Nano-Roughness coating reduces the fluid/solid interaction leading to super-hydrophobicity or the Lotus effect. The objective of this study is to determine how this phenomenon can be applied in petroleum production system to enhance fluid flow in propped fractures using nano-roughness coating on the surface of proppants. The permeability and the wettability of coated proppant packs are compared with non-coated packs to determine the reduction in friction or enhancement in fracture conductivity.
The simulation of flow in a proppant pack is done using sand packs of different permeabilities. The base case for the work is established using sandstone samples with various permeabilities. The sandstone samples include Gray-Berea with uncoated absolute permeability of 86 mD, Buff Berea with uncoated absolute permeability of 374 mD, Bentheimer sandstone with uncoated absolute permeability of 277 mD and Leopard sandstone with the uncoated absolute permeability of 803 mD. The sand packs used are 20/40 mesh with uncoated absolute permeability of 31 D, 40/60 mesh with uncoated absolute permeability of 22 D and 50/70 mesh with uncoated absolute permeability of 21 D. After measuring the absolute permeability, wettability (using contact angle method) and relative permeability, all the samples were coated and the properties were measured again.
The results show that the modification enhances fluid flow through pores. The surfaces for all the samples were altered from a hydrophilic to a hydrophobic surface. The contact angle between the fluid and samples was observed to be almost 90° with water and >60° for oil, after modification. This confirms modification of samples to partial-wetting state. An increase in absolute permeability is observed from 14.54% for Gray-Berea to 184% for Leopard sandstone. The increase in absolute permeability for sand packs is observed from, 23% for 20/40 mesh sand, to 5.28% for 50/70 mesh sand. It was observed that modification is more efficient for a sample with a higher permeability, but further studies are in process to relate the permeability enhancement to total surface area.
Since the production rate of tight sandstone and shale reservoirs is low, especially in liquid-rich reservoirs and significant amount of water is injected for reservoir stimulation, enhancement in fracture conductivity resulting from proppant surface modification can have a meaningful impact on the recovery of these reservoirs. This study uses experimental techniques to show the effectiveness of nano-roughness coating on the reduction of friction which can lead to enhancement in fracture conductivity.