This paper explores the strong observed correlation between liquid yield (Condensate Gas Ratio) profiles and choke management in the gas condensate wells operated across the Eagle Ford and Duvernay.
Forecasting of condensate production for liquid-rich wells in nano-Darcy reservoirs is a challenge due to its deviation from conventional expectations suggested by classical PVT, with variations even when the well is operating above the saturation point. Multiple hypotheses have been introduced in the recent years to explain the anomaly, including molecular sieving, adsorption, and fluid heterogeneity. This paper looks at how drawdown strategy has a direct and key impact on liquid yield.
The study has included production profiles of over a hundred wells (initial CGR ranging from 50 to 250 STB/MMscf) in both Eagle Ford and Duvernay. These profiles were analyzed against the respective drawdown strategy (evolution of choke size) and flowing bottom hole pressure history. In addition to the single well evaluation, production CGR from pads with staggered wells in the Eagle Ford were examined to understand whether vertical fluid heterogeneity within the net pay can potentially alter the CGR behavior. The correlation between initial production CGR (CGRi) and the average compound depth of the horizontal extent of these wells along the navigation zone was also investigated to contribute to the staggered wells' analysis.
The condensate yield has been observed to change above the phase envelope depending on the choke strategy. While a stabilized (relatively constant) choke size promotes a stabilized CGR value (at CGRi), a drawdown strategy that follows a rapid choke ramp-up from the onset of production causes a decreasing trend for CGR starting from CGRi, above the saturation point. The CGR declination continues with pressure drawdown until it reaches a plateau when the choke size stabilizes, and a minimum flowing bottom hole pressure is reached.
The relationship between drawdown strategy and the CGR trend is a valuable information that can be leveraged in optimization of the field development design and operations. Once the CGR profiles are established based on a planned choke schedule, these profiles can be utilized to generate accurate forecasts of condensate recovery. Conversely, drawdown strategy can be optimized considering enhancing liquid yield at the surface to maximize revenue generation.
