Quantifying CO2 Injection Performance in Depleted Reservoirs for Operational Optimization in CCUS Projects

Carbon dioxide (CO₂) injection into depleted oil reservoirs routinely implement subsurface models to track and understand multiphase system dynamics. This study uses full-physics compositional simulations of a depleted reservoir with a simplified radial geometry to numerically investigate the efficiency of horizontal wells for our program partners to plan field workover activities for similar reservoirs in the MRCSP project in northern Michigan, USA. The model consists of a single vertical well in the center which acts as a producer during an initial primary recovery phase and is then converted into a CO₂ injector during a subsequent CO₂ injection period with predetermined injection-falloff periods. The simplified configuration enabled numerical investigation of different desirable basic well configurations such as (a) horizontal well versus vertical well with sensitivities to horizontal well length and (b) vertical well with lateral sections of different well lengths for reservoirs of varying permeability.

The injectivity index is a commonly used concept in petroleum reservoir engineering to evaluate the well’s capability for injecting fluids into a porous and permeable formation. Our earlier work established that pressure and rate data can be successfully integrated using this metric to assess and compare performance of different wellbore-reef complexes [Mishra et al., 2017 and 2018]. Numerical evaluation of improvement in injectivity index in reservoirs with different absolute permeabilities is performed using sensitivity analyses of above-mentioned injector configurations. Horizontal well sections are found to be more efficient as expected with higher injectivity index corresponding to longer horizontal well cases. Cross-plots reveal clear trends that correlate the injectivity index with the intrinsic reservoir permeability and the horizontal well length.

This work establishes a reliable quantitative performance comparison between different injection well configurations using a simple yet effective injectivity index metric. Such simplified models can be valuable resources for cost-benefit analysis by operators during preliminary project optimization.