Abstract
Shale reservoirs are the hot issue in unconventional resources. The key to the development of shale reservoirs lies in the complex fractures, which are the only path for fluid to migrate from the matrix to the wellbore in shale reservoirs. Therefore, the characteristics of shale fracture surface morphology directly affect fluid migration in shale reservoirs. However, there are few reports about the characteristics of shale fracture surface morphology as the parallel plate model was commonly used to characterize the fracture, neglecting its surface morphology characteristics and leading to great deviation. Thus, description methods were introduced to characterize shale fracture surface morphology with the aim to provide a foundation for the development of shale resources. Three shale samples were fractured by the Brazilian test, and the height distribution of the fracture surface was captured by a three-dimensional profilometer. Then, three-dimensional fracture surface morphology was regarded as a set of two-dimensional profiles, which converted three-dimensional information into two-dimensional data. Roughness, joint roughness coefficient, fractal dimension, tortuosity, and dip angle were employed to characterize shale fracture surface morphology, and their calculation methods were also, respectively, proposed. It was found that roughness, joint roughness coefficient, fractal dimension, tortuosity, and dip angle were all directional, and they varied greatly along with different directions. Roughness, joint roughness coefficient, fractal dimension, tortuosity, absolute dip angle, and overall trend dip angle were among 0.0834–0.2427 mm, 2.5715–10.9368, 2.1000–2.1364, 1.0732–1.1879, 17.7498°–24.5941°, and −3.7223°–13.3042°, respectively. Joint roughness coefficient, fractal dimension, tortuosity, and dip angle were all positively correlated with roughness.
Highlights
Introduction distributed under the terms andWith the increasing depletion of hydrocarbon resources, unconventional resources such as shale, tight sandstone, and other reservoirs, which were previously considered to be undevelopable, have become hot issues in recent decades [1,2,3]
Sample standard deviation was introduced to characterize the roughness of shale fracture surface morphology, and the specific methods are shown in Equations (1)–(3): v u m
The absolute dip angle was calculated by Equation (13), and the arithmetic square root of the absolute dip angle product in both directions was taken as the absolute dip angle of shale fracture surface morphology
Summary
With the increasing depletion of hydrocarbon resources, unconventional resources such as shale, tight sandstone, and other reservoirs, which were previously considered to be undevelopable, have become hot issues in recent decades [1,2,3]. The volumetric fracture network structure is the key to the effective development of shale reservoirs. In the early studies of fluid migration in fractures, the influence of fracture surface morphology was generally ignored, and the fracture was usually equivalent to a smooth parallel plate model [15,16,17,18]. In order to understand the characteristics of fluid migration more accurately, the characteristics of the fracture surface morphology cannot be ignored. Only one single parameter was usually selected for the characteristics description of fracture surface morphology in specific applications [19,20,21,22,23,24]. This research will provide a reference for fracture description in other unconventional reservoirs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
