Drawdown management optimization in overpressured formations is recognized as challenging by reservoir engineers. Well flowback operational procedures can vary widely and have an impact not only in the first months of production but on the long term performance as well. In this study, the results of choke management in more than a hundred horizontal wells in Loma Campana block, located in Vaca Muerta Shale Oil window, will be evaluated to investigate the potential impact on estimated ultimate recovery (EUR) and net present value (NPV).
Using different flowback strategies, production data of wells in the same interval within Vaca Muerta Fm. have been analyzed using diagnostic plots commonly applied in unconventional reservoirs to identify early flow regimes. The evolution of stress over hydraulic fractures have been evaluated as well, which may contribute to a permanent conductivity loss due to hysteresis effects. Several forecasts have been created using Rate Transient Analysis (RTA) to quantify EUR loss due to aggressive choke management and to establish a relationship between drawdown and productivity degradation.
The study found out that an aggressive choke management may cause a reduction in EUR of up to 20%. This can be attributed to a loss in fracture conductivity as a result of geomechanical-related factors. Therefore, an aggressive drawdown management is prone to minimize value, but understanding the tradeoff between the financial benefit due to production acceleration versus loss in reserves (as a result of fracture degradation) is the key issue that will be investigated in this paper. Furthermore, the proposed methodology used to integrate production performance analysis with the economic evaluation has allowed defining an optimum drawdown management for Vaca Muerta wells. Therefore, a standard procedure based on best practices is proposed for managing new wells put on production.
As summary, this work provides evidence of production dependence on drawdown based on empirical data of horizontal wells in Loma Campana Oilfield. Complementing the study with RTA analysis has allowed quantifying the loss in EUR, estimating the effect of fracture degradation and verifying the economic impact. Finally, a workflow is proposed to accomplish optimum pressure decline with the right choke selection over time to optimize well performance.