San Martin and Cashiriari Gas/Condensate Accumulations, Camisea Area, Southern Ucayali Basin, Peru

Hanspeter Mohler

In early 1994 a new agreement was signed between PeruPetro and Royal Dutch/Shell for the evaluation of the commercial potential of the 1983-1987 Camisea discoveries. Two giant gas/condensate accumulations were encountered west of the Fizcarrald high, in thrusted anticlines of the Picha trend of the frontal Sub-Andean fold-belt. They contain large volumes gas in place and associated liquids (condensate C5+, and LPG C3/C4). Most of the reserves are contained in the Cashiriari structure (80% of the gas, 70% of the liquids).

The Pre-Andean (Paleozoic) sedimentary mega-cycle is represented by up to 5,000 m of deeper-shallow marine clastics of Ordovician-Early Carboniferous age, which contain Silurian, Devonian and Carboniferous source rocks of variable type and richness. They are overlain by up to 1,200 m of Permo-Carboniferous platform carbonates and of 600-1000?m of Early to early Late Permian coastal-continental, partly euxinic and evaporitic clastics (Mitu Group). The latter begins at its base and locally well developed excellent source rocks for oil (Ene Formation). The Andean (Mesozoic-Tertiary) mega-cycle starts with the marine transgressive Chonta (Camapanian), succeeded by coastal regressive clastics of the Vivian Formation (Maastrichtian). This is followed by several thousand meters of continenta Molasee-type infill of the Tertiary foredeep, which was created during the compressional phases of the Peru, Inca and Quecha phases of the Andean orogeny. Complex neotectonic activity in the form of local uplift and subsidence is accompanying the ongoing mountain building process.

Excellent and fair sandstone reservoirs respectively are present in the Vivian Formation, and in a newly recognized Permian sequence (Mitu Group). The Mitu Group had previously been correlated with the Cretaceous objective formations well known from the northern Ucayali and Maranon basins (Cushabatay-Esperanza-Agua Caliente Formations) and assigned new names (Noipatsite-Shinai-Nia Kaatsirinkari).

The source for the gas/condensate has recently been confirmed to be derived from Carboniferous source rocks of mixed kerogenous-humic type associated with shales and coaly shales (Ambo Group). Charge and migration modelling remain a challenge but are critical for the prediction of the regional gas and oil distribution.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995