Methods of producing alkylated hydrocarbons from an in situ heat treatment process liquid

A method for producing alkylated hydrocarbons, comprising:

• producing formation fluid from a subsurface in situ heat treatment process;
• separating the formation fluid to produce a liquid stream and a first gas stream, wherein the first gas stream comprises olefins;
• fractionating at least a portion of the liquid stream to produce at least a second gas stream comprising hydrocarbons having a carbon number of at least 3;
• and
• introducing at least a portion of the first gas stream and at least a portion of the second gas stream into an alkylation unit to produce alkylated hydrocarbons, wherein at least a portion of the olefins in the first gas stream enhance alkylation.