Work

Blockage mechanisms of suspended particles in fractured ultra-low permeability reservoirs and optimization of water quality standards for post-fracturing injection

Year: 2026

Type: article

Abstract: The ecological and environmental management department require the treatment of oilfield produced water to comply with the "Technical Requirements and Analytical Methods for Water Quality Indicators of Clastic Rock Reservoir Water Injection" SY/T 5329–2022. This standard imposes strict limits on injected water quality indicators, including suspended solids concentration, median particle size, and oil content, which are generally determined according to reservoir permeability. However, Hydraulic fracturing creates complex "pore-fracture" dual-media systems in ultra-low permeability reservoirs and the blockage mechanisms of suspended solids during post-fracturing water injection remain unclear—rendering conventional homogeneous-media water quality standards inadequate. In this study actual cores from the Ansai and Jiyuan oilfields, Brazilian-split fracture analogues, proppant-filled fractured cores, and controlled water-quality variations were combined to investigate blockage behavior after hydraulic fracturing. The main novelty of this work is the establishment of a fracture-specific blockage framework: an experimentally observed transition near PC = 1.059 separates internal throat plugging from inlet-face filter-cake formation in the tested cores. Fractures exhibit a dual effect: they mitigate overall permeability damage as preferential flow pathways, while simultaneously facilitating the invasion of solids and oil, complicating subsequent removal. Water-quality optimization tests with 40–70 mesh ceramic proppants showed that Class IV water (particle size < = 5 μm, suspended-particle concentration < = 25 mg/L, and oil content < = 30 mg/L) kept core-scale permeability loss below 25% under the tested conditions. By clarifying fracture-induced blockage mechanisms and validating relaxed standards, this study provides theoretical insights and practical guidance for cost-effective water injection in fractured ultra-low permeability reservoirs.

Source: Scientific Reports

DOI: 10.1038/s41598-026-56744-7