Mechanism of Nano-depressurization and Injection-Augmenting Technology and Its Application in China’s Oilfields: Recent Advances and Perspectives

Abstract

In China, most oilfields have entered the late stage of water injection development. Considering that the injected water quality has not reached the standard for a long time, the formation of organic and inorganic scale blockage has become increasingly serious, resulting in a continuous increase of injection pressure in water injection wells. The difficulty of water injection and low recovery ratio have mainly limited oilfield development. Considering the small size, large specific surface area, and other excellent properties of nanoparticles, they can easily enter the pore channel without reducing the permeability and damaging the formation, thus attracting extensive research attention at home and abroad. This work reviews the mechanism of depressurization and injection-augmenting and the application of nanomaterials in China’s oilfields. The future development prospects are also forecast. The mechanism of nano-depressurization and injection-augmentation mainly includes the following: (1) viscosity reduction, scale inhibition, and removal of wax and colloidal asphalt deposition; (2) inhibition of hydration and swelling of clay minerals; (3) change in the wettability and enlargement of the water flow path; (4) hydrophobicity of the nanoadsorption layer and drag reduction by water flow sliding; and (5) micro–nano double hydrophobic and self-cleaning effects. Through the strong chemical adsorption force between nanoparticles and the rock surface, the wettability of rock is changed by expelling the water film, and the permeability of the reservoir is improved by the sliding effect and the mechanism of preventing clay swelling. Nano-depressurization and injection-augmenting technology has been applied in China’s oilfields for many years, and studies have mainly summarized field tests in the past 10 years. The construction blocks include some typical middle–low-permeability reservoirs, such as the Bohai, Changqing, Daqing, and Jianghan Oilfields. Nano-depressurization and injection-augmenting technology has achieved obvious results, biological nanomaterials have obvious advantages over chemical additives, and its characteristics of environmental friendliness and long validity provide a new research direction for oilfield water injection and oil recovery, with broad development prospects.