The phrase "extensively read" is correct and usable in written English.
You can use it to describe someone who has read a lot of material on a particular subject or in general.
Example: "She is extensively read in classical literature, having explored works from various authors and time periods."
Alternatives: "well-read" or "widely read."
Revisionist satire spurred Alice Randall to create The Wind Done Gone (2001), a parody of the 20th century's most extensively read historical novel, Margaret Mitchell's Gone with the Wind (1936).
Since the Bureau of Historiography was next to the Bureau of Statistics, he extensively read 213 original historical documents gathered to the Bureau of Historiography by that time, and compiled two books: food history of Japan and the disaster history of Japan.
He extensively read the works of Wilhelm von Humboldt, who had written on Mesoamerica, and started corresponding with the historian Washington Irving, the Swiss writer Sismondi and the French historian Jacques Nicolas Augustin Thierry.
Carell researched du Pont extensively, reading reams of material about the Pennsylvania dynasty of industrial tycoons and watching the documentaries they commissioned about themselves.
When I felt I had some understanding of the culture, I went to more recent history, extensively reading articles and books about the drug cartels.
I researched the disease extensively and read accounts of the survivors.
Hull is exhuming the ghost of its grumpy former librarian Philip Larkin, whose poetry is extensively quoted, read by the actor Sir Tom Courtenay, in a film supporting its bid.
Now EMI has released the recordings as an eight-CD boxed set with extensive notes from Ms. Lim, who has read extensively on Beethoven's life and works.
He read extensively in Dutch, English, and Malay, and drew on these readings after becoming a writer.
He read extensively and wrote legibly.
(She has also read extensively about Nigeria).
