L. J. Drew — Page 3 | USGS Science

USGS1976

The area of influence of an exploratory hole

A method is presented for calculating the area of influence of exploratory drill holes by using the size and shape of resource targets. The solution presented is for elliptical and circular targets, but the method is applicable to any shaped target. The degree to which points have been explored depends upon their distance away from a drill hole and the possible orientations of the target. Several hypothetical examples demonstrate how: (1) maps can be generated that show the degree to which areas within the region of interest have been explored; (2) graphs can be constructed to evaluate the possibility of undiscovered targets of specific sizes and shapes in a region; (3) the sequence of physical exhaustion in a region can be used to make estimates of undiscovered resources.

Economic Geology↗

USGS1975

Analysis of the rate of wildcat drilling and deposit discovery

The rate at which petroleum deposits were discovered during a 16-yr period (1957–72) was examined in relation to changes in a suite of economic and physical variables. The study area encompasses 11,000 mi 2 and is located on the eastern flank of the Powder River Basin. A two-stage multiple-regression model was used as a basis for this analysis. The variables employed in this model were: (1) the yearly wildcat drilling rate, (2) a measure of the extent of the physical exhaustion of the resource base of the region, (3) a proxy for the discovery expectation of the exploration operators active in the region, (4) an exploration price/cost ratio, and (5) the expected depths of the exploration targets sought. The rate at which wildcat wells were drilled was strongly correlated with the discovery expectation of the exploration operators. Small additional variations in the wildcat drilling rate were explained by the price/cost ratio and target-depth variables. The number of deposits discovered each year was highly dependent on the wildcat drilling rate, but the aggregate quantity of petroleum discovered each year was independent of the wildcat drilling rate. The independence between these last two variables is a consequence of the cyclical behavior of the exploration play mechanism. Although the discovery success ratio declined sharply during the initial phases of the two exploration plays which developed in the study area, a learning effect occurred whereby the discovery success ratio improved steadily with the passage of time during both exploration plays.

Journal of the International Association for Mathe↗