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

摘要

La Paz oil field is one of the most famous, well-documented fractured reservoirs inthe world. Sine 1945 it has produced more than 830 million bbl of oilfrom both low porosity Cretaceouslimestones and underlyinggranitic basement. The field is situated ona large inversion structure, partially uplifted in the late Eocene, having the majority of the inversion occurring in the Miocene-Pliocene. Fracture distributions, initial rate and cumulative production distributions,and trendsinformation water chemistry all suggest that reservoir quality and reserves are controlled by natural fractures associated with Miocene-Pliocene and younger strike-slip faults and possibly by secondary microporosityrelated to thegeometry ofthe earlier Eocene block uplift. Productionlevels within the area of Eocene uplift are anomalously high, with one well producing 59 million bbl of oil. Typical wells in other parts of the field produce 1 million bbl ofoil. Analysisof the distributions cited previously suggests that production hasoccurred from highly elliptical to l8inear drainage areassurrounding faults These restricted zones of faultrelated fractures allow for communication of hydrocarbons stored in the low porosity rock carbonate matrix to the wellbore. In addition, diagenetic microporosity may bean important component in matrixstoragein the carbonates andmay bedueto local subaerial exposure during the Eocene uplift. This article shows that analysis of thenatural fracture system with respect to the production characteristics in even old fields can give rise to new reservoir models, leading to new infill locations within the fied limits or additional exploration opportunities in the area