CO2 Storage in a Giant Depleted Carbonate Gas Reservoir -Addressing Feasibility and Design Challenges with Field Data

Abstract

Abstract An integrated study on CO2 storage in a giant depleted gas reservoir was completed. The objectives were to assess feasibility, potential capacity and timing for CO2 storage. Significant design challenges were addressed, including thermal-geo-mechanical impact on cap-rock integrity due to injection CO2 cooling, hydrate, injection well life cycle design and clusters location and surface facilities options. Further de-risking is recommended and ongoing. An integrated approach was adopted combining/optimizing requirements from reservoir, injection wells, cap rock integrity, surface clustering, CO2 transportation and compression/pumping. Key impacts were accounted for: injection J-T effect, hydrate, stress changes, cap rock integrity, well life cycle design, existing well integrity, costs, and surface facilities. Single well models were developed for injection cooling simulation and well design options. 3D reservoir simulations were performed for reservoir pressure changes, storage options, thermal and geo-mechanics for cap rock integrity. Surface facilities options were evaluated, arrival pressure and temperature impact. Several iterations were carried out aiming at optimizing project economics with uncertainty analysis. Results from a CO2 field injection test are presented, part of key design input. Detailed 3D reservoir simulations show that CO2 injection start-up timing and ramping up strategy are important: starting early helps additional gas recovery, late would exacerbate injection CO2 J-T cooling. Placing CO2injectors further away from producers helps enhanced gas recovery. The results of an extended actual field CO2 injection tests are presented, showing downhole temperature changes with injection rate and transient stabilization. Existing well logs and stress profile measurements were combined. Single well models were developed to simulated cooling around well-bore. Velocity strings, small tubing sizes, are potential injector design options. Hydrates formation was found in certain scenarios. Thermal-Geo-mechanics analysis show appreciable stress changes possibly propagating > 150m into cap-rock. Although CO2 surface arrival temperature can be boosted by installing heaters, but would incur higher costs and additional requirements on wellhead design. It became apparent that individual subject requirements would affect the overall design. An iterative-looping integrated approach was adopted with CO2containment and maximizing project economics as over-riding objectives. Overall CO2 storage capacity was maximized. Adequate field data/measurements are essential and critical modelling input. Further de-risking recommendations include core laboratory geo-mechanical testing, further CO2 field higher rate testing, and comprehensive existing well integrity assessment.