Hydrocarbon Play Types in the Tertiary Rocks of the Magallanes Basin, Chile, Revealed by Seismic Stratigraphy

Pigott, John D.¹, Sara Elgueta² (1) University of Oklahoma, Norman, OK (2) Sipetrol S. A, Santiago, Chile

The Magallanes Basin of Southern Chile is a polyhistory basin with three distinct episodes of geomechanical strain responses to tectonic stress: 1. An elastic pre-Cretaceous rifting stage, 2. A flexed downwarping and upwarping Turonian stage, and 3. A Tertiary vis­coelastic response to loading and unloading. These three geomechanical episodes have resulted in the evolution of a variety of possible petroleum systems with vertical, lateral, and mixed vertical-lateral migration pathways. Though the Chilean-Argentine Mesozoic petrole­um systems of the basin are still productive, most of the Magallanes Tertiary Foreland Basin remains unexplored. However, regional seismic stratigraphy integrated with borehole data and basin modeling of this largely frontier basin reveals seven distinct hydrocarbon play types for the Tertiary rocks:

1. Paleocene TST (“Zona Glauconítica”) on-lapping sands on an Eastern Turonian ramp of principally horizontal migration pathways. 2. Offlapping Oligo-Miocene LST deltas proxi­mal to deep faults for secondary lateral migration with viscoelastic deformation from origi­nal vertical elastic fault conduits from deeper strata. 3. Structurally rotated Oligo-Miocene deltas with secondary migration. 4. Basin floor fan channel sands with hydrocarbons feed­ing updip from viscoelastic deformation and basin floor fan feeder channels. 5. Sub decolle­ment folded and faulted Eocene basin floor sands of secondary migration. 6. Paleocene incised LST valleys filled by ensuing TST shales and sands of Lower Eocene upon a Turonian ramp with lateral migration upon a viscoelastic flexed basement flank. 7. Miocene HST flu­vial and estuarine channels associated with alluvial/estuarine complexes with vertical migra­tion from deeper Cretaceous strata (eastern margin).