重庆合川地区须二段岩石断裂韧度

探讨重庆合川地区上三叠统须家河组第二段储层岩石在水力压裂过程中的裂纹扩展特性。通过50 kN电子伺服试验机及“人”字形切槽巴西圆盘试件对须二段致密砂岩进行断裂韧度实验研究,获得Ⅰ型及Ⅱ型断裂韧度的数据,并对断裂韧度的特征及其与岩石力学参数的关系进行分析。结果表明须二段砂岩轴向和径向上的Ⅰ型断裂韧度都小于Ⅱ型断裂韧度。随着砂岩粒度的增大,Ⅰ型和Ⅱ型断裂韧度都逐渐减小,且与弹性模量、抗压强度、抗张强度及内聚力呈现较强的正相关性。Ⅰ型张开型的裂缝扩展特征和贯通程度要比Ⅱ型滑开型的简单且破坏较弱,若岩样中含有纹层等弱的岩石力学结构面,岩样的裂纹扩展样式更加复杂,断裂韧度测试值也相应地减小。合川地区须二段砂岩在纵向上进行压裂作业时,更容易在纵向上形成延伸较远的纵张裂缝。

Study on rock fracture toughness of the second member of Xujiahe Formation in Hechuan area,Chongqing ,China

The crack propagation characteristics of reservoir rocks in the second member of Upper Triassic Xujiahe Formation in Hechuan area,Chongqing during hydraulic fracturing are discussed.In the study,the sandstone fracture toughness of the second member of Upper Triassic Xujiahe Formation is tested through 50 kN electronic servo testing machine and the inverted“V”glyph grooving Brazilian disc specimen.Data of typeⅠand typeⅡfracture toughness are obtained and the characteristics of fracture toughness and its relationship with rock mechanics parameters are analyzed.Results show that,in the axial and transversal directions,the typeⅠfracture toughness is less than typeⅡfracture toughness.With the increase of sandstone grain size,typeⅠand typeⅡfracture toughness decreases,and displays a strong positive correlation with elastic modulus,compressive strength,tensile strength and cohesion.The crack propagation characteristics and penetration degree of the typeⅠopen type are simpler and weaker than those of the typeⅡslip open type.If the rock sample contains weak rock mechanics surface,such as laminae,the crack propagation pattern of the rock sample becomes more complicated and the test value of fracture toughness decreases accordingly.When the sandstone of the second member of Xujiahe Formation in Hechuan area is fractured in the longitudinal direction,it is easier to form transverse-extended extensional fractures.