Investigation and Observations on the Stability of Water-Oil Ratio WOR during Chemical Floods in Heavy Oil Reservoirs

Abstract

AbstractLong periods of up to several years of production at a Water-Oil Ratio (WOR) at or close to 1 have been observed in polymer floods in heavy oil reservoirs in Western Canada. A similar behavior had been noted by some authors in waterflood projects in heavy oil; however, this has never been documented in chemical floods before. Such long periods of WOR stability at low values, with very unfavorable Mobility Ratios, are not expected from theory. The aim of this paper is to review chemical floods in heavy oil reservoirs in Canada to better understand this phenomenon and try and identify the potential mechanisms by investigating reservoir and operational factors. If the phenomenon can be controlled through adequate operational practices, it would allow to operate chemical floods under very favorable WOR conditions for long periods.The production data of hundreds of wells in 8 large scale polymer and ASP floods in heavy oil reservoirs in Western Canada has been reviewed to investigate the occurrence of periods of stable WOR close or equal to 1. A significant number of wells that display this kind of behaviour were identified and studied. The impact of Gas Oil Ratio, oil viscosity, injection rate and other factors was analysed to try and identify some potential factors causing the phenomenon.Long periods of WOR stability at or around 1 have been confirmed in 3 of the 8 chemical floods reviewed; 2 cases are polymer floods and 1 is a mixed polymer/ASP flood. The behaviour has been observed during primary, secondary as well as tertiary polymer flood. There appears to be a link with the injection and liquid production rates i.e. WOR stability occurs in a given range of rates; but no other obvious factors have been identified so far.The existence of long periods (up to several years) of WOR stability around 1 is documented for the first time in chemical floods in heavy oil reservoirs. This behavior is unexpected from theory and deserves further study; if it could be controlled through adequate operational practices, it would allow to operate chemical floods under very favorable WOR conditions for long periods.