English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Open

Laboratory and field observations of stress-wave induced changes in oil flow behavior Peter M. Roberts*, Los Alamos National Laboratory, Sergey A. Kostrov, William O. Wooden, Applied Seismic Research Corp., Ernest L. Majer, Thomas M. Daley, Lawrence Berkeley National Laboratory Summary We present recent results of laboratory and field experiments designed to validate and quantify the phenomenon of seismically enhanced oil production in marginal reservoirs. Controlled laboratory experiments were performed where mechanical stress oscillations at 100 Hz or less were applied to sandstone cores while flowing oil and/or brine at constant flow rates. Steady-state flow and simulated flooding experiments indicated that stress stimulation causes significant changes in the ability of one fluid to displace the other and on the preference that the rock has for trapping one fluid over the other. For Berea sandstone, which is highly water wet, stress stimulation caused oil production to be impeded during water floods and caused the bulk fluid pressure drop across the core to increase during steady-state simultaneous flow of oil and brine. A possible explanation of these observations is that stimulation caused the core to become more oil wet. Field stimulation tests on producing reservoirs at Lost Hills, California were performed using a downhole fluid pressure pulsation device. Stimulation was applied in one well for 50 days total during July - November 2000. Two groups of producing wells were monitored for changes in oil cut and oil production during the test. A control group of 26 wells displayed an oil-cut increase of 29% and an oil production increase of 26% which are clearly correlated with the stimulation treatment. A larger group of 60 wells showed 11% oil-cut and 17% production increases. Similar increases were observed during the October 1999 Hector Mine earthquake, magnitude 7.1, in the Mojave Desert about 230 miles from Lost Hills. Downhole seismic monitoring of the stimulation wavefield is being used to help quantify the frequency range and energy threshold required for effective production enhancement. Introduction Roughly 60% of domestic oil resources remains unproduced, partially due to limitations in existing EOR methods. Anecdotal production data, as well as historic field and laboratory experiments performed by Russian and U.S. researchers, have shown that seismic (stress) wave stimulation can enhance oil mobility and total recovery in mature reservoirs (Beresnev & Johnson, 1994). Low- amplitude seismic waves in the frequency range of roughly 10-500 Hz can directly increase oil mobility over large distances. Previous field tests with different seismic sources have yielded mixed or inconclusive results for enhancing oil production. In some cases seismic stimulation increased production rates by 50% or more, but in other cases production was unchanged or actually declined. This is due primarily to the fact that existing laboratory and field experimental data are not comprehensive enough to allow prediction of the physical conditions under which stress- wave stimulation is most effective. Recent laboratory and field research is beginning to provide the experimental data needed to identify physical mechanisms which govern the seismic stimulation phenomenon (Nikolaevski et al., 1996; Roberts & Sharma, 1999; Roberts et al., 2001). The new results presented here are compelling because they were obtained under controlled experimental conditions and show a clear correlation between applied stress waves and fluid production behavior. As more data are collected for a wider range of physical conditions and downhole source technologies, stress-wave stimulation should eventually become one of the more valuable and predictable enhanced recovery tools available to the oil and gas industry. Laboratory Experiments and Results A specialized laboratory core flow apparatus, shown schematically in Figure 1., was assembled to study the effects of low frequency stress oscillations on fluid flow behavior in rock core samples. The main component of the system is a triaxial core holder, capable of applying up to 10,000 psi axial and radial confining pressure to the core samples. It is designed to hold cores 1 inch in diameter and up to 24 inches long, and accommodates single-phase and two-phase flow at static fluid back-pressures up to approximately 9,000 psi. Constant-flow-rate pumps are used to produce pulse-free flow of oil and water mixtures through the cores. Currently, accurate flow rates of 0.02 to 800 cc/min can be achieved. Stress cycling at frequencies from DC to approximately 2000 Hz are generated by direct mechanical coupling of the core to a Terfenol-D magnetostrictive actuator attached to one end of the core holder apparatus. The actuator can deliver dynamic force as high as ±200 lbf P-P with a maximum displacement of ±0.002” P-P. Thus, we can create Young’s mode strains as high as approximately 10 -4 in a 1-inch-diameter sandstone core. Permeability of the core samples is obtained by measuring the pressure drop across various sections of the core during constant flow. A load cell in series with the actuator and core provides calibrated measurements of applied stress and strain gauges attached to the side of the core allow dynamic measurements of Young’s modulus to be made during stress excitation of the samples.

Laboratory and field observations of stress‐wave induced changes in oil flow behavior