Combining large-sized model flow experiment and NMR measurement to investigate drilling induced formation damage in sandstone reservoir

Abstract

Abstract 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 core plug is still open to question. By using a multifunctional physical simulation system of drilling mud invasion, this paper introduces a novel experimental methodology which organically combines large-sized model flow experiment and NMR measurement to investigate drilling induced formation damage in sandstone reservoir. A large-sized sandstone formation module (55.9\u202fcm in radial depth, and 10\u202fcm in thickness) instead of the conventional core plug is proposed. This new type of experimental aliquot is able to provide enough space for observing a relative greater damage depth in a long-term drilling mud invasion. The effects of formation permeability and overbalance pressure on the damage are analysised. 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 damage depth of the drilling mud in the sandstone reservoir with a lower permeability is greater than that with a higher value. The former formation damage degree is also more severe than the latter one. For the same sandstone reservoirs, a higher overbalance pressure results in a greater damage depth and a more severe damage degree at the same radial depth. 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. With the variation of decrease ratio of movable water, the permeability damage rate changes faster in the sandstone reservoir with a lower permeability. The results obtained in this paper provide some helpful insights for enlightening new laboratory evaluation methodologies, improving numerical simulation of drilling induced formation damage and researching formation damage caused by any other working fluids, such as completion, workover, and stimulation fluids.