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Nonlinear Highlights


An Integrated Approach to Assessing Seismic Stimulation of Oil Production

Approximately 60% of domestic oil resources remain unproduced, partially due to the limitations of enhanced oil recovery methods such as water flooding. Because historical data on seismic stimulation are inconclusive, we are performing additional laboratory and field tests to quantify the conditions and physical mechanisms under which seismic stimulation can increase oil recovery. Our major objectives are to determine the optimum wave-field parameters for effective treatment over a wide range of field conditions and to obtain a fundamental scientific understanding of the relative importance of the physical mechanisms governing the stimulation phenomenon.

Right - Conceptual diagram of how ground vibrations stimulate increased production of oil and gas. The increase is transient but can be produced by surface vibroseis truck or vibration source in a borehole.

To quantify the effects of dynamic stress stimulation on multiphase fluid flow in porous media, we are conducting laboratory experiments at a unique new Los Alamos core-flow facility. We are also monitoring field tests of existing downhole seismic stimulation sources that are being developed commercially. These field experiments are being guided by the results of our laboratory work. We tested simultaneous two-phase fluid flow through a sandstone sample at several flow-rate ratios. We found that low-frequency (10-100 Hz) stress cycling decreases the fluid pressure drop across the core during steady-state flow of decane and brine. The magnitude of the decrease in pressure drop depended on the input stimulation amplitude and frequency. Lower frequency and higher amplitude produced the largest pressure decreases.

When 10-weight oil was used instead of decane, the effect of stimulation was reversed and the pressure drop increased during stress cycling. To further investigate this phenomenon, several experiments were performed. Instead of flowing two fluids simultaneously, non-steady-state displacement was used to simulate enhanced oil recovery (EOR) flooding procedures. During drainage and imbibition runs on sandstone cores, automated, real-time measurements of changes in oil and water production were obtained using an oil/water separation column. Our data indicate that mechanical stimulation may temporarily change the wettability of the rock, which results in the nonwetting fluid phase becoming trapped in the pore space, thereby releasing previously trapped wetting-phase liquid. The implication is that stimulation may be more effective at increasing production in reservoirs that are at least partially oil-wet.

We also monitored production and seismic stimulation sources in two separate oil fields, using two different seismic sources. Initial reports indicate that in both cases, oil production increased. During one field test at Lost Hills, California, seismic stimulation caused an increase in oil production of approximately 20%. This is similar to increases observed previously in the same field that were caused by the magnitude 7.1 Hector Mine earthquake.

Contact Peter Roberts.

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