Genesis and Evolution of Paleozoic Algal Mounds – Application to Reservoir Distribution

Ritter, Audrey L. and G. Michael Grammer
Carbonate Sedimentology Laboratory, Western Michigan University, Kalamazoo, MI

During the Late Paleozoic, calcifying green algae termed “Phylloid Algae” were the dominant reef builders in many parts of the world. Hydrocarbon reservoirs in phylloid algal mounds are known from the Paradox, Orogrande and Permian Basins in the U.S., and are also common elsewhere in the world, including some of the supergiant fields in Russia and Kazakhstan.

Current dogma on the formation of phylloid algal mounds is that they formed in situ through constructional processes. These processes included sediment baffling and binding by the algae and various other organisms, coupled with abundant submarine cementation. Recent evaluation of phylloid algal mounds exposed along the San Juan River in Utah, however, have shown that these 10-12m amplitude mounds are distributed in a near sinusoidal pattern suggesting that they may have formed under the influence of wave- or tide-generated ocean currents. In modern environments, both wave and tide generated currents may pile loose sediment into dunes or sand waves along the sea floor with a similar near-sinusoidal distribution.

Ascertaining the conditions under which these mounds initiated and grew may have important implications to exploration concepts devised for these reservoirs. High energy, current-induced mounds, for instance, may be areally limited in the subsurface and may trend preferentially along strike (e.g. wave currents) or conversely along dip (e.g. tidal currents). In contrast, constructional mounds may have formed in much broader areas across an entire shelf or platform. Relative percentages of primary matrix muds, which are lower in current-induced mounds, may also affect reservoir quality and should be considered at both exploration and production scales.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004