DAD m by 0.10 m deep. Three different well configurations were used: (1) VIHP-a vertical injector with horizontal producer; (2) HIHP-a horizontal injector placed normal to a horizontal producer; and (3) parallel HIHP-a horizontal injector parallel with a horizontal producer. AIl of the horizontal producer wells were placed in a line drive arrangement. A matrix of 60 thermocouples was used to obtain temperature profile information, in the vertical mid-plane and horizontal top, bottom and mid-planes of the oil layer. The experiments used sandpacks containing a high saturation of heavy crude oil, 80%. The injected gas was either air, or enriched air containing 35% oxygen.

Combustion peak temperatures up to 747 °C were recorded for the dry combustion tests, and up to 531 °C for the wet combustion test. High oil recoveries were achieved duririg dry combustion, ranging from 64.3 to 72.3% oorP, and 78.8% OOIP during wet combustion. The type of injection well, and its placement with respect to the horizontal producer well, had a very significant influence on the width of the combustion front formed initially, following ignition. This subsequently also had a significant effect on the propagation of the combustion front. In the case when the horizontal injector was placed normal to the horizontal producer (HIHP), the combustion front was formed across the entire width of the sandpack.

During the dry combustion tests it was noticeable that the size of the high temperature region tended to diminish with an increase in combustion time, regardless of the extent of the combustion formed initially. However, no reduction in size of the high temperature region occurred during wet combustion, which exhibited an almost total ‘sweep-out’ of the stored heat behind the combustion front.

Gas override condition was not a major problem using the horizontal producer well in direct line drive. The volumetric sweep efficiencies calculated from the vertical and horizontal temperature profiles were generally in good agreement with the measured oil recovery values, indicating almost complete recovery of oil from the swept regions of the sandpack.

The oil produced by in situ combustion was substantially upgraded, with the API gravity increasing in the range 17.3 to 20.5 °API compared to 10.95 °API for Wolf Lake crude.

Introduction

There are three major reasons why over half the oil in place in the average reservoir is unrecoverable by conventional production methods. First, only a portion of any reservoir can be contacted by the displacing fluid due to the geophysical and hydrodynamical complexity of the reservoir formation. Second, not all of the oil can be displaced from the reservoir rock that is contacted by the displacing fluid because of the physicochemical ‘trapping’ forces. Third, heavier, low gravity oils are frequently too viscous to move to the production well at rates sufficient to support an economic operation.