Paleozoic expulsion in Bolivia-its influence on field size and distribution

Conference · Mon Feb 01 04:00:00 EST 1993 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5942177

Beer, J A ^[1]; Lopez, O ^[2]

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1. Pecten International Company, Houston, TX (United States)
2. YPFB, Santa Cruz (Bolivia)

Production within the Chaco Basin of Bolivia may be grouped into three areas: a northern area with several large fields (> 100 MMBOE), a central area nearly devoid of fields, and a southern area with numerous small fields. Models for the timing of hydrocarbon charge suggest that field size and distribution can be tied to spatial variation in the magnitude of a Paleozoic expulsion event. In the central Chaco, the Devonian Los Monos Formation source rock interval was deeply buried beneath a Carboniferous depocenter (1600 to 2000 m of sediment). An in-house thermal modeling program, constrained by vitrinite reflectance data, indicates that the source rock interval entered the oil window as early as 270 Ma. Basal Los Monos kerogen was completely converted to oil prior to Neogene trap formation, making oil accumulations impossible. In the southern Chaco, an intermediate Carboniferous thickness (1300-1600 m) resulted in a less pronounced pre-Cenzoic expulsion event. Expulsion began at 150 Ma, with 80% of basal Los Monos kerogen converted to oil prior to trap formation. The southern Chaco thus has limited exploration opportunity for large accumulations. The northern Chaco has a thin Carboniferous veneer (01300 m), and experienced insignificant pre-Cenozoic expulsion. As a result, 90% of the basal Los Monos kerogen was available for conversion to oil at the time of trap formation, and large accumulations were possible. Given the relationship between field presence/size and subsidence history, a Carboniferous isopach map is a powerful exploration tool. Where there is a thin Carboniferous section, unconverted Devonian source rocks are able to charge Cenozoic structures. One area that meets this criterium is the western Subandean, a relatively unexplored province adjacent to the Chaco Basin.

• OSTI ID: 5942177
• Report Number(s): CONF-930306--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 77:2
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
BITUMINOUS MATERIALS
BOLIVIA
CARBONACEOUS MATERIALS
CONVERSION
DEVELOPING COUNTRIES
DIMENSIONS
EXPLORATION
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGIC TRAPS
GEOLOGY
KEROGEN
LATIN AMERICA
MACERALS
MAPPING
MATERIALS
MATTER
MINERAL RESOURCES
OIL FIELDS
ORGANIC MATTER
PALEOZOIC ERA
PETROLEUM DEPOSITS
PETROLEUM GEOLOGY
RESOURCE POTENTIAL
RESOURCES
SEDIMENTARY BASINS
SOURCE ROCKS
SOUTH AMERICA
THICKNESS
VITRINITE