--> Abstract: Ramos Field, a Giant Gas Field in a Subandean Belt (NW Argentina), by R. Gómez Omil and J. Lúquez; #90933 (1998).

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Abstract: Ramos Field, a Giant Gas Field in a Subandean Belt (NW Argentina)

Gómez Omil, Ricardo and Lúquez, José - Pluspetrol E&P

During the last 25 years the Subandean Range in the NW of Argentina (Thrust and Fold Belt) had been explored looking for Oil and Gas by many companies. Up to now all the traps discovered are related to large four-way closured anticlines elongated North-South. Ramos Field about 20 km long by 4 km wide is located in the middle position of the folded belt.

Fluid Characterization: Gas and Condensate are the main producing fluids from Huamampampa and Icla formations. The Gas Molar Composition shows a large heavy molecular weight fraction's recoveries at surface as Condensate, Propane, Butane and Gasoline (LPG). Santa Rosa F. has a Volatile Oil ring in relationship with a Gas Cap (Gas and Condensate).

Petroleum System: the structure (trap) is defined as a duplex involving Paleozoic (Silurian, Devonian, Carboniferous) and Tertiary (Miocene, Pliocene) units. It is perhaps the unique duplex anticline in Ramos-Acambuco-San Alberto trend, for that reason all the reservoirs are in the highest structural position known and, at the same time, the most fractured zone recognized.

Source Rock: Los Monos F. (Middle-Upper Devonian marine shales) had been defined as the main source of Gas and Oil in Northwest Argentina and South Bolivia. Kerogen type II-III are the main component. TOC ranges between 0.6 to 1, and the Ro indicated for this position values not higher than 0.8 in the anticlines. Generation and Migration began not before the Miocene and today this source rock is still in the Oil-window for the anticline and in the Gas-window for the synclines.

Seals and Reservoirs: are related to Huamampampa and Icla formations (fractured) and the seal with a thick deformed Los Monos shales (more than 2000m) highly overpressurized with Gas.

Reservoir Characterization: the reservoir is a naturally fractured Devonian quartzitic Sandstone from Huamampampa, Icla and Santa Rosa Formations. Open Fractures provide the effective porosity and control fluids movements toward the wellbore, being the matrix porosity less than 1%. The most important fractured zones are located in the forelimb and the crestal zone, while the less fractured ones are in the backlimb and plunges.

Conclusions: this field is the biggest discovery in the whole Subandean Belt of Argentina and Bolivia due to the following reasons: a) the intensive deformation recognized (duplex) gave to this anticline the highest structural position and an intense fractured system with more than 1500m thick in the culmination; b) very large Gas kitchen at both sides of the structure not always present in the Subandean Belt due to the intense thrusting; and, c) originally enough source rock available in the region about 500 to 900m thick surrounding the anticline.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil