| CPC C09K 8/516 (2013.01) [E21B 33/138 (2013.01); C09K 2208/10 (2013.01)] | 9 Claims |

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1. A method comprising:
introducing a water shut off composition into a water producing zone in a wellbore, the water shut off composition comprising alkaline nanosilica particles and hydrolysable ester-based 3D engineered non-convex particles having a cross-shaped cross-section in each of the xy-plane, the yz-plane, and the xz-plane, and wherein the hydrolysable ester-based 3D engineered non-convex particles have a surface consisting of 6 protrusions;
degrading the hydrolysable ester-based 3D engineered non-convex particles to release an acid within the water producing zone in the wellbore; and reacting the acid and the alkaline nanosilica particles, thereby forming a solid within the water producing zone in the wellbore.
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