Fracture flow

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-... 

Using the criteria referred to in the introductory section, the deposition rate constants given in Table II can be used to estimate transit times necessary to achieve equilibrium in laboratory or field fracture flow studies For example cesium sorption from GGW in a 100-ym aperture fissure in unweathered Lac du Bonnet granite requires a minimum water transit time of 3 d for site 1, and 12 d for site 2, in order to be able to assume equilibrium sorption. Water transit times of the order of hours will produce only tailing. Transit times required in brine groundwaters are an order of magnitude higher than those in GGW. 

Fig. 12.27 Surface morphological features of mLLDPE (ExxonMobil Exceed 350D60) extrudates obtained at 160 °C with a tungsten carbide die D — 0.767 and L — 25.5 mm just above and in the sharkskin melt fracture flow-rate region. [Reprinted by permission from C. G. Gogos, B. Qian, D. B. Todd, and T. R. Veariel, Melt Flow Instability Studies of Metallocene Catalyzed LLDPE in Pelletizing Dies, SPE ANTEC Tech. Papers, 48, 112-116 (2002).]...

The above evidence establishes that fracturing and seismic behavior can extend well into the zone of mid to lower crustal metamorphism at rock pressures of —0.5-1 GPa. Veins preserve a valuable record of this brittle deformation they are fractures in which mineral mass has been deposited. The most common vein-forming minerals are quartz, calcite, and the feldspars, but a huge variety of other minerals are also observed. Fractures tend to focus flow, because they are zones of elevated permeability. Fracture flow is commonly approximated using the well-known expression from fluid mechanics for laminar flow between two parallel plates (e.g., White, 1979). For a set of parallel fractures, the flux is approximated by (e.g., Norton and Knapp, 1977) ... 

Fracture flow and fracture cross flow experiments... 

The tests were conducted in three different fracture flow cells. All three devices allow the measurement of fracture flow and bulk flow and normal and shear displacement. 

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). 

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. 

Fig. 9. Fracture flow versus shear displacement large scale polyaxial testing.

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

Stress dependent fracture flow experiments on various rock types and different sample sizes have... 

The sensitivity of the hydraulic conductivity and other transport properties of discontinua (fractured media) to normal stress is typically substantially greater than that of continua (unfractured media). The stress-sensitivity has been demonstrated in numerous studies of fracture flow (e.g.. Gale, 1982). Natural fractures are a suspected cause of anisotropic water-flooding with a maximum rate of flood front advance approximately in the direction of the maximum horizontal stress (Heffer and Dowokpor, 1990). Natural fractures were recognised as significantly contributing to Clair well productivity (Coney et al., 1993). These fractures are aligned with the present day direction of the maximum horizontal stress in at least one of the wells in the Clair Field. 

The potential to extend the proposed approach to model hydraulic conductivity on rough fracture surfaces (Or Tuller, 2000), and to model the combined matrix and fracture flow in fractured porous media (Or Tuller, 2001) is illustrated in examples. 

Neretnieks, I. 1983, A note on fracture flow dispersion mechanisms in the ground. Water Resour. Res. 19 364-370. 

Successful fradure acidizing treatments do not depend solely on good fluid-loss properties (30). Adequate fracture flow capadty must be established by the add system used. The quantity of rock removed and the pattern in which it is removed from the fracture face are important. Fracture flow capadty is dependent on the nature of the rock and the characteristics of the add, such as add type, volume, and concentration. Other factors that lead to increased fracture flow conductivity include foam quality and pumping rate. As long as the foam is stable, foamed add of any quality increases the fracture flow conductivity when compared with non-foamed adds. As well, increases in total treatment pumping rates achieve better fracture conductivities because of greater acidized fradure lengths. 

Foamed stability afreets add-etched fradure flow capacity in the same way that it affects fluid loss control. By indeasing foam stability, a substantial indease in fradure flow condudivity will occur. By indeasing the foam stability, the pattern of rock removal is more effedive without overetching the fradure face (30). Using lower quality foams, gelling the reaction phase and indeasing the viscosity of the foam achieve maximum fracture flow capacity. 

Harris (37) determined by experimentation that fracturing foam fluid bubble sizes varied from 300 to 1200 fjtm with a size distribution varying by a factor of 10. Because of the narrow size distribution of fracturing foam bubbles and the small bubble size in relation to the fracture-flow passages, foams can be considered to be homogeneous. Density is a function of temperature, pressure, and quality. 

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