The paper presents laboratory testing approach to evaluate DIF (Drill-In-Fluid) damage and wellbore cleanup effectiveness in open hole horizontal producer wells. It also investigates the fine movement damage and also the side effect of mud cake removal if it is left in wellbore for long period. The formation damage tests were carried out on sandstone core plugs from 3 different formations with permeability varying from several milidarcy to hundreds milidarcy. The WBM (Water Base Mud) was used with mostly consisted of CaCO3, NaCl, and KCl. Prior to formation damage test, critical velocity test was performed to investigate the fine movement damage. The formation damage tests were started by circulating the mud with 300 – 400 psi overbalance across the core plugs to create mud cake. The mud was then displaced by brine 8.8 ppg and high viscosity fluid was circulated to simulate the real condition in field for hole cleaning process. Several mud cake removals were then circulated and soaked for 1 and 5 days in the system. Finally, the oil return permeability was measured and compared with initial permeability. Throughout the study, it is observed that the critical velocity is mainly controlled by the clay content. Porosity and permeability also plays significant role in the plugging behavior due to fine migration. Acid based mud cake removal can enhance the formation permeability if it is allowed to leak-off through the rock matrix. It also depends on the mineral content of the formation (acid soluble minerals). Delayed acid based mud cake removal outperformed other mud cake removals in this study. The most optimum soaking time using the delayed acid based mud cake removal in this study is 1 day. However, there is no permeability impairment identified if the mud cake removal is left up to 5 days.
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