Southwest Section AAPG Annual Convention

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QUANTITATIVE SEISMIC STRATIGRAPHIC INTERPRETATION OF CARBONATE REEF GEOMORPHOLOGY AND RESERVOIR QUALITY

Abstract

When coupled to petrophysical analysis and quantitative interpretation, a 3D seismic stratigraphic analysis reveals Leonardian eastern shelf Midland Basin buildups to respond to changes in sea level and to be accompanied by systematic changes in lithology and reservoir quality.

Identification of three major seismic sequences bounded by regional unconformities and six seismic operational sequences (parasequence sets) integrating “Vail” seismic methodology and “Galloway” petrophysical motif analysis demonstrates allocyclic rather than autocyclic controls, as the cycles correspond to the Leonardian global sea level curve. Within these sequences, parasequence set buildups (identified as reefs) are identified with distinctly differing geometries and associated seaward dipping slope angles. Negating the paradigm of a simple evolution of carbonate platforms from ramp to rim, episodic changes are instead observed which reveal the HST buildups to be the largest and have the steepest slope angles while RST and LST buildups are smaller and have the lowest angles with more planar geometries. Shelf edge ridge and channel (mega spur and groove) geomorphologies are also evident and once formed tend to persist through sea level cycles.

Quantitative seismic interpretation constrained with petrophysical analysis reveals dolomitization and porosity associations to sea level position and imply coupled allocyclic-diagenetic controls with reservoir quality best in distal buildup features downdip from the shelf edge. This integrated petrophysical-seismic sequence approach provides insight into the relationships among the lithology, reservoir quality, and reservoir geomorphic geometries. Similar systematic applications of quantitative carbonate seismic stratigraphy may assist in exploration strategies in ancient reefal carbonates in the Permian Basin.

The quality of production from Soldier Mound's two reservoirs stimulated a frenzy of activity for the next several years in southwest Dickens. This activity resulted in the discovery of 18 official new field discoveries in 29 distinct reservoirs over the next few years. When down dip, basinal reservoirs were correctly recognized as being equivalent to shelf deposits to the east and a common oil type was found throughout the system it became obvious there had to be traps in between. All of these new fields are within a now very noticeable gap in the Tannehill's 100 mile long productive trend.

This presentation will discuss regional concepts that led to identification of the play along with trap, reservoir and production characteristics of both reservoirs.