Fracture orientation

Fig. 5. Diagram showing lithology, fracture frequency, fracture orientation and rock strength of Fuglen Formation in (a) well 7321/9-1, (b) well 7219/9-1, (c) well 7120/2-2, (d) well 7120/6-1, (e) well 7120/12-1 and (f) well 7228/9-1.

Fig. 6. (A) Location of the mapped foreshore transect (see Fig. 5) the Main Limestone is exposed above in a 15-20 m cliff section 175 m south of the foreshore. (B) Map of dolomite-cemented fractures on a 100 m x 20 m transect some fractures extend landward of the transect. (C) Summary of fracture orientations measured across the transect. (D) Summary of fracture dimensions measured across the transect.

Neretnieks 1993) formulated a simple channel network model that does not use detailed information on aperture variations and fracture orientations. It uses information obtained from hydraulic measurements in boreholes on the flowrate distribution and the frequency of conductive fractures found in the boreholes. The model assumes that every measured flowing fracture in a borehole represents a channel with constant properties... 

The stress-strain behaviour of the rock, including fracture formation, is a crucial component of the aperture changes. As mentioned before the deformation normal to the fracture is considered in equation (S) in order to obtain aperture changes. If an elastoplastic model is considered for the rock mass behaviour, fracture initiation can be associated with tension stresses. Fracture orientation is sensitive to the stress tensor orientation so the plane where the minimum principal stress (compression positive) occurs defines the plane of fracture formation. 

Microseismic monitoring is currently the best available method for obtaining three-dimensional information about reservoirs and fracture systems at locations remote from boreholes. The primary problem of the method is its location accuracy. When located with conventional location algorithms, the events are frequently seen to be distributed as a cloud with little macro- or microstructure. It is difficult to meaningfully correlate such images with logging data of existing wells. Therefore, information on detailed reservoir structure, fracture orientation, and hydraulic behavior cannot be obtained from the application of conventional microseismic location techniques. 

Figure 1. Basic mechanisms of stress induced permeability change in fractured rock, (a) normal closure/opening, (b) shear dilation/contraction, (c) effects of fracture orientation in multiple fractures.

Fracture orientation is assumed to follow a Fisher law. Average dip dip direction as well as the Fisher coefficient (kf) has to be given for the different fracture sets ... 

Tenzer, H., Schanz, U., 1997. Development and characterization of HDR heat exchanger. Reprocessing of fracture orientation in drill hole GPK2 ami evaluation of production logging data in drill holes GPKl and GPK2. Periodic report from SWBU, 01/02/96-31/01/1997. 

Directional properties also occur in coal and these properties can affect the direction of flow of gases. For a particular coal seam, analyses of natural fracture orientation, directional permeability, directional ultrasonic velocity, and directional tensile strength (Berenbaum and Brodie, 1959 Ingles, 1961) may disclose distinct coal structures that are important for gas flow through the coal (Skawinski et al., 1991 Puri and Seidle, 1992). 

An alternative method is the freeze-etching technique [24, 25], which consists of producing platinum shadowed replicas of fractures created in rapidly frozen biological systems or lyotropic liquid crystals. The fracture orientation is somewhat haphazard, but occurs preferentially within the paraffinic level of the bilayers. These methods offer the possibility of viewing bilayers directly and preparing stereoviews. Beautiful pictures of liquid crystalline DNA, both cholesteric and hexagonal, have been obtained, but individual molecules are not easily resolved. However, the director distribution can be deduced from the images [26],... 

Milodowski, A. E, Gillespie, M. R., Shaw, R. P. Bailey, D. E. 1995. Flow-zone characterisation Mineralogical and fracture orientation characteristics of the PRZ and Fleming Hall Fault Zone area boreholes, Sellafield. Nirex Science Report No. SA/95/001. 

Aligned ellipsoids can be used for modelling of fractured rocks with a preferred fracture orientation (Sen et al., 1981). Equations can be adapted from Section 11.1.4. 

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