摘要
极地地质钻探是获取地层样品、研究极地地质和气候演变等的重要手段。钻遇脆冰层、暖冰层和冰岩夹层等复杂冰层时,易出现孔壁失稳问题,尤其是冰孔液压致裂,造成钻井液流失和钻孔事故。针对冰孔裂缝萌生和扩展问题,基于近场动力学方法(PD),建立了冰孔裂缝模型,实现了对冰孔周边连续和非连续空间的统一描述,避免了经典连续介质力学微分方程在裂缝尖端的奇异性,分析了裂缝动态扩展过程,探究了液压和断裂韧度的影响机制。实例研究表明,孔内液柱压力促进裂缝萌生和扩展,液压从4.0 MPa增加到6.0 MPa和8.0 MPa,冰孔裂缝萌生和分支数量显著增加,裂缝体积占比从4.88%增加到9.61%和12.54%。断裂韧度阻碍冰孔裂缝扩展,从155 kPa·m0.5加到165 kPa·m0.5和175 kPa·m0.5,裂缝体积占比从13.72%降低到12.13%和9.61%。基于近场动力学的冰孔液压致裂分析表明,钻遇韧脆转换冰层时,应及时调整钻井液密度和液柱高度,控制孔内液压,保证安全高效钻进。
Polar geological drilling is an important means to obtain ice cores and study the evolution of Earth’s climate.When drilling into complex formations such as brittle ice,warm ice,or ice‑rock interlayer,hole wall instability frequently occurs,especially the hydraulic fracturing of ice holes,resulting in drilling fluid loss and drilling accidents.Aiming at the initiation and propagation of ice hole fractures,an ice hole fracture model is established based on Peridynamics(PD)to achieve a unified description of the continuous and discontinuous spaces around ice holes,avoid the singularity of the classical continuum mechanical differential equation at the crack tip,analyze the dynamic propagation process of cracks,and explore the influence mechanism of hydraulic pressure and fracture toughness.The case study shows that hydraulic pressure promotes fracture initiation and propagation,and the hydraulic pressure increases from 4.0MPa to 6.0MPa and 8.0MPa,the number of fracture initiation and branches increases significantly,and the fracture volume ratio increases from 4.88%to 9.61%and 12.54%.Fracture toughness hinders fracture propagation,and the fracture volume ratio decreases from 13.72%to 12.13%and 9.61%when fracture toughness increases from 155kPa·m0.5 to 165kPa·m0.5 and 175kPa·m0.5.The results of hydraulic fracturing analysis of ice holes based on PD show that the drilling fluid density and liquid column height should be adjusted in time to control the hydraulic pressure in the hole to ensure safety and efficiency when drilling into the formation with the prominent ductile‑brittle transition.
作者
刘永升
许浩然
杨甘生
李冰
LIU Yongsheng;XU Haoran;YANG Gansheng;LI Bing(School of Engineering and Technology,China University of Geosciences(Beijing),Beijing 100083,China)
出处
《钻探工程》
2023年第S01期90-97,共8页
Drilling Engineering
基金
国家自然科学基金项目“气举反循环连续取心混合流中岩心运移机理与调控机制研究”(编号:42272362)
国家重点研发计划“南极冰下复杂地质环境多工艺钻探理论与方法”(编号:2021YFA0719100)。
关键词
极地钻探
冰孔
液压致裂
近场动力学
断裂韧度
polar drilling
ice hole
hydraulic fracturing
peridynamics
fracture toughness
