水化作用对页岩孔隙结构及声波特性的影响  

Hydration controls on pore structure and acoustic attributes in shale

作　　者：高可攀 GAO Kepan(Exploration and Development Research Institute,Sinopec North China Company,Zhengzhou,Henan 450046,China)

机构地区：[1]中国石化华北油气分公司勘探开发研究院,河南郑州450046

出　　处：《天然气勘探与开发》2025年第2期39-48,共10页Natural Gas Exploration and Development

基　　金：国家自然科学基金项目(编号:41872167)。

摘　　要：在钻完井过程中,工作液侵入到页岩气储层内部,在物理作用及化学作用下有可能诱发页岩的水化损伤,造成裂缝扩展和延伸,甚至导致页岩地层井壁失稳,严重影响页岩气藏的安全钻井及压裂改造效果。为了明确水化作用对页岩孔隙结构及声学参数的影响,选取四川盆地志留系下统龙马溪组页岩样品,开展了页岩水化实验、超声波透射实验及核磁共振实验测试,对比分析了不同水化时间下页岩孔隙结构、声波速度及频域信号的变化规律,揭示了页岩孔隙结构变化与声波速度变化的内在联系,建立了一种以弹性参数为依据的页岩水化损伤程度的定量表征方法。研究结果表明:①页岩水化作用过程中,其孔隙结构表现为小孔隙数量增加、小孔隙朝着大孔隙方向发展、大孔隙及微裂缝产生;②页岩声波速度随着水化时间的增大而减小,下降幅度呈现先急剧减小而后逐渐趋缓的变化趋势,水化作用后页岩频域信号中的低频成分明显减少;③水化损伤速度表现出先逐渐加快然后逐渐减缓的特征,1~6 h水化损伤速度较快,6~24 h水化损伤速度逐渐减缓,24~48 h水化损伤速度趋近于稳定。Working fluid invading into shale gas reservoirs may trigger hydration damage to shale under physical and chemical interactions during drilling and completion,further leading to fracture propagation and extension or even borehole instability,which may badly affect drilling safety and stimulation performance.Therefore,some experiments about hydration,ultrasonic transmission and nuclear magnetic resonance(NMR)were implemented on shale samples from the Lower Silurian Longmaxi Formation of Sichuan Basin in an effort to figure out hydration controls on shale’s pore structure and acoustic attributes.Variations in pore structure,acoustic velocity,and frequency-domain signals at different hydration times were discussed for these samples to reveal an intrinsic relation between the first two variations.Furthermore,dependent on elastic parameters,the quantitative characterization was established on the degree of hydration damage to shale.Results show that(i)in term of the pore structure throughout the hydration,small pores increase in their number,the size gets bigger successively,and large pores and microfractures emerge;(ii)with the increase of hydration time,the velocity decreases in a dramatic and then gentle manner.Low-frequency components evidently become lesser in frequency-domain signals after shale hydration;and(iii)the hydration damage accelerates and then slows down little by little,fast damage in the first six hours,sluggish in the following eighteen hours,and tending to be stable in the later twenty-four hours.

关 键 词：页岩 水化作用 超声波透射 核磁共振 孔隙结构 声波速度 

分 类 号：TE21[石油与天然气工程—油气井工程]