ANALYSIS OF ELASTIC WAVES RESPONSES FOR WATER SATURATED WEAKLY COMPACTED SANDSTONES BASED ON MODELING AND LABORATORY MEASUREMENT

• Main Author: FIKRI NIYARTAMA (NIM : 30210006), THAQIBUL
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/31274
• Institution: Institut Teknologi Bandung

This dissertation describes the analysis of elastic properties responses on weakly compacted sandstones saturated with water based on modeling and experimental of <br /> <br /> <br /> <br /> Ngrayong rock samples. 3D finite difference method for modeling of elastic wave propagation in fluid-saturated medium by means of Biot's theory has been developed in this study. Effective fluid density &#61480; &#61481; fl &#61554; and effective fluid bulk modulus &#61480; &#61481; fl K were used to replace the monophasic fluid to comply model on the <br /> <br /> <br /> <br /> Biot’s theory for fully saturated rocks. In accordance with the objectives of this study, the two-phase fluid mixing approach was then applied for modeling of <br /> <br /> <br /> <br /> partially saturated medium. <br /> <br /> <br /> <br /> The modeling of Biot wave propagation showed that the elastic wave signals that were sensitive to the degree of water saturation. The signals output of FD_Biot <br /> <br /> <br /> <br /> program displayed variations on P wave velocity and amplitude shift. The FD_Biot modeling was compared with the modeling of elastic medium (Seismic Un*x) and <br /> <br /> <br /> <br /> poroelastic medium (Cabrillo 1.0) at low and high frequencies with correlation factor (R) values larger than 0.9. <br /> <br /> <br /> <br /> Our experiment showed that the P wave velocity (Vp) was reduced significantly at the beginning of the imbibition process as compared with the value of Vs at the same degree of saturation. The variations on travel times and the amplitude changes were detected at any degree of saturation. The first and second amplitude peaks of P wave decreases as water imbibition (Sw) increases in the range of 0.1 to 0.45 for B2 and B5 samples, and 0.1 to 0.6 for B7 sample, amplitude peaks increase again afterwards. The shifting of peaks that indicated attenuation were also observed in the experimental. <br /> <br /> <br /> <br /> The modeling and experimental results showed the decrease of Vp in Sw 0.1 to 0.8. It could be explained by the rise of water volume that increased the overall density of the rock. Meanwhile, the bulk modulus was relatively remains constant due to the presence of air bubbles and contribution of clay mineral (Nontronite) in the porous rock. Air bubbles were detected from the image of a rock &#956;CT Ngrayong after fully water saturation. <br /> <br /> <br /> <br /> The changing of Vp due to water saturation in the experimental results could not be explained by either the FD_Biot modeling and other approaches. The results of modeling and approaches Gassman and Gassmann-Hill-Wood was higher above the experimental results. The modeling and experiments results showed a similar tendency for changes amplitude due to water saturation.