The characterization of high clay volume reservoirs is a challenge in terms of cut-offs determination, saturation modeling, and simulation setup. These can be even more complicated when it incorporates zero water production from the transition zone. In transition zone, both hydrocarbon and water are expected to move. However, dry hydrocarbon production from transition zone is a common phenomenon observed in many parts of the world. Modular Formation Dynamic Tester (MDT) and Drill Stem Test (DST) in three (3) appraisal wells in a high clay volume sandstone reservoir show no evidence of water production in spite of the long perforation interval just above the contact. This could be explained by different reasons depending on the type of reservoir lithology and mineralogy. One of the common reasons in sandstone reservoirs including this case is the presence of Smectite clay mineral in shale, which can immobilize large amount of water. There are many challenges in characterization and modeling of this high clay volume, dry producing gas reservoir. For instance, how to estimate the amount of mobile and immobile water saturation in the transition zone, how to incorporate the capillary pressure (Pc) data in simulation while still maintaining the production performance, and whether or not the potential reserve and flow characteristics can be captured if petrophysical cut-off applied into the model. This paper will illustrate the case study in characterizing and building the dynamic model with immobile water in transition zone whereas the mentioned challenges are addressed. A novel method is presented to construct the model to estimate the total immobile water saturation using core and log data, and different approaches to initialize the model while evaluating the impact of Pc on reservoir performance are also further discussed.

Production Data Analysis (PDA) has been widely accepted as a valuable analytical tool for well performance evaluation, production forecasting and reservoir characterization. It is fast, practical, and inexpensiveand it can answer many questions about the connected volume to the well, flow regime, average permeability and skin, as well as any boundary within the radius of investigation of the well. It becomes even more important in the case of complex systems such as finely laminated sand reservoirs, or highly heterogeneous multi-stacked reservoirs where sometimes numerical simulation model miscarries in predicting the reservoir performance. Analytical approaches for PDA are variants and require different levels of details in the input. Each is established based on certain assumptions and concepts, and comes with specific limitations. Despite overlap amongst the various methods, each has an advantage in particular application over the others. Therefore, one must be vigilant to use each method for the right purposes in addition to confirm the results and unveil possible uncertainties through using several different methods. This paper integrates basic production and reservoir data through different platforms and methods. Diagnostic plots, General Material Balance (GMB), Pressure Transient Analysis (PTA), deconvolution, nodal analysis, Rate Transient Analysis (RTA), and Flowing Material Balance (FMB) are extensively used to explain the reservoir behavior through PDA. It validates RTA and FMB as an approach for reservoir characterization and reserve estimation without the need to shut-in the well, and defer the production. The benefit of continuously monitoring Flowing Bottom Hole Pressure (FBHP) using Permanent Downhole Gauge (PDG) and applying deconvolution to detect well interference and reservoir boundaries is also discussed. We have also looked at the limitation and advantage of each method and how the integration of those can provide a full picture and enhance the results. We have studied several gas fields. The results of analysis provided an accurate perception and understanding of reservoir behavior and characteristics, well interaction and interference, potential for infill wells, production issues and well constraints, estimation of the connected volume, and eventually led to generation of a reliable analytical reservoir model for the production forecast. The estimated connected volume was tested and proved to be reliable based on infill drilling. The workflow focuses on examining the data quality, confirming the validity of work, and achieving the maximum possible insight through integration of different analytical methods. An integrated workflow is introduced for PDAand successfully applied on different cases of highly heterogeneous conventional gas reservoirs with huge complexities. The paper demonstrates one of the case study as example. The proposed workflow shows to be very powerful particularly when large volume of data from pressure downhole gauges (PDG) is available. It saves significant time for the study team in determining the potential value of a project.