In the creation of Engineered Geothermal Systems, water is typically injected at pressures just below the least principal stress of the formation in order to open, through shear failure, partially sealed fractures that intersect the wellbore. Once a fracture (or set of fractures) is created, however, the stimulation fluid flows into the newly created fractures and is unavailable for subsequent fracture stimulation elsewhere along the wellbore. Fluid diversion agents are compounds that can serve to temporarily plug newly stimulated fractures and make the injected water available to stimulate new fractures. The diversion agent is subsequently removed to allow for flow from those previously sealed fractures. The in situ precipitation of calcium carbonate was studied for use as a diversion agent in Engineered Geothermal Systems. Urea thermally decomposes starting at about 150oC to ammonium and carbonate. In the presence of CaCl2 the carbonate subsequently precipitates to form CaCO3. This series of reactions was studied using a high temperature/pressure flow reactor over the range of 140-190°C. Results indicate CaCO3 formation increases nonlinearly as a function of temperature.

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