Carbon dioxide flooding

Fig. 1. Carbon dioxide flooding. The WAG process, in which a CO2 slug is followed by alternate water and CO2 injections, is usually employed. The...

The appHcation that has led to increased interest in carbon dioxide pipeline transport is enhanced oil recovery (see Petroleum). Carbon dioxide flooding is used to Hberate oil remaining in nearly depleted petroleum formations and transfer it to the gathering system. An early carbon dioxide pipeline carried by-product CO2 96 km from a chemical plant in Louisiana to a field in Arkansas, and two other pipelines have shipped CO2 from Colorado to western Texas since the 1980s. EeasibiHty depends on cmde oil prices. 

Carbon dioxide flooding is the most promising enhanced oil-recovery method. To overcome the tendency of CO2 to bypass the smaller pores containing residual oil, one approach is to plug the larger pores by chemical precipitation. Several relatively inexpensive water-soluble salts of the earth alkali group react with CO2 to form a precipitate. 

Medium to large systems (greater than 30 MMscfd). In general, membrane systems are too expensive to compete head-to-head with amine plants. However, a number of large membrane systems have been installed on offshore platforms, at carbon dioxide flood operations, or where site-specific factors particularly favor membrane technology. As membranes improve, their market share is increasing. 

In principle, the combination of membranes for bulk removal of the carbon dioxide with amine units as polishing systems offers a low-cost alternative to all-amine plants for many streams. However, this approach has not been generally used because the savings in capital cost are largely offset by the increased complexity of the plant, which now contains two separation processes. The one exception has been in carbon dioxide flood enhanced oil-recovery projects [49,54], in which carbon dioxide is injected into an oil formation to lower the viscosity of the oil. Water, oil and gas are removed from the formation the carbon dioxide is separated from the gas produced and reinjected. In these projects,... 

In order to avoid the necessity of operating at the high pressures typical of carbon dioxide flooding (1500-3000 psig, or 10-20 MPa), which would require heavy bracing of the model faces and highrpressure inlet and production systems, substitute fluids were used. In place of carbon dioxide, a non-aromatic kerosene-range hydrocarbon was used, with a viscosity of 1.3 cp (or kPa-s). This is about 20 times the viscosity of carbon dioxide under normal... 

Figures 1 and 4 show the water flood matches to the water-wet and oil-wet lab model curves, respectively. The carbon dioxide flooding runs in the lab model were then matched by computer simulation. In the simulations, as in the lab model, the carbon dioxide slug was followed by waterflooding to an assumed economically limiting water cut of 98%, and the enhanced oil recovery was calculated as the difference between the ultimate total recovery at this point and that of a water flood starting from initial oil saturation and continued until a 98% water cut was reached. Secondary carbon dioxide floods started from the same initial oil saturation, while tertiary carbon dioxide floods started with the condition at the 98% water cut point in the simple water flood. Since the foam or emulsion tests involved a 1 1 ratio of water and carbon dioxide, comparisons are shown only for the case of 1 1 WAG operation vs foam.

In the meantime, the significant advantage indicated by our laboratory work for injection of carbon dioxide as a foam or emulsion rather than alternately with water (WAG) will, we hope, serve as a stimulus to the oil companies carrying out carbon dioxide floods to give consideration to this version of the process. Many of these companies have the Todd, Dietrich and Chase Multiflood simulator, or one which is similar. The option to precipitate or adsorb a component is necessary. Then the surfactant component can be adsorbed and can also provide a higher viscosity when it is not adsorbed (simulating foam). 

Enhancement of Crude Oil Recovery in Carbon Dioxide Flooding... 

Results of Immiscible Displacement Tests. The results of the tests show that immiscible carbon dioxide flooding followed by waterflooding is effective in increasing the oil recovered from a core. The oil recovered by a conventional waterflood was equal to about 30.4% of a pore volume, PV. Immiscible carbon dioxide flooding increased the recovery to a total of 50.5% PV. The addition of a mobility control agent increased the recovery further to 58.3% PV this amounts to 39% additional tertiary oil due to the effectiveness of the mobility control in the carbon dioxide immiscible process. 

The average oil produced in the two initial waterfloods was 305 cc. With an initial oil volume of 870 cc, the recovery in the initial waterflood phase is 35% of the original oil in place. The total oil produced in the case of the conventional carbon dioxide flood was 510 cc which is 58.1% of the initial oil. When mobility control was used the total oil recovered increased to 585 cc which represents 67.4% of the original oil. A summary of the results are shown in Table II. 

Figure 10. Stepanflo-50 mobility controlled carbon dioxide flood.

Figure 12. Mobility controlled carbon dioxide flood using EXXON LD 776-52 in tap water.

The displacement tests show that a signiflcant increase in tertiary oil production can be achieved when one of the better additives is utilized in 1-dimensional laboratory immiscible carbon dioxide floods. In the miscible displacement case no adverse effect on the miscibility process was found. In... 

Dutton Flanders examined the diagenesis and reservoir quality of the East Ford Field, Texas, which is undergoing a carbon dioxide flood. The compartmentalization of the arkosic sandstone reservoir is chiefly controlled by authi-genic calcite layers associated with the tops and bottoms of turbidite sandstone units. Gases produced from zones below low permeability calcite cemented sandstone intervals in new infill wells have high carbon dioxide contents. These, together with geophysical log interpretations, indicate that the calcite-cemented zones are laterally continuous and act as vertical barriers in the reservoir. 

Solubility. Solubility in the primary process solvent is a mandatory criteria which is easily met in most extraction processes conducted in water. But, new applications such as polymeric viscosifiers for supercritical carbon dioxide flooding in enhanced oil recovery present enormous solubility problems for candidate polymers. If the polymer must remain soluble in secondary fluids encountered during the extraction process, then solubility requirements on the polymer will span large ranges of solvent pH, solvent-and-other-solute activity, and solvent polarity. 

Carbon Dioxide Flood. Smith et al. [SO] studied the impact of wettability on tertiary oil recovery by carbon dioxide flooding after a secondary waterflood. It was reported that oil recovery could be improved by the wettability alteration of reservoir rock surfaces using surfactants. In this study, water-wet sandstone rock surfaces were modified by treatment with solutions of surfactants to neutral and even moderately oil-wet states. The laboratory results indicated that maximum tertiary oil recovery, after waterflood, by carbon dioxide flooding increased as the wettability of the sandstone decreased from highly water-wet to a neutral-wet or a slightly oil -wet surface. 

Results of the study of corrosion control by inhibitors in producing oil wells in carbon dioxide flooded fields showed imidazolines are successful in protection in CO2 brines. The inhibitor was found to be incorporated in the carbonate corrosion product layer but was still more effective if the surface film contained sulfide. Also, better results were obtained with inhibitors, such as nitrogen-phosphorus compoimds or compounds with sulfur in the organic molecules. 

Fixed fire control systems such as firewater monitors or water sprays over critical or high-risk equipment or carbon dioxide flooding of enclosures should also be considered. Except for combustion gas mrbine enclosures, situations warranting such protection are not common. 

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