Fractures shear slip

ESTIMATION OF CRITICAL PORE PRESSURE FOR SHEAR SLIP OF FRACTURES AT THE SOULTZ HOT DRY ROCK GEOTHERMAL RESERVOIR USING MICROSEISMIC MULTIPLETS... 

CALCULATION OF CRITICAL PORE-PRESSURE FOR SHEAR SLIP OF FRACTURE... 

We estimate distribution of critical pore-pressure of fractures for shear slip during hydraulic stimulation. 

The estimated critical pore-pressure for shear slip suggests that the fluid pressure in fractures is higher value near the fractured zones 1 and 2 around 2,900 m, and declines as the fractures are away from the zones. 

Figure 5. Calculated critical pore-pressure for shear slip of fractures versus depth of estimated fractures. The zone of permeable fracture, which are detected by well loggings are indicated by shaded rectangles.

It is considered that some fractures opened with increasing pore-pressure maybe after shear slip because the maximum wellhead pressure is about lOMPa. However, Mode I fractures can not radiate seismic events having enough energy, and we can not detect these seismic events. Therefore, we consider only shearing fractures for estimation of critical pore-pressure using induced microseismic events. 

A recent bond strength model proposed by Chen and Teng [47] combines the fracture mechanics analysis with experimental data and provides a better prediction of the basic parameters and Pu. The model is a modified form of the model originally proposed by Yuan and Wu [45] and Yuan and co-workers [46] and based on a shear-slip behaviour of FRP plate to concrete as shown in Figure 5.15. The critical slip values of dj at peak shear stress and df at failure are taken as 0.02 mm and 0.2 mm, respectively, and the following forms are proposed for and P, ... 

De Gennes (2007) has constructed a model for slippage planes in a sheared melt, based on a balance between reptation bridging and shear debonding (slip stick model). He proposed that slippage occurs on solid walls either at the container surface or on dust particles floating in the melt. There is critical stress for slippage, approximately equal to Ys of the plateau modulus, which means that melt fracture is expected at moderate stresses. 

Polymer chains anchored on solid surfaces play a key role on the flow behavior of polymer melts. An important practical example is that of constant speed extrusion processes where various flow instabilities (called sharkskin , periodic deformation or melt fracture) have been observed to develop above given shear stress thresholds. The origin of these anomalies has long remained poorly understood [123-138]. It is now well admitted that these anomalies are related to the appearance of flow with slip at the wall. It is reasonable to think that the onset of wall slip is related to the strength of the interactions between the solid surface and the melt, and thus should be sensitive to the presence of polymer chains attached to the surface. 

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