Tengiz is a supergiant oil field with 30 billion STBOOIP located in the Pricaspian basin of western Kazakhstan. The field produces from an isolated carbonate platform of Devonian to Pennsylvanian age, with a flat-lying central platform surrounded by a relatively steep depositional slope. Fractures are common and significantly enhance productivity in the outer platform and slope. Understanding the flow behavior of the matrix-fracture system is a key to successful field development. The characterization of naturally fractured reservoirs is especially challenging due to a high degree of heterogeneity and uncertainty. When modeling carbonate reservoirs - and particularly those where fractures play a significant role - we lack a consistent and robust methodology for utilizing dynamic data collected from pressure buildup tests, production logging, pulse tests between wells, and from increasingly deployed permanent down-hole gauges. Instead, this data, which contain rich information about wells and reservoir, is often neglected in the conventional production history matching. This project aims to fill this technology gap to better characterize fractured carbonate reservoirs. We apply numerical well testing techniques with discrete fracture modeling to understand and characterize the fracture-matrix properties. The effective utilization of pressure transient data should narrow the uncertainty, improve the characterization, and help optimize field development. First the numerical solutions from both Discrete Fracture Models (DFM) and Dual-Porosity Models using numerical reservoir simulator were validated against analytical pressure-transient solutions for a dual-porosity system. Next a systematic workflow to integrate single-well buildup test data into numerical models was developed based on synthetic case study results. Finally the new method was applied successfully to a sector model of Tengiz field. Some preliminary techniques were also developed to honor pulse test data and analysis results between wells with numerical simulation models. Continuous efforts are being made to improve field-scale reservoir simulation models using dynamic and static data of fracture-matrix systems for more accurate field performance forecast in Tengiz. The successful integration of all types of data would have a big impact on reservoir management by potentially minimizing the number of wells to be drilled, maximizing the production from each well, and substantially increasing reserves.