A large multidisciplinary study was undertaken following non acceptable drilling surprises in the Santa Barbara field in wells SBC-109 and SBC-110 (Venezuela). Some of the numerous lessons learned during a period of three years of extensive work will be described with illustrations from the most relevant examples.

Despite the existence of several 3-D seismic volumes and more than 100 wells in an area of 190km² (120 square miles), after drilling more than 13000 feet of continuous Carapita shale, the reservoir in well SBC-109 was unexpectedly missing the upper 600 feet and was structurally 1259 feet shallower than SBC-110 whose top came 800 feet below prognosis. These surprises came while the seismic was indicating a flat reservoir top around these wells located 400 meters apart.

Whereas other seismic to well mismatches were observed (e.g. against dipmeter data), the focus of the work was on additional data type such as geochemistry and production data. The tools and procedures used will be elaborated in a case study.