Normal Compliances Research Articles

Azimuthal variation in AVO response for fractured gas sands

Natural fractures in reservoirs play an important role in determining fluid flow during production, and hence the density and orientation of fractures is of great interest. In the presence of aligned vertical fractures, the reflection amplitude at finite offset varies with azimuth. The effect of natural fractures on the azimuthal AVO response from a gas‐sandstone reservoir encased within shale is investigated. A simple expression for the difference in P‐wave reflection coefficient from the top of the reservoir parallel and perpendicular to the strike of the fractures is obtained in terms of the normal and tangential compliances, ZN and ZT, of the fractures. This expression is valid for small anisotropy and material contrasts and is compared with the results of numerical modelling. For a given value of ZT, the azimuthal variation in reflection coefficient at moderate offsets is found to increase with decreasing ZN/ZT. For gas‐filled open fractures ZN/ZT ≈ 1, but a lower ratio of ZN/ZT may result from the presence of cement or clay within the fractures, or from the presence of a fluid with non‐zero bulk modulus. For ZN/ZT = 1 and moderate offsets, the variation with offset of the reflection coefficient from the top of the fractured unit is dominated by the contrast in Poisson's ratio between the gas sand and the overlying shale, the effect of fractures only becoming noticeable as the critical angle for the unfractured sandstone is approached. However, for reflections from the base of the fractured unit, the variation in reflection amplitude with azimuth is much greater at conventional seismic offsets than for the reflection from the top. Azimuthal variations in the strength of the reflection from the top of the reservoir depend only on the variation in reflection coefficient, whereas the raypath is also a function of azimuth for reflections from the base of the fractured unit, leading to stronger, more visible, variations of AVO with azimuth. It follows that an azimuthal variation in AVO due to fractures in the overburden may be misinterpreted as due to the presence of aligned fractures in the reservoir.

Normal and tangential compliance for conforming binder contact II: Visco-elastic binder

This article extends the previously derived elastic solutions to visco-elastic solutions of normal and tangential compliances for a system comprised of two elastic particles bonded by a thin layer of visco-elastic binder. Rate dependent compliances are derived for both Maxwell and Voigt visco-elastic binders. Similar to the elastic particle-binder system, the time-dependent governing equation of this problem is also a Fredholm integral equation of the second kind. We employ the monotonical property of the kernel function to obtain the upper and lower bounds for the rate-dependent compliance relationship. Guided from the upper and lower bound solutions, we derive the best estimated solution based on physically consistent approximations.

47. Comparison of Devices Used While Ventilating a Non-Intubated Mannikin Model

Purpose: The purpose of this study was to determine if there were differences in tidal volume (Vt), minute volume (MV), average mask leak per breath (ML), gastric insufflation (GI), and peak airway pressure (PAP) when ventilating a non-intubated mannikin with a bag-valve (BV), manually triggered ventilator (MTV) and automated ventilator (AV). Our hypothesis was that there would be no differences among devices for any of these variables.Methods: This was a prospective in vitro experimental model. A convenience sample of 19 emergency medical technicians (EMTs) ventilated a non-intubated mannikin-mechanical test lung model with BV, MTV (flow rate 40 L/min; pressure relief 55 cm H2O), and AV (800 ml/breath; rate 12). Each subject, blinded to volume and pressure gauges, used each device for two minutes at both normal (0.1 cm H2O) and poor (0.04 cm H2O) compliances. Vt, MV, GI, and PAP were measured directly and ML was calculated. Data were analyzed with repeated measures ANOVA and Bonferoni-Dunn multiple comparison test with alpha set at 0.05.

Friction and elasticity on a molecular scale

A molecular scale atomic force microscopy study of friction and elasticity is presented on a one-component lipid bilayer system - a model boundary lubricant. With a real area of contact on the order of the lattice spacings of the sample, the elastic compliances of single lipid molecules are recorded - the first report of a molecularly resolved elasticity map. The anisotropic and highly ordered structure of the lipid bilayer has been observed to cause contrast information in friction on molecularly flat areas, and to be dependent on the sliding direction. This anisotropic behavior of friction has been measured to be independent of normal elastic compliances. Only asymmetric indentation which causes in-plane compliances leads to heterogeneities in the elasticity map. In this fundamental study of friction, the effects of adhesion and elasticity are discussed.

Elastic Properties and Stresses in Polyimide thin Films and Coatings

AbstractPolyimide thin films and coatings (< 20μm) for electronic applications have been fully characterized. Analysis of residual stresses and determination of all 21 anisotropic constants are necessary for a better understanding of these coatings in complex geometries. The residual stresses have been measured by a real-time vibrational holographic interferometry technique. The number of elastic constants is reduced to 9 independent constants by finding the orthotopic axes. All the 9 orthotropic constants - 3 normal compliances, 3 shear compliances and 3 independent Poisson’s ratios - have been determined. Moisture diffusion constants have also been measured.

Stress-induced anisotropy in sediment acoustics

A model to describe seismic wave propagation in both dry and water-saturated, particulate materials is derived on the basis of the response of a regular array of like elastic spheres. The theories of Hertz and Mindlin are used to model the normal and tangential compliances at the intergranular contacts and the overall response of the array is found to be governed by a set of nonlinear equations that depend on the quasistatic loading history. These equations are integrated over a particular stress history that simulates the normal buildup and relief of geostatic stress (overburden pressure) in nature. Wave velocities are evaluated at various stages during this stress history and the response is found to be anisotropic with respect to both p- and s-wave velocities. In order to simulate the response of marine sediments, the effects of water saturation are investigated by using the compliances calculated for the dry skeletal frame in conjunction with the Biot theory. Predictions of the model were compared with laboratory experiments and all the general trends in response were found to agree.

Stress‐induced anisotropy in sediment acoustics

A model to describe seismic wave propagation in both dry and water‐saturated particulate materials is derived on the basis of the response of a regular array of like elastic spheres. The theories of Hertz and Mindlin are used to model the normal and tangential compliances at the intergranular contacts, and the overall response of the array is found to be governed by a set of nonlinear differential equations. These equations are integrated over a particular stress history that simulates the normal buildup and relief of geostatic stress (overburden pressure) in nature. Wave velocities are evaluated at various stages during this stress history and the response is found to be anisotropic with respect to both P and S wave velocities. In order to simulate the response of marine sediments, the effects of water saturation are investigated by using the compliances calculated for the dry skeletal frame in conjunction with the Biot theory. Finally, the predictions of the model are compared with recent laboratory experiments and found to be in general agreement. [Work supported by ONR, Code 1125 OA.]

Finite-Width correction factors for sen testing of orthotropic materials in opening mode

Calculations of finite-width correction factors, Y, for mode I SEN tension testing of orthotropic materials have been made using a J integral implemented on results from finite element analyses. Y depends on the ratio of principal normal compliances S11/ S22 and another dimensionless quantity involving the material compliances. Aspect ratio is fixed at 1 and normalized crack depth varies between 0.3 and 0.6. S11/ S22 is fixed at four values; 20, 10, 1/10, and 1/20. Ranges of the other dimensionless material parameter relevant to existing materials are chosen. The use of linear interpolation for Y at intermediate values of S11/ S22, and the relevance of the results to specimens with aspect ratios in excess of 1, are discussed. Y is presented at each value of S11/ S22 in the form of a Chebyshev series in two variables. The results show that, if Y factors already established for isotropic materials are used to calculate stress intensity values for orthotropic specimens, errors in the stress intensity factor can be as high as 50 per cent.

Ventilation during CPR: Two-rescuer standards reappraised

Current American Heart Association standards for ventilation during two-rescuer CPR recommend that a 0.8- to 1.2-L breath be delivered in 0.5 second after every fifth chest compression. Delivering a high-volume breath over a brief inspiratory time (TI) may lead to hypoventilation and gastric insufflation in victims with an unprotected airway. We reasoned that lengthening TI would lower peak inspiratory pressure and peak inspiratory flow rate, and thus improve lung inflation. To study this possibility, a mechanical model of the airway and upper gastrointestinal tract was designed. A ventilator delivering a sinusoidal wave form was used to simulate artificial ventilation. A 0.8-L breath was delivered at 0.5, 1.0, or 1.5 seconds at three lung compliances (CLs). Also, the effect of lengthening TI was studied with increased airway resistance. Lengthening TI improved lung inflation and decreased gastric insufflation at all CLs, but more so with normal CL than with decreased CL. This study demonstrates the need for evaluating alternative ventilatory patterns with longer TI during CPR.