Abstract
The filter cake removal is still an important concern both for producers and injectors. Mainly in long horizontal completion sections, the cleanup of the filter cake does not always occur spontaneously because sometimes the drawdown in the production direction is not enough. For injection wells a chemical treatment is usually required for an efficient cleanup. Acids and oxidizers may not be applied in high sensitive and/or in low temperature formations but the use of a proper enzyme breaker may lead to an efficient degradation of the polymeric materials preventing great permeability impairment.
The use of linkage specific enzymes instead of mixture of generic hydrolytic enzymes has given in the last years a significant improvement to the breaker performance. Linkage specific enzymes give the possibility to select the specific chemical linkage to be broken within a well defined polymeric substrate. This means that the enzyme activity can be tailored according to the well conditions as well as to the drilling fluids properties and composition. Breaker efficiency is also related to the size distribution of generated polymeric fragments. However, previous studies suggested that although the filter cake degradation seems effective from a fluid loss point of view, the polymeric fragments produced by the filter cake degradation may contribute to formation damage. It is therefore important to gain information on the degradation reaction mechanism by studying not only the enzyme specificity on a particular polymeric substrate but also the chemical nature of the end point products.
The laboratory data presented in this study show that starch specific enzymes such as amylases, cellulases and glucosidases are highly efficient to degrade native and chemically modified (cross linked) starches. The specificity of the enzyme activity on the different polymeric substrates as well as the molecular weight distribution of the degradation fragments were studied and characterized. It was found that each enzyme is not only linkage specific but also regio-specific, that is, it is able to degrade chemically different regions of the starch polymeric chain. The effects of the activity of different enzyme breakers were investigated by filter cake treatment tests.
