By Florence Tan and Sabrina Valle (Reuters) -Exxon Mobil Corp said on Wednesday that its Russian unit Exxon Neftegas Ltd has declared force majeure for its Sakhalin-1 operations, where it has become increasingly difficult to ship crude due to sanctions on Russia. The Sakhalin-1 project produces Russian Sokol crude oil off the coast of Sakhalin Island in the Russian Far East, exporting about 273,000 barrels per day, mainly to South Korea, and to other destinations including Japan, Australia, Thailand and the United States. Exxon said on March 1 it would exit about $4 billion in assets and disco…