Geomechanical characterization of reservoir and caprock integrity for CO2 sequestration assessment in the Jaisalmer Basin, India
摘要
The main objective of this study was to estimate the geomechanical properties of the formation to identify the potential nature of the caprock for CO2 sequestration in the investigated area of Jaisalmer Basin. The study concentrated on the Goru and Pariwar formations based on the depositional sequences and characters of the Cretaceous age as caprock and reservoir formations, respectively. Significant faulting systems and high structural heterogeneities are observed within the formations of the study area, underscoring the importance of estimating geomechanical properties for CO2 sequestration. This study focused on two key components: estimates of mechanical rock properties, including elastic moduli, BI, stress ratio, and unconfined compressive strength (UCS), and variations in formation pressure across different components. A couple of analyses were carried out based on established empirical relationships for similar geological setups within the correlated depth of the investigated formations. The correlation was initiated based on static correlation and implemented as dynamic correlation as well. Components of the pressure estimated in both formations based on the depth-dependent normal compaction trend line (NCTL) with the considerable support of Eaton’s method. Spatial pressure variations within the study formations were captured through seismic velocity changes, where significant differences were observed in the faulted zone, which are strongly correlated with estimated formation pressures from well data. The result for variations in elastic moduli shows a higher compaction trend with depth and an increase in overburden load. Geomechanical analysis based on pressure-component estimates yields a specific stress pattern that varies with pore pressure and is also linked to estimated elastic properties. The estimated elastic parameters and pore-pressure measurements provide useful information on rock mechanical properties, facilitating the successful injection of CO2. A good number of both brownfield and greenfield sites are present in the Jaisalmer Basin based on their reservoir nature and production history. CO2 injections, along with the store, play a crucial role during tertiary recovery from these brownfield reservoirs. The study of the caprock integrity of the Goru Formation, towards CO2 sequestration in the Pariwar Formation shows the effective sealing potential for injection in the reservoir rock, as long as the injected fluid pressure does not exceed the fractured pressure. A risk assessment study was conducted based on the estimated parameters in the wells, where Well C shows low risk, while Well B shows the highest risk to conduct CO2 sequestration through injection; however, overall results from all three wells, integrated with seismic velocity analysis, show moderate risk. The current study, along with field-based analysis, shows the typical geological challenges in the reservoir rock and caprock, including structural deformation – such as caprock failure, fault reactivation, and wellbore integrity loss – in the study area during sequestration. To avoid these kinds of challenges to successful sequestration, the change in pore pressure should be less than 15–20% of the original pressure post-sequestration. This kind of integrated study approach, supported by limited geoscientific data for assessing the feasibility of CO2 sequestration in this area of the Jaisalmer Basin, is unique based on significant outcomes and also applicable in other regions with a similar geological setup.
Research highlightsStudy of the geomechanical properties of the formation, along with different components of the formation pressure, has shown the significance for capturing the feasibility of CO2 sequestration. Both seismic and well log data are used suitably to characterize the reservoir formation and caprock. The result related to the variations of elastic moduli shows the higher compaction trend with depth, with an increase in overburden load. Estimated pressure components provide a specific stress pattern that changes with pore pressure variation, which is also connected to estimated elastic properties. A study has shown that CO2 sequestration in the Pariwar reservoir is a feasible option, with the Goru Formation acting as a caprock in the Jaisalmer Basin, while maintaining injection limits and pressure within the specified risk range for sequestration.