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Lawrence Berkeley National Laboratory Recent Work Title THERMAL EFFECTS OF REINJECTION IN GEOTHERMAL RESERVOIRS WITH MAJOR VERTICAL FRACTURES Permalink
| Content Provider | Semantic Scholar |
|---|---|
| Copyright Year | 2013 |
| Abstract | In many geothermal fields there is evidence for rapid migration of injected fluids along "preferential flow paths", presumably along fractures. The potential for unacceptable fluid temperature decline at production wells as a consequence of large scale injection is of obvious concern to geothermal developers, and methods are needed for evaluating the thermal response of "fast-paths" to injection. One difficulty encountered in analyzing test data is that the geometry, of the flow path( s) may be speculative and ambiguous, leading to unreliable predictions of thermal interference. Fast pathways may often be provided by major vertical or nearly vertical fractures and faults with approximately linear flow geometry. This paper discusses possibilities for characterizing the thermal properties of fast paths by means of different types of tests (tracers, pressure transients, non-isothermal injection). Thermal breakthrough in vertical fractures is examined in some detail, using an idealized model for which an analytical solution is available. The model shows that rapid tracer returns are not necessarily indicative of rapid thermal interference. "Thermal breakthrough predictions can be made from tracer data only, if both fluid residence time and tracer dispersion are taken into account. However, due to the geometric simplifications necessary in analyzing the tracer data, thermal interference estimates on this basis appear questionable. Pressure transient tests can provide additional parameters for thermal interference predictions, but they cannot resolve the problem of non-uniqueness. A more reliable determination of thermal characteristics of fast paths appears possible from non-isothermal injection tests, combined with numerical simulation. We employ a mixed numerical/ semi-analytical approach to model the three-dimensional fluid and heat flow in injection-production systems in vertical fractures, with heat transfer to and from the adjacent rock matrix. Illustrative cal culations of thermal recovery after di fferent References and illustrations at end of paper. injection periods suggest that shutting-in an injection well can prevent unacceptable temperature declines at production wells. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://cloudfront.escholarship.org/dist/prd/content/qt8rk843q5/qt8rk843q5.pdf?t=p0kha5 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
