On the applicability of Gassmann model in carbonates

Abstract

SummaryIt is important to choose an acquisition technique and geometry, which produces minimum footprints. Uniform distribution of fold, offset and azimuth for all the bins will reduce the footprints to a great extent but it is not achievable in any 3D practical geometry. Achieving the uniform nominal fold and minimizing the variation of offset and azimuth sampling across the bins is also the prime objective of the designer in designing the 3D survey geometry so that the geometry creates minimum footprints.The Slant geometry, which provides better offset distribution but narrow azimuth, is widely used in acquisition of 3D seismic data by Geophysical Crews of ONGC. In all the investigations carried out with Slant Geometry in acquiring 3D seismic data, the active spread for all the shots of salvo had been kept same. But the variation of Xmin, Xmax provided by the slant geometry as used in ONGC is more. It has been analyzed and found that by keeping the near offsets same for all the shot points of the salvo will provide uniform fold, equally good unique foldage, offset and azimuth but with minimum variation of Xmin, Xmax and Xavg across the bins. Hence, this suggested option of slant geometry will minimize the acquisition footprints. The analysis of the two options is compared in detail and it is shown that new options will have minimum acquisition footprint

Rock physics template from laboratory data for carbonates

“…Rogen et al (2005) presented the results of laboratory measurements of chalk samples and stated that porosity was the main controlling factor for v p and v s . Sharma et al (2006) agreed with this statement and mentioned as additional influencing factors: pore type, pore fluid compressibility and variations in shear modulus. The shear modulus weakening effect in saturated samples was also presented by Baechle et al (2005).…”

Laboratory measurements of the effect of fluid saturation on elastic properties of carbonates at seismic frequencies

“…In accordance with Gassmann's theory, fluid substitution increases the bulk modulus of a rock (Gassmann 1951), whereas the shear modulus remains constant (Berryman 1999). In most laboratory research carried out at ultrasonic frequencies, Gassmann's predictions mismatch the velocities observed in fluid-saturated carbonates (Wang et al 1991;Wang 1997;Marion and Jizba 1997;Assefa, McCann, and Sothcott 2003;Baechle et al 2005Baechle et al , 2009Røgen et al 2005;Sharma et al 2006;Misaghi et al 2010;Lebedev et al 2014;Wang, Wang and Schmitt 2015). In some studies, considering that Gassmann's theory was established for low frequencies and that viscoelastic properties of fluid-saturated rocks displayed at ultrasonic (high) and seismic (low) frequencies might differ markedly, one possible cause of the difference between Gassmann-predicted and measured velocities may be the difference between high-and low-frequency regimes.…”

“…One main implication of the laboratory studies conducted at ultrasonic and sonic frequencies is non-conformance of carbonate rocks to the assumptions of Gassmann's fluidsubstitution theory (Wang, Hirsche, and Sedgwick 1991;Marion and Jizba 1997;Baechle et al 2005;Sharma et al 2006;Misaghi et al 2010). In accordance with Gassmann's theory, fluid substitution increases the bulk modulus of a rock (Gassmann 1951), whereas the shear modulus remains constant (Berryman 1999).…”

An experimental study of solid matrix weakening in water‐saturated Savonnières limestone

“…; Sharma et al . ). The main factors inferred to be responsible for that reduction are carbonate pore types (Wang ; Baechle et al .…”