moveout inversion in azimuthally anisotropic media with lateral velocity variation : Theory and a case study
Reflection moveout recorded over an azimuthally anisotropic medium (e.g., caused by vertical or dipping fractures) varies with the azimuth of the source-receiver line. Normal-moveout (NMO) velocity, responsible for the reflection traveltimes on conventional-length spreads, forms an elliptical curve in the horizontal plane. While this result remains valid in the presence of arbitrary anisotropy and heterogeneity, the inversion of the NMO ellipse for the medium parameters has been discussed so far only for horizontally homogeneous models above a horizontal or dipping reflector. Here, we develop an analytic moveout correction for weak lateral velocity variation in horizontally layered azimuthally anisotropic media. The correction term is proportional to the curvature of the zero-offset traveltime surface at the common midpoint and, therefore, can be estimated from surface seismic data. After the influence of lateral velocity variation on the effective NMO ellipses has been stripped, the generalized Dix equation can be used to compute the interval ellipses and evaluate the magnitude of azimuthal anisotropy (measured by P-wave NMO velocity) within the layer of interest. This methodology was applied to a 3-D “wide-azimuth” data set acquired over a fractured reservoir in the Powder River Basin, Wyoming. The processing sequence included 3-D semblance analysis (based on the elliptical NMO equation) for a grid of common-midpoint “supergathers,” spatial smoothing of the effective NMO ellipses and zero-offset traveltimes, correction for lateral velocity variation, and generalized Dix differentiation. Our estimates of depth-varying fracture trends in the survey area, based on the interval P-wave NMO ellipses, are in good agreement with the results of outcrop and borehole measurements and the rotational analysis of fourcomponent S-wave data.
Shear-wave sourced 3-D VSP Depth Imaging of Tight Gas Sandstones in Rulison Field , Colorado Prajnajyoti Mazumdar
Rulison Field, Piceance Basin, Colorado was approved for development drilling to 10-acre spacing in 2003. The down spacing and hydraulic fracturing within this unconventional reservoir has increased its production five fold in less than a decade. A significant portion of the gas production is from low permeability fluvial discontinuous sandstones within the Williams Fork Formation of the Mesaverde Group. The gas is generated in the thick thermally mature coals of the Cameo Coal interval within the lower part of the Williams Fork Formation and migrates through the natural fractures that connect the reservoir and the coal interval. Development of this reservoir section is a challenge because the sandstone reservoir bodies are thin, generally below resolution of conventional compressional-wave (P-wave) seismic data, and lack acoustic impedance contrast with the surrounding shales. However, these sandstone bodies have a shear-wave impedance contrast with the encasing shale and that is what potentially makes shear waves attractive for imaging of these productive sand bodies.
The role of prolactin in andrology: what is new?
Prolactin (PRL) has been long deemed as a hormone involved only in female reproduction. However, PRL is a surprising hormone and, since its identification in the 1970s, its attributed functions have greatly increased. However, its specific role in male health is still widely unknown. Recently, low PRL has been associated with reduced ejaculate and seminal vesicle volume in infertile subjects. In addition, in men consulting for sexual dysfunction, hypoprolactinemia has been associated with erectile dysfunction and premature ejaculation, findings further confirmed in the general European population and infertile men. Several metabolic derangements, recapitulating metabolic syndrome, have also been associated with low PRL both in men with sexual dysfunction and from the general European population. In men with sexual dysfunction, followed-up for more than 4 years, low PRL was identified as an independent predictor of the incidence of major adverse cardiovascular events. Finally, an association with anxiety or depressive symptoms has been found in men with sexual dysfunction and from the general European population. While a direct role for impaired PRL function in the pathogenesis of these reproductive, sexual, metabolic and psychological disorders is conceivable, the possibility that low PRL is a mirror of an increased dopaminergic or a decreased serotonergic tone cannot be ruled-out. Hyperactivity of the dopaminergic system can explain only a few of the aforementioned findings, whereas a hypo-serotonergic tone fits well with the clinical features associated with low PRL, and there is significant evidence supporting the hypothesis that PRL could be a mirror of serotonin in the brain.