• Last week, we discussed the human belief system and its use in decision making. It is of course fair to ask if the concept of belief has any mathematical backing.

    Thankfully, it does. Belief = Probability; the subjective kind, the kind promoted by those who call themselves Bayesians. To understand the mathematics of belief, it is good to know Bayes’ rule. And to understand the reasons for the existence of Bayes’ rule, it is good to know that there are many interpretations to probability. See below slides for the three main ones.

    The concept of belief falls under the category of subjective probability. It is the probability that is assigned by an individual (or an algorithm) of a particular event happening, based on whatever information is available. Now you may ask: But isn’t objective better than subjective?

    Good question: Yes. Unfortunately, drilling events (washouts, stuck pipes, etc.) are too complex to be analyzed theoretically (required for classical probability) and cannot be repeatedly observed (required for frequentist probability). Every well is different and the only means to determine an event’s probability during the drilling of such unique wells is subjective estimation based on knowledge and (or) other information collected and processed. And that is why the concept of beliefs is extremely important in a drilling advisory.

    We will start discussing some of the Bayesian networks inside Sentinel RT next week. Stay tuned.

    Click below for additional slides on this topic:

    Belief = Probability