8Where an asset was acquired jointly by persons who are participators in two or more different oil fields (whether or not any one of those persons is a participator in more than one of those fields), then in determining for the purposes of section 4 of this Act, in the case of any one of those fields, the use which has been, or which it is reasonable to assume will be, made of the asset otherwise than in connection with that field, no regard shall be had to its use or possible use in connection with any other of those fields.