Sunday, April 29, 2007

Use of amylases for filter-cake removal in completation operations

Etel Kameda, Biochemical Engineering Department, Universidade Federal do Rio de Janeiro, Cidade Universitária, Centro de Tecnologia, Escola de Química, sl 203, Rio de Janeiro, Brazil, Marta A.P. Langone, Analytical Chemistry, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, PHLC, IQ, sl 427, Maracanã, Rio de Janeiro, Brazil, João C. Queiroz Neto, Cenpes, Petrobras, Av. Jequitiba 950, Rio de Janeiro, Brazil, and Maria Alice Z. Coelho, Biochemical Engineering Department, Universidade Federal do Rio de Janeiro, CT, Bl. E, Cidade Universitária, 21949-900, Rio de janeiro, Brazil.

The technology relating to horizontal, high angle, multilateral, and open hole completions is the most efficient and cost effective method to drain hydrocarbons from a reservoir. Drilling fluid has been developed to improve horizontal well drilling. Drilling fluids usually comprise natural polymers as starch and xanthan gum. These polymers are deposited as a filter cake on the wellbore wall that can reduce the permeability of fluid invasion. A common approach to remove this filter-cake is the application of acids or strong oxidative solutions. However, these are non-specific species and a possible alternative is the use of enzymatic preparations that are able to hydrolyze such polymers.  The aim of this work was to study the viability of use a commercial amylase to hydrolyze starch molecules as an alternative method for filter-cake removal. The effect of process parameters such as temperature (65, 80 and 95oC), enzyme concentration (1, 5, and 10 % v/v), and pressure (100, 500, 100 and 6000 psi) on the stability of two commercial enzymatic preparations was investigated. Both preparations were able to degrade starch in the experimental conditions used. The increase of reaction temperature caused a decrease of the amilolytic activity. The thermostability of the enzymatic preparations was not significantly affected by the presence of a high NaCl concentration in a brine solution. Hydrostatic pressure (6000psi) did not influence the amilolytic activity in brine solution. Combined pressure-temperature assays showed that temperature is the most important parameter to the stability of the enzymatic preparations used in polymeric filter-cake removal.