ABSTRACT
Studies have been carried out on the stability of a well brine, using the DKR control method, based on the numerical computational methods. The DKR Control method was elaborated following some experiments and tests, both in the laboratory and in-situ, for some salt exploitations situated in Romania. The general form of the method consists of three mains steps:
Analyzing of the available geologic, mechanical and topometric information:
the dynamics of the exploitation (the evolution during the time) and the exact geometry of the cavities today;
physical and mechanical properties of the material (the creep law), following laboratory and in-situ tests;
cavernometric measurements, made during the exploitation, containing the level of subsidence at several time steps;
the evolution of the exploitation in time.
It should be noted that the information available for the study was not complete following the analysis. The degree of knowledge available was estimated at 79.24%, which reduced the confidence of the numerical simulation.Creating the numerical computational model:
several two-dimensional model studies have been performed, representing characteristic sections of the well;
a diagram of the evolution in time for every section, according to the available data, corresponding to the total time of exploitation, from the initial opening of the well.
Calibrating the numerical computational model:
the main control parameter was the measured subsidence; unfortunately, data was available for only a few points; and this subsidence level was accepted for the whole section;
the results have been compared to the results of the numerical simulation, considering both the dynamics of the exploitation and the creep law obtained in the laboratory. The creep law parameters have been corrected until an error of 5% has been 356achieved. At this point it was considered that the calibration of the numerical model was accurate to within 95%.
Exploitation using the numerical model:
With the calibrated model, the analysis with time was continued, considering that the actual geometry changes were only due to the collapse of some parts, where the admissible stresses have been overpassed. The analysis was carried on for 12,978 days, computing the possible subsidence and stresses.
Due to the fact that the well is situated in a seismic area, some seismic analysis was performed, computing the supplementary stresses induced by earthquakes, at several moments of the exploitation evolution. By this superposition, the collapse risk increases because the geometry changes faster than that predicted by the creep analysis, and the well behavior moves toward an unstable condition. Estimates the effect on stability of the Slanic brine, with or without seismic effects, and evaluates the risk for its collapse as a function of time.
