Fracture flow results

Fracture flow results from large scale laboratory tests in NGI s polyaxial cell (see Fig. 4) are also presented, and compared to the fracture flow tests conducted in the CSFT cell. The block size for all three tests was 30 x 30 x 40 cm with fracture planes oriented either diagonally (Lagerdorf chalk, 42 x 40 cm) or parallel to the 30 x 40 cm horizontal block sides (both sandstone tests). 

The migration of iron mineral fines, primarily hematite and magnetite, is a common occurrence in portions of the Appalachian Basin. The phenomenon often occurs after well stimulation and can result in the continuing production of iron mineral fines which pose a significant disposal problem. The migration of iron mineral fines through propped fractures can substantially reduce the fracture flow capacity. Many of these are mineral fines are native to the formation and are not formed by precipitation of acid-soluble iron salts present in injection waters during or after acidi-... 

Figs. 6 and 7 show the results from the CSFT fracture flow experiments with Red Wildmoor (RWS) and Yellow Brumunddal sandstone (YBS) samples. Tests on non-fractured RWS and YBS samples resulted in permeability values of 3.5 X 10 cm and 1.0xl0""cm respectively. These measurements are about four orders of magnitude below the total flow measurements. It can therefore be assumed that the measured flow is predominantly due to flow through the fractures. 

In Fig. 18 all cross-flow results from YBS, RWS and LC have been combined in one plot. This is done under the simplifying assumption that the combined effect of factors such as porosity, grain geometry, mineralogy and cementation on the rock strength can represented by the uniaxial compressive strength a, and therefore the normalization procedures applied (o /a and KJK ) allow comparison of results from different rock types. Because of the limited data set available, the only conclusion drawn from Fig. 18 so far, is that the KJK ratio seems to reach minimum values when the effective fracture normal stress approaches two times the uniaxial strength of the intact rock.. 

Based on the results presented, the following factors controlling fracture flow and bulk flow have been identified ... 

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. 

The complex geometry of flow padis in fractured rock results, primarily, fivm rock discontinuities that are present on aU scales, extending from the microscale of microfissures (ammig the mineral components of the rock) to the macroscale of various types of joints and fruits (29, 30). The complexity of the fracture-network geometry can cause either divergence or convergence of localized and nonuniform flow paths in different parts of fractured media, as well as cq>illary barrier effects at the intersection of flow paths. 

Analysis of fracture-flow dynamics. The results of investigations by Su et al. (27) demonstrated phenomena of intermittent flow imder unsaturated... 

The vortex or the circulating stagnant region encompasses a flow cone which becomes unstable with increasing flow rate and eventually fractures periodically as the flow rate is increased further. When the flow cone fractures, the result is melt fracture and the flow is sustained by the intermittent drawing of the fluid from the recirculating vortices. 

Different physical interpretations. Several important points must be emphasized when translating aerodynamics results into petroleum solutions. First, with respect to the preceding comments, the additional circulatory flow associated with the Kutta condition must be subtracted out before airfoil solutions can be applied to flows past impermeable shales. Second, not all aerodynamics solutions contain Kutta conditions the results for fractures derived in Chapter 5, for example, are taken from slender body crossflow theory where circulatory solutions are not needed. Third, in aerodynamics, the airfoil surface is a streamline of the flow having a constant value of the streamfunetion, supporting variable pressure in Darcy fracture flows, the fracture surface is not a streamline, but pressure is (or may be) constant along it. On the other hand, shale surfaces do represent streamlines, although Kutta s condition does not apply. Careful attention to the physics is obviously required. 

Specializing Carleman s results to fracture flow. In our particular... 

Write and validate a general numerieal program to evaluate Cauchy principal value integrals. What kinds of gridding problems arise Compare results with those previously obtained analytically. Use this subroutine as the basis for a general fracture flow simulator you design. 

Thermal Gradients may be measured or calculated by means of heat flow formulas, etc. After they are established it is likely to be found from the formula that for most cyclic heating conditions the tolerable temperature gradient is exceeded. This means that some plastic flow will result (for a ductile alloy) or that fracture will occur. Fortunately, most engineering alloys have some ductility. However, if the cycles are repeated and flow occurs on each cycle, the ductility can become exhausted and cracking will then result. At this point it should be recognized that conventional room temperature tensile properties may have little or no relation to the properties that control behavior at the higher temperatures. 

There is considerable evidence in the thermoset literature that the fracture energy decreases with increasing crosslink density, consistent with the intuitive result that crosslinking inhibits flow. In the limit of very high crosslink density, where for example we approach the structure of diamond, fracture can occur on a single crystal plane such that... 

---