Single well injection withdraw (SWIW) - based tracer test approach for in-situ permeability estimation in an enhanced geothermal system

Efficient estimation of near-wellbore permeability is critical for evaluating fracturing effect and updating fracturing plan. However, due to technical or cost constraints, there is still a lack of methods for in-situ testing and estimating near-wellbore permeability in deep geothermal reservoirs. Considering that the hydraulic fracturing is often associated with injection breaking and back drainage to control the reservoir pressure, this study proposes a single-well-injection-withdraw-based tracer test approach and two permeability interpretation methods based on numerical and analytical solutions, which allow in-situ permeability estimation at low cost. Implementation of the proposed method at a realistic enhanced geothermal system indicates that the numerical interpretation method can still reasonably estimate near-wellbore permeability under the condition of incomplete tracer breakthrough curve in the single well injection and withdraw test, but the computational efficiency is low. Once the tracer breakout curve is relatively complete (i.e. the peak tracer concentration is monitored), the analytical method can be used to quickly estimate the permeability. However, the analytical method cannot accurately consider the long-distance tracer migration process inside wellbore and the influence of dispersion on the tracer breakthrough curve, hence the accuracy is relatively low. The numerical and analytical permeability estimations are at the same order of magnitude. The results suggest that in addition to the numerical method, the analytical method can still be used as an effective method for in-situ rapid permeability estimation. The proposed methodology may provide a new tool for in-situ permeability estimation in deep geothermal reservoirs.