Evaluation of injection well patterns for optimum fracture network generation host-rock formations: an application in in-situ leaching

Artificial fracture stimulation in host-rock using soundless cracking demolition agents (SCDAs) is a potential alternative for rock fragmentation in enhanced in-situ leaching applications of mineral ores because conventional mining techniques are becoming increasingly uneconomic with declining ore-grade. In this study we investigated the impact of different injection well patterns on the fracture network propagation of an SCDA charged rock mass using a discrete element numerical simulation. First, a laboratory scale fracturing experiment was conducted on a simple specimen having two injection wells filled with SCDA. The results of the experiment were used to validate the numerical simulation, and the model was then extended to assess the SCDA charged fracture propagation in a host-rock formation with different injection well patterns typically found in the field. A two-staged fracturing process was identified from the numerical simulation observations and was defined as pre-fracture coalescence and post-fracture coalescence stages. The expansive pressure development within injection wells from the SCDA charging and the corresponding fracture growth was found to be dependent on the number of injection wells surrounding a centre injection well. With the increasing number of injection wells, the fracture connectivity between wells was found to decrease and consequentially a diminishing return of fracture density was observed. This is a result of the larger compressive stress fields generated within the rock mass with the increasing number of SCDA injection wells. The optimum number of injection wells surrounding a centre injection well was found to be four or five (five or six injection well pattern), which produces the highest fracture connectivity and the fracture density for enhanced ISL applications.