The Colon Formation Shale (Southern area of Lake Maracaibo) and The Carapita Formation Shales (Northern area of Monagas) have been frequently drilled with invert emulsion oil base mud (IEOM) for shale inhibition purposes. However, this fluid is not the most desirable for use in drilling the Cretaceous and Oligocene productive Formation since the IEOM requires high concentrations of surfactant emulsifiers which have proven to be damaging to the pay zone. The problem described above led to the search for a mud system formulated with 100% Oil continuos phase. It was required that this system be stable to high temperatures; have no interaction with the shale cores taken from the Colon and Carapita formations; and be formulated without strong emulsifiers. The first part of the research was carried out in the laboratory where many formulations were tested to very high temperatures and under contaminated conditions. Return permeability tests were also run to ensure that the system would minimize formation damage. The 100% Oil mud formulation from the laboratory was then used in the Southern area of Lake Maracaibo on the well SLB-4 and in the Northern area of Monagas on the well BOQ-8. Excellent results were achieved on the trial wells in both areas and improved production rates obtained on well SLB-4 compared to other wells in the field which were drilled with standard IEOM.

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