3-D SUBSURFACE SEQUENCE STRATIGRAPHY OF A PERMO-PENNSYLVANIAN FLUVIAL-EOLIAN SANDSTONE

3-D Sequence Stratigraphy has become an indispensable exploration and developmental tool for the location of hydrocarbon deposits. In order to decipher the often complex heterogeneity of a terrestrial reservoir, analysis of high frequency fluctuations in base level defined from sedimentological studies has become a potent tool when complemented by seismic lines and calibrated on well-log signatures.

Analysis of (246m) 810ft of core from one well shows good correlation between genetic sequence sets obtained with the previously identified eolian and fluvial intervals within the target formation. 10 lithofacies (7 eolian and 3 fluvial) were identified. Thereafter, the lithofacies were grouped into 6 logfacies defined by patterns from common well logs to characterize the main sedimentary facies.

Analysis of the core have shown 6 diagnostic facies associations e.g.; (i) fluvial channel sand at base, overlain by reworked eolian and over bank deposits, (ii) dune grading into paleosol overlain by over bank and pond deposits, (iii) sand sheet and wet eolian grading up into dry eolian etc.

Candidate Sequence Boundaries were recognized by using the tops of the fining upward cycles in the eolian sands of the genetic sequence sets. They occur generally at dune tops with high bioturbation which then are overlain by dunes showing prominent lag deposits at their base.

We are extrapolating the Sequence Boundaries to nearby wells using well logs and 3-D seismic imagery. This allows determination of the 3-D geometry of the Sequence Boundaries which are good candidates for seals and permeability barriers.