Fractures intersections

Flow in undisturbed rock normally is radial toward a site of lower pressure (the wellbore). The fracture crack created by high pressure injection usually forms perpendicular to the least principle stress that exists in the rock. The induced fracture intersects and disrupts the radial flow pattern such that flow becomes linear and more direct to the well. This phenomenon has been intensively examined and discussed by authors working in the discipline of rock mechanics as applied to hydrocarbon reservoirs. Hydraulic fractures created in oil and gas wells grow mainly vertically, parallel to the wellbore as depicted in Figure 1 and extend on either side of the perforated wellbore as "wings11 (7-11). 

I ig. 5-29. Relation between fracture intensity and gas leakage (A) plan showing lineament, fractures and gas sample sites (B) distribution of fracture intersections with distance from lineament (C) distribution of anomalous gas sample sites with distance from lineament (reproduced with permission of the American Association of Petroleum Geologists, whose permission is required for future use, from Richers et al 1986, AAPG Bull., vol. 70, no. 7, Fig. 13, p. 885, AAPG 1986). 

Transport of stable isotopes in a moving fluid phase is called advection. Here infiltrating fluids move the isotopic species of interest. Fluid flow is restricted to connected pore spaces. The amount of connected pore space and the manner of connection determines the permeability of a rock. Mixing of stable isotope ratios by a flowing fluid on grain boundary intersections, micro crack intersections, and fracture intersections results in dispersion. Dispersion is similar to diffusion (at least mathematically), since this is a mixing process. 

In the appendix the solution of the equations for flow and matrix diffusion in a channel with variable properties is derived. The solution shows that one can follow a constant stream q through a path with arbitrarily varying velocities, widths and material properties. When one attempts to follow a packet of water through the network the packet, however small, will have to divide at fracture intersections. If it is a well-mixed stream it will divide into the outgoing streams in proportion to the total flowrates in the outgoing streams. 

This paper focuses on a repository located in sparsely fractured rock with a hydraulic conducting horizontal fracture intersecting the vertical deposition hole (Figure lb). The analysis for the case of a homogenous intact rock (Figure la) is presented in Millard et al., (2003). This paper... 

In Phase C (Rutqvist et al. 2003), the research teams performed calculations for the case where one or several water-bearing discrete fractures intersect the repository. As in Phase B, the temperature field shows nearly no difference between THM, TH, TM calculations and is very similar to the one in Phase B. The fracture(s) accelerates the resaturation of the buffer/backfill and prevents the desaturation of the rock mass. From a mechanical point of view, the fracture(s) constitutes a zone of weakness and results in a more extended zone of damage as compared to the homogeneous scenario. TH or THM calculations produce very similar pore pressure fields. With respect to the stresses in the buffer, the conclusions are similar to the homogeneous case, with a predominant effect of pore pressure on total stresses, compared to the thermal stresses. 

A series of numerical experiments are conducted to calculate the equivalent permeability of the model under various stress conditions. The flow through fractures is calculated by the Cubic law and blocks are treated as impermeable medium. Mass conservation is assured at each fracture intersection and in domains between them, through an iterative process. Lateral sides of the model are set impermeable and x- and y-directional permeability with the specified hydraulic pressure boundary conditions are calculated by the following equations. 

Hydraulic tests were conducted at 356-m depth on a single fracture intersecting a 500-m deep borehole in crystalline rock at the Rock Mechanics Laboratory of Lulea University of Technology in Sweden. Three types of hydraulic tests were included (i) pulse test. 

Velocity variations (perturbations) at the fracture intersections could cause chaotic advection, as well. For example. Figure 4a schematically depicts... 

Glass, R. J. Nicholl, M. J. Rajaram, H. Wood, T. R. Unsaturated Flow through Fracture Networks Evolution of Liquid Phase Structure, Dynamics, and the Critical In ortance of Fracture Intersections. Water Resour. Res. 2003.39(12), 1352. 

Carbonate rocks are more frequently fractured than sandstones. In many cases open fractures in carbonate reservoirs provide high porosity / high permeability path ways for hydrocarbon production. The fractures will be continuously re-charged from the tight (low permeable) rock matrix. During field development, wells need to be planned to intersect as many natural fractures as possible, e.g. by drilling horizontal wells. 

The life of a component, as measured in a fatigue test, is the number of cycles needed to initiate a crack and cause it to propagate across the wall until it intersects the outside surface or until fast fracture intervenes. 

The PF system creates a fracture network by forcing compressed gas into a formation at pressures that cause stress failure. These fractures increase the formation s permeability. Increased permeability can greatly improve contaminant mass removal rates. PF can also increase the effective area that is influenced by each extraction weU and can intersect new pockets of contamination that were previously trapped in the formation. The ARS PF technology is patented and is commercially available. According to the vendor, it has been used at over 135 federal and private sites in the United States, Canada, Japan, and Belgium. 

Both basalt samples (DC3-3600 and DH5-2831) are composed primarily of glass (40-50 percent) and plagioclase feldspar (35-40 percent). They contain in addition minor amounts of clinopyroxene (3-5 percent) orthopyroxene (1 percent), and opaques (1-2 percent). The relatively unaltered basalt (DC3-3600) possesses several intersecting fractures filled with clay. There are dark gray alteration zones adjacent to certain fractures where a smectitic clay has replaced... 

Graphical solution of the problem of finding the aluminum alloy that will support the maximum load without either yielding or fracture. The intersection at a yield strength of 57 ksi gives the optimum. 

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