A study of offshore viscous oil production by polymer flooding
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Due to capillary pressure, reservoir heterogeneity, oil mobility, and lack of reservoir energy, typically more than 50 % of the original oil in place is left in the reservoir after primary and secondary recovery oil production. With relatively easy-to-get conventional oil resources diminishing and the price of oil hovering around triple digits, enhanced oil recovery methods, such as polymer flooding, have become very attractive ways to recover oil effectively from existing reservoirs. Enhanced oil recovery methods can be categorized into three categories: water or chemical based, gas based, and thermal based. This thesis will focus on the chemical injection of surfactants, alkali, and polymer of the water based methods. Surfactants are used to alter the interfacial tension of the aqueous and oleic phases in order to facility oil production. Alkali chemicals are used to create surfactants by reacting with acidic oil. And polymer is used to reduce injection water mobility to effectively displace the contacted oil in heterogeneous reservoirs by improving the volumetric and displacement sweep efficiencies. This research presents several laboratory results of polymer and alkali/surfactant/polymer core floods performed in the Center for Petroleum and Geosystems Engineering laboratories. Properties of polymer and surfactant phase behavior were measured and modeled and each coreflood was history matched with UTCHEM, a three-dimensional chemical flooding simulator. The coreflood results and the history matched model parameters were then upscaled to a pilot case for viscous oil in offshore environment with four wells in a line drive pattern. The potential of polymer flooding was investigated and several sensitivity cases were performed to evaluate the effect of various physical property parameters on oil recovery. Water salinity and hardness (i.e. amount of calcium and magnesium) has detrimental effects on polymer viscosity and its stability. The potential benefits of low salinity water injection by desalinization of seawater for polymer flood projects have been discussed in recent publications. The effect of low salinity polymer flood was also investigated. A series of sensitivity studies on well pattern and well spacing is carried out to investigate the impact on recovery factor and recovery time.