Study Of The Reservoir Fluid Flow By Fractal Method And Its Application

The dynamic reservoir is a non-linear complex system far away from equilibrium for its versatile original state, variable dynamic process and uncertain problems. The simple linear percolation law couldn't satisfy the description of the nonlinear law in the dynamic reservoir and new theories, methods should be used to build new models for prediction. In this paper, aiming at the heterogeneous pore structure and the inside multiphase flow characteristics, A comprehensive method including fractal mathematics, laboratory studies and computer simulations was used for research on the bases of the extensive investigation about the new theories and new methods related to dynamic reservoir system home and abroad.According to the fractal power law relationship, based on the intrusion-extrusion mercury capillary pressure curves, the correlation was analyzed between the heterogeneous pore structure and the fractal dimension for reservoirs with different permeability. The characteristic fractal curve of the low permeability rock samples was also compared to that of the moderate and high permeability rock samples. The results show the low permeability reservoir pore structure has a multi-fractal feature.The analysis of the fluid movement kinetics within porous medium indicates the important effect of the viscous fingering on the formation of the residual oil. With the experimental sets as Hele-Shaw cell and the particle packed model of injection-production well pattern, several visual experiments were performed to analyze such factors that greatly cause viscous fingering as the heterogeneous media and the unstable interface between the displacing phase and the displaced phase, particularly the non-linear percolation near the injection and the production points. The results show that the initial viscous fingering pattern has great influence on the subsequent axial fingering shape and the remaining oil distribution. The viscous fingering is the consequence of the surface/interface nucleus formation of the displacing phase particles and their fractal growth. The viscous fingering pattern is of self-similarity. The growth pattern models of fractal bodies were presented according to the analysis of energy transformation.According to the randomicity of the moving particles and the consistent formulations between the front viscous finger evolution and the Diffusion-Limited-Aggregate model, the fractal growth laws was analyzed for the viscous fingering evolution based on the DLA modeling. Also some suggestions were given for the remaining oil stimulation. The initially prominent growth direction determines the axial pattern of the overall fractal cluster. And the interfacial tension has effect on the transverse diffusion probability of particles and then determines the transverse pattern of the overall fractal cluster.After analysis of the effects of wettability on the formation fluid flow laws and the retaining oil distribution, the generalized capillary pressure model including the displacement and the imbibition processes and the new relative permeability model were derived by the fractal method. In comparison with experimental results, the generalized capillary pressure enhanced the curve fitting effect and was particularly fit for describing the capillary pressure curves that couldn't be described by Brooks-Corey model. The prediction method for relative permeability curves based on the fitted parameters from capillary pressure curves is especially suitable for acquiring the relative permeability curves of the fluid system including phase transition or interphase mass transfer. The variation range of the fluid phase transition and the mass transfer between phases correlates to the degree of reaction of the non-linear percolation: the stronger degree of the non-linear reaction, the wider variation range of the fluid phase transition and the mass transfer between phases.The application of the fractal method showed that the plugging of the clay particles might make the pore distribution change a lot, reduce the number of the big pores and increase the fractal dimension of the rock. It will increase the rock heterogeneity to enhance the irreducible water saturation and residual oil saturation, to narrow the permeability area of the two phases, and then to make the oil well wasted earlier. While the front viscous finger approaches near the oil-wells through reservoir, because of the formation heterogeneity and the great non-linear percolation within this area, the dynamic performance of the oil wells could be diagnosed from special parameters of the fractal model of the time series of oil wells.