Lost Soldier field (T26N, R90W) is one of several fields that parallel the Granite Mountains uplift. The subsurface structure at the Lakota level is a northwest-trending, doubly plunging anticline. The Lakota Formation at Lost Soldier field is a complex, fluvial-sand sequence, representing braided- and meandering-stream environments. Lakota channels have both podlike and sheetlike geometries, and grade laterally into crevasse splay and floodplain deposits.

The Lakota reservoir was discovered in 1922. Between 1922 and the early 1950s, the reservoir produced about 5 million bbl of oil. The early Lakota wells were drilled mainly on the top of the structure and along lease lines. These early wells were all shut-in by the early 1950s when the Lakota reservoir, thought to be depleted, was abandoned.

During the late 1970s, following Amoco's purchase of Lost Soldier field, Amoco geologists noticed high-resistivity anomalies in the Lakota Formation. In 1979 a well was recompleted in the Lakota with an IP of 65 BOPD and 22 BWPD. The successful recompletion proved that the early Lakota producers had not completely drained the reservoir.

Since 1979 Amoco has completed or recompleted 22 Lakota producers. These wells have been drilled to define the oil-water contact for the Lakota, to develop a thick net-sandstone trend on the southern end of the structure, and to test the Lakota production potential in other parts of the field. It is estimated that the recent Lakota wells will produce about 1 million bbl of oil. The average IP for the wells is 67 BOPD and 104 BWPD.

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