Fractal study on fault system of Carboniferous in Junggar Basin based on GIS
Fault system is a significant evidence of tectonic movement during crust tectonic evolution and may play an more important role in oil-gas accumulation process than other tectonic types in sedimentary basin. Carboniferous surface faults in Junggar Basin developed well and varied in size and distribution. There are about 200 faults in Carboniferous, and 187 of them are thrust faults. Chaos-fractals theories have been widely investigated and great progress has been made in the past three decades. One of the important conception-fractal dimension had become a powerful tool for describing non-linearity dynamical system characteristic. The clustered objects in nature are often fractal and fault system distribution in space is inhomogeneous, always occurs in groups, so we can describe spatial distribution of faults from the point of fractal dimension. Fractal dimension of fault system is a comprehensive factor associated with fault number, size, combination modes and dynamics mechanism, so it can evaluate the complexity of fault system quantitatively. The relationship between fault system and oil-gas accumulation is a focus and difficulty problem in petroleum geology, and fractal dimension is a new tool for describing fault distribution and predicting potential areas of hydrocarbon resources. Geographic Information System (GIS) is a kind of technological system collecting, storing, managing, computing, analyzing, displaying and describing the geospatial information supported by computer software and hardware. In the last 15–20 years, GIS have been increasingly used to address a wide variety of geoscience problems. Weights-of-evidence models use the theory of conditional probability to quantify spatial association between fractal dimension and oil-gas accumulation. The weights of evidence are combined with the prior probability of occurrence of oil-gas accumulation using Bayes'rule in a loglinear form under an assumption of conditional independence of the dimension maps to derive posterior probability of occurrence of oil-gas accumulation. In this paper, we first vectorize the fault system in Carboniferous of Junggar Basin in GIS software and store it as polyline layer in Geodatabase of GIS to manage and analyze, then calculate the fractal dimension of three types which are box dimension, information dimension and cumulative length dimension using spatial functions of GIS, in the last use weights-of-evidence model to calculate the correlation coefficients in GIS environment between oil-gas accumulation and three types of fractal dimension in order to quantity the importance of fault system.
GIS-based Approach for Measuring the Fractal Box Dimension of Watershed Topography
The fractal dimension measure of watershed topography is the unsubstantial part of topography fractal study, and it is very important for the prediction model of soil and water loss in small watershed. Based on the principle of measuring the fractal box dimension and the character of watershed topography, the approach for measuring the fractal dimension of watershed topography is put forward by the technique of GIS, whose data is from contour line. We operated demonstration research by taking Chabagou watershed as an example. The results show that this approach is fast, exact, credible and can get the fractal box dimension of watershed topography of different scope.
Seismic volume attributes for fracture analysis
Abstract Seismic volume attributes are introduced for the characterization of subtle fault patterns. These patterns are important in understanding the flow behaviour in reservoirs. The seismic attributes are based on neighbourhood analysis of the seismic signal and take 2D or 3D information into account. In the case of fracture systems, attributes such as coherency, that quantify change in the seismic signal are used. Case studies are presented to show the impact of the attribute analysis on the description of reservoirs.