Seismic Stratigraphic and Quantitative Interpretation of Leonardian Reefal Carbonates, Eastern Shelf of the Midland Basin: Insight Into Sea Level Effects, Geomorphology and Associated Reservoir Quality

Abstract

When coupled to petrophysical analysis and quantitative interpretation, a 3D seismic stratigraphic analysis of Leonardian shelf margin reefal buildups on the eastern shelf of the Midland Basin reveals carbonate buildups which respond to changes in sea level and are accompanied by systematic changes in lithology and reservoir quality. Identification of six seismic operational sequences (parasequence sets) and three major seismic sequences bounded by regional unconformities with the utilization of Vail seismic methodology and corresponding Galloway petrophysical motifs demonstrate allocyclic rather than autocyclic controls, as the cycles approximately correspond to the Leonardian global sea level curve in the Midland Basin. Within these sequences, parasequence set buildups are identified with distinctly differing geometries and seaward dipping slope angles, interpreted as reefs. They are HST, RST, and LST buildups with changes in the buildup geometry controlled by the relative changes in the sea level. Highstand buildups are the largest and with the steepest angles, while smaller Regressive and Lowstand buildups have more planar slope geometry. Information from the petrophysical analysis and the quantitative seismic interpretation revealed that fluctuations in sea level also control the mechanisms behind the dolomitization and the increasing trend in porosity from shelf edge to the distal buildup features. This systematic integrated petrophysical-seismic sequence analysis provides better understanding of the relationship among the lithology, interpreted reservoir quality, organic content, and regional geometries. Such a systematic knowledge of the Leonardian strata may assist in both new nonconventional and conventional exploration strategies.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016