The Key Lab. of Petroleum Geochemistry China National Petroleum Corporation Beijing 100083 China;
Wuhan Uniuersity of Geosciences of China Wuhan 430074 China;
Department of Biology and Chemistry central Uniuersity of Nationalities Beijing 100081 China;
PVT experiment; evaporative fractionation; pressure decrease; gas-washing; crude oil geochemistry; forming conditions of petroleum reservoirs;