The main objective of the third phase of the project 680 was to develop a more phys-ics based numerical approach to simulate the proppant transport with the considera-tion of settling effect in the 3D FDM program “FLAC3D”. Through the adaptive calculation and the comparison with the calculated results of the analytical model the new computing concept was validated. Then the fracture closure in the developed model was also verified. After the verification, two numerical applications are illustrated. The first one is the numerical modelling of a hydraulic fracture operation in a tight gas borehole in the North German Basin, in which the fracturing treatment was done in the 1980s. As the conclusion of this simulation, it could be said, that the stable state of the proppant placement is achieved. The second numerical example is the fracture operation at Frac5 in the tight gas reservoir XYZ2. As introduced in the report of the second phase, the hydraulic fracturing was operated in 2009 with four stages respectively: perforation, injection test, data and main fracturing. Both issues caused problems on the tight gas fracture/wellbore connections.

This volume contains papers presented at the 3rd Sino-German Conference, Underground Storage of CO2 and Energy. It details different perspectives on  recent research to reduce greenhouse emissions while ensuring a sufficient supply of clean energy.

This volume contains papers presented at the 3rd Sino-German Conference, Underground Storage of CO2 and Energy. It details different perspectives on  recent research to reduce greenhouse emissions while ensuring a sufficient supply of clean energy.

This volume contains papers presented at the 3rd Sino-German Conference, Underground Storage of CO2 and Energy. It details different perspectives on  recent research to reduce greenhouse emissions while ensuring a sufficient supply of clean energy.

The main objective of the fourth phase of the project 680 was to optimize a complete fracturing operation in horizontal wellbores for maximum productivity. Thus, a workflow and numerical tool chain Frac- and Frac-Produ simulators were developed with consideration of the thermo-hydro-mechanical coupling for the history matching and optimization of stimulation and production, respectively. After the verification of the developed simulators, a full 3D reservoir model was generated based on a real tight gas field in North German Basin. The simulated fracturing results are comparable with the treating pressure measurement, while the simulated gas production rate has the similar tendency to that of in-situ measured data. The numerical sensitivity analysis results show that the influences of proppant type on fracture geometry and fracture conductivity is much larger than that of the fluid viscosity, while the influences of the injection time are the smallest. The optimization simulation results show that the injection rate is not the higher the better. The fracture spacing should also not be too small. Thus, there is no universal criterion to determine the optimal number and spacing of the fractures, should be analyzed and decided from case to case.