Abstract
Conventional or overbalanced drilling process is fraught with formation damage in the near-wellbore region because of drilling mud and cement slurry invasion, permeability loss attributed to change of the net reservoir stress, and other reasons. One of the ways to overcome negative effect of drilling fluid interaction with reservoir rocks is balanced or underbalanced drilling. This technology is however cash-consuming. The purpose of this work was to analyze the efficiency of underbalanced drilling compared with the conventional (overbalanced) technique. For the analysis, the results of pressure transient analysis (PTA) were used, which provide information about formation flow characteristics and effective drainage area in actual in-situ conditions. Performance of slanted and horizontal wells drilled in different geologic environment was analyzed. Main causes of underperformance were identified and selection criteria of well candidates for underbalanced drilling were justified.
