Abstract
Deep drilling require non polluting fluids stable at temperature up to 390 °F. In terms of formation damage, it is now well accepted that prevention is better than remediation since well treatment using washing fluids can be hazardous. This is of major importance for complex well configuration using openhole completion.
Novel polymeric structures were investigated. The additive structure and molecular weight were selected in order to limit the damage due the filtrate invasion. The selected additive was proved to be stable at temperature up to 360 °F. This novel additive was implemented in different water based formulations such as classical bentonite formulation or drill-in fluid and tested in a large range of experimental conditions. The possible damage arising from overbalanced conditions was evaluated in terms of static and dynamic filtration properties, cake permeability, fluid loss characterization and reduction in oil permeability after mud exposure.
Compared to other commercially available fluid loss reducers, it presents better rheological and filtration properties. After ageing at 320°F, no fluid gelation was observed. Under dynamic filtration conditions, the formulation presents a very low filtration rate.
The approach was validated on long core filtration test performed under representative reservoir conditions. Use of a stable additive limits the formation of degradation products that could badly affect the reservoir permeability by plugging effect. Such a design of chemical additive within a water based formulation effectively prevents the well known formation damage arising from the use of water based formulations.
