788 Subsurface Geologic Methods 



proved to be quite successful, and undoubtedly has been a contributing 

 factor to the maintenance of production in the Osage field during recent 

 years. 



Colorado 



Former gas-injection projects in the Wellington and Fort Collins 

 fields of Larimer County, Colorado, have been abandoned, and there are 

 no secondary-recovery projects in operation in the state at the present time. 



Gas injection into the Morrison sand reservoir of the Wilson Creek 

 field of Rio Blanco County, is a recent pressure-maintenance project. The 

 same may be said for the injection program in the North McCallum field, 

 of Jackson County, which has been in operation since 1944. The North 

 McCallum pressure-maintenance project is unique because the gas which 

 is injected is about 94 percent carbon dioxide. 



Consideration has been given to a pressure-maintenance program in 

 the Rangely field of Rio Blanco County. Unaided primary recovery from 

 the Rangely field probably will be very inferior on account of the low 

 permeability of the producing formation and because of excessive waste 

 of gas from the gas-cap. The original oil content of the Weber sand reser- 

 voir of the Rangely field was about 1.5 billion barrels, most of which will 

 not be recovered by the present method of operation. Therefore, an un- 

 usual opportunity exists for the application of some form of improved re- 

 covery technology. 



Some Limiting Factors of Secondary Operations 



The production of the large secondary reserve of the United States is 

 limited, just as primary production is limited, by the ability to produce 

 oil at a profit. Profitable secondary production can be assured in many 

 fields by the ability to utilize existing production facilities and by the 

 establishment of unit and cooperative projects. 



The ability to utilize existing production facilities, thereby reducing 

 development costs to a minimum, is going to have a great bearing on the 

 secondary possibilities in deeper fields and in fields possessing thin pay 

 sections, even though the productive horizons are otherwise suitable for 

 gas or water injection; for it may not be profitable to redrill the field 

 for secondary-recovery operations. Obviously, this is a problem which 

 merits careful consideration by operators who desire to continue in the 

 business of oil production in fields which are approaching or have reached 

 the point of primary depletion. Except for mining operations, all known 

 and proposed methods for increasing oil recovery require the utilization 

 of wells for the injection and production of fluids into and from oil-bearing 

 rocks. For this reason, it should be evident that no well should be aban- 

 doned until consideration is given to the effects that such abandonment 

 might have on future attempts to increase recovery. Also, the completion 



