PRATSCH, JOHANN-CHRISTIAN, Consulting Petroleum Geologist, Houston, TX

ABSTRACT: South American Oil and Gas Fields: Reasons for Their Presence and Distribution

South American oil and gas fields occur in geographic clusters. Their concentration in relatively small producing areas depends on the present location of the hydrocarbon generating depocenter and results from the basinal oil and gas migration history. By defining both, existing field locations can be explained and new field occurrences can be predicted, including those in overthrust plays. One-and two-stage hydrocarbon migration processes exist: In one-stage migration oil and gas migrate directly from the generating source beds into reservoirs, like in Maturin Basin or Maranon Basin fields. In two-stage migration oil and gas first migrate into a primary reservoir level, from there during a second migration phase into a (commonly younger) secondary reservoir level. Here, the original ource beds may be over-mature or even metamorphosed today; examples here are the Maturin, Llanos and Oriente Basins, possibly offshore Trinidad. Definition of generating depocenters is the task of regional exploration. Oil and gas migration analysis is one result of semi-detailed structural mapping using gravity, magnetic, seismic reflection and geochemical data. Oil and gas exploration in two-stage migration basins are especially challenging, like in the Austral Basin of southern Argentina and Chile or possibly in the Parana Basin.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.