Browsing by Subject "CO2 Flooding"
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Item Study of CO2 Mobility Control Using Cross-linked Gel Conformance Control and CO2 Viscosifiers in Heterogeneous Media(2011-10-21) Cai, ShuzongCO2 has been widely used as a displacement fluid in both immiscible and miscible displacement processes to obtain tertiary recovery from the field. There are several problems associated with the application of CO2 flooding, especially when there is a significant presence of heterogeneous elements, such as fractures, channels and high permeability streaks within the reservoir. With flooding, CO2 will finger through the target zone while leaving most of the residual/trapped oil untouched. As a result, early gas breakthrough has been a very common problem in CO2-related projects, reducing the overall sweep efficiency of CO2 flooding. This research aims at improving the CO2 flood efficiency using cross-linked gel conformance control and CO2 viscosifier technique. A series of coreflood experiment studies have been performed to investigate the possibility of applying CO2 mobility control techniques. Corresponding simulation works have also been carried out to predict the benefits of applying CO2 mobility control techniques in the field. In the laboratory study, the CO2 coreflood system was integrated with the CT (Computed Tomography)-scanner and obtained real-time coreflood images of the CO2 saturation distributions in the core. This system was applied to the research of both cross-linked polymer gel treatment and CO2 viscosifier study and produced images with sharp phase contrasts. For the gel conformance study, promising results were obtained by applying cross-linked gel to eliminate permeability contrast and diverting CO2 into low permeability regions to obtain incremental oil recovery; also studied were the gel strength in terms of leak-off extent with the aid of CT (Computed Tomography) images. For the CO2 viscosifier research, we tested several potential viscosifier chemicals and found out PVAc (Polyvinylacetate)/toluene combination to be the most promising. The follow-up study clearly demonstrates the superiority of viscosified CO2 over neat CO2 in terms of sweep efficiency. This research serves as a preliminary study in understanding advanced CO2 mobility control techniques and will provide insights to future studies on this topic.Item Using Polymer to Maximize CO2 Flooding Performance in Light Oils(2014-12-17) Li, WeirongCarbon dioxide has been used to recover oil for more than 40 years. Currently, about 43% of EOR production in U.S. is from CO2 flooding. Although CO2 flooding is a well-established EOR technique, its density and viscosity nature is a challenge for CO2 projects. Low density (0.5 to 0.8 g/cm3) causes gas to rise upward in reservoirs and bypass many lower portions of the reservoir. Low viscosity (0.02 to 0.08 cp) leads to poor volumetric sweep efficiency. In heterogeneous reservoirs with high-permeability zones and natural fractures, the condition is even worse. Two methods related to polymers are studied to improve CO2 flooding performance. One is adding polymers to water to increase water viscosity during the water-alternating-gas (WAG) process, named polymer-alternating-gas (PAG) flooding. The other one is adding polymers with cosolvent to CO2, named CO2 viscosifier, to increase CO2 viscosity. To analyze the feasibility of PAG, couples model considering both miscible and polymer flooding processes are built to study the performance of PAG. Polymer adsorption and concentration, reservoir permeability, permeability variation and fluid viscosity are studied. Results show that PAG process could get higher recovery than WAG if not injectivity problem occurs. The Upper Ness formation in Spe10 model is used to study the PAG performance in a reservoir with channels. Oil recovery from PAG with a polymer concentration of 0.20 lb/stb is 6% higher than WAG process in this model. To analyze the impact of CO2 flooding in the North Burbank Unit, five sections that best represent the characteristics of the field were selected for reservoir modeling. Based on simulation results, the conventional WAG process increased average oil recovery in the North Burbank Unit by 10-13%, PAG are forecasted to increase average oil recovery 4-7% more than conventional WAG flooding in the North Burbank Unit. Based on assumptions, PAG could get positive NPV when oil price higher than $40/bbl while PAG could also obtain higher NPV than WAG in all these five sections, which indicates that PAG is both technically and economically feasible in the North Burbank unit. A black-oil pseudo-miscible model is used for study CO2 viscosifier performance in synthetic model, SPE10 model and Section TR78 in the North Burbank Unit. Results show that higher cumulative oil recovery and better sweep efficiency was observed for viscosified CO2 case in homogeneous, heterogeneous and channels reservoirs.