LOSS CIRCULATION AND FORMATION DAMAGE CONTROL ON OVERBALANCED DRILLING WITH DIFFERENT FORMULATIONS OF WATER BASED DRILL-IN FLUIDS ON SANDSTONE RESERVOIR

The oil well drilling should not damage formation, mainly the interest region: the reservoir. Drilling without damaging the reservoir is a hard challenge, and therefore the development of technologies and optimization process, including, for example, the design of fluids in order to minimize damage, is been stimulated. Drilling fluids may interact with reservoir rocks resulting on permeability impairment, which reduces well productivity. It has been reported that a detailed fluid management plan can help to minimize formation damage and improve well productivity. This work is focused on formation damage analysis due to drilling fluids invasion in high permeability sandstone oil reservoir. Water-based fluids were prepared with the following components: distilled water, salt (NaI), polymer (Partially Hydrolyzed Polyacrylamide - HPAM, and Xanthan Gum - XG) and clay (Bentonite). Samples were submitted to an invasion process, simulating an overbalanced drilling, and to an oil reverse flow, simulating oil production beginning. Results showed that all fluids containing clay presented less deep invasion than the fluids prepared with polymer only. Moreover, clay concentration influenced on permeability impairment and productivity ratio return results. HPAM fluids, when injected, invaded more deeply the samples than XG fluids, but productivity ratio return was also higher.