Geology topics

L. J. Drew

Publications and source records attributed to L. J. Drew.

42 records · Page 3Linked to original sources

USGS1980

Computational methods for a three-dimensional model of the petroleum-discovery process

A discovery-process model devised by Drew, Schuenemeyer, and Root can be used to predict the amount of petroleum to be discovered in a basin from some future level of exploratory effort: the predictions are based on historical drilling and discovery data. Because marginal costs of discovery and production are a function of field size, the model can be used to make estimates of future discoveries within deposit size classes. The modeling approach is a geometric one in which the area searched is a function of the size and shape of the targets being sought. A high correlation is assumed between the surface-projection area of the fields and the volume of petroleum. To predict how much oil remains to be found, the area searched must be computed, and the basin size and discovery efficiency must be estimated. The basin is assumed to be explored randomly rather than by pattern drilling. The model may be used to compute independent estimates of future oil at different depth intervals for a play involving multiple producing horizons. We have written FORTRAN computer programs that are used with Drew, Schuenemeyer, and Root's model to merge the discovery and drilling information and perform the necessary computations to estimate undiscovered petroleum. These program may be modified easily for the estimation of remaining quantities of commodities other than petroleum. ?? 1980.

Computers & Geosciences↗

USGS1979

Pattern drilling exploration: Optimum pattern types and hole spacings when searching for elliptical shaped targets

In this study the selection of the optimum type of drilling pattern to be used when exploring for elliptical shaped targets is examined. The rhombic pattern is optimal when the targets are known to have a preferred orientation. Situations can also be found where a rectangular pattern is as efficient as the rhombic pattern. A triangular or square drilling pattern should be used when the orientations of the targets are unknown. The way in which the optimum hole spacing varies as a function of (1) the cost of drilling, (2) the value of the targets, (3) the shape of the targets, (4) the target occurrence probabilities was determined for several examples. Bayes' rule was used to show how target occurrence probabilities can be revised within a multistage pattern drilling scheme. ?? 1979 Plenum Publishing Corporation.

Journal of the International Association for Mathe↗

USGS1977

An exploratory drilling exhaustion sequence plot program

The exhaustion sequence plot program computes the conditional area of influence for wells in a specified rectangular region with respect to a fixed-size deposit. The deposit is represented by an ellipse whose size is chosen by the user. The area of influence may be displayed on computer printer plots consisting of a maximum of 10,000 grid points. At each point, a symbol is presented that indicates the probability of that point being exhausted by nearby wells with respect to a fixed-size ellipse. This output gives a pictorial view of the manner in which oil fields are exhausted. In addition, the exhaustion data may be used to estimate the number of deposits remaining in a basin. ?? 1977.

Computers & Geosciences↗

USGS1977

Field expectations and the determination of wildcat drilling

There is currently some dissatisfaction with macroeconomic approaches to modeling the supply of domestic crude oil. One problem that has been pointed out is that the estimated supply responses of new discoveries brought about by price increases appear to be unrealistically high. Because data frequently used in these models are highly aggregated over time and include diverse geologic regions, this criticism may not be unwarranted. Moreover, with highly aggregated data testable hypotheses relating to operator behavior at the field level are limited. Because of the somewhat decentralized nature of firm decision making, operator field behavior significantly affects the wildcat drilling rate and hence the interarrival times, i.e., temporal sequence, of expected discoveries.

Southern Economic Journal↗

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↗