Evaluating Feasibility of Gas Displacement of Water in an Injector with Limited Entry Liner Completion
Authors: Shandilya Prakalp , Kasina Pratap , Jackson Matthew S. , Pankaj Piyush , Alyan Mohand Ahmed , AlHarbi Manal Saeed 
Published: November 2024

In recent years the use of extended reach drilling wells with ultra long completion intervals (greater than 10,000 ft) have become a regular practice to increase reservoir contact and decrease the number of wells needed to optimally produce oil from massive carbonate resources in the middle east. This approach has been applied for oil producers and injectors, however water alternating gas (WAGI) has not been largely utilized in long lateral wells. Full displacement of the well is critical due to the potential impact of flow conformance as well as the potential for stranded water corrosion.

The intent of the study was to assess feasibility of full displacement of water with gas within a 20,000 ft lateral, limited entry liner (LEL) well while maintaining flowing bottom hole pressures below fracture pressure of the formation. Modeling methodologies using adequate wellbore hydraulic computations were utilized that could be operationalized to assess well specific designs in the future development wells. Furthermore, possible displacement inefficiencies related to high leak-off due to permeability heterogeneity and difficulty to displace into zones with high reservoir pressure were considered. Hence, reservoir property sensitivities to explore the impact of reservoir pressure and permeability heterogeneity on displacement were simulated in the integrated modeling approach.

A coupled reservoir, transient wellbore hydraulics approach was developed to accurately capture wellbore displacement, wellbore pressure drops, and reservoir dynamics including relative permeability and near wellbore pressure buildup to predict amount of water that is displaced at a given injection condition over time. Subsequently, realistic reservoir sensitivities were run to assess the worst-case pressure and permeability profiles for a given well and how water displacement was affected. This resultant coupled model of Wellbore Transient Hydraulic Simulator and Reservoir Simulation modeling was validated by a 3-D Computational fluid dynamics (CFD) model to ensure physics of gas-water interface evolution is properly captured.

Modeling predictions for the expected reservoir pressure and permeability demonstrated that, with the proposed limited entry liner design, displacement was achieved at a manageable gas injection rate (25 MMSCFD) without going above fracture pressure. Full displacement was feasible within a matter of hours. Furthermore, reservoir conditions with higher pressure buildup at the toe required additional rate to achieve effective displacement across the length of the well. Higher gas injection rates resulted in higher flowing bottom hole pressures driving more fluid displacement to the higher pressured region of the well ultimately leading to improved outflow.

This work provides a methodology framework for modelling complex, transient, multi-fluid displacements problems within a wellbore, incorporating leak off into the formation while capturing multiphase flow phenomena within the formation and well. Relative to 3D-CFD modelling, this modelling approach is fast and flexible and captures well specific WAG fluid swap displacement hydraulics.