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Maximization of pore-fluid motions in poroelastic formations for wave-based enhanced oil recovery (EOR)

We discuss maximization of pore-fluid wave motions or volume of mobilized oil in a target oil reservoir, stimulated by vibrational operations. Motivation stems from post-earthquake observation and experimental data, using active wave sources, which reported improved production rates of remaining oils from existing oil fields. In this work, we attempt to identify optimal wave source conditions, e.g., timings and frequency contents, that can maximize desired metrics for the wave-based EOR by using a systematic approach. The desired metrics include: (i) relative pore-fluid wave motions, which could drive dislodging of trapped oil droplets and (ii) volume of coaxed-out bypassed oil from low to high permeability areas in a highly-heterogeneous reservoir, due to cross-flow oscillation recovery mechanism.

To this end, we cast this problem into an inverse-source problem, and the associated minimization problem is addressed by using a partial-differential-equation(PDE)-constrained optimization approach. We obtain pore-fluid wave motions within a one-dimensional poroelastic solid embedded in a semi-infinite elastic solid by using the mixed finite element method for the Biot’s wave equations coupled with the elastic wave equation. Our numerical optimizer recovers optimal loading signals, of which dominant frequencies correspond to amplification frequencies, leading to the maximum relative pore-fluid wave motions.

To estimate a net volume of mobilized oil from low to high permeability areas, a fluid flow hysteresis model is adopted to consider the flow behavior of pore-fluids at the interface between areas of different permeability. A frequency sweep shows that a sizable amount of oil could be mobilized via the wave stimulation. It is also observed that certain wave frequencies are more effective than others in mobilizing remaining oil from low to high permeability areas. This numerical work also shows that the wave-based mobilization of bypassed oil in a heterogeneous oil reservoir could be more feasible when combined with another EOR method, e.g., low-concentration surfactant injection, to improve fluid mobility in rocks.

Author(s):

Chanseok Jeong    
Department of Civil Engineering, The Catholic University of America
United States

Loukas Kallivokas    
Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin
United States

Chun Huh    
Department of Petroleum and Geosystems Engineering, The University of Texas at Austin
United States

Larry Lake    
Department of Petroleum and Geosystems Engineering, The University of Texas at Austin
United States