Combining Large-sized Model Flow Experiment and NMR Measurement to Investigate Drilling Induced Formation Damage

Since the dynamic process of drilling operation often cannot be duplicated realistically in laboratory environment, the methodology to evaluate drilling induced formation damage using the conventional core plug is still open to question. This paper introduces a novel type of experimental aliquot, namely, the formation module (55.9 cm in radial depth, and 10 cm in thickness). An experimental methodology which combines large-sized model flow experiment and NMR measurement to investigate drilling induced formation damage in sandstone reservoir is proposed. The patterns of permeability impairment and pore structure change caused by the fresh water-based mud invasion are summarized. The results show that the formation permeability plays a negative leading role in both the damage depth and the damage degree. The decrease ratio of movable water based on NMR T2 distribution is an excellent index for describing the relationship between macroscopic performance and microcosmic essence of the formation damage. An obvious positive correlation between the permeability damage rate and the decrease ratio of movable water is observed. And the correlation changes faster in the sandstone reservoir with a lower permeability. The results provide some helpful insights for enlightening new laboratory evaluation methodologies, and improving numerical simulation of drilling induced formation damage.