Production characteristics of the fractured reservoirs of the La Pat field, Maracaibo basin, Venezuela

La Pat oil field is one of the most famous, well-documented fractured reser voirs in the world. Since 1945 it has produced more than 830 million bbl of oil from both low porosity Cretaceous limestones and underlying granitic b asement. The field is situated on a large inversion structure, partially up lifted in the late Eocene, having the majority of the inversion occurring i n the Miocene-Pliocene. Fracture distributions, initial rate and cumulative production distributions, and trends in formation water chemistry all sugg est that reservoir quality and reserves are controlled by natural fractures associated with Miocene-Pliocene and younger strike-slip faults and possib ly by secondary microporosity related to the geometry of the earlier Eocene block uplift. Production levels within the area of Eocene uplift are anoma lously high, with one well producing 59 million bbl of oil. Typical wells i n other parts of the field produce 1 million bbl of oil. Analysis of the di stributions cited previously suggests that production has occurred from hig hly elliptical to linear drainage areas surrounding faults. These restricte d zones of fault-related fractures allow for communication of hydrocarbons stored in the low porosity rock carbonate matrix to the wellbore. In additi on, diagenetic microporosity may be an important component in matrix storag e in the carbonates and may be due to local subaerial exposure during the E ocene uplift. This article shows that analysis of the natural fracture system with respec t to the production characteristics in even old fields can give rise to new reservoir models, leading to new infill locations within the field limits or additional exploration opportunities in the area.