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Nonlinear Highlights


Los Alamos Dynamic Stress Stimulation Laboratory


The Los Alamos Dynamic Stress Stimulation Laboratory is a unique facility designed to study the effects of low frequency stress waves on permeability and multi-phase fluid flow in rock core samples. If this phenomenon can be understood and harnessed it will lead to improved technologies for enhancing oil production and groundwater remediation.

Experiments are conducted using a range of different formation rock types as well as composite samples with varying initial permeability versus axial position.

Core Holder

The main component of the laboratory 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 will accommodate single-phase and two-phase flow at static fluid back-pressures up to approximately 9,000 psi. With additional parts, cores as large as 3 inches in diameter can be tested.

Constant-flow-rate pumps are used to produce pulse-free flow of water and non-aqueous-phase liquid (NAPL) mixtures through the cores. Currently, accurate flow rates of 0.02 to 800 cc/min can be achieved. Absolute and relative permeabilities are measured using differential pressure gauges connected to pressure taps positioned at selected lengths along the core.

Stress cycling at frequencies from DC to approximately 2000 Hz is 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 10e-04 in a 1-inch-diameter sandstone core. 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 dynamic stress stimulation of the sample.

In addition to the mechanical matrix-stressing mode of stimulation, the core holder has been designed to allow non-deformational shaking of the core to study inertial effects, as well as direct fluid pressure pulsation under static mechanical load to study relative pore pressure effects.

Understanding the importance of these 3 modes of stimulation will be useful for assessing various technological approaches to downhole and surface acoustic field stimulation that are currently being pursued by the oil and gas industry.


The lab apparatus is computer controlled through GPIB bus interfaces to the various instruments, gauges and pumps. Using National Instruments' LabVIEW software, an entire suite of experiments can be carried out automatically and unattended. This allows testing a large number of initial conditions and stimulation parameters in a short period of time.


The equipment primarily consists of function generators, amplifiers, oscilloscope, scanner, multimeter, analog-to-digital converters, temperature sensor, differential pressure transducers, current probe, accelerometer, pumps, vacuum pump, air compressor, compressed nitrogen cylinder, back-pressure regulator, ultrasonic bath, pressure gauges, strain gauges, load cell, LVDT displacement sensors, actuator, pressure chamber, valves, tubing, glassware, cables, and Apple PowerPC.

Image Gallery - Analytical Instruments

View of the dynamic-stress stimulation apparatus from the fluid-inlet end (right). A sandstone core sample and rubber confinement sleeve are shown in the foreground. These are inserted into the large cylindrical pressure vessel for testing. Radial confinement is applied by pressurizing the main vessel. Static axial confinement is applied with the load piston attached to the right end of the pressure vessel.

View of the dynamic-stress stimulation apparatus from the fluid-outlet end (left). Dynamic stress stimulation is applied to the core sample by the mechanical actuator attached to the left end of the pressure vessel.

Close-up view of the dynamic stress stimulation source (mechanical actuator).

View of (from bottom up) the fluid-flow pumps, actuator power amplifier, strain gauge amplifiers, A/D converter and temperature gauge used during stimulated flow experiments. Additional electronics are located in the rack just visible to the right.

Schematic diagram of the dynamic-stress stimulation apparatus, electronics and computer control equipment configured for single-phase fluid flow enhancement experiments. An additional constant-flow-rate pump is used for 2-phase immiscible flow experiments.

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