All Dunga field wells to date have been producing from a low permeability sandstone reservoir of Aptian age. However, while drilling an exploration well, formation evaluation revealed the existence of hydrocarbons in a shallower horizon (Albian) which was not known to be hydrocarbon bearing in the Dunga area. This raised a need to further appraise the accumulation and reduce geological uncertainties.
In this paper we discuss the unique properties and uncertainties that will affect future development of the Albian reservoir, and present results from a detailed wireline logging program, fluids pressure-volume-temperature properties, and extended well testing results to evaluate the hydrocarbon find in order to reduce those uncertainties.
Conventional interpretation of petrophysical logs was complemented by wireline formation testing (WFT) pressure data and formation fluid samples. The laboratory analysis of hydrocarbon samples is compared to real time downhole optical analysis of formation fluids.
Additionally, pressure transient analysis (PTA) from WFT was compared to conventional PTA results from DST completed well testing, in order to help understand the vertical permeability profile.
We also propose additional future work to complement the work presented in this paper by suggesting a vertical interference test and well-to-well data evaluation.
All these studies will help to answer key decisions on developing an Albian reservoir which has no analog in this region.