Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.
An analysis of the use of hot inert gas for the exploitation of thin sulfur deposits was made. This analysis included theoretical heat transfer and economic investigations. The heat transfer study involved the numerical solution of equations written in cylindrical coordinates describing convection-conduction heat transfer in the zone of gas flow and conduction heat transfer in the bounding media. Of particular interest in this work was the volume of rock swept by the 250 degrees F and 350 degrees F isotherms. This is because sulfur becomes liquid at 250 degrees F but loses its mobility again at 350 degrees F.
Results showed there is probably sufficient time for sulfur movement before arrival of the 350 degrees F isotherm. The volume of rock traversed by the 250 degrees F isotherm was found to be almost porportional to the heat-injection rate. It was porportional to the heat-injection rate. It was found that injection temperatures would have to be in the 1000 to 1500 degrees F range for economic heat transfer by gas.
An economic study indicates that a hot gas drive process for sulfur production could be economical providing that a recovery efficiency greater than 50 percent could be achieved in a bed containing 25 percent sulfur. Pilot testing would be required to develop appropriate production techniques. A combination inert production techniques. A combination inert gas-water-steam process might prove superior to straight gas.
The Frasch process has been used since the turn of the century for the insitu recovery of elementary sulfur. Favorable economics for the Frasch process depend on shallow thick deposits because it involves water injection and water and sulfur production through the same well. Therefore, the exploited zone for each well is of limited areal extent. The Frasch process also needs large quantities of water requiring a minimum amount of chemical treatment. The process, therefore, cannot be used economically to exploit many relatively thin deposits (less than 100 feet thick) especially in areas where large quantities of water are not available or require prohibitive water treatment. prohibitive water treatment. No other methods have been developed to economically exploit thin sulfur zones where operating costs are high because of the water costs. At least two processes or combinations thereof might be considered to recover elementary sulfur from thin beds. These are the injection of either (1) hot inert gas or (2) steam into certain wells and production of either inert gas and sulfur or water and sulfur from others.