MINLP optimization of the underground lined rock cavern

The paper presents the cost optimization of a lined rock cavern (LRC), designed for an underground gas storage (UGS). The optimization was performed by the mixed-integer non-linear programming (MINLP) approach. GAMS/DICOPT was used. For this purpose, the MINLP optimization model was developed. The model comprised the cost objective function, which was subjected to geomechanical and design constraints. The rock mass strength stability and safety of the system were assured by these constraints. In the near past, the non-linear programming (NLP) optimization of a single gas cavern, of a whole underground gas storage and of a UGS in different rock environments was performed. Contrary to the mentioned NLP optimizations, where only the theoretical optimal results with continuous variables were obtained, in this paper the MINLP optimization of the LRC is proposed in order to handle the discrete alternatives explicitly. In this way, the solution obtained is a real optimal engineering solution with the calculated discrete values of different design parameters like cavern depth, diameter, height, wall thickness and inner gas pressure. A numerical example at the end of the paper shows the MINLP optimization of the investment costs of the lined rock cavern for the UGS in Senovo, Slovenia.