The Microscopic Experiments And Modeling For Residual Oil Distribution After Water Flooding

Presently most oilfields in China have been at the stage of high water-cut, which means the serious problem in improving oil recovery furtherly even though taking some measures of tertiary oil recovery such as polymer flooding. Residual oil distributes very dispersively at the stage of high water-cut due to macroscopic anisotropy and microscopic anisotropy. Traditional seepage researches were focused on describing and studying the macroscopic anisotropy of reservoirs, from which we do not know or do not exactly know the physical and chemical details. Microcosmic study can make compensation for the defeats in macroscopic research. We can deepen the study of flow mechanism by combining macroscopic research and microcosmic research, which can provide sturdy theoretical foundation for the application of flow mechanism. Therefore, conducting 3-D characterization of pore-throat structure which can reflect the microscopic anisotropy of rocks, studying microscopic mechanisms for water-flooding even to polymer-flooding and constructing the relationship between residual oil genesis and pore-throat structure, fluids parameters as well as the facial property parameters are very important for residual oil tapping and improving development result. It can provide some theoretical supports for improving oil recovery after water flooding.Therefore, the main contents in this thesis is to construct 3-D pore-throat structres for rocks through CT scanning, based on which 3-D network models will be built. Then the processes of water flooding and polymer flooding are modeled through microscopic modeling. The validity is testified by comparing the results with CT experiments. Finally, based on the results of simulation, the features and rules of residual oil distribution as well as it microscopic affecting factor are studied, which can provide some theoretical support for residual oil tapping.Firstly, CT experiments are conducted and relevant images at different flooding stages are obtained, based on which image process is performed and some parameters are calculated. At the same time, some data including permeability, porosity, capillary pressure curves and relative permeability curves are also obtained through relevant physical experiments. Then 3-D image reconstruction is conducted based on 2-D CT images, including the information of 3-D pore-throat structure and residual oil distribution at different flooding stages. After determining the anisotropy and macroscopic representativeness, pore space microscopic description and network model construction for water flooding as well as polymer floodiing are performed. The validity is testified by comparing with the experiment results. Finally, the effect of reservoir microscopic parameters on residual oil distribution is studied. Method for predicting residual oil is set up by the combination of fuzzy comprehensive evaluation.The results show that the wettability of pores and throats as well as pore radius, shape factor, coordination number and aspect ratio have an important impact on residual oil distribution. For mix-wet rocks, the result of flooding in water-wet pores is better than that in oil-wet pores. For different wettability pores, the existence of residual oil can be predicted accurately based on the microscopic parameters such as pore radius, shape factor, coordination number, aspect ratio. The accurance can be up to 75%, which is meanful for the formation of residual oil.