On Bicriterial Decisions in Well-Drilling Processes Using Fuzzy Logic

Drilling a borehole includes the choice of equipment, drilling method, geometrical size of the well, type of chisel, quality and quantity of the washing liquid and technological parameters such as axel loading on chisel and its rotation speed. There is also a demand for organisation of dropand-lifting operations, forecasting of emergency and completition of the well. Problems of well-drilling optimal control can be divided into problems which are to be solved at the optimal project planning stage and those ones to be solved during the well-drilling process. The second group is most difficult and important, since the efficiency of drilling enterprise’s activity heavily depends on them. As numerous investigations show, succesful handling of these problems make it possible to decrease well-drilling costs by 25-30%. At the same time the development of new drilling technique does not significantly influence the decreasing of costs. Adaptation of technological parameters, quality and quantity of the washing liquid and chisel’s type can be performed in accordance with the chosen optimality criterion. In general case these criteria are devided into economical, technical, technological, and informational ones. The economical criteria are more preferable for deep oil and gas well-drilling, because the cost-price is one of the deciding indicators. The most important economical criterion is the well-drilling cost-prise Bc. It includes material expences, expences for chisels, pipes, usage of equipment and organizational and technological elements, as well [6,8]. Cost-prise Bc essentially depends on the well-drilling time T and borehole depth H. So, the optimization problem sound