Monitoring and maintenance is a continuous process in the various phases of a well’s life. One of the essential part of monitoring is well testing. Just as a regular medical checkup is advised for humans so is well testing advised for a target formation. Well testing provides a means of obtaining information about the well and the reservoir as well as diagnosing a problem if any is present. The objective for a well test determines the type and design to be carried out. In this study, build-up test was the main focus. Obtaining relevant data in order to characterize a reservoir and determine initial pressure is a major objective of a build-up test. The results required from the tests cannot be directly obtained from the well test data. Hence, the importance of analysis. There are various methods used to analyze well test data such as manual plotting, excel analysis and software analysis. In this study, a build-up test data was obtain from an XYZ field for two dual string oil producing wells (4 wells) and was analyzed using a tool called Saphir. The result from tool showed the properties of the reservoir required for characterization i.e. pressure, permeability and boundary conditions. It was seen that one well has undergone a successful stimulation and the other three damaged with one of them severely damaged. The highly damaged well was recommended for stimulation and the rest was recommended to have future plans for stimulation. Further studies were made to ascertain the effect of stimulation on the damaged wells and significant gain in barrels produced were observed. Well property such as bottom-hole flowing pressure was calculated using the results obtained from the analysis.