Horizontal Producer Wells In In Situ Combustion (ISC) Processes
Authors: Greaves M. , Tuwil A.A. , Bagci A.S. 
Published: March 2010

A simple 3-D physical model has been developed to investigate the use of horizontal producer wells in in situ combustion processes. The semi-scaled 3-D model was a rectangular box with 40 cm by 40 cm by 10 cm dimensions. Dry in situ combustion experiments were conducted with three different well configurations (1) a vertical injector and horizontal producer; (2) a vertical injector and two horizontal producers; and (3) injector and producer, both vertical. A matrix of 60 thermocouples was used to obtain temperature profile information, ill the vertical and horizontal mid-planes. Most experiments were conducted with sandpacks containing a high saturation of heavy crude oil SOi ≈ 0.80. For each horizontal well configuration, the effect of oxygen flux and oxygen enrichment (21% and 35% oxygen) was investigated.

Combustion peak temperatures up to 400 ºC were recorded, with oil recoveries exceeding 66% OOIP for the single horizontal producer well case. The recovery using two horizontal producer wells was 71.5% OOIP, higher than both the vertical producer and horizontal producer well cases. Generally, a much more stable propagation of the combustion front was observed for the single horizontal well vs single vertical well configuration. The vertical sweep especially was noticeably stabilized compared to the progressive tendency for gas override developing along the mid-plane of the vertical well experiment. Both single and double horizontal wells gave an earlier commencement of oil production and at a higher rate subsequently. However, the additional incremental oil recovery achieved by the double horizontal well was proportionately lower than indicated by theperformance of the single horizontal well, owing to interference between wells. At increased injected oxygen flux, the oil recovery reduced due to oxygen channelling through to the production end, causing higher rates of low-temperature oxidation ahead of the combustion from. Significant improvement of the combustion efficiency occurred with enriched air, but the oil recovery was lower due to higher fuel consumption. Overall, there was a very significant improvement in the quality of the produced oil using the horizontal well arrangement, Compared to that achieved with the single vertical well.

Introduction

The demand for crude oil and the increasing difficulty of discovering new large reservoirs, as well as the decrease in Conventional oil reserves, has generated special interest in heavy oil and tar sands. The high viscosities of heavy oils at reservoir conditions is the predominant factor limiting economic recovery. Any reduction in the oil viscosity will create an increase in oil mobility and therefore improve production. The most effective method of lowering the viscosity is by the application of heat to the reservoir. Heat may be introduced into the reservoir in the form of hot water, gases or steam lt may also be generated in situ by burning part of the oil in the reservoir, This process is known as in situ combustion or ISC.

Fireflooding or ISC is a thermal EOR method in which heat is generated within the reservoir by igniting the formation oil and then propagating a combustion front through the oil bearing media.