A Unified Approach for Quality Control of Drilled Stem Test (DST) and PVT Data

Finding a representative fluid in a hydrocarbon reservoir is crucial for integrated reservoir management. In this study, a systematic approach for screening and selecting consistent fluid samples in a reservoir was developed. The model integrated quality control (QC) of well conditioning before sampling, QC of PVT data, thermodynamic modeling and compositional gradient within a reservoir. Well and separator conditioning were examined as essential steps before sampling at equilibrium conditions. Sampling criteria were deduced according to available data, sampling standards, and tolerance of field measurement devices. Then, PVT data of consistent fluid samples were carefully screened for efficient phase behavior studies. This model suggests that thermodynamic modeling and equation of state (EOS) tuning be performed on screened fluids using only consistent experimental data. The proposed model was implemented on PVT samples of a supergiant gas condensate reservoir in the Middle East. Results show that only 10% of collected samples are at equilibrium, good candidates for PVT studies. Also, ±0.1% change in composition of C12+ causes ±300 psia change in dew point pressure, revealing no substantial difference between validated samples for the reservoir under study, and one representative fluid suffices throughout the reservoir.