摘要
阐述了决定断裂封闭性能的力学和化学因素。力学因素包括岩石破裂性质、断面正应力和断裂变形机制,其影响规律为:1岩石破裂性质和断面正应力决定了断裂的开敞程度;2三维应力实验已证实随温压升高,变形程度加深,而孔隙度和渗透率递减,但低压脆性变形中存在膨胀扩容阶段,并且膨胀扩容程度随有效应力增加而减小。化学因素包括化学沉淀作用、压溶作用和元素迁移,其影响规律为:1化学沉淀作用在开启性断裂中发育;2随温压的升高,压溶发育增强,随含水量的增加,压溶发育减弱;3形成断层岩的变形变质过程中,发生较大规模的体积损耗和元素迁移,大部分体积损耗是压溶-迁出作用造成的。认为在不同力学性质的断裂中,各因素对其封闭能力的影响程度不同。假设各种力学性质的断裂形成于同一构造应力场,并发育在同一力学强度的岩层或岩体中,则压性断裂相对高温、高压,其裂隙和断面紧闭程度高、变形程度深、压溶作用发育,压性断裂带为封闭系统,主要发生还原作用和脱水作用;张性断裂相对低温、低压,其裂隙和断面开启、压溶作用不发育、化学沉淀作用强,张性断裂带为开放系统,主要发生氧化作用和水解作用;扭性断裂的裂隙和断面张开度介于压性和张性断层之间,断裂核部因剪切热而压溶发育、变形程度高,封闭能力强,向断裂边部裂隙发育,封闭性能减弱,而疏导性能增强,扭性断裂带在垂向上为开放系统,主要发生氧化作用和水解作用。认为变形的程度不同,体积损耗和元素迁移的量不同:脆韧性的双山断裂在蚀变过程中,体积亏损量与变质反应的强弱正相关,变质程度强的F1断层亏损量可达到50%左右,而变质程度弱的F2断层亏损量最低仅为8%左右;不同性质断裂中,元素迁移规律不同:压性断裂中自断裂边缘向中心SiO2的含量增加、氧化系数减小,而扭性和张性断裂中则反之。
Mechanical and chemical factors, which influence fault＇s action to fluid, are detailed discussed inthis paper. The mechanical factors include mechanical property of fractures, normal stress of fault planeand deformation mechanism of faults, and their actions are as follows： ①The open degree of fault isdetermined by mechanical property of fractures and normal stress of fault plane; ②It has been testified by tri-axial compression experiments that the higher temperature and pressure, the deeper the deformation degree, the less porosity and permeability, but there is dilatancy during brittle deformation in low pressure. The dilatancy is reduced with the increase of effective stress. The chemical factors include chemical precipitation, pressure solution and element migration, and their actions are as follows： ① Chemical precipitation develops in unsealing fault；②The development of pressure solution increases with the increase of temperature and pressure, and weakens with moisture content, ③Volume loss and element migration happen during deformation and metamorphism to form fault rocks, and most of volume loss is caused by pressure solution and element outmigration. The quantities of volume loss and element migration vary with deformation degree, for example, their correlation is positive in brittle-ductile Shuangshan fault. In F1 fault of Shuangshan fault, whose metamorphic grade is higher, the volume loss isas high as 50%, but in F2 fault, whose metamorphic grade is lower, it is only 8%. The regularity of element migration varies with mechanical property of faults, and it is as follows： the content of SiO2 increases and coefficient of oxidation decreases from the margin to the center in compressive faults, and on the contrary in shear and tensile faults. In different mechanical faults, the influence degree of each factor is different. The comparing precondition is the assumption that faults form in the same stress field and their original rocks is the same. In compressive fault, there is relative fractures and fault plane, and high deformed and metamorply high temperature and pressure, closedhic grade；Pressure solution develops.Compressive fault zone is closed system whose reactions mostly are reduction and dehydration. In tensile fault, there is relatively low temperature and pressure, open fractures and fault planes pressure solution doesn＇t develop and chemical precipitation develops. Tensile fault zone is open system whose reactions mostly are oxidization and hydrolyzation. The aperture of fracture and fault plane in shear fault is intervenient between that in compressive and tensile faults. In the center of shear fault, pressure solution develops and deformed and metamorphic grade is high because of shear heats, and its sealing capacity is better; to its margin, fractures develop, sealing capacity weakens and flowing capacity increase gradually.Shear fault zone is open system in vertical.
出处
《天然气地球科学》
EI
CAS
CSCD
2005年第4期485-491,共7页
Natural Gas Geoscience
基金
国家自然科学基金项目(编号:40172072
40472074)
国家重点基础研究发展规划项目(编号:2001CB209133)联合资助.
关键词
断裂性能
化学因素
压溶作用
元素迁移
Fault mechanical factors
Chemical factors
Pressure solution
Element migration.
