Novo sistema de pasta solúvel em ácido para perda de circulação em reservatórios carbonáticos macroporosos

Abstract

Pre-salt drilling has brought huge challenges, not least circulation losses. Any loss of circulation increases the total cost when added to the non-productive time (NPT) to contain the problem. When drilling pre-salt carbonate reservoirs, there is a risk of severe loss of drilling fluid when invading macroporosity intervals, reaching loss rates of more than 700 barrels/hour. The vast majority of the time, traditional fighting techniques are not effective against severe circulation losses in carbonate reservoirs with vugulars, and it is necessary to fight with cement paste. Cement plugs are effective in combating loss of circulation in reservoirs, but they cause irreversible damage. To replace cement, it was necessary to study and develop new alternative materials that could be reversible in terms of damage to the formation when applied to combat loss of circulation in the reservoir. Acid-soluble paste systems formulated with a water/hemihydrate ratio were studied to assess their potential as a buffer against loss. The paste systems were first studied using consistometry under conditions of 9500 psi and 54 °C, mechanical strength tests, and phase identification by x-ray diffraction of the systems cured at 9500 psi and 80 °C. The results indicate that the consistometry time and mechanical strength are consistent with the intended application. The cured paste systems underwent a static acid attack test in 9 and 15% HCl, with total dissolution of the specimen. The effects of the saturated CO2 atmosphere on the specimens for a period of 30 and 45 days were also evaluated. The results indicate that the specimens have undergone changes in their microstructure, causing physico-chemical alterations to the specimens. The paste systems studied showed great innovative potential for application as a solution to combat loss of circulation in vug zones.