Secondary Recovery of Petroleum 787 



Oligocene, and under a multitude of structural conditions. Classical ex- 

 amples of anticlinal accumulations, such as Salt Creek and Lost Soldier 

 in Wyoming, and Rangely in Colorado are found in this region. The Cut 

 Bank oil and gas field, in northern Montana, is one of the largest fields 

 ever discovered w^here accumulation has been controlled by a stratigraphic 

 trap. Many of the Rocky Mountain fields are highly faulted and produce 

 from more than one formation, and a wide variety of reservoir conditions 

 and reservoir performance prevails throughout the region. It is believed 

 that there are many opportunities for eifective application of secondary 

 methods in reservoirs which will not have an efficient primary recovery. 



Montana 



Secondary-recovery operations in Montana are restricted to experi- 

 mental gas injection on several properties in the Cut Bank field of Glacier 

 County. Primary recovery from the large Cut Bank field will be inferior, 

 and it is estimated that some 318 million barrels of oil will remain un- 

 recovered by the present methods of production in the 53,000 acres of 

 proved oil land in the field. It is believed that there is a distinct possibility 

 that the primary recovery of the Cut Bank field can be doubled by the 

 application of secondary methods. 



Wyoming 



Thirteen separate secondary-recovery projects currently are in opera- 

 tion in Wyoming. Several of these projects are in different sands in the 

 same field. Ten projects employ gas injection, two are experimental water 

 floods, and one is a unique sand-heating operation. Three earlier gas- 

 injection projects have been abandoned. 



Gas injection was first commenced in the Elk Basin and Salt Creek 

 fields in 1926, and has been continued with little interruption to the pres- 

 ent time with a substantial increase in recovery resulting. Injection of gas 

 in the Grass Creek field has been primarily for gas storage, although some 

 increase in oil recovery is indicated. Recent gas injection into the Ten- 

 sleep reservoir of the Elk Basin field and the injection projects in the 

 Lance Creek, Lost Soldier, and Wertz fields are classified as pressure 

 maintenance operations. 



Experimental water floods are in operation in the Shannon sand of the 

 Cole Creek field and in the Second Wall Creek sand of the Salt Creek field. 



The deposition of excessive amounts of paraffin over the exposed 

 surface of the Newcastle sand in wells of the Osage field, Weston County, 

 was a serious operating problem until portable electric heaters were de- 

 vised to be lowered into the wells for the purpose of melting the paraffin, 

 which could then be pumped to the surface before it had a chance to 

 solidify. This heating operation must be repeated periodically, but it has 



