Applications of Organic Geochemistry in Rayoso Formation Characterization: Chihuido De La Sierra Negra, Lomita Field, Neuquina Basin, Argentina

Abstract

Organic geochemistry has been widely used in oil exploration industry. However, only in the last decades, innovative applications of its methods have become known in field development activities and reservoir characterization. One powerful application is the lateral and vertical fluids continuity in reservoirs. This study was made in Chihuido de la Sierra Negra-Lomita field, Neuquina Basin, which produces from three main reservoirs: Low Troncoso Formation, Avilé Formation and Rayoso Formation. In the mature stage of field development, RepsolYpf developed an analytical technique based in organic geochemistry to discriminate the production from each reservoir in commingle produced oil samples. The goal of the present paper is the integration of the geochemistry results and the geological model of the Rayoso Formation in order to establish the lateral and vertical continuity of the reservoir fluids, seal rock quality variations and support the field developments activities. According to the obtained results, the following conclusions were reached:Rayoso Formation produces oils with different geochemistry characteristics andThe geochemical characterizations of the oils produced in Rayoso Formation is going to be used as a powerful supporting technique for field development. Introduction Organic geochemistry has been widely used in oil exploration industry like source rocks identification, source rocks maturity evolution, estimation of hydrocarbon volumes generated by the same ones and the source rocks and oils geochemical characterization to establish petroleum and petroleum - source rocks correlations. From 1985 several examples of applications of organic geochemistry to help the resolution of production and reservoir problems were published in different specialized bibliography 1–6. The main difference between an exploration and a reservoir/production studies is the sampling scale. In the regional studies, petroleum and source rock samples are selected according to the different petroleum systems, managing to determine the genetic tendencies of maturity and relationship between petroleum and source rocks. In reservoir and production studies, a detailed sampling of producing layers is made. One of the most surprising observations of reservoir geochemistry is that all the fluids (water, gas, petroleum) are heterogeneous in composition as much in vertical as lateral direction. Therefore, the analysis of these heterogeneities allows characterizing individual layers and helps to allocate the production. The quality of the fluids present in the analyzed levels can be determined by means of this study and lateral and vertical correlations of them can be established. This information allows to determine the trap filling mechanisms, to establish the processes of alteration undergone by the fluids in the reservoirs or during the migration and, by means of integration with the geologic model, can be understood the interrelation of the reservoir architecture with the dynamics of the fluids. This information allows establishing a fluid distribution model on independent data from the geologic information since it is a direct determination on the fluid and it does not require previous calibration. The fluid distribution in reservoir can help to a better understanding of the reservoir behavior. The present article shows the characterization of petroleum produced from Rayoso Formation reservoir and their integration with the geological model of Chihuido de la Sierra Negra-Lomita field (Fig. 1). The goal is to establish the lateral and vertical continuity of the reservoir fluids, seal rock quality variations and support the field developments activities.