Fault reactivation during fluid production, modelled as a multi-physics multi-scale instability

During fluid production in carbonate reservoir rock under high Pressure and Temperature conditions, the production-enhanced shear-heating of a creeping fault can lead to a thermal run-away. The reactivation of the fault is then accompanied with a large increase of permeability (by orders of magnitude) due to the dissolution of the rock. As a detrimental consequence for the industry, pressure equilibrates between the two compartments of the reservoir delimited by an initially sealing fault. To model such behavior, we present a three-scale framework implementing a THMC fault reactivation model. The framework links the three different scales of the problem: (a) the poro-elastic reservoir (km) scale, where faults are treated as frictional interfaces with the equivalent friction law being determined from the meso-scale; (b) the thermo-poro-chemo-visco-elasto-plastic fault at the meso-scale (m), encompassing all the physics at hand; and (c) its chemo-mechanically altered pore structure at the micro-scale (μm), where meso-scale properties (like permeability) are upscaled. In the present approach, the multiscaling approach allows us to replace the common use of empirical laws to the profit of upscaled physical laws. The framework is used to simulate the fault valve behavior appearing during induced reactivation coming from the production scenario next to a sealing fault.

Assessment of left atrial function

The left atrium (LA) plays an important role in cardiovascular performance, not only as a mechanical contributor, elastic reservoir, and a primer for left ventricular filling, but also as a participant in the regulation of intravascular volume through the production of atrial natriuretic peptide.Although LA diameter in the parasternal long-axis view has been routinely employed, LA volume is a more robust marker for predicting events than LA areas or diameters. The assessment of LA performance based on two-dimensional volumetrics, Doppler evaluation of mitral, pulmonary vein flow, and annular tissue Doppler, as well as deformation imaging techniques, may provide incremental information for prognostic purposes and for the evaluation of severity and duration of conditions associated with LA overload.The aims of this chapter are to explain the basics of LA function, and to describe the role of Doppler echocardiography techniques, and how to implement them, for the non-invasive evaluation of LA in clinical practice.

The Importance of Vascular Elasticity in the Circulatory System of the Cephalopod Octopus Vulgaris

The passive mechanical properties of the dorsal aorta and the vena cava of Octopus vulgaris were investigated in vitro. Both vessels are highly distensible structures that exhibit non-linear elasticity, but have substantially different material properties. The volume compliance of each vessel is maximal within the resting physiological pressure range (2–3 kPa in the aorta and 0–0.5 kPa in the vena cava) but is five times greater in the vena cava than in the aorta. The aorta is mechanically suited to function as an elastic storage reservoir in the arterial circulation, while the vena cava is appropriately designed to be a low-pressure capacitance element. Pressure wave velocity in the aorta was calculated from the elastic modulus to be 1.8 ms−1 under resting conditions. Therefore, pressure changes will occur almost simultaneously throughout the arterial tree and pressure wave transmission properties can be described by a two-element Windkessel model. Predictions of vascular impedance amplitude made from this model are presented. The effectiveness of the aorta as an elastic reservoir appears to be severely reduced during exercise in Octopus. Because blood pressure increases while heart rate does not, the efficiency of the Windkessel will be diminished as the time constant of the system decreases and the pulsatile work of the heart subsequently increases. Note: Address for reprint requests.