Abstract

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 inhibitions.

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.

Field History And Primary Production

The Townsend Newcastle Sand Unit is located in the northeastern part of Wyoming. The field is situated on the eastern edge of the Powder River Basin as seen in Figure 1. Discovered in June, 1960, the initial producing rate was 150 BOPD. The peak primary producing rate of 273 BOPD occurred in 1970 after in-fill wells were drilled. Under solution gas drive recovery was 367,000 STBO or 13.0% OOIP. Water injection began in May, 1986. There are currently 8 injection wells and 12 producing wells.

Geologic And Reservoir Data

The Newcastle formation is a laver cretaceous sandstone found on the eastern side of the Powder River Basin. In the central and western regions of the Basin the same formation is known as the Muddy sandstone.

The unit is part of a southwest to northeast local productive trend. The reservoir is the result of stratigraphic trapping caused by permeability variations in the channel at the time of deposition. Figure 2 is a structure map which shows the reservoir to dip from northeast to southwest. Figure 3 is an Isopach map of the unit.

The reservoir parameters for the field are in Table 1. the permeability of the reservoir averages 40.5 md based on core work. The Dykstra-Parsons permeability variation is 0.65. Thus, the reservoir matrix is low in permeability and heterogeneous.

An engineering technical committee was formed to study the feasibility of waterflooding the townsend Newcastel Sand Unit.1 The committee concluded that waterflooding was economically warranted and recommended the field be placed under flood.

The committee used the Secondary Recovery Analysis Model (SRAM) as the basis for field performance under waterflooding condition.

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