Revitalizing Seismic Facies Analysis

Abstract

In sedimentary basins worldwide, numerous 2D seismic lines and 3D seismic volumes have been acquired for hydrocarbon exploration and development. However, seismic stratigraphic interpretation is traditionally based on physical appearance of stacked and migrated reflection events. As presented in a series of papers in AAPG Memoir 26 in 1977, Vail and his colleagues showed how reflection configurations, external geometry, and statistical characteristics of amplitude, frequency, continuity, etc., could infer depositional systems. Nonetheless, the interpretations are largely geologic model driven, and the results are deemed to be qualitative and non-unique for the lack of lithological identification of sedimentary rocks in the system. In practice, well calibration could provide lithofacies information near well sites, which, however, is difficult to populate in long distance.

A quick and efficient interpretation of lithology on the basis of rock impedance model is the key to improve seismic facies analysis. To understand how a seismic signal responds to thin-bedded depositional elements in the context of impedance stacking pattern is essential; it is a function of thickness, wavelet phase, and frequency. Basic methods include (1) adjusting wavelet phase for the best fit between seismic traces and a wireline log-measured sandstone unit without seismic inversion; typically -90° phase trace is our choice because it provides symmetrical waveforms for a seismically thin bed and thus has the best correlation with wireline lithologic logs (e.g., gamma ray), and (2) performing frequency recomposition to expand the range of sandstone thickness imaging of seismic events by detuning amplitude from the single tuning point at a quarter wavelength. As a result, new seismic profiles can either keep as wiggle trace form with lithological labeling, which is familiar to geologists, or be displayed in RGB color-blended sections for more lithofacies details.

With a proper software tool, the methodology has a potential to revitalize seismic facies analysis by making use of millions of idled seismic lines for renewed exploration efforts. Examples from marine (GOM) and non-marine (Bohai basin in China) basins will be presented.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018