| Title | Investigating Well Connectivity Using Ionic Tracers |
|---|---|
| Authors | Matthew W. BECKER, Krystle REMMEN, Paul W. REIMUS, Georgios P. TSOFLIAS |
| Year | 2013 |
| Conference | Stanford Geothermal Workshop |
| Keywords | tracer, lithium, bromide, fractures |
| Abstract | Fluid circulation in geothermal reservoirs is often impacted by an uneven sweep of water between injection and pumping wells. Poor sweep efficiency may lead to poor hydraulic connection or, at the opposite extreme, short circuiting of flow and premature thermal breakthrough at an extraction well. Multiple ionic tracer tests have been proposed as one method by which reservoir conformance issues may be identified. Inverse transport modeling of non-reactive anionic and reactive (exchanging) cations, for example, has been used to extract surface area to volume ratios from multi-well field tests. Inter-well tracer tests were conducted at the Altona Flatrock Fractured Bedrock experimental site during the Summer of 2011. Lithium was used as a reactive tracer and bromide the non-reactive tracer (verified with deuterium oxide). Separation between cation and anion tracers in the breakthrough was minimal except in cases where tracer was circulated between wells with poor hydraulic connection. The larger separation of ionic tracer breakthrough was generally, but not always, consistent with larger residence time of the conservative tracers, which presumably also corresponded to flow pathways with larger surface area to volume ratios (i.e., smaller fracture apertures). The hydraulic structure of the single fracture reservoir has also been characterized using harmonic cross-well slug tests and saline tracers imaged using ground penetrating radar. Thermal exchange between fracture and matrix has been evaluated by circulating hot water in the fracture and measuring temperature exchange with the matrix. We present interpretation of the tracer breakthrough with reference to these companion experiments and theoretical modeling. |