They could have ran casing for a variety of reasons...
1) Sloughing Shale 2) Low Pressures / Lost Circulation
I'm going with Sloughing Shales as being the issue because ZN's press release states the following:
1) They had drilled through a "Material Section of Shale" 2) They decided to run casing to ensure well-bore integrity - which also points to Sloughing Shale...