Evaluation of safe operating envelope for CO2 injection under uncertain rock mechanical parameters and earth stresses

Abstract

Carbon Capture and Storage (CCS) is a pre-requisite to decarbonize CO₂ emissions from industrial sectors and as an industry capable of compensating for hard-to-abate emissions in a net zero scenario. A method was developed to evaluate the geomechanical constraints and safe operating envelope as function of pore pressure and temperature. The probability of failure was estimated from uncertain input stiffness and strength data, and as cooling and re-pressurization shifts the in-situ effective stresses, the safe operating envelope was determined, here given by pressure and temperature.

Onshore storages nearby industrial clusters enable energy and cost-effective handling of CO₂. In the South-Eastern European region, onshore depleted oil and gas fields located nearby high-emitting industries may developed into CO₂ storages. This paper describes a method for determining maximum fluid pressure as function of temperature from geomechanical restrictions. The method was employed on a practical example used to evaluate the safe operation envelope for a pilot CO₂ injection site into a depleted onshore naturally fractured carbonate oil and gas field. The tool uses Monte Carlo simulations to perform geomechanical stability analyses by sampling from the inherent uncertainty of the input parameters to probability of failure as function of pressure and temperature. The risk of re-opening natural fractures, induced fracturing and fault reactivation are evaluated so the safe operating envelope can be obtained. The uncertainty of the input parameters is thus directly reflected in the safe operating envelope – thus providing an effective communication of value information to external stake holders when maturing a CO₂ storage pilot.