Challenge: For exploration well CLX-1, operator Tecpetrol required an oil-based drilling fluid which could be managed effectively at high density as it would have to penetrate a pressurized zone. Additionally, the operator requested that the system will initially deliver a low oil/water ratio (OWR) to reduce diesel consumption. The ratio would be adjusted upon entering the target zone. Ideally, the client wanted to convert a conventional oil-based mud (OBM) stored from a previous job to a system with optimum rheological properties and OWR to drill the planned CLX-1 well.
Solution: M-I SWACO recommended the operator to convert its used conventional VERSADRIL oil-base drilling fluid to a MEGADRIL system, by incorporating the MEGAMUL stabilizer, emulsifier and wetting agent. The system was formulated to deliver the required parameters for an OWR between 70/30 and 80/20, much lower than the OWR necessary for a conventional OBM of thus lowering inventory requirements, diesel consumption of and the rheological profile. The MEGADRIL OBM, will also be required to be stable at the high density required to penetrate a pressurized zone.
Results: The results justified the selection. Losses in the poorly consolidated sands of the 17 ½ in. section were controlled easily with lost circulation materials (LCM) while the rheology and OWR were maintained easily 70/30 for the entire well. The system maintained stable properties during drilling, cementing and casing run. The 9 ? in. casing was run and cemented trouble free.