Core Drilling in Geological Exploration

Abstract

Geological explorations by oil companies, state and federal surveys, andprivate consulting geologists, have resulted in the mapping of the greater partof the structures to be found in the Rocky Mountain region. Most of thepromising structures have been drilled and few remain that are generallyregarded as favorable for the accumulation of oil and gas. Undoubtedly, a fewstructures, some of which may produce, exist beneath Tertiary overlaps and morerecent gravel terraces and soil-covered areas. The finding and investigation ofthese structures must be done by core drilling or by geophysical methods. A consideration of the area of oil-producing land compared with the totalarea of the region will show the folly of systematic core drilling of coveredareas in the hope of picking up structures that will produce oil and gas. Suchan exploration would inevitably result in financial disaster unless theinvestigator were exceptionally endowed with luck. Consequently, all coredrilling done in the Rocky Mountain region has been to supplement and checkfield work which has demonstrated folding, but has been unable to demonstrateclosure or amount of closure due to lack of outcrops. Before the advent of coredrilling, pits were sometimes dug to a depth of 125 ft. to obtain dips. As suchinformation was expensive and often unreliable, because of local crumpling andslumping in shale and crossbedding in sandstones, the advent of core drillingwas inevitable. Up to the present time the Midwest Refining Co. has investigated tenstructures with the core drills and of these, six were found unworthy of a testwell, three are being drilled, and one is still being investigated. Operating Data Local operating conditions are materially different from those of other oilfields. The Midwest Refining Co. is employing two Longyear 2N Fordson-drivendiamond drills.