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In one exploration well north of Bogota, Colombia, mud losses and wellbore instability were expected in a formation consisting of micro-fractured limestones and interbedded shales and clays. Problems were also encountered while drilling the upper sections in this well. The operator planned to drill the last two sections, the 8½-in. and 6-in. intervals, with the same drilling fluid properties, incorporating FLC 2000 at an effective concentration to stabilize the wellbore and prevent stuck pipe, partial or severe fluid losses, downhole motor loss, or gas influx.
FLC 2000 was added to the water-based mud (WBM) at 5 lb/bbl while drilling the 8½-in. section. A sand bed test (SBT) was used to ensure the ultra-low invasion properties were maintained while FLC 2000 was in the active system.
While drilling the 8½-in. interval, no losses or wellbore instability was encountered. The operator decided to eliminate the planned 6-in. section and the well was completed in 8½-in. hole. The hole remained stable and no losses were experienced throughout the drilling phase. By eliminating the 6-in. interval and subsequent six days of logging, five drilling days were saved on the well, and the associated costs of the intermediate casing string was eliminated. Additionally, a higher rate of penetration (ROP) was achieved. The program assumed an average ROP of 6.33 ft/hr; however, using FLC 2000 increased the ROP to 6.90 ft/hr. Lastly, the total depth (TD) reached was deeper than the programmed depth while eliminating losses, stuck pipe, back reaming, and cavings.