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Larry J. Amateis1, Steve R. Clawson1
(1) Texaco, Denver, CO

Abstract: Modeling the Aneth Unit incorporating geological data from horizontal drilling to fit production and injection results

The Aneth Unit, one of four units in the Greater Aneth Field, has been under waterflood since 1962. Estimated ultimate recovery under secondary recovery was thirty-nine percent of oil in place. Forty-three wells have been re-entered and one hundred forty-three laterals drilled to attempt to recover an additional fifteen percent of oil in place. CO2 injection in line drive patterns is expected to recover an additional ten percent of oil in place.

Original geological models were inadequate to drill horizontal laterals in the field. A three-dimensional geologic model was generated from existing data from vertical wells and used to target intervals for horizontal drilling. This worked very well and results from the drilling were quite good.

Analogy and simulation predict CO2 breakthrough would take from six to nine months. However, when CO2 injection was begun, rapid breakthrough was observed; indicating the existing model was inadequate for flood management. A new model using data from horizontal drilling was built. All elevations were adjusted using the latest survey data, since drilling indicated minor structure was more significant than it first appeared. Rate of penetration data was available in digital form and modeled to compare to the porosity model. Fracture indicators from the sample logs were also modeled.

Surface topography from digital elevation maps was also studied to determine structural trends. The current model shows stratigraphic modeling is not enough to explain the production and injection trends in the Aneth Unit. Structure although small scale is extremely important in explaining production results. Using GoCAD for data analysis, geological model building and visualization a better subtle structure and petrophysical model has been generated. Results of this earth model will be shown.

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