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The AAPG/Datapages Combined Publications Database

Alaska Geological Society


Alaska Geological Society 2001 Geology Symposium, 2001
Page 24

Lisburne Formation Fracture Characterization and Flow Modeling - Abstract

Previous HitAlexandreNext Hit Karpov,1 Jerry L. Jensen,2 Catherine L. Hanks3

The fracture system of Lisburne carbonates has been recognized to be critical to optimal reservoir management. A number of problems with the reservoir, including poor productivity and early water breakthrough, have been associated with inadequacies in the fracture description and characterization. Wells contact only small parts of reservoirs and may not provide sufficient information about fracture geometry, location and distribution. Also, medium and small fractures are below seismic resolution. Outcrops can serve as a significant source of data on fracture geometries and properties to bridge the gap between well and seismic information. Lisburne outcrop data are used in this study to assess fracture statistical properties and fluid flow behavior.

Data from the lower Wahoo Limestone in the eastern Sadlerochit Mountains were analyzed to develop fracture distribution models. The data contained quantitative information on fracture orientation, height, length, and spacing for two sets of large-scale fractures (NNW and ENE orientations). Several procedures were used to find appropriate statistical models describing the megafracture properties. This included analysis of descriptive statistics, probability plots, evaluation of L-moments, Monte-Carlo and “jack-knife” simulations. For NNW fracture height, both gamma and lognormal models appear to adequately describe the distribution. NNW fracture spacing and ENE fracture height and spacing are lognormally distributed. These results for fracture spacing and height are in agreement with results from studies of other formations. Such spacing distributions imply that the massive lower Lisburne is not saturated with respect to fractures, ie., fracturing is under-developed.

Results of the statistical analyses were used as input for fracture set generation using the FracMan program. Modeling different borehole orientations and locations in the fractured domain revealed an optimal wellbore trajectory with the maximum number of fracture intersections. It is a horizontal wellbore with orientation 10 – 30° from the north i.e., NNE. The theoretically calculated optimal borehole orientation is 18°, which is almost a bisector of the two fracture sets (22.5°).

Further work will focus on fluid flow modeling of the simulated fractures. This work will comprise transmissivity and sensitivity studies to assess the effects of the fractures on flow. This includes both a sensitivity analysis of the parameter values used in the fracture modeling and an assessment of the relative contributions to flow of the various fracture sets.

Acknowledgments and Associated Footnotes

1 Previous HitAlexandreTop Karpov: Department of Petroleum Engineering, Texas A&M University, 3116 Tamu College Station, TX 77843-3116

2 Jerry L. Jensen: Department of Petroleum Engineering, Texas A&M University, 3116 Tamu College Station, TX 77843-3116;

3 Catherine L. Hanks: Geophysical Institute, University of Alaska Fairbanks 99775

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