A Gravity Override Analytical Predictive Model Of Steamflood

Nowadays, steamflooding is the most effective thermal recovery technique of heavy oilof all the EOR methods. To make a quick and accurate performance prediction ofsteamflooding, an analytical predictive model for steamflooding, based on a predominantlysteam override mechanism, is developed and the corresponding computer program is coded inthe thesis. The analytical model is tested with data from twenty-six field cases reported in theliterature. Acceptable matches are readily obtained with twenty-one of them. Petrophysical,geological and operational parameters of the remaining five field cases preclude thesuccessful history matching of the analytical model. By comparison with the hypotheticalmodel run on CMG simulator, the analytical model is further tested and the calculation of theanalytical mode is validated.The method used to solve and calculate the oil rate differs from previous methods. Oilrate is calculated by heat conservation of the expansion of steam zones in most models.However, the analytical model proposes that oil is driven essentially downward from bothsteam and steam condensate zones to the colder original oil zone below, from where oil isproduced. Oil production rate is determined by the pre-steamflood oil production rate, thethickness of the oil layer, and the thermal reduction of oil viscosity due to conductive heating.This is contrary to the generally accepted production mechanism, i.e. the growth of the steamzone is the principle determining factor of oil production. The main innovation of the paper istaking the contribution of steam condensate to the oil production into consideration.An “effective steam condensate zone size” is used, with the consideration of condensedsteam produced, to match the analytical model to field production data. It is found that, thedeveloped model is best applied to relatively thick reservoirs of small dip angle, with amedium heavy crude oil. Introduction of a “lag time” to account for mature steam overrideand steam breakthrough time and an areal sweep efficiency function expand the model’sapplication to large pattern areas.What’s more, based on data of the field case, sensitivity studies of the main petrophysical,geological and operational parameters are carried out, and the results are compatible withother results in the literature.