砂岩储集层微波加热产生微裂缝的机理及意义

微波加热无需介质传热,具有升温速度快、热惯性小、选择性加热、穿透力强、过程易于控制等优点,已被试验性地应用于石油开采中。但有关微波加热对储集层岩石微观结构影响的研究还很缺乏,限制了该项技术在油气开采领域的广泛应用。通过实验手段研究了微波加热前后砂岩岩样微观结构变化、微裂缝产生机理及特征。结果表明,砂岩在微波加热过程中容易产生微裂缝,且不同岩石的微波加热致裂机理不尽相同,主要包括:矿物失水收缩、颗粒粒间开裂和颗粒内部开裂,低渗透致密砂岩刚性颗粒的粒内开裂作用显著。微波加热产生的微裂缝具非定向特征,即使在应力的作用下有一部分裂缝会发生闭合,但仍有大量微裂缝可以起到增加渗透率的作用。井下微波加热的致裂作用有助于改善近井区域渗流能力,提高低渗透油气藏的开采效率。图4参15

Mechanisms and significance of microfractures generated by microwave heating in sandstone reservoirs

For its unique characteristics of none heat conduction needed,rapid temperature rise,little thermal inertia,selective heating, strong penetration power and easy control,microwave heating(MWH) has been experimentally applied to oil exploitation.However,few researches focused on the microstructure changes of reservoir rocks during MWH.This hinders the application of the MWH technology.Microstructure changes,microfracture characteristics and its generation mechanisms during MWH were studied through laboratory experiments.Compared with conditional heating,as the results have shown,MWH was more likely to induce sandstone to generate microfractures with different mechanisms.Three major mechanisms were noted,including mineral shrinking due to dehydration,cracking among granules and cracking inside granules.Microfractures generated by MWH were undirectional.It is concluded that it is helpful to improve near wellbore permeability and enhance the recovery efficiency of low-permeability oil/gas reservoirs through downhole MWH.