--> Abstract: Resistivity Response as an Indicator of Oil-Bearing Fracture Proximity, Niobrara Formation, Denver Basin, by R. A. Johnson and T. Bartshe; #91017 (1992).

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ABSTRACT: Resistivity Response as an Indicator of Oil-Bearing Fracture Proximity, Niobrara Formation, Denver Basin

JOHNSON, REED A., and R. TIMOTHY BARTSHE, Energy Foundation, Inc., Lakewood, CO

Vertically fractured formations recently have been the focus of considerable attention, largely due to the application of horizontal drilling technology. The key factor in the success of such exploration is predicting the occurrence and distribution of oil-bearing fracture systems. In the Niobrara Formation of the Denver basin, the resistivity tool provides a means of direct detection of oil-bearing fractures.

Anomalously high resistivity indicates the presence of oil-bearing fractures within the radius of investigation of the resistivity tool, and is caused by two factors: (1) the averaging effect of partly oil-saturated matrix and fully saturated fractures, and (2) the confining effect of oil-saturated fractures on the area of investigation of the resistivity tool. Quantification of the threshold resistivity, above which oil-bearing fractures are indicated, is demonstrated by comparing temperature-corrected resistivity vs. the degree of thermal maturation in wells throughout the basin. The triangulated resistivity anomaly (TRA) is a measurement of the degree to which resistivity exceeds the threshold value, and is a semi-quantitative indicator of oil-bearing fracture proximity.

TRA values may be used to map fracture trend orientations. Confirmation and application of the technique is demonstrated in two fields productive from the Niobrara formation. In Berthoud field,

anomalous resistivity correlates with oil-bearing fractures as indicated by core and drill-stem test data. In Silo field, the technique indicates the presence of two fracture orientations, only one of which has been the target of most horizontal wells to date.

 

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)