The flatulence, contain methane gas and butane gas, or only methane?

No butane. Only 20%: Of people produce methane. 99% of the gas volume does not smell. More recent evidence proves that the major contribution to the smell of flatus comes from a combination of volatile sulphur compounds (vsc).[5][12] it is known that hydrogen sulphide (h2s), methyl mercaptan, mm (also known as methanethiol, mt), dimethyl sulphide (dms), dimethyl disulphide (dmds) and dimethyl trisulphide (dmts) are present and cause the smell.Those compounds are the one percent that cause the smell. Source: wikipedia. Best wishes.