NEOGENE OIL AND GAS RESERVOIRS IN THE PROGRESO BASIN, OFFSHORE ECUADOR AND PERU: IMPLICATIONS FOR PETROLEUM EXPLORATION AND DEVELOPMENT
J. A. Deckelman*, F. X. Connors, A. W. Shultz, P. A. Glagola,
W. M. Menard, S .R. Schwegal and J. N. Shearer
*ConocoPhillips Company, 600 North Dairy Ashford, Houston, Texas, 77079, USA.
author for correspondence, email: email@example.com
The Progreso Basin is an Oligocene to Recent forearc basin of pull-apart/translational origin. In Peru, the basin contains proven petroleum reservoir sandstones of Early Miocene age at the Albacora field and the Barracuda-4 well. In Ecuador, Middle Miocene sandstones tested oil at well Golfo de Guayaquil–1, and Middle/Upper Miocene and Pliocene (?) sandstones produce gas at the Amistad field. Neogene sandstones are dominated by litharenites and feldspathic litharenites derived from uplifted and eroded Andean, Amotape (metamorphic), and oceanic crustal terranes. These are interpreted to have been deposited in neritic, brackish/coastal, and continental environments with locally steep gradients. The oil-producing sandstones at Golfo de Guayaquil–1 (~12,300 to 12,418 ft RKB) and a gas-producing sandstone of anomalously high porosity and permeability at Amistad–1 (9,870 to 9,895 ft RKB) are of interpreted fluvio-deltaic origin.
Sidewall core and wireline log data indicate that reservoir storage capacity is good to very good. Porosity ranges from 15% to 30%, and is consistently greater than 20% where overburden is less than 10,000 ft. Compaction is the principal porosity occluding mechanism; sequential precipitation of authigenic chlorite, clinoptilolite (zeolite), and authigenic calcite has occluded porosity to a variable extent. Porosity preservation is assisted by disequlibrium compaction related to overpressuring throughout the basin.
Reservoirs at the Amistad field have variable flow capacity. While the permeability of many sandstones is less than 20 mD, other sandstones, with probable Darcy-scale permeability, have sustained commercial flows of gas since the onset of production in 2002. The flow capacity of offshore Peruvian reservoirs is limited. The most productive well at the Albacora field flowed at an average rate of only 451 b/d oil prior to abandonment.
DST data from the Amistad field and the interpreted fluvio-deltaic environment of deposition of some sandstones indicate that stratigraphic compartmentalization can be expected locally. Structural compartmentalization due to faulting occurs at Albacora field and is likely in other tectonically active areas. The sands are multistoried; they are interbedded with mudrocks and they typically are on the order of 100 ft or less in thickness.
Gross-sand thickness decreases westward and reservoir–presence risk increases westward due to a number of factors including increasing distance from the sediment source; erosion of Miocene strata and complete truncation of Pliocene strata at an intra-Pleistocene unconformity; onlap of the Neogene sequence onto the accretionary complex; and the presence of local bathymetric highs related to active mud diapirism.
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