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AAPG Bulletin

Abstract


Volume: 32 (1948)

Issue: 2. (February)

First Page: 302

Last Page: 302

Title: Geology of Mattoon Field, Illinois: ABSTRACT

Author(s): C. Doh

Article Type: Meeting abstract

Abstract:

The interesting features of the Mattoon field are: (1) the history of its discovery; (2) the dual-completion methods used; and (3) the very lenticular condition of its sands.

1. The Mattoon anticline in Coles County--180 miles south of Chicago--was generally known in 1937. The first well, drilled in 1939, made a total of 132 barrels. In 1940, four more wells, with only one producer (the discovery well), had practically condemned exploitation in spite of the verification of the structure. Three years later a small well extended the potential field and was followed by a series of mediocre wells.

In 1945, or five years after the discovery well was completed, an independent operator completed a 100-barrel well, 3/4 mile from the discovery, renewing the general interest. A boom soon developed when a well was completed, producing 1,200 barrels. Rapid extensions defined a potential area of 7,000 acres, a major field.

2. Wells in the two main shallow producing sands, less than 2,000 feet deep, soon were dually completed with successful results. The Cypress sandstone, with as much as 40 feet of saturation, produced with the more commonly developed Rosiclare sand and sandy limestone. A 7-inch oil string was set on the top of the lower sand with aluminum pipe opposite the Cypress sand. Both sands were shot with nitroglycerine, tested individually by setting a temporary, drillable plug, and produced together.

Wells are drilled to 2,000 feet in 7 days, with two rock bits and four retips. However, the dual completion takes 20 days of spudder time. Average total cost of single completion is $15,000. The dual method increases the cost to $18,000.

Electric logs were made on all wells and gave good quantitative results. One problem could not be solved by electric logs: differentiation between gas and oil in the Cypress. However, a gas-oil level was determined by drill-stem tests on the crest of the structure.

Within 14 months 114 wells had been drilled, of which 22 were dry holes and 92 were producers, with an average initial production of 148 barrels. Peak production was reached in June, 1946, with 15,500 barrels daily. Steady decline was experienced during the next 12 months, and in June, 1947, the daily production was down to 5,500 barrels daily. Total recovery from 5,500 producing acres is estimated at 17 million barrels.

3. Detailed electrical-log cross sections are presented to show the extremely lenticular condition of the sands. A considerable area on the top of the structure remains undrilled. A gas cap in the upper Cypress sand has not been exploited. The west part of the City of Mattoon also remains undrilled due to communitization problems, in spite of its potential productivity.

The Aux Vases sand was found extremely shaly, excepting the southwest part of the field. Its development, estimated at only 50 acres, will produce approximately 6,000 barrels.

Six Devonian wells on the structure have produced only 1,100 barrels of oil. However, potential production from the Devonian can not be ignored at this time.

The total accumulated production of the Mattoon field on September 1, 1947, is 6,280,000 barrels.

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Copyright 1997 American Association of Petroleum Geologists