| Title | Mechanical and Hydraulic Aspects of Rock-Proppant Systems: Experimental Approaches and Implications for Reservoir Treatments |
|---|---|
| Authors | Reinicke, A., Zimmermann, G., Blöcher, G., Naumov, D., Stanchits, S., Dresen, G., and Huenges, E. |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Enhanced Geothermal Systems, gel-proppant treatment, fracture performance, fracture face skin |
| Abstract | Reservoir stimulation technologies are standard in the hydrocarbon industry to overcome formation impairments for more than four decades (Economides and Nolte 2000). In the context of Enhanced Geothermal Systems (EGS) (Gérard et al., 2006; Calcagno and Sliaupa, 2008) the technologies are adopted to enlarge the access to the heat in the reservoir and to stimulate low permeable formations. The application of hydraulic fracturing to hydrothermal reservoirs in order to create an EGS requires a technique that is able to produce considerable higher amounts of fluids than is required for production from hydrocarbon reservoirs. A fracture - perpendicular to the direction of minimum principle stress – is created due to pumping of fluids at sufficiently high pressure through the wellbore into the formation. In general, the availability of the newly created fracture area is limited for production if no propping agent (sieved sands or ceramic spheres) is placed in the fracture to keep it open. These propping agents interact mechanically with the reservoir rock. In particular, proppant embedment and proppant crushing leads to fines production and can impair the fracture performance. In order to achieve sustainable long term productivity from a geothermal reservoir, it is indispensable to understand the hydraulic and mechanical interactions in the reservoir rock - propping agent - system. Consequently, a reservoir simulator was set up in the laboratory and different propping agents were investigated. Numerical and analytical modeling of the reservoir rock - propping agent – system identified high stress concentrations, which are responsible for the observed mechanical damaging effects. The modeling approaches highlighted mitigation strategies to attenuate proppant embedment effects, to reduce fines production and to avoid mechanically induced impairments of fracture performance. A high strength ceramic proppant type turned out to be the best candidate for the hydraulic stimulation operations in the geothermal reservoir Gross Schoenebeck, Germany. Subsequently, the hydraulic stimulations in the Lower Permian sandstones of Gross Schoenebeck reservoir were successfully performed. |