--> --> Abstract: Use of Reactive Transport Modeling to Predict the Impact of Seawater – CO2 Injection for EOR in Carbonate Reservoirs, by Guoxiang Zhang, Conxita Taberner, Alan Devlin, and Jan Stammeijer; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Use of Reactive Transport Modeling to Predict the Impact of Seawater – CO2 Injection for EOR in Carbonate Reservoirs

Guoxiang Zhang1; Conxita Taberner2; Alan Devlin3; Jan Stammeijer4

(1) Shell International Exploration and Production B.V., Houston, TX.

(2) Carbonate Reservoirs, Shell International Exploration and Production B.V., Rijswijk (ZH),, Netherlands.

(3) Shell U.K. Limited, Aberdeen, United Kingdom.

(4) Shell International Exploration and Production, Aberdeen, United Kingdom.

We are presenting the results of geochemical reactive transport modeling using TOUGHREACT to simulate a full WAG (water alternating gas) cycle for enhanced oil recovery (EOR) in a chalk reservoir. The simulation covers 15 years of seawater injection followed by 2 years CO2 injection and 2 years seawater injection.

Model results show that (1) the 15-year injection of seawater promotes a slight dissolution of calcite, which is considered negligible although can be slightly enhanced near the producer; (2) the 2-year injection of CO2 acidifies the reservoir brine around the injector causing an increased dissolution of calcite in the CO2 plume (up to 0.1% rock volume fraction change) and near the injector (up to 0.2 % volume fraction change), and precipitation of calcite near the producer; (3) during the subsequent 2-year injection of seawater, dissolution of this mineral is strongly enhanced near the injector (up to 0.5% volume fraction change) and precipitation is significant at the producer. The enhancement in dissolution is a consequence of the acidification of the reservoir brine caused by the previous 2-year CO2 injection, and the significant precipitation at the producer is a result of depressurization; (4) scaling by barite, dolomite, gypsum and anhydrite is expected minor, however, calcite precipitation near the producer, primarily due to depressurization at constant temperature, is highly expected to scale the producer; (5) sensitivity analyses illustrates that the dissolution/precipitation of this mineral will be complicated near the producer due to the heterogeneity in rock hydraulic properties, some fluid-mixing scenarios might be expected to cause dissolution (e.g. “coned” aquifer), (6) dolomite is predicted to precipitate as the injection of seawater introduces Mg into the reservoir and carbonate ions are produced from dissolution of calcite, the amount of dolomite precipitation is small (< 0.001% volume fraction change) compared to the dissolution of calcite; and (7) anhydrite or gypsum will precipitate because injection of seawater introduce sulphate in to the reservoir, however, precipitation of these minerals will not cause a significant change of rock porosity.

This work shows the potential of the application of RTM to evaluate and quantify the impact of rock-fluid interactions in highly reactive carbonate during EOR operations.