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Combining wavelet transforms with conventional log differential curves is used to identify fractured sections is a new idea. In this paper, we fi rst compute the mother wavelet transform of conventional logs and the wavelet decomposed signals are compared with fractures identified from image logs to determine the fracture-matched mother wavelet. Then the mother wavelet-based decomposed signal combined with the differential curves of conventional well logs create a fracture indicator curve, identifying the fractured zone. Finally the fracture density can be precisely evaluated by the linear relationship of the indicator curve and image log fracture density. This method has been successfully used to evaluate igneous reservoir fractures in the southern Songnan basin and the calculated density from the indicator curve and density from image logs are both basically consistent.

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Economic development has accelerated the consumption of oil, natural gas, coal and other traditional energies, leading to the depletion of traditional fossil fuel resources, heavy pollution and degradation of the natural environment (Dincer and Acar 2015; Li and Xue 2015). Therefore, there is a growing need for clean energy (Fridleifsson 2001). Geothermal energy is one of the most important clean energy options that has attracted growing attention worldwide (Barbier 2011). Geothermal resources have the advantage over traditional fossil fuels of possessing large reserves that are clean and environmentally friendly (Kütahyali et al. 2011; Croteau and Gosselin 2015). An increase in the global use of geothermal resources would reduce the emissions of particulate matter and harmful gases that result from the combustion of fossil fuels (Lior 2010). Researchers have developed and implemented various methods to investigate the potential reserves and exploitation of geothermal resources with promising results. For example, geophysical methods have been employed to predict the geothermal potential of the Baja California Peninsula (Arango-Galván et al. 2015); deep-buried faults in geothermal regions have been successfully identified using microtremor arrays (Xu et al.

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Gas-bearing volcanic reservoirs have been found in the deep Songliao Basin, China. Choosing proper interpretation parameters for log evaluation is difficult due to complicated mineral compositions and variable mineral contents. Based on the QAPF of volcanic rocks using log data and a genetic algorithm. According to the QAPF scheme,

One of the key issues to a successful EGS (Enhanced or engineered Geothermal System) is the creation of a great density of fractures. The detection and characterization of the created fractures is crucial in evaluating the geothermal energy resources in such EGS projects as well as in reservoirs for CO 2 sequestration and storage. Methods to evaluate the fractures after stimulations are few, and limited in application. To this end, an approach to detecting and evaluating the fractures using resistivity data measured at different frequencies was developed in this study. The effects of fractures on resistivity measurements at different frequencies have been investigated as a function of water saturation in rocks with different porosity, permeability and lithology. Different rocks (Berea sandstone, and greywacke from The Geysers geothermal reservoir) were used in this study. The permeability of the samples ranged from 0.5 to over 1000 md for the matrix. The frequency ranged from 100 to 100,000 Hz. It was found that the effect of frequency on resistivity is different in rocks with and without fractures, especially in the range of low water saturation. The validity of the Archie equation depends on the existence of fractures, the frequency, and the range of water saturation. The relationship between resistivity and water saturation did not follow the Archie equation at low water saturation in some rocks with fractures. Models for characterizing different types of rocks with specific fracture patterns have been established using the resistivity data measured at different frequencies and different water saturations.