Abstract

In oil industry, it is important to decrease water production and improve oil sweep efficiency. A newer trend in gel treatments is using preformed particle gel (PPG) to reduce fluid channels through super-high permeability streaks/fractures. The success of a PPG treatment depends primarily on whether or not PPG can selectively penetrate into highly permeable channels or fractures while minimizing penetration into lower permeable, unswept zones/areas. The purpose of this work was to determine what factors influence the damage of strong PPG on low-permeable, unswept zones. A filtration apparatus was designed to determine the possible penetration of PPG into low-permeable sandstone rocks. Filtration curves (the relationship between injection times vs. filtration volume) were obtained, and the permeability of sandstone cores, both before and after PPG treatment, was measured to determine whether or not PPGs reduce the permeability of low-permeable rocks. Daqing (DQ) gel was used as a PPG sample for our filtration experiments. DQ is a strong gel particle with an elastic module of ~6500 Pa at 1% of NaCl (wt%). The particle sizes of the gel ranged from 30 to 120 meshes. Filtration test results showed that 30–80 meshes of DQ did not impair the rocks with the permeability of of 3–25 mD. However, a powder of DQ gel with 100–120 meshes formed a cake on rock’s surface and reduced the core permeability up to 92.93 %. The damage of particle gel on unswept, low-permeable zones/areas was found to be effectively reduced by controlling both the particle size and the concentration of brine that was used to prepare swollen PPG.

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