Use of Geostatistics in Planning Optimum Drilling Program

Shankhar Ghose

Application of geostatistics in the natural resources industry is well established. In a typical process of estimation, the statistically dependent geological data are used to predict the characteristics of a deposit. The estimator used is the best linear unbiased estimator (or BLUE), and a numerical factor of confidence is also provided. The natural inhomogeneity and anisotropy of a deposit are also quantified with preciseness.

Drilling is the most reliable way of obtaining data for mining and related industries. However, it is often difficult to decide what is the optimum number of drill holes necessary for evaluation. In this paper, sequential measures of percent variation at 95% confidence level of a geological variable have been used to decipher economically optimum drilling density. A coal reserve model has been used to illustrate the method and findings. Fictitious drilling data were added (within the domain of population characteristics) in stages, to obtain a point of stability, beyond which the gain was insignificant (diminishing marginal benefit). The final relations are established by graphically projecting and comparing two variables--cost and precision. By mapping the percent variation at each s age, the localized areas of discrepancies can be identified. These are the locations where additional drilling is needed. The system can be controlled if performed at progressive stages and the preciseness toward stability is monitored.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.