THE IEA WEYBURN CO_2 MONITORING AND STORAGE PROJECT - INTEGRATED RESULTS FROM EUROPE

摘要

The IEA Weyburn CO_2 Monitoring and Storage Project has analysed the effects of a miscible CO_2 flood into a carbonate reservoir rock at an onshore Canadian oilfield. Anthropogenic CO_2 is being injected as part of an enhanced oil recovery operation. The European research was aimed at analyzing long-term migration pathways of CO_2 and the effects of CO_2 on the hydrochemical and mineralogical properties of the reservoir rock. The long term safety and performance of CO_2 storage was assessed by the construction of a Features, Events and Processes (FEP) database which provides a comprehensive knowledge base for the geological storage of CO_2. The pre-CO_2 injection hydrogeological, hydrochemical and petrographical conditions in the reservoir were investigated in order to recognise changes caused by the CO_2 flood and assessing the fate of the CO_2. The Mississippian aquifer has a salinity gradient in the Weyburn area, where flows are oriented SW-NE. The baseline gas fluxes and CO_2 concentrations in groundwater and soil were also researched. The dissolved gas in the reservoir waters has allowed potential transport pathways to be identified. Experimental studies of CO_2-porewater-rock interactions in the Midale Marly unit have indicated slight dissolution of carbonate and silicate minerals, but relatively rapid saturation with respect to carbonate minerals. Equivalent studies on the overlying and underlying units show similar reaction processes, but secondary gypsum precipitation was also observed. Carbon dioxide flooding experiments on samples of the Midale Marly unit demonstrated that porosity and gas permeability increased significantly and calcite and dolomite were shown to have undergone corrosion. Hydrogeological modelling indicates that if any dissolved CO_2 entered the main aquifers, it would be moved away from Weyburn in an E-NE direction at a rate of c. 0.2 m/year due to regional groundwater flow. Analysis of reservoir fluids proved that dissolved CO_2 and CH_4 increased significantly in the injection area between 2002 and 2003 and that solubility trapping accounts for the majority of the injected CO_2, with little apparent mineral trapping. Twelve microseismic events were recorded and these are provisionally interpreted as being possibly related to small fractures formed by injection-driven fluid migration within the reservoir. Pre- and post-injection soil gas data are consistent with a shallow biological origin for the measured CO_2. Isotopic (δ~(13)C) data values are higher than in the injected CO_2, and confirm this interpretation. No evidence for leakage of the injected CO_2 to ground level has so far been detected.