Filtrate losses from drilling mud is a serious issue because it gives rise to several problems during the drilling phase and the production phase of the well. Such problems range from pipe sticking, formation damage to loss of productivity due to phase trapping. Several methods have been proposed and applied to manage this problem but most have been ineffective. Some researchers in the past sought to reduce filtrate invasion by formulating muds capable of forming a seal over the formation pores using bridging agents with properly distributed particle sizes. Others tried to leverage the mud cake permeability by ensuring a high proportion of coarse particles in the mud but only succeeded in controlling invasion to a small extent. The main objective of this work is to reduce filtrate losses and formation damage through investigation of the effect of particle sizing of mica and alumina nano particles on filtrate loss. Four muds were prepared—mud #1: base mud; mud #2: base mud + 60microns mica; mud #3: base fluid + 40microns mica; mud #4: base fluid + alumina nano particles. The names 40 mics mica and 60 mics were derived from the d50s of the 20-200microns mica and 20-325microns mica respectively. Results from the API filtration experiment showed that muds containing large percentage of fine particles, produce filter cakes that have very effective sealing ability. This was evidenced in the respective 30mins fluid loss values obtained for the different muds: base mud (23ml), mud #2 (20ml), mud #3 (17ml), mud #4 (13ml). The alumina nano mud offered the least mud cake permeability, hence the very low amount of filtrate. Field application of this discovery in mud formulation will reduce costs of treating damage and optimize hydrocarbon recovery as phase trapping will become a non issue.

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