Integrated Studies of The Petroleum Systems of The Potiguar, Sergipe & Reconcavo Basins Onshore Brazil
These studies provide an integrated analysis of the petroleum systems of the onshore basins of Brazil based on geochemically oriented studies that were performed by Geochemical Solutions International (GSI). The goal of these studies is to provide a consistent and objective analysis of the various petroleum systems that can be used as an exploration tool.
The spec surveys in which this work is based include results obtained from the analysis of more than 2000 soil samples, geochemical data from numerous crude oil samples representing the major fields in the different basins, available source rock data and, where necessary, basin modeling studies based on available geological section(s).
Onshore geochemical surveying is one of the oldest and most successful surface prospecting methods. It is based on the fundamental premise that light hydrocarbons generated from deep subsurface sources can migrate vertically to surface and near surface soils. The migrating hydrocarbons are manifested as chemical, physical or biological anomalies in the soils, which can be detected using a variety of means. When integrated with surface geological structures derived from analysis of satellite images, this approach represents a powerful tool for evaluating the exploration prospectivity of different regions within a basin.
Crude oil studies provide an understanding of the origin of liquid and gaseous hydrocarbons in order to assist exploration efforts in the less developed regions. This is accomplished by the geochemical analysis of crude oils representing the major fields and stratigraphic horizons. Results are used to develop an understanding of how generative petroleum systems, maturity, and biodegradation affect oil quantity and quality. This information together with available source rock data is used to 1) Determine the number of distinct oil families and determine the age and paleoenvironment of the associated source rocks, 2) Map the stratigraphic and geographic distribution of the oil families and distinguish areas where oil mixing has occurred, 3) Assess oil quality with respect to alteration by bacteria or by water washing, 4) Identify distinct kitchen areas and estimate migration directions by comparing oil family distributions with the location of known source rocks, and 5) Utilize the geographic, stratigraphic and structural distribution of the oil families to identify, map, and rank petroleum systems.
The results of these 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 each basin.
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 Sergipe-Alagoas Basin is situated along the northeastern region of Brazil and spans the states of Sergipe and Alagoas. The majority of the basin is situated offshore; the onshore portion comprises an area of approximately 13,000 square km. To date, 28 oil and gas fields have been discovered in the basin, 23 onshore and 5 offshore. The current production reaches approximately 23,000 boepd.
The Recôncavo Basin is located in the Bahia State, northeastern Brazil, and currently produces about 55,000 barrels of oil equivalent per day, with estimated reserves of 564 million bbl oil. The Recôncavo Basin is divided into northern, central, and southern sub-basins by two major faults: the Itanagra-Araças and Mata-Catu faults. Petroleum system studies indicate that hydrocarbon generation has occurred within the lacustrine shales of the Candeias Formation, and that migration occurred mainly through fault planes and/or permeable zones from the Agua Grande System, as well as through direct contact between source and reservoir intervals.