Experimental Study on Threshold Pressure Gradient of Heavy Oil Reservoir

The studies about threshold pressure gradient of heavy oil reservoirs at home and broad are made mainly in theory,little in experiment,and dominated by conduit flow model.The results have bigger differences than those from real flow state of heavy oil reservoirs.According to the percolation characteristics in heavy oil reservoir,an experimental method for rational determination of the threshold pressure gradient is designed,by which the threshold pressure gradient of heavy oil and flow velocity vs.pressure gradient under irreducible water saturation are studied using the natural cores of Karamay oilfield.The empirical formulas of relations between the threshold pressure gradient,flow velocity vs.pressure gradient parameters and rock gas permeability,fluid viscosity are obtained by regressing experimental data.The experimental results indicate that the effect of crude viscosity on threshold pressure gradient of heavy oil reservoir is bigger than that of reservoir petrophysical properties.The application of these formulas to the heavy oil reservoir can obtain theoretical calculation methods for determination of ultimate drainage radius and reasonable well spacing through threshold pressure gradient.