Experimental Study On Natural Seepage Of Matrix Core In Fractured Reservoir

Naturally fractured oil reservoirs constitute an important percentage of the world’s petroleum reserves, and Spontaneous imbibition is one of the key mechanisms for oil production from naturally fractured reservoirs. In spontaneous imbibition, wetting fluid is drawn into the rock by capillary suction and the non-wetting fluid is expelled from the water wet rocks. The final oil recovery and the rate of oil recovery by spontaneous imbibition depend on many rock and fluid properties and wettability of the rock. Understanding the factors that affect imbibition process has an important guiding significance to the oil recovery by spontaneous imbibition in fractured reservoirs.Based on the experimental research and theory analysis, thesis mainly has carried out the following research work and obtained the corresponding results:(1) Based on the single capillary model, and combine the Poiseuille-equation to analysis the fluid in horizontal capillary only by the capillary force under the action of oil-water interface speed and position changing with the time under different oil/water viscosity ratio and oil recovery by spontaneous imbibition with the relationship of normalized time. Also analyzed the vertical capillary under the effect of capillary force and gravity, the two-phase fluid interface height and rise velocity under different capillary force and gravity ratio changes with the time.(2) Introduce the porosity and permeability, combined with Darcy’s law, applied the dynamics theory about single capillary model into the porous medium, the spontaneous imbibition theory of porous media was analyzed, and obtained the oil volume displaced by the imbibition water in porous media with the relation of the time.(3) Through indoor experiment research of spontaneous imbibition, this paper analyses the fluid viscosity, wettability, permeability, boundary conditions and water velocity on the influence law of recovery by spontaneous imbibition. When the permeability change only within a certain range, the bigger of permeability is the core final recovery is higher; Boundary conditions has almost no effect on the core final recovery, the introduction of the concept of shape factor analysis the boundary factor’s influence on the rate of imbibition. The bigger the shape factor is, the greater the rate of imbibition; The smaller the water phase viscosity, the greater rate of imbibition; The smaller the oil phase viscosity is, the final recovery will be greater; The smaller the water wet index is, the final recovery will be lower; confirm the critical speed experiment of core, the smaller the permeability, the smaller the critical speed.(4) Use the spontaneous imbibition scaling model to analyze the experimental results. And confirm the oil recovery and the relationship between the dimensionless time, and the results of the analysis was applied to predict the recovery of reservoir under the influence of different factors.