Experimental Study On Increasing Tight Oil Recovery By DC Electric Field

The resources exploration research shows that tight oil and gas resources in China are widely distributed and rich in reserves.Due to the problems of high-viscosity fracturing fluid contaminated reservoirs,blocking percolation channels,and environmental pollution caused by commonly used tight reservoir production technologies,this paper proposes a new clean and unpolluted tight oil exploration technology-EEOR(Electrical Enhanced Oil Recovery).This thesis starts from the theoretical and experimental researches,and profoundly analyzes the feasibility of EEOR technology which has sort of guiding significance for the field development of tight oil.Firstly,in the micro-scale,a single capillary model is used to simulate a percolation channel in a porous medium.An analytical expression of the charge density and electric potential is obtained by solving the Poisson-Boltzman equation,and then combined with the Navier-Stokes equation to obtain the electroosmotic flow velocity expression in a single capillary expression and dimensionless apparent viscosity expression.Secondly,the electrokinetic phenomenon in porous media at the macro-scale is analyzed.By using fractal theory,a bundle of irregular capillary model is used to characterize the porous media.The electrokinetic theories in single-capillary theories are used to derive the analytic expression of electroosmotic effect and electro-viscous effect.Finally,the outcrop cores of the Chang-7 formation are used as the experimental object for indoor physical simulation experiments,and the theoretical knowledge of the previous chapter is used to analyze the effect of the DC electric field to improve the displacement efficiency of tight sandstone.During the experiment,the main influencing factor are electric potential gradient,displacement fluid concentration,displacement method,and crude oil viscosity.The experimental results show that there is an optimal potential gradient and displacement fluid concentration(10V,0.7mol/L respectively in the scope of this experiment),which makes the displacement efficiency of tight sandstone reach the maximum value,and compared with regular water displacement,displacement efficiency is increased by 50%;Under the conditions of sequential flooding and simultaneous flooding,the oil displacement efficiency are higher than that of conventional water flooding without applied DC.In addition,the oil production rate under the simultaneous flooding is higher than that of sequential flooding.In view of the effect of enhanced oil recovery,the effect of simultaneous flooding at low concentration is good,and the effect of sequential flooding at high concentration is good.The above research shows that the DC electric field has a good application effect on improving the physical properties of tight reservoirs,reducing flow resistance,and improving oil recovery.