Sedimentary Geology and Petroleum Potential of Eocene Foredeep Deposits of the Magallanes Basin, Southern Chile

Abstract

Abstract

The Magallanes foreland Basin in southern Chile contains numerous hydrocarbon producing blocks, each in a different phase of its exploration and exploitation history. Although most of the proven reservoirs discovered to date are found in the Upper Jurassic-Lower Cretaceous of the eastern platform areas, exploration and development activity has increased significantly during the past few years in Eocene strata of that part of the basin. Thermogenic gas can also be found in the lower to middle Eocene foredeep deposits of the basin, which comprises a ∼3 km thick succession of sandstones, siltstones and shales deposited in deep marine to shelf systems. The exploration of this play is made difficult by a remarkable tectono-sedimentary complexity, both at regional and local scales. Traps are said to be small and the quality of the reservoirs is generally poor. The purpose of this study is to stablish a correlation between subsurface and outcrop data to assess the gas potential in the foredeep area. The work is based on available and new biostratigraphic and detrital-zircon dating, digital elevation model, seismic, geochemistry and well data.

The study interval lies at a depth of ∼2000-5000 m. It is overpressured and has produced gas and condensate from a depth of 2500 m. A total of 157 samples were analyzed using Rock-Eval pyrolysis. Values of 0.6 %Ro between 2000-2500 m indicate that all samples are mature. From 2500-5000 m thermal maturity increases, reaching 1.3 %Ro at 4000 m and 2 %Ro at 5000 m. Total organic carbon is commonly low, ranging from 0.2 to 0.8 wt. %, but may be as high as 1.2-1.8 wt. %. Quality analysis indicate gas-prone Type-III kerogens.

The results also suggest that a number of tight gas intervals are found in the lower-middle Eocene, most of them have not seen production in the past because relatively low rates and low recoveries. Tight intervals located in the platform areas of the basin are just recently attracting attention for development with multi-well pad and hydraulic fracturing techniques. In general, these gas deposits were known to exist but large areas of the formations were considered to be uneconomic with conventional vertical wells.

Geological, geochemical and geophysical studies are underway to better understand the stratigraphy, structure, and petroleum history of four selected leads; when completed, these studies will provide a framework for an assessment of undiscovered petroleum resources in the basin.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016