| The classification of fractures can be divided into structural fractures and non-structural fractures.The study of non-structural is very weak,but the Shale Diagenetic Fracture is a very important non-structural fracture,which is closely related to the exploration and development of oil and gas.In addition,for the hydraulic pressure,the place where the fracture existed is weak and the hydraulic fractures can extend along the diagenetic crevices and rotate to form a complex fractured network..And there is similarity or evenness between the crack of muddy sediment and the shale diagenetic fracture,both in origin,morphology and development.In this paper,to solve the problem that the development laws of diagenetic fracture is not clear,based on the experimental study of the crack of muddy sediment,the method of field observation and research of the desiccation crack of modern mud sediment and the method of physical simulation experiment were used.the main controlling factors and development laws of shale diagenetic fracture were studied,mainly achieved the following understandings:The first fracture place of the modern muddy sediments is mainly the location where the muddy sediments are suddenly missing(the edge or the inner missing)or the area where the internal stress is suddenly concentrated,and it will be formed the skeleton of the final crack is formed,and then it will cut the the whole area,formed some big bulk cracks after that the secondary crack will be formed vertically from the the first one.The main geometries of the crack are mainly triangular,quadrangular,pentagonal and hexagonal,and the inflection point is mainly dominated by the three line points.The range of the growth angle of the main fracture is mainly 0 ~ 60 °,and the growth angle of the secondary crack is in the range of 60 ~ 120 °.Its main control is mainly due to mineral content,sediment thickness and salinity.It is found that the thickness,salinity and clay mineral content of the sediments are the main controlling factors of the cracks,the thickness increases,the number of cracks is gradually reduced,and the crack length gradually increased,the crack width gradually increased,the crack angle gradually increased.The increase of salinity,the substitution between the lattice,makes a large amount of Na +,Ca2 + filled in,resulting in double electric layer effect,so that the electrostatic repulsive force VR greater than van der Waals force VA,less prone to cracking.For clay mineral content,clay minerals generally better than brittle minerals,mainly clay minerals have a strong water absorptionAccording to the type of cause,Shale Diagenetic Fracture can be divided into: compaction joints,shrink joints,dissolved joints,overpressure joints,the formation of different conditions.Subject to different diagenetic effects.Due to the similarity of the crack of muddy sediment and the shale diagenetic fracture,we can see that the shale diagenetic fracture can be divided into main fractures and sub-fractures by observing t the shale diagenetic fracture under actual and electron microscopy.The growth angle of the main fractures is mainly 60 °.Its main control factors are mostly shale thickness,clay mineral content and so on.The physical model of shale diagenetic fracture is mainly divided into three types: controlling model of holes or large particles,controlling model of the beddings or the original cracks,stochastic growth model and it has a positive significance for finding fractures and Hydraulic fracturing... |
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