William H. Sydow¹, Marvin P. Carlson²
(1) Nebraska Oil and Gas Commission, Sidney, NE
(2) Nebraska Geological Survey, Lincoln, NE

Abstract: Acorn Field, Dundy County, Nebraska: The importance of understanding compartments in carbonate reservoirs

The Acorn Field, in southwest Nebraska, is a prime example of the value of identifying high-porosity compartments in an area that has been mainly explored for carbonate production in the more widely distributed, lower porosity/permeability zones in the Upper Pennsylvanian. Forty-two fields have produced nearly four million barrels of oil (BO) in the county. The township in which the Acorn Field is located has produced 2,467,171 BO, nearly 62% of the county's production.

The Acorn Field discovery well was completed in 1995 for 113 barrels of oil per day (BOPD) from the Lansing-Kansas City (L-KC) D zone. After three apparently unsuccessful offset wells, production was established in the L-KC E zone in 1997 for 494 BOPD. By March 1998, six additional development wells were completed resulting in four producers and two plugged. Several additional zones in the L-KC were productive however the E zone is the major reservoir. The Acorn Field production peaked in 1998 at over 1,000 BOPD and averaged 614 BOPD from six wells - the highest daily oil production rate in the state.

Analysis of original bottom-hole pressures, production tests, and stratigraphy indicate that the E zone consists of multiple carbonate buildups and is locally more complex than the other L-KC zones. The structural trend in the Acorn Field area on the L-KC A zone is interpreted as being generally northwest-southeast parallel to the Cambridge Arch. This varies from the usual interpretation of southwest-northeast trends. With only about 400 wells, Dundy County is under-explored both in area and in interpretation of the numerous subtle, complex reservoirs.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana