W ell test, a test to determine the condition of the well based on price permeability thickness (kh) and skin (s). To be able to generate parameter calculation is done manually by applying the applicable formula as well as using a variety of charts required. But sometimes the results of calculations obtained a lot of inaccuracies that have an impact on the conclusions of analysis are obtained. It is due to some inaccuracies in the calculation or chart usage. It required a method that can provide accurate interpretation, Saphir is a software that allows a minimum of inaccuracies. Stages of test wells at the end of the task is done by injecting cold water at fixed rate and measure the pressure and temperature of the wells to determine the profile (ramp) of temperature and pressure. Generally, testing performed several times with the pumping rate different. In the Field X where the research is well done in the development wells Geothermal Project. Data permeable zone, the overall permeability, and its characteristics are useful parameters to provide information about the truth targetting achieved in drilling. Implementation includes measurement of the depth of Well Test (Assessment depth of the well), the measurement slope temperature and pressure in the wells, measurement of Lost Water Test, testing the overall permeability (permeability Gross Test) which consists of Injectivity Test and Fall Off Test which is the subject of this thesis. Of well test can be generated kh and skin (s), which is calculated using the applicable formula and using Saphir as a comparison software. Based on these results it can be concluded that the software Saphir can be applied to the geothermal field