Abstract
The objectives of this study were (1) to assess the fate and impact of CO2 injected into the Morrow B Sandstone in the Farnsworth Unit (FWU) through numerical non-isothermal reactive transport modeling, and (2) to compare the performance of three major reactive solute transport simulators, TOUGHREACT, STOMP-EOR, and GEM, under the same input conditions. The models were based on a quarter of a five-spot well pattern where CO2 was injected on a water-alternating-gas schedule for the first 25 years of the 1000 year simulation. The reservoir pore fluid consisted of water with or without petroleum. The results of the models have numerous broad similarities, such as the pattern of reservoir cooling caused by the injected fluids, a large initial pH drop followed by gradual pH neutralization, the long-term persistence of an immiscible CO2 gas phase, the continuous dissolution of calcite, very small decreases in porosity, and the increasing importance over time of carbonate mineral CO2 sequestration. The models differed in their predicted fluid pressure evolutions; amounts of mineral precipitation and dissolution; and distribution of CO2 among immiscible gas, petroleum, formation water, and carbonate minerals. The results of the study show the usefulness of numerical simulations in identifying broad patterns of behavior associated with CO2 injection, but also point to significant uncertainties in the numerical values of many model output parameters.
Highlights
Central to assessing the feasibility of CO2 sequestration in the Farnsworth Unit (FWU) is determining the behavior of the injected CO2, including where and at what rate the CO2 will migrate, how the CO2 will be distributed among the pore fluid phases and minerals, and how the hydraulic properties of the reservoir and the composition of the pore fluids will be changed
In addition to providing a rigorous comparison of the TOUGHREACT, GEM, and STOMP-enhanced oil recovery (EOR) simulators, the first of its kind and which will help build confidence in these simulators for future research, the present study extends the previous reactive transport modeling studies of the FWU in the following ways:
1, the1,STOMP-EOR, TOUGHREACT, and GEMand models predicted predicted similar in evolutions in temperature and pressure, though the pressures in the similar evolutions temperature and pressure, though the pressures in the GEM model were approximately
Summary
Central to assessing the feasibility of CO2 sequestration in the FWU is determining the behavior of the injected CO2 , including where and at what rate the CO2 will migrate, how the CO2 will be distributed among the pore fluid phases (i.e., aqueous, gas, and nonaqueous liquid) and minerals, and how the hydraulic properties of the reservoir and the composition of the pore fluids will be changed. Answering these questions requires the ability to quantify the flow of multiple fluid phases, their transport of solute and heat, and chemical reactions involving the fluid phases and minerals in the reservoir. Limitations of the model were that it did not include petroleum, only CO2 was injected into the reservoir rather than water and CO2 through a water alternating gas (WAG) scheme as implemented in the field, the model did not implement the actual regional pressure gradient occurring in the field, and the model was only carried out to 30 years
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