
TY  - JOUR
A1  - Chapman, Richard E. 
T1  - THE ROLE OF CHANCE IN EXPLORATION
JF  - The APPEA Journal
JO  - The APPEA Journal
Y1  - 1970
VL  - 10
IS  - 1
SP  - 23
EP  - 27
KW  - 
UR  - https://doi.org/10.1071/AJ69004 
N2  - In the early stages of speculative mining ventures, when extrapolation of scanty data is unavoidable, the role of chance can be at least as important as that of professional skills.Having drilled n consecutive successful wells without a failure, at what point can it be said that the chances of ultimate failure of the venture are negligible?Conversely, having drilled n consecutive failures, at what point can it be said that the chances of ultimate success are unacceptably remote?Having estimated the area required to be underlain by hydrocarbons for a venture to be profitable, how many wells should one be prepared to drill to ensure at least one success with a specified probability?Defining Relative Area as the area underlain by what is sought, expressed as a fraction of the total area of interest, the probability of success in a well drilled at random is precisely this Relative Area.Drilling may be regarded as random if the outcome of a well cannot be predicted. When the goal of the geologist &#x2014; the construction of a deterministic model &#x2014; has been achieved, the drilling is not random and the methods of this paper are not valid.When all n wells drilled so far have been successful, the minimum-likely Relative Area is given by where p is the probability of success and also the Relative Area (0 &#x2264; P &#x2264; 1); P is the degree of confidence required (0 When all n wells have been failures, the maximum-likely Relative Area is given by If a specified Relative Area p&apos; exists, the minimum number of wells required to ensure at least one success is given by the nearest integer n that satisfies the inequality When some wells have been successful and others failures, the probability of exactly r successes (irrespective of order) in a total of n wells is This may be of little value when n is small. But when n is large (say 20 or more), and when &apos;success&apos; refers to the finding of something that did not influence the siting of the wells (such as the presence or absense of a particular facies), then the probable range of the Relative Area is given by where z may be taken as 1.6 for 90 percent confidence, and 2.0 for 95 percent confidence.These relationships are aids to geological judgement, not substitutes for it. 
ER  -

