Pressure Barrier Applicability to Polymer Flood Design

Abstract

Effective oil displacement from a reservoir requires adequate and properly directed pressure gradients in areas of high oil saturation. If the polymer bank is too large or too viscous during a polymer flood, the pressure drop from the injection well to the polymer front may act as a pressure barrier by usurping most of the downstream driving force for oil displacement. Polymer injection pressures must be limited. The maximum allowable injection pressure is commonly constrained by caprock integrity, injection equipment, and/or regulations, even though fractures can be beneficial to polymer injectivity (and even sweep efficiency in some cases). This paper examines when the pressure-barrier concept limits the size and viscosity of the polymer bank during a polymer flood. Both analytical and numerical methods are used to address this issue. We examine the relevance of the pressure barrier concept for a wide variety of circumstances, including oil viscosities ranging from 10-cp (like at Daqing, China) to 1650-cp (like at Pelican Lake, Alberta), vertical wells (like at Tambaredjo, Suriname) versus horizontal wells (like at Milne Point, Alaska), single versus multiple layered reservoirs, permeability contrast, and with versus with crossflow between layers. We also examine the relation between the pressure-barrier concept and fractures and fracture extension during polymer injection. We demonstrate that in reservoirs with single layers, the pressure-barrier concept only limits the optimum viscosity of the injected polymer if the mobility of the polymer bank is less than the mobility of the displaced oil bank. The same is true for multi-zoned reservoirs with no crossflow between layers. Thus, for these cases, the optimum polymer viscosity is likely to be dictated by the mobility of the oil bank, unless other factors (like fracture extension) intervene. For multi-zoned reservoirs with free crossflow between layers, the situation is different. A compromise must be reached between injected polymer viscosity and the efficiency of oil recovery. The relevance of our findings is applied to operations for several existing polymer floods. This work is particularly relevant to viscous-oil reservoirs (like Pelican Lake and others) where the injected polymer viscosities are substantially lower than the oil viscosity

Influence of the Concentration of Polymer Solutions on the Filtration Properties of Reservoirs

“…Модель пласта представляет собой стальную трубу с приваренными с обоих концов фланцами, закрывающимися в свою очередь съемными фланцами, на которых установлены вентили, позволяющие подсоединять модель к установке. Выбор длины модели пласта (1 м), был проведен в соответствии с рекомендациями о моделировании процесса извлечения нефти водой [8,11,12,13,14]. В качестве модели пористой среды в опытах использован молотый кварцевый песок.…”

Recent Advances in Polymer Flooding in China

“…Recent advances in CO 2 EOR were reviewed in [ 12 ]. Despite the progress that was made in applying polymer flooding to very viscous oils in the Pelican Lake in Canada [ 13 , 14 , 15 , 16 , 17 ] and the Alaska North Slope in the USA [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ], the selection of polymer viscosity and slug size to recover very viscous oils [ 25 , 26 , 27 , 28 , 29 ] remains quite different from that in China because of the not well-understood mechanisms under an unfavorable mobility ratio. Polymers have been regarded as not having an effect on residual oil saturation (ROS) reduction [ 5 , 30 ].…”

Pressure Modification or Barrier Issues during Polymer Flooding Enhanced Oil Recovery

“…Finally, another new feature is in providing understanding of the performance of certain field polymer floods (Daqing, Pelican Lake, Milne Point, and Tambaredjo) and in some cases recommending improvements. Some of the original analysis associated with this work can be found in a proceeding paper of Wang et al [29].…”