Abstract: A downhole wellbore filtercake breaker is disclosed comprising one or more breaker chemicals (or activators thereof) capable of being activated with radiation to form one or more breaker reaction products which in turn are capable of reacting with the filtercake to chemically break down the filtercake. There is also disclosed a conventional reservoir drilling fluid modified to include an inactive, delayed, or sequestered breaker chemical or an activator thereof, wherein the breaker chemical (or activator) may be activated directly or indirectly by radiation, such as, microwave, visible, uV, soft x-ray, or other electromagnetic radiation. Also disclosed are methods for creating these filtercakes, and then breaking them via deploying a source of radiation that can be energized proximate to the filtercake. The breaker may be regenerated downhole by reaction with the filtercake breakdown products, and subjected again to a source of radiation to continue the breakdown of filtercake.