Novel Technique to Enhance Hydraulic Fracture Permeability by Controllable Biomimetic Mineralization: Transitioning from Liquid Injection to Solid Propping.

Unconventional oil and gas have been playing an increasingly important role in the global energy market. The primary development technique for shale and tight reservoirs is hydraulic fracturing, which aims to create high-permeability channels propped by quartz sand or ceramsite, enabling oil and gas to flow out smoothly and steadily. However, during the transportation of the fracturing fluid, proppants continuously settle, leaving narrow fractures and the distal end unsupported. These are critical zones, where conductivity loss severely limits production efficiency. To address this challenge, this study innovatively proposes an in situ propping technique based on controllable biomimetic crystallization of hydroxyapatite (HAP). We developed an inorganic formulation capable of transitioning from liquid injection to solid propping under reservoir temperature conditions (>75 °C). Through formulation optimization and adding an organic regulator, the diameter of the in situ formed HAP proppant can be controlled to range from 100 nm to 300 μm, ensuring its capability of reinforcing fractures against crushing under stress. Core permeability experiments demonstrated that after proppant placement at 30 MPa pressure, the fracture permeability of the treated cores was 36 times higher than that of unsupported fractures. This novel technique offers new insights and broad prospects for hydraulic fracturing. It enables more coverage support of fracture networks and extensive enhancement of fracture permeability, with its potential to resolve proppant settling issues and maintain long-term fracture conductivity. This represents a promising pathway for future unconventional petroleum production and enhanced oil recovery (EOR).