The Pine field is located on the northwest-trending Cedar Creek anticline in Dawson, Prairie, Wibaux, and Fallon counties, Montana. Pine Unit No. 1, the discovery well, was drilled to test a subsurface seismic closure located near the crest of the known surface anticline. The well was completed in January, 1952, daily pumping 467 barrels of 33° gravity crude and 148 barrels of water, from the Upper Ordovician Stony Mountain (Gunton) formation. Subsequent outstep drilling was notable in that improved reservoir conditions were found in the Ordovician, and Silurian production was established in zones found water-bearing in the discovery well.

Thin Devonian strata, shales and shaly dolomites, are effective barriers to vertical migration over Silurian productive zones. Silurian rocks thicken and rise structurally southeastward with associated development of porous and productive intervals. Upper Ordovician strata contain the major productive zones with included shale zones acting as effective cap rocks.

Development indicates oil accumulation in the Pine field to be controlled by structure, but with stratigraphic variation important in reservoir properties. The structure is basically an asymmetric anticline, modified by minor culminations and saddles. Structure contours indicate a closure of approximately 200 feet.

No gas caps are present in the field. Porosities of the pay intervals vary from 6 to 16 per cent with a mean of 11 per cent. The average permeability is approximately 5 md. Connate water in the pay intervals is estimated to average 30 per cent.

The crude oil produced is black, 35° A.P.I. gravity with sulphur content of 0.44 per cent and a GOR of 150. Reservoir pressure is on the order of 4,150 psi. The greater part of the recovery will probably be determined by liquid expansion, and no active water drive has been ascertained.

Approximately 3,800 acres are considered proved productive in the Pine Unit. Eighteen wells have been completed in the Unit, of which 14 are commercial producers, 2 are dry holes, and 2 are

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non-commercial wells. One dry hole was drilled on the steep west flank by the California-Canadian Company. Three Unit wells are being drilled at present, and one competitor location is drilling. Development is on an 80-acre pattern.

For the week ending, December 10, 1954, 13 wells produced an average of 1,789 barrels of oil per day. Cumulative production to December 1, 1954, was 681,390 barrels of oil; 94,467 MCF gas.

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