A Method to Interpret Cycle Stratigraphic Framework at Wireline Log-Resolution Using Seismic Data

Abstract

To interpret high-resolution (or log-level, meters to low tens of meter scale) sequence stratigraphic framework by using wireline-log data is a standard procedure pioneered by Van Wagoner et al. (1990). A high-resolution sequence framework directly from 3D seismic data, however, is a formidable task, if not just a dream. Seismic visual resolution is primarily dependent on the predominant frequency (15-60 Hz, depending on data quality and depth), not the bandwidth of the data, which is typically about half of the high-frequency limit and is too low for high-resolution interpretation. Also, a seismic reflection is basically referred to a reflection surface, not thickness of a stratal unit. Continuity of a reflection does not necessarily represent stratal continuity because of the amplitude tuning effect. As a result, high-resolution sequence stratigraphy has been reserved for outcrop and core/wireline log studies. Direct seismic correlation of higher-order sequences is more symbolic than real. Some progress has been made by a three-step process. First, seismic cube was converted to relative impedance volume, such that a seismic event can be viewed as representing a stratal unit. Then, the converted seismic volume was properly decomposed into selected panels of high, moderate, and low frequency components. Finally, a combined rendering of these panels was realized by using RGB or other color-blending schemes, creating a new display of seismic sections. A seismic modeling study based on a geologically realistic sandstone-shale model revealed value to use the method to achieve a good tie between impedance (lithology or gamma ray) trace and its seismic response and to drastically improve seismic visual resolution and true stratal continuity. In the new display, the designated colors and the width of a seismic event both indicate thickness of a lithofacies unit. Sand content (or clay content) cycles, therefore, can be identified in a way similar to interpretation of gamma ray logs, with adequate resolution to correlation high-resolution sequences. To verify the results, controlled tests were done on previously published case studies with dense well control in GOM and lacustrine basins in China. In all those examples, high-resolution cycle stratigraphy was able to be established quickly using 3D seismic data, with a resolution similar to gamma ray-based sequence-stratigraphic framework and comparable interpretation of SB, mfs, and systems tracts.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017