The invasion of solids in the drilling mud into the pay zones have significant consequences on reservoir evaluation and production, hence composing a substantial challenge for the mud design. In principle, the mud contains solid particles denoted as bridging materials that are utilized to build up a mudcake at the wellbore to minimize the invasion of solids into the formation. The failure to build up proper mudcake might drive serious formation damage i.e. serious porosity and permeability reduction that are not reversible.

The purpose of this work is to characterize the effect of the particle size of the bridging materials on the integrity of the mudcake and its influences on filtrates invasion. An integrated approach is introduced combing formation damage experiments at reservoir conditions and Nuclear Magnetic Resonance relaxometry (NMR) to monitor any change in the formation properties. The mud flow experiments were performed on two sandstone and one carbonate rocks with two drilling muds in which the size of the carbonate particles was varied, however all the other mud properties were kept fixed. The barite particles are utilized to simulate the solids invasion. The obtained results showed that the growth of the mudcake is independent of the mineralogy of the rock, though, its porosity and permeability are key elements in determining the proper sizes of the bridging materials.

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