--> Abstract: Geochemical Evaluation of the Petroleum Source Rock Potential of the Villeta Formation, Neiva Sub-basin, Upper Magdalena Province, Colombia, by F. Córdoba and A. F. Luiz; #90933 (1998).

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Abstract: Geochemical Evaluation of the Petroleum Source Rock Potential of the Villeta Formation, Neiva Sub-basin, Upper Magdalena Province, Colombia

Córdoba, Fabio - Ecopetrol and Trindade, Luiz A. F. - Petrobras/Cenpes

The Neiva petroleum sub-province belongs to the Upper Magdalena Province located in south-central part of Colombia. 19 oil fields have been discovered in this area, with ultimate estimated recoverable reserves of 425 million barrels of oil with gravities between 12 and 33º API. The main production comes from Cretaceous sandstone reservoirs of the Caballos and Monserrate formations. Secondary reservoirs are fluvial sandstones of the Upper Miocene Honda formation.

Based on geochemical evaluation it was possible to identify that the lower and middle parts ("Calizas de Tetuán" and "Caliza La Luna" of late Albian to early Cenomanian, and Turonian to Coniacian ages, respectively), of the Villeta formation contain the best potential intervals for hydrocarbon generation in the Neiva sub-province of the Upper Magdalena Province. The thickness of this formation varies from 1000 to 1800 feet, with a total organic carbon (TOC) up to 7%, Hydrogen Index to 700 mgHC/gTOC, composed mostly of Type II kerogen. A total of about 3000 samples from 13 wells were analysed and integrated to previous data in the present study. The maximun depth for some of the analysed samples is about 13500 feet (4100 m).

The organic matter richness for the upper part of the Villeta formation is low, with maximum values of 1% of COT, showing a tendency to increase Eastward. Tmax on this part of the section is bellow 430º C In the southern area the sub-province, Hydrogen Index is below 200 mg HC/g TOC and corresponds to Type III kerogen. In the northern area, Type II kerogen is dominant and Hydrogen Index reaches values about 500 mg HC/g TOC. According to these parameters, the upper Villeta formation does not have potential for oil generation.

At the southern area of the sub-province, the lower and middle parts of the Villeta formation have maximum values of 1.5% of TOC, whereas in the northern area it reaches 7%. Most of the samples corresponds to Type II kerogen with hydrogen index up to 700 mg HC/g TOC. In the western area of this sub-province, Tmax is comprised between 425 and 430º C increasing to the central part where it is close to 440º C. According to these data, the lower and middle parts of Villeta Formation have the best potential for oil generation and have an early stage of maturity.

The thermal evolution of these samples presents maximum values of Tmax close to 440º C and vitrinite reflectance of 0.65%, indicating an early stage of generation. The low maturity is supported by low thermal evolution of the oils found in this sub-province. Analysis of 40 oil samples allow the identification of two main hydrocarbon families. Family SA1 located in southern area, is associated with a source rock deposited under carbonate influence. Family SB1 located in the northern part of this sub-province is, derived from a siliciclastic source rock.

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