Tracking Condensate Banking in Tight Gas Reservoirs Through Well Test Analysis: Right Well Test Design Leads to Factual Reservoir Characterization

Abstract

Abstract Understanding gas condensate reservoirs require comprehensive data acquisition efforts to collect representative PVT samples, measure the effective reservoir permeability and characterize reservoir behavior through well test. Right well test design is key in tight gas reservoirs to reveal all flow regimes and characterize reservoir to have valid FDP formulation including well trajectory design, well completion design and well locations and proper facility sizing. Well test design was done and updated in appraisal to reflect condensate banking in tight reservoir with moderate condensate gas ratio (CGR). The main objective was to measure the well deliverability and reservoir characterization to get condensate banking fingerprint (signature) on pressure derivative in Modified Isochronal Test (MIT) section. This design allows to measure the permeability and radius of impaired region due to condensate banking, while extending test enough allows to measure gas zone permeability as well. A single well radial model (SWRM) was constructed to reflect the condensate banking in simulation model as well. The log data been up-scaled to well test data in free gas zone to analyze the flow behavior of condensate banking in near-wellbore. The condensate bank radius was estimated for different test rates in MIT test. The estimated permeability of condensate bank at different flow rates (and draw-down) are different as per expectation. This is due different saturation at different draw-down based on liquid drop-out. The permeability of single-phase gas zone (far from near-wellbore) is constant in all flow periods of MIT consistently. The results from well test is in perfect agreement with up-scaled single well model. The wellbore hydro-dynamic is modeled using transient well models (OLGA application) and showing liquid loading in long term which suggest to couple the model with transient model to consider the impact of liquid hold-up in the wellbore for proper completion design, well trajectory design and production profile forecast. The liquid drop-out from PVT analysis was used to estimate the saturation near wellbore at each pressure and then from different draw-down periods the effective permeability of each test period correlated to this saturation. This resulted to estimate relative permeability from well test and PVT data (CVD test) which is more reliable due to extra-large scale compare to core analysis tests.