Evaluation of Safe Operating Envelope for Co2 Injection Under Variability and Uncertainty in Rock Mechanical Parameters and Earth Stresses

Abstract

Carbon Capture and Storage (CCS) is a pre-requisite to decarbonize high CO2 emitting industrial sectors and to compensate for hard-to-abate emissions. A method was developed to evaluate the geomechanical constraints of a safe operating envelope as function of pore pressure and temperature. The probability of failure is estimated from uncertain input data, as cooling and re-pressurization shifts the in-situ effective stresses. The safe operating envelope is constrained by maximum injection pressure that in turn is limited by thermal-elastic effects.Onshore storages nearby industrial clusters enable energy and cost-effective handling of CO2. In South-East European region, located far from the sea, depleted oil and gas reservoirs located nearby high-emitting industries may be used for CO2 storages. This paper focuses on evaluating geomechanical restrictions of a near depleted oil and gas natural fractured carbonate field in the South Moravia. The risks of re-opening natural fractures, induced fracturing and shear failure (fault reactivation) is based on laboratory experiments of intact reservoir rocks and estimated Earth stresses.Monte Carlo simulations use the inherent uncertainty of the input parameters to estimate the probability of failure as function of pressure and temperature so the safe operating envelope can be obtained. The variability of the input parameters enables effective communication of uncertainty to external stake holders, and an evaluation of which key parameters to constrain when maturing a CO2 storage pilot.

Keywords: Mechanical stability, CO2 storage, safe operating envelope, strength, stress, Monte Carlo simulation, probability of failure