No sweet gas produced from a gas well may be used for any purpose except:
(1) light or fuel;
(2) efficient chemical manufacture, other than the manufacture of carbon black, provided that sweet gas produced from wells located in a common reservoir producing both sweet and sour gas may be used for the manufacture of carbon black if it is used in a plant producing an average recovery of not less than five pounds of carbon black to each 1,000 cubic feet of gas;
(3) bona fide introduction of gas into oil or gas bearing horizon in order to maintain or increase the rock pressure, or otherwise increase the ultimate recovery of oil or gas from the horizon; and
(4) the extraction of natural gasoline when the residue is returned to the horizon from which it is produced.