This paper summarizes the waterflood performance of the Townsend Newcastle Sand Unit (TNSU). Production is from the Muddy Newcastle sandstone located in the Powder River Basin of northeastern Wyoming. The field was discovered in June, 1960 and was depleted under solution gas drive to recover 13.0% of the original oil-in-place (OOIP) of 2.8 million STBO.
Waterflooding the TNSU faced three obstacles; first, the reservoir is naturally fractured; second, the reservoir contains clays which can swell and migrate to reduce injection rates; and third, the matrix rock is heterogeneous and low in permeability (40 md average).
A process approach was taken to overcome these adverse waterflooding conditions. First, the injection wells were pretreated with potassium hydroxide to permanently stabilize the clays. Then, cationic and anionic polyacrylamides and aluminum citrate crosslinker were injected to reduce flow through the factures as well as through any high permeability channels in the matrix rock. This was followed by a blend of phosphates and anionic polymer to maximize imbibition.
The flood began in May, 1986. Oil production went from 3 BOPD prior to injection to a peak flood rate of 343 BOPD in November. 1988. Ultimate recovery is now projected to be 29.8% OOIP. Without the use of this process technology it is doubtful the field could have been economically flooded.