Reexploration in Reconcavo Basin, Brazil: ABSTRACT

Abstract

The Reconcavo basin, a major oil and gas rift basin in northeast Brazil, has reached exploration maturity relative to traditional structural trap prospects. The basin has gone through 2 phases: an initial phase from 1940 to 1960 when the major existing fields were discovered, and a development phase from 1960 to 1980, during which addition of new field reserves was small, recovery factors of the major fields were increased, and production decline began. In the early 1980s a third phase, one of reexploration, was initiated, with exploration oriented toward prospects not systematically tested before, and exploitation strategies aimed at increasing recovery from existing fields. In the past, the exploration in Reconcavo was for structural highs with two targets: a basal Jurassic prerift fluvial section brought into structural contact with a core of lacustrine source beds, and a supra-core Cretaceous deltaic section that is part of the rift fill. Discoveries of stratigraphic traps in the intermediae turbiditic rift section were commonly fortuitous, made while testing structural highs. Current structural and stratigraphic analysis of this tract of the rift fill shows that it consists of turbiditic and non-turbiditic sublacustrine fans, and indicates that the more prospective areas tend to be the structural lows of the prerift section. A major element of the reexploration strategy is testing these combined structural-stratigraphic prospects in the rift section. Ultimate recovery from existing Reconcavo reservoirs, based on conventional development practices, is estimated to be 33% of oil in place. An estimated 450 million m3 (2.8 billion bbl) is left unrecovered, of which above 60% is residual oil requiring advanced tertiary techniques for recovery, and about 40% is a target for strategically deployed conventional recovery. Additional recovery depends on detailed reservoir characterization identifying isolated zones and internal heterogeneities that control fluid behavior. With these strategies, overall recovery can be increased from an average of 33-42%, leading to a doubling of current remaining reserves, rated at about 60 million m3 (377 million bbl). End_of_Article - Last_Page 512------------