Abstract
The first integrated characterization of limestone in Ecuador was performed in the M1 and M2 limestones in the Puma field of the Oriente basin. The characterization was performed by using available information from open hole logs and by applying the dual porosity methodology, which requires the use of porosity curves, including density, neutron, and sonic.
The method used enabled estimates to be made of secondary porosity, "variable M" system cementation exponent fracture porosity, fracture intensity index, and effective porosity of the system. The effective porosity model was calibrated with nuclear magnetic resonance (NMR) logs. The results were validated with pressure transient analysis (PTA), which confirmed the dual porosity system and fracture system properties, and identified the λ and ω parameters.
The petrophysical interpretation of the M2 limestone is characterized as a unit of good thickness with an interconnected pay zone, accurate fracture intensity for the entire section, and excellent effective porosity estimate (fracture plus matrix porosity). Because the matrix has connected effective porosity and includes the presence of fractures, this unit, according to the Nelson classification of fractured natural reservoirs (NFR), may be a Type II. The M2 limestone is thicker than the M1; its fracture intensity index and its correspondent matrix effective porosity are greater than M1 (NFR type I). PTA through λ and ω values confirmed the classification of the reservoirs.
This paper describes the first integrated petrophysical evaluation for M1 and M2 limestones in the Oriente basin of Ecuador. This evaluation involves a dual porosity characterization in which the connected porosity system helped to reduce the uncertainty in the original oil-in-place estimate. The method used could be applied in other Oriente basin fields to assess the potential of carbonate reservoirs.
