| Title | A Numerical Study of the Effects of Cold Water Injection on the Pressure Transient Response and Injection Capacity of Geothermal Wells |
|---|---|
| Authors | Jefferson Villacorte, Michael J O'Sullivan |
| Year | 2011 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | cold water injection, pressure transient simulation, well-testing analysis, inverse modeling |
| Abstract | The current study examines how the formation permeability varies during injection/fall-off tests of various wells and how the injection process affects the injectivity of the well thereafter. Pressure data measured during cold water injection tests were analyzed and simulations were conducted to obtain a match to the data. In some cases the data were divided into separate sections during different rates of injection and during the fall-off phases. Simulation matches of the data were carried out with commercially available well testing software (SAPHIR and AWTAS), and established multiphase, multicomponent numerical codes (TOUGH2 and FEHM). Various model configurations were defined and several well/rock parameter combinations were specified to achieve improvement of fit of the transient data. Inverse modelling were performed utilizing PEST and iTOUGH to achieve further enhancement of correspondence between actual and simulated values. The response and trends of permeability values and other parameters were observed and were correlated with the injection capacity. The analysis was applied to three types of geothermal wells on which injection tests have been performed. These wells were either (i) newly drilled, (ii) had undergone workover or (iii) had experienced stimulation with acid injection or prolonged water injection. The simulated profiles showed that there is noticeable increase in permeability during the actual injection tests but it is slightly diminished again upon termination of the test. Thus there is an apparent improvement in permeability which could result to increase injection capacity but this change is smaller in magnitude compared to the permeability enhancement during the actual test. |