Abstract: Challenges of Petroleum Source-Rock Evaluation using Sonic and Resistivity Logs and the AE Log R Method, Northeastern Alaska

KELLER, MARGARET A., and KENNETH J. BIRD, United States Geological Survey, Menlo Park, CA

Assessment of the petroleum resources of the 1002 area of the Arctic National Wildlife Refuge in northeastern Alaska by the U. S. Geological Survey included evaluation of the petroleum source potential of Mesozoic and Cenozoic rocks with the AE log R method (Passey and others, 1990). This method uses porosity and resistivity logs in combination with maturity data to produce a continuous depth profile of total organic carbon (TOC). Estimation of TOC variation with the AE log R method seemed appropriate because of numerous log suites and samples available from wells adjacent to the 1002 area and the heterogeneous nature of source rock intervals indicated by outcrop and well data.

TOC profiles produced by this method were compared to TOC measurements on core and cuttings samples in selected wells. Close agreement was obtained for certain intervals, but not for others where the required boundary conditions could not be met. The main challenges we faced in applying the method were: (1) poor quality of sonic and resistivity logs due to caving source rock units-- also causing contamination of cuttings and erroneous TOC values; (2) source rock intervals with maturity or log parameters outside the range of calibration of the lE log R method -- immature and post-mature rocks and well cemented calcareous units such as the Shublik Formation; and (3) absence or uncertain presence of non-source shales needed to re-establish the method's baseline as log parameters change down the borehole.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California