An Integrated Approach of CO2 Injection and Storage Assessment in Tight Gas Condensate Carbonate Reservoir, Case Study: Central Kalimantan, Indonesia
Authors: Magfirah A. 
Published: March 2023

Geological storage is a potential solution for storing carbon dioxide (CO2) emissions from stationary sources such as fossil-fuel-fired power stations over lengthy periods. The typical geological formation for storage is a massive saline aquifer or oil and gas reservoir with good permeability (>100 mD). However, what if the targeted geological formation is a massive reservoir with tight properties (<0.1 mD)? Does it have the potential to store CO2? Currently, the study of CO2 storage in a tight reservoir is limited. Therefore, this study presents a comprehensive subsurface analysis of CO2 storage potential in a tight gas condensate carbonate reservoir located in Central Kalimantan, Indonesia. The study analyzes the characteristics of CO2 injection and storage in tight formation, which covers the entire GGR (geology, geophysics, reservoir) aspects. The reservoir is a platform carbonate and based on the geoscience assessment the reservoir can be clustered into several depositional elements (DE), such as reef complex and platform interior. A static & dynamic model is created to capture the reservoir behavior, variations, and physics. As such, it is utilized to assess the field's effective storage capacity, reservoir injectivity, CO2 plume migration, pressure connection potential, CO2 breakthrough phenomena, and stimulation effectiveness. Additionally, coupled reservoir-geomechanical models are also performed to assess the relevant geomechanical concerns upon three separate phases of pre-injection, during injection, and after injection/monitoring. Initially, a well-calibrated 3D compositional reservoir model is prepared for performing a series of CO2 injection scenarios. It is started by performing a well-by-well assessment and continued by a full-field assessment. Firstly, the sensitivity of well locations indicates that the reef complex has higher injectivity five times compared to the platform interior. However, the CO2 injected into the reef complex also has a quicker breakthrough to the producer wells than the other DE-s. Moreover, the streamline analysis confirms this finding by showing distinct features of pressure path and flow behavior. Subsequently, the sensitivity of well stimulation treatment is also performed. The wells with acid fracturing stimulation can deliver double the injectivity of untreated wells. As for the full-field assessment, the coupled reservoir-geomechanical model is calibrated by a series of rock mechanic tests (triaxial, uni-axial pore volume compressibility, and permeability under a series of confining stresses). These tests indicate that the reservoir consists of hard rock (>3 million psi Young’s Modulus) and behaves as an intact structure until the end of the injection period. Overall, this study of CO2 Injection and Storage in a tight gas reservoir shows that this formation has the potential to store the CO2. Neither injectivity issues nor geomechanical risks are forecasted for the optimized injection. Finally, the coupled reservoir-geomechanical model also shows that the case study reservoir is intact and can sustain the stresses until the end of the injection period.