Abstract
The article examines primary causes of problems occurring during the drilling of geotechnical wells (injection, production and monitoring wells) for in-situ leaching to extract uranium in South Kazakhstan. Such a drilling problem as hole caving which is basically caused by various chemical and physical factors (hydraulic, mechanical, etc.) has been thoroughly investigated. The analysis of packing causes has revealed that this problem usually occurs because of insufficient amount of drilling mud being associated with small cross section downward flow and relatively large cross section upward flow. This is explained by the fact that when spear bores are used to drill clay rocks, cutting size is usually rather big and there is a risk for clay particles to coagulate.