Up to now the well performance department within Total Exploration and Production Netherlands (TEPNL) base the assessment of well inflow performance on experiences in the field. No tools are available to systematically monitor and assess the reservoir-completion-tubing performance in the longer term (years). This makes that normal production decline cannot be discriminated from abnormal production decline and productivity decline over long periods of time cannot be observed. The well management process is complicated by the large number of small reservoirs operating in different circumstances. As a result well performance interventions have largely become a remedial activity rather than a pro-active way of increasing production. In this thesis we will discuss the development of two tools that will allow the performance engineers to monitor all 52 TEPNL productivities over the entire period of time digital production data is available. Problematic wells are selected based on their initial productivity and their current productivity. Productivities are determined using Forchheimers correlation. Tagged well are coupled to an appropriate analytical skin model, depending on the well configuration. Evolution of certain parameters that are identified as being impactful on the PI of the specific are calculated. Certain mechanisms have been proposed which cause well performance deterioration. The root cause for the decline is interpreted based on well historics, surface measurements of salinity and the evolution of PI. Finally, when a cause has been established and it appears to be skin related an intervention can be proposed and potential production gains can be estimated. The new tools can also be used to review past interventions in a systematic and simple manner. At this moment well interventions are not or hardly reviewed on their impact. The tool can now help to quantify the problem, as well as give an objective measure of the success of past interventions. The approach proposed in this thesis is new, and only limited data is available to validate the approach. Some promising results are observed based on the 4 interventions done in the past as well as well historics currently available. At this stage, the method tags an additional 9 wells as declining faster as expected. 4 of which are suspected to be related to skin buildup, 1 to water invasion, 1 to interference with another well and 1 due to tubing damage. The remaining 2 wells could not be linked to a single specific cause, 1 well is either suffering from salt deposition or water advancement, while the other either salt deposition or tubing damage.