Mining Technology Assists Oil Recovery From Wyoming Field
Authors: Dobson W.F. , Seelye D.R. 
Published: December 2007

Summary
An unusual oil recovery project in Wyoming combines aspects of mining and petroleum engineering technologies to increase production from the North Tisdale field. The project basically consists of a horizontal tunnel, or adit in mining terminology, conventionally mined into a hillside (Fig. 1). The adit provides access to the oil sand from which an array of horizontal drainholes were drilled to various lengths. At the present time it is the only project known to exist in the U.S. that produces oil with this method.

History
Using mining methods to produce petroleum from shallow deposits is not a new concept. Mining, in one form or another, has been used to recover various forms of petroleum for centuries. Its importance, however, has been overshadowed by conventional oilwell development since Col. Drake successfully drilled for oil in 1859. Petroleum mining can be traced back in history to before 5000 B.C. when deposits were mined in the Sinai Peninsula, Persia, and the Euphrates River valley. Ancient Egyptians used mined petroleum for embalming, and sailors have long known the value of tar mined from pits for making their vessels watertight. In more recent history, petroleum mining has been attempted in the U.S. with various degrees of success. Projects have been attempted in Pennsylvania, Ohio, California, Texas, Kansas, Utah, and now Wyoming. It was used in the late 1800's primarily as an alternative to conventional oilwell drilling and later as a means of recovering additional reserves from shallow, pressure-depleted reservoirs. In addition to the early U.S. oil mining attempts, two famous mining operations were developed successfully in the Pechelbronn field in France and in the Wietze field in Germany from 1917 to 1930. These mines were developed during a period of European history when oil was a commodity that was required almost regardless of the cost. In general, however, the petroleum industry has turned away from oil mining as a viable recovery method because of the more favorable economic factors associated with conventional drilling development. Recent developments in world oil supplies and prices now are providing producers with incentives to experiment with mining as an oil-recovery technique.

Lakota Development
The North Tisdale oil field is located in the Powder River basin approximately 70 miles (112.6 km) north of Casper, WY (Fig. 2). Production was discovered in the field in 1952 from the Curtis sandstone at a depth of 1,000 ft (304.8 m). The discovery well had oil shows in the shallower Lakota sand, and the following year the first productive Lakota well was drilled. It was completed with 24 BOPD (3.8 m /d oil) and 2 BWPD (0.3 m /d water) from a zone at 210 ft (64 m). Before this discovery, the Lakota was known to be oil-productive in the area. Local history relates tales of early homesteaders and travelers who used oil obtained from seeps to lubricate wagon wheels. The Lakota has provided a special challenge since development began in 1953. Production from early wells indicated that the reservoir initially produced through a weak gas drive that was replaced by gravity drainage shortly after completion. Local outcrops have allowed gas to escape and deplete the Lakota reservoir pressure. Conventional oil wells exhibit low initial producing rates and long producing lives typical of gravity drainage. Lakota development was slow because of marginal economics of the low-volume wells. A total of six producing wells were drilled during 1953-62 that had average initial producing rates of 8 BOPD (1.3 m /d oil) and 3 BWPD (0.5 m /d water) (Fig. 3). Engineers recognized that less than 2% of the oil in place would be recovered from the Lakota by primary methods.
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