Velocity analysis and imaging in transversely isotropic media: Methodology and a case study

Anisotropic P-wave velocity analysis and seismic imaging in onshore Kutch sedimentary basin of India

“…The inversion of η requires either the NMO velocity of a dipping event with a dip of at least 25°or long-spread (non-hyperbolic) moveout from a horizontal reflector. Parameter η is also responsible for anisotropy-induced nonhyperbolic moveout, which may distort the stack section derived from relatively long spreads where the spread length to depth ratio is in the order of 1.5-2 (Alkhalifah et al, 1996). Therefore a correct time image for a VTI media can be generated using only P-wave seismic reflection data with correct estimation of NMO velocity and η from the respective semblance analysis.…”

“…These parameters are described as (i) V P0 (the P-wave velocity in the direction of the symmetry axis), (ii) V S0 (the Swave velocity in the same symmetry direction), (iii) ε (a dimensionless quantity close to the fractional difference between the P-wave velocities in the direction perpendicular and parallel to the symmetry axis), (iv) δ (another dimensionless quantity that predominantly governs the P-wave velocity variation close to the symmetry direction, which is vertical for VTI media), and (v) γ (measures the velocity of SH-waves). Measured values of the ratio of horizontal to vertical P-wave velocity, an often quoted measure of anisotropy in some sedimentary basins can be more than 1.3, and the values of ε in sedimentary sequences range from 0.1-0.3 for moderately anisotropic rocks to 0.3-0.5 or even higher for compacted shale formations (Alkhalifah et al, 1996;Thomsen, 1986). There are rocks or materials in which ε N1.0 like 1.161 for Gypsum-weathers material, 1.222 for Biotite crystal, 1.12 for Muscovite crystal and can become negative with measured values of − 0.038 for Ice I crystal, − 0.096 for Quartz crystal, −0.005 for Lance Sandstone, −0.026 for Mesaverde sandstone (Thomsen, 1986).…”

“…(9)] due to the influence of non-hyperbolic moveout. Still, the anisotropic contribution to the NMO velocity seems to be the most pervasive reason for errors in converting time to depth in many exploration areas (Alkhalifah et al, 1996).…”

Inversión Sísmica Por Algoritmo Genético Con Migración De Poblaciones Para Estimar Anisotropía Hti

“…Convencionalmente el proceso sísmico asume un medio isótropo, sin embargo, con el advenimiento de la sísmica multicomponente, las secciones sísmicas de onda P y onda convertida CS no permitían su amarre sin considerar un modelo anisótropo. Un gran avance en la parametrización de la anisotropía fue lograda por Thomsen (1986), Alkhalifah et al (1996), al introducir una notación sencilla e implementar un parámetro anisótropo para el procesamiento de onda P. El énfasis inicial en el desarrollo de la teoría de la anisotropía se centró en la onda S, pero por ser la prospección con onda P más económica y tener un alto grado de sofisticación, muchos autores se volcaron al desarrollo en esta área. Según Crampin et al (1985) la anisotropía sísmica se asocia a factores como: anisotropía intrínseca causada por minerales, granos o cristales alineados preferencialmente, anisotropía litológica debida a partículas de lutita o arcillas alineadas, anisotropía por capas horizontales finas de roca sedimentaria (anisotropía VTI), anisotropía por orientación preferencial de fractura o diaclasas (anisotropía HTI) y anisotropía inducida por esfuerzos.…”

Optimized nonhyperbolic moveout correction equation of long-offset seismic data for TI media with an arbitrary spatial orientation

“…TI media exists widely in the crust which has significant impact on seismic wave propagation and further processing and interpretation of seismic data (Alkhalifah et al, 1996;He and Castagna, 2000;Isaac and Lawton, 1999;Toldi et al, 1999;Yan and Lines, 2001). For instance, the effect of TI must be taken into consideration in processing and interpretation of long-offset seismic data.…”