Modeling above-zone measurements of pressure and temperature for monitoring CCS sites

Abstract

Geologic storage of CO2 for atmospheric emissions reductions imposes unique requirements to document containment. Monitoring pressure in strata above the injection interval is a fit-to-purpose technique to document performance of the confining system and the degree of isolation provided by existing wellbore completions. The Cranfield (Mississippi, USA) enhanced oil recovery and sequestration project provides downhole high-precision pressure and temperature measurements at an observation well at two depths: at the injection interval and at a selected above zone monitoring interval (AZMI). To attempt to reconcile disparate observations from the pressure and temperature measurements, we present a simple set of coupled analytical models that enable diagnosis of above-zone monitoring data. Concurrent pressure and temperature measurements are especially valuable because they independently constrain the effective permeability of a leakage path along wellbore. Application of the models to the Cranfield data shows that the observed pressure elevation requires a model with an extremely large leakage rate and an effective wellbore permeability in order of tens of darcies. The temperature model shows that this rate would be large enough to raise the temperature in the monitoring zone significantly, which is not observed. We conclude that the observation well is unlikely to be leaking.