Automated Geological Evaluation of Continuous Slim-Hole Cores

Abstract

Summary Slim-hole continuous coring and drilling techniques applied to oil exploration are receiving wide recognition. Slim-hole coring methods produce high-quality continuous cores that yield valuable exploration information. Amoco Production Co.'s geological evaluation modules furnish an on-site automated instrumentation system to extract a maximum of information from the core, thus providing the vital link in developing high-speed slim-hole coring into an integrated exploration tool. "Inverse logging" (logging the core instead of the borehole) is the primary goal of on-site geological evaluation. Up-hole measurements on cores include gamma scan, magnetic susceptibility, infrared mineralogy, ultraviolet fluorescence, nuclear magnetic resonance porosity, and pyrolysis (source rock) data; macroscopic and microscopic video images for analysis and archiving; and sedimentological/lithological description. Continuous rock samples through entire basin-filling sequences are used to calibrate seismic and well log data. This information provides insight into opportunities and risks associated with exploration and development in all types of basins. Introduction In recent years it has become apparent that the oil and gas industry needs major innovative changes to improve exploration effectiveness and decrease the costs of finding. The results of studies done to assess the technical risk associated with exploration and development indicate a need to better understand the actual geological and geophysical characteristics of reservoir, seal, and source packages. In both basin reconnaissance and subtle-trap exploration modes, the need has never been greater to pursue the acquisition of continuous cores actively to better analyze subsurface hydrocarbon systems and improve technical databases. Continuous cores acquired through complete sedimentary sections enhance geological and geophysical data. Direct observation of lithology, sedimentary structures, fossils, reservoir pore geometry, source-rock characteristics, seal characteristics, and petrophysical rock properties permits fact (instead of interpreted, indirect information) to guide subsequent exploration and exploitation programs. Traditional slim-hole continuous coring and drilling techniques are receiving wide recognition in their application to oil exploration; core analytical capabilities are considered deficient and present a challenge to the oil industry. Automated geological analysis of continuous slim-hole cores results in on-site, real-time evaluation. The geological evaluation modules provide the critical link for connecting high-speed slim-hole coring into an integrated exploration system, and, thus, have the potential to revolutionize exploration and development philosophies and create entirely new oil and gas paradigms. Slim-hole drilling and on-site evaluation can be applied to all phases of exploration and development, including rank wildcat well analysis, field development studies, and regional trend or basin analysis studies.