Mudcake formation while performing overbalanced drilling prevents intensive mud filtrate invasion into the formation. The hydrodynamic resistance that grows together with the mudcake blocks filtration through its boundary and gradually puts formation fluid motion under the effect of the gravity force determined by the difference of filtrate and formation fluid densities. This effect can be traced using wireline electromagnetic (EM) logging a day (or a few days) after reservoir penetration. This paper presents the results of 2D filtration and electromagnetic modeling for analysis of fluid saturation and formation resistivity alterations after drilling a well in a highly permeable reservoir. It contains Multi-Laterolog resistivity logging signal distribution diagrams for different time moment after well drilling. The wide time frame of the modeling (up to one month) has made it possible to determine characteristic time intervals, where the gravity force seriously affected the invaded-zone structure and the tool's measurements. The study has also revealed the conditions that result in incorrect interpretation of these measurements.

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