| Title | Numerical Pressure Transient Analysis of a Low Permeability Well with Water Hammer Effects During Injection Falloff Test: Belgium |
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| Authors | Azhari S. ADIPUTRO, Sadiq J. ZARROUK, Richard J. CLARKE Virginie HARCOUËT-MENOU and Stijn BOS |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Deep geothermal well, fractured reservoir, PTA, numerical model, injection fall-off test, fractional dimension, water hammer. |
| Abstract | Deep geothermal wells and geothermal wells targeting naturally fractured/fissured reservoirs often encounter low matrix permeability in the target reservoirs (pay zone). In some cases, extended pressure fall-off data of such wells display oscillations that cannot be easily interpreted by using the existing analytical pressure transient analysis (PTA) methods. Additionally, water hammer effects resulting from the shutting off the well are sometimes observed immediately after valve closure. A new numerical PTA framework using the TOUGH2 simulator (Pruess, Oldenburg, & Moridis, 1999) was developed to analyse wells with such a typical behaviour. The approach was applied to a case study in Belgium (well MOL-GT-03) for which extended injection-fall-off well test data were analysed. A 1-D numerical radial model with a fractional dimension (fractal) grid structure was set up. A PyTOUGH scrpt (Croucher, 2011) was written for correcting the measured wellhead pressure field data to reflect reservoir conditions and for automating the models running and historical data matching (during the injection and fall-off stages). For well MOL-GT-03 the good match between the fractional dimension numerical model and the field data clearly indicated that the low reservoir permeability is dominated by small fractures and not rock matrix permeability. In addition, the water hammer effect (appearing as a sinusoidal wave) visible during the first 90 seconds after shutting down the injection test master-valve (very beginning of the pressure fall-off) was investigated by solving the wave equation. This new approach helps identify the extent of the well reach and provides a new estimate to the distance between the well and the reservoir boundary. |