Modeling the Effects of Capillary Pressure and the Manipulation of Viscous to Capillary Forces to Recover Residual Saturation Using the Pore N-Let Model
The difficulty in recovering residual oil is created by (1) the reservoir pore geometry (length, number, and size of tubes and throats), (2) the fluid properties and interfaces, (3) viscous and capillary forces acting on the fluids, and (4) reservoir heterogeneity. This research is intended to expand the pore doublet model and use it to model flow in reservoirs. By first modeling scenarios of simple flow, a better idea of the nature of the pore doublet is gathered. Then the model is expanded to a pore n-let and used with experimental data on mercury injection with the intent of applying it to reservoir models. Further experiments are done with field data taken from the San Juan and Greensburg fields and the following conclusions are made. Capillary forces govern flow in small tubes while viscous forces govern flow in large tubes. Over a distribution of small and large tubes, increasing capillary number will cause larger tubes to flow faster and trap oil in smaller tubes quicker. A strong assumption is made that only large pores will trap oil, and small tubes will displace oil. This assumption leads to complete displacement of the trapped oil over a range of increasing capillary number. Capillary desaturation curves are produced from these calculations and qualitatively agree with curves produced in other work. Results show that displacing residual oil is heavily dependent on pore geometry and pore size distribution. Well sorted distributions caused low initial non-wetting residual saturation, but larger pores required a higher capillary number to remove trapped oil. In most cases, complete desaturation typically occurred over capillary number range of one order of magnitude. These experiments and conclusions are discussed in detail.