Primary Production Considerations of the Challis Oilfield
Engineering Design Project, 2006
University of Adelaide
This paper examines the primary production stage of the Challis Oilfield. In particular five facets of the development are examined these being; Geology, Reservoir Volumetrics, Well Engineering, Reservoir Engineering and Economics.
Geological aspects are taken from technical SPE papers and are intended to provide background information on the field.
Reservoir Volumetrics covers the determination of reservoir properties and the calculation of P10, P50 and P90. Overall reservoir volumes appear promising with P50 estimated at 55MMstb. Standard deviation of reservoir volumes is quite high due to the uncertainty associated with the rock volume.
Preliminary studies indicate quite high well PI, up to nearly 290stb/d/psi. Initial flow rates are in the order of 20,000stb/d per well.
Material balance calculations estimate the recovery factor to be in the order of 1% above the bubble point, and about 10% below the bubble point assuming gas production can be minimised. The drive mechanism is believed to be solution gas, which will need to be supplemented with water injection in order to improve the recovery factor.
Theoretical decline models were run indicating short field life under solution gas drive, about 700 days, although the field will become uneconomical prior to this. Actual decline is believed to fall between the decline rates predicted by the two models; exponential and harmonic.
Two economic scenarios were run, 1989 and 2006 market conditions. Neither of them was found to be economical based on estimated costs and decline curve analysis. The primary reason for this is the very low recovery factors associated with a solution gas drive.
In order to make the field economical supplementary recovery will be needed. Other studies investigating the response to a water injection program are very promising; with recovery factors estimated at about 66% with a water injection rate of 10,000stb/d7.