After 70 years of continuous exploitation in the Bolivar Coast region of Lake Maracaibo, Venezuela (Fig. 1), advanced reservoir depletion is causing drilling problems such as severe loss of circulation, hole instability, and extensive formation damage. In an attempt to optimize drilling performance, several operation practices were implemented through 1997, such as air-, mud-, foam-, and oil-base mud systems, etc., without achieving the expected success.
Because of the challenges of working in these mature fields, the operator and the oilfield services company created a services alliance contract called PRISA (a Spanish acronym for Integrated Drilling and Workover Alliance Services). This paper describes the drilling technologies and best practices used to improve drilling performance in these mature reservoirs, the learning curve evolution, and process improvement. The results included a cost reduction of 12% (in investment cost/barrel), a production increase of 4%, a 58.7% reduction in drilling time, and a drilling cost reduction of 3.6% (Figs. 2 through 3B). In addition, nonproductive time (NPT) has been reduced from 24.1% in 1999 to 3.8% in 2002 (Fig. 4).