Abstract
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.
