--> Why is the Codell Sandstone, Denver-Julesberg Basin, Colorado, Economically Attractive?, by D. G. O'Brien, J. W. Crafton, R. E. Johnson, J. H. Ladd, and D. R. Shaw; #90986 (1994).

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Abstract: Why is the Codell Sandstone, Denver-Julesberg Basin, Colorado, Economically Attractive?

Darien G. O'Brien, James W. Crafton, Rodney E. Johnson, John H. Ladd, Donald R. Shaw

The Codell Sandstone in the Denver-Julesberg Basin is currently undergoing some of the most active oil and gas development in the world. About 3000 wells have been drilled during the past three years and during 1994 alone, upwards of 1500 additional wells will be drilled. Integration of virtually all disciplines of the oil and gas industry has allowed the profitable exploitation of this classic basin-centered hydrocarbon occurrence.

The Codell is a widespread, silty, marine shelf sandstone of uniform thickness, generally between 15 and 20 feet thick. There is no trap other than the low permeability of the reservoir, normally less than 0.5 millidarcy. The reservoir parameter that has the greatest influence over production is the gas-oil-ratio (GOR), with the highest GOR, and most of the development activity, occurring over a 250 sq mi area where it is in excess of 10,000 scf/stb. Dry hole risk is about 2%, due to the chance of pay being faulted out by one of the numerous, small listric faults.

The economic viability of the Codell play is based on the highly predictable reserves, the negligible dry hole risks and its widespread occurrence, which allows for economies of scale in its development. Drilling and completion costs have been lowered through multiple well pad and deviated well drilling, slim-hole completions, multi-zone fracture treatments and collaborative alliances with contractors and service companies. Profitability has been improved by commingling production with other horizons, producing several wells through common tank batteries, and devising methods to increase natural gas liquids production.

The cooperative, collaborative and experimental practices used in the Codell offer an analog for the exploitation of other low-permeability reservoirs worldwide.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994