Multi-variable operations

A system for use in operation of a controllable multi-variable well- or shaft-drilling process, comprising means for deriving a multi-dimensional display representation of drilling process variables of the process according to individual coordinate axes, means for defining one of bounds or envelopes for prospective operation of the drilling process, said one of bounds or envelopes being defined in accordance with sets of values for drilling process variables accumulated respectively from previous multiple operations of the process, means responsive to input signals in accordance with current values of the drilling process variables for indicating current values of the drilling process variables on respective axes of the display representation, the current values of the drilling process variables being real-time values of the drilling process variables and at least some of the drilling process variables being drilling process variables that are directly controllable in performance of the drilling process, calculating means for calculating, for each drilling process variable according to the current values of other drilling process variables, a viable range of values for that individual drilling process variable consistent with operation of the drilling process within said bounds or envelopes, the calculated viable ranges of the drilling process variables being demarcated on respective axes of the display representation, and means operable for defining tentative change from the current values of a selected one or more of the drilling process variables, said calculating means being responsive to the tentative change so defined for calculating the viable ranges as aforesaid that would be applicable in the event of implementation of said change, for demarcation on the respective axes, and wherein the system further comprises means for detecting a condition in which the current value of any said drilling process variable is outside the viable range calculated for the drilling process variable, and means responsive to the rate of occurrence of the condition for changing the sets of values defining the one of bounds or envelopes during course of operation of the drilling process for other sets of values for the drilling process variables accumulated respectively from the previous multiple operations of the drilling process.