An arbitration panel that will decide a high-profile clash between Exxon Mobil and Chevron will delve into the secret value of Hess' oil riches in Guyana, people familiar with the matter said.Chevron last October offered to pay $53 billion for Hess, one of the two biggest deals in the largest wave of consolidation in the oil industry in decades. The asset most coveted by Chevron in the takeover is Hess’s stake in a Guyana field operated by top U.S. rival Exxon.Exxon and China's CNOOC have challenged the deal…