Seismic Anisotropy Modeling from Well Log in Talang Akar Formation, South Sumatra, Indonesia

Thariq Guntoro¹, Intan Andriani Putri¹, and Dwa Desa Warnana²

¹Physics Department, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia

²Geophysical Engineering Department, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia

Abstract

Old seismic modeling assume that the seismic wave propagate in the earth have a same value for every directions. In the real condition, earth layers is not as ideal as that. It has a very complex structure and a wave do not propagate as ideal as isotropic modeling. It propagate with a velocity which varying with the directions. Seismic wave velocity varying with the direction of propagation caused the anisotropy characteristics of rock. Because of that, the petrophysical analysis should consider the anisotropy parameters. The parameters can be aimed from physical characteristics measurement in laboratory and seismic reflection data. In this research, the anisotropy parameters or Thomsen parameters generated from well log data. Those parameters are ε, γ, and δ which known as Thomsen parameters. It represent elastics tensor constant aimed from stress and strain relationship in linear anisotropic medium and solid elastic. Generally, anisotropy characteristics influence by clay volume fraction, density, and seismic wave velocity. In this paper, the effect of clay content to the anisotropy analysis in sandstone reservoir discussed. The case study is in G402 well in Talang Akar formation in South Sumatera, Indonesia. Anisotropy parameters aimed from the empirical relationship between clay content and body (compressional and shear) wave velocity. The value are ε = 0.14; γ = 0.15; and δ = 0.04. Those value are less than 0.2 so the well has a low anisotropy characteristics. Then, anisotropic AVO (Amplitude Versus Offset) equation used to extract synthetics seismogram from isotropy and anisotropy model. The different between two models are shown in the synthetics seismogram. The Different of them shows that the anisotropy model give the clearer amplitude, thus providing ease of interpretation and reduce the risk of failure in determining the location of the target zone.