Potiguar Basin

Integrated Study of The Petroleum Systems

This study presents an integrated analysis of the petroleum systems of the Potiguar basin, northeastern Brazil, based on geochemically oriented spec surveys and other geochemical studies that were recently performed by Geochemical Solutions International (GSI). The goal of this project is to provide a consistent and objective analysis of the petroleum systems of that basin to be used as an exploration tool.

The spec surveys in which this study was based include a soil gas campaign conducted in blocks BT-POT-3 and BT-POT-4, involving the collection and analysis of 637 samples, geochemical data from 46 crude oil samples representing the major onshore and offshore fields in the basin, and a quantitative basin modeling study in which all geochemical data was used to calibrate the known geological parameters.

The Potiguar Basin covers an area of 119,295 km2 both onshore and offshore in the Rio Grade do Norte and Ceará states of northeastern Brazil. Total current production is estimated at 125,000 barrels of oil equivalent per day, making it the second largest producing basin in the country after the Campos Basin.

The soil gas spec survey is based on 637 soil samples collected along regular grids. The sampling depth ranged from 1.2 to 1.5 m below the surface, in order to minimize interferences from biologically derived hydrocarbons that occur naturally in the soils. Landsat® satellite images were acquired and processed in order to evaluate the relationship between fault zones (possible pathway of gas) and the incidence of gas anomalies. Soils were analyzed to determine the content and composition of "free" light hydrocarbon (C1-C5) gases at the Center of Excellence in Geochemistry (CEGEQ) in Rio de Janeiro. These data are treated statistically in order to identify "outliers" indicative of geochemical anomalies.

Results of the Potiguar soil gas survey include: 1. Samples Logs with location, sample depth, soil type, soil color, soil humidity, location relief and vegetation for each site. 2. Geochemical Data for 637 soil samples documenting light hydrocarbon concentrations and composition. 3. Maps of sample locations (including interpreted surface faults) and various parameters indicative of geochemical anomalies. 4. Data CD-ROM with database (MS Access 97) containing all analytical results and sample log information. 5. Interpretative Report in both printed and HTML formats describing the locations and magnitude of geochemical anomalies.

In addition, GEOCHEMICAL SOLUTIONS INTERNATIONAL undertook the task of modeling a regional cross-section in the Potiguar basin with the main goal of understanding the factors controlling the petroleum systems in the basin under a numerical modeling perspective. In order to have a better view of the functioning of such systems, the following main aspects have been addressed: 1) location and evolution of petroleum kitchen areas; 2) timing of petroleum generation, expulsion and migration; 3) migration pathways, accumulation and losses; 4) oil and gas compositions.

The combination of soil gas spec surveys combined with geochemical analysis of crude oils and basin modeling studies will be used to construct an integrated and valuable characterization of the petroleum systems in the Potiguar basin.

The results of these individual studies have been integrated in a petroleum systems context to define the principal source rocks and kitchen areas, migration pathways and hydrocarbon compositions expected for the Potiguar basin.