- Copyright © 2000 Society of Exploration Geophysicists
Editor's Note: The Geologic Column, which appears monthly in TLE, is (1) produced cooperatively by the SEG Interpretation Committee and the AAPG Geophysical Integration Committee and (2) coordinated by M. Ray Thomasson and Lee Lawyer.
Using rotary sidewalls cores from a deep natural gas exploration well, a small E&P company recently measured natural fracture intensity, orientation, and openness in four separate potential target horizons. Results pin-pointed one zone having high fracture intensity and open fractures. Another zone with similar fracture intensity was identified as having closed fractures. Along with information on fracture strike, results were used to evaluate the risk of stimulating the well versus drilling a horizontal lateral. Historical production data from the play suggest that natural fractures are key to outstanding production, yet conventional well logs provided little usable information on natural fracture attributes in the four potential completion targets. Why? The vertical well did not intersect visible fractures. Sidewall cores also lack fractures visible to the unaided eye. So how were the measurements used in the fracture evaluation obtained?
The methods used in this well to diagnose natural fractures represent innovative use of microfracture and diagenesis data as surrogates for the large fractures that are so difficult to sample. The University of Texas at Austin is conducting the research in cooperation with an industry consortium. Many questions remain, but the potential is clear for these new directions in fracture characterization to have application in exploration and development. One application that will be tested this year in a study supported by the U.S. Department of Energy (DOE) is to use these core-based fracture characterization methods to calibrate seismic fracture detection.
An important target
Petroleum in fractured rocks is a growing target of exploration and development, making finding new methods to successfully predict, characterize, and simulate reservoir-scale natural fractures an important …