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Energy & Fuels 2008, 22, 504–509
Wettability Determination of the Reservoir Brine-Reservoir Rock System with Dissolution of CO2 at High Pressures and Elevated Temperatures Daoyong Yang,* Yongan Gu, and Paitoon Tontiwachwuthikul Petroleum Technology Research Centre (PTRC), Petroleum Systems Engineering, Faculty of Engineering, UniVersity of Regina, Regina, Saskatchewan S4S 0A2, Canada ReceiVed July 6, 2007. ReVised Manuscript ReceiVed October 16, 2007
An experimental method has been developed to determine the wettability, i.e., the contact angle, of a reservoir brine-reservoir rock system with dissolution of CO2 at high pressures and elevated temperatures by using the axisymmetric drop shape analysis (ADSA) technique for the sessile drop case. Prior to the experiment, a rock slide is horizontally placed in a specially designed rock slide holder in a see-through windowed high-pressure cell, which is subsequently filled with CO2 at a prespecified pressure and a constant temperature. Then, a reservoir brine sample is introduced by using a syringe delivery system to form a sessile brine drop on the rock slide inside the pressure cell. The sequential digital images of the dynamic sessile brine drop are acquired and analyzed by applying computer-aided image acquisition and processing techniques to measure the dynamic contact angles at different times. It is found that the dynamic contact angle between the reservoir brine and the reservoir rock remains almost constant at a given pressure and a constant temperature, though CO2 is gradually dissolved into the sessile brine drop which is eventually saturated with CO2. It is also found that the equilibrium contact angle increases as the pressure increases, whereas it decreases as the temperature increases. Such wettability alteration may significantly affect the storage capacity when CO2 is injected into a saline aquifer or a depleted oil reservoir at high pressures.
1. Introduction Geological sequestration of anthropogenic CO2 has been considered as a potential technology for greatly mitigating greenhouse gas emissions. In this way, CO2 is either sequestrated in a depleted oil/gas reservoir or disposed from stationary sources into a saline aquifer or an unminable coal seam.1,2 Recently, a field-scale project for CO2 enhanced oil recovery (EOR) and CO2 sequestration has been undertaken in the Weyburn oilfield3 and a large-scale CO2 sequestration project is underway in the Sleipner saline aquifer.4 The International Energy Agency (IEA) Greenhouse Gas (GHG) Weyburn CO2 Monitoring and Storage Project is recognized as the world’s largest joint field test for sequestrating CO2 in a depleted oil reservoir, although it is currently still at the EOR stage. It has been well-accepted that successful sequestration of CO2 is largely controlled by the interfacial interactions among the reservoir brine, CO2, and the reservoir minerals.4–7 The major interfacial interactions include interfacial tension, wettability, capillarity, and interface mass transfer, among which the wettability has strong effect on capillary pressure,5,6 relative * Corresponding author. Tel.: 1-306-337-2660. Fax: 1-306-585-4855. E-mail:
[email protected]. (1) Bachu, S. Sequestration of CO2 in Geological Media: Criteria and Approach for Site Selection in Response to Climate Change. Energy ConVers. Manage. 2000, 41, 953–970. (2) Siemons, N.; Bruining, H.; Castelijns, H.; Wolf, K. H. Pressure Dependence of the Contact Angle in a CO2-H2O-Coal System. J. Colloid Interface Sci. 2006, 297, 755–761. (3) Moritis, G. EOR Continues to Unlock Oil Resources. Oil Gas J. 2004, 102, 45–65. (4) Arts, R.; Eiken, O.; Chadwick, A.; Zweigel, P.; van der Meer, L. Monitoring of CO2 Injected at Sleipner Using Time-Lapse Seismic Data. Energy 2004, 29, 1383–1392.
permeability,6 and phase distribution8 and can cause dramatic change in the displacement mechanisms.8 However, the wettability phenomenon of the CO2-reservoir brine-reservoir rock system has not yet been quantified at high pressures and elevated temperatures. Numerous techniques, either quantitative or qualitative, have been developed to evaluate the wettability of a fluid-liquid system on a solid surface. The quantitative methods available for determining the wettability of the reservoir rock are the Amott method,9 the US Bureau of Mines (USBM) method,10 and the contact angle method.11 Both the Amott method and the USBM method determine the average wettability of a reservoir core, whereas the contact angle method measures the wettability of a specific solid surface. In general, contact angle measurements can be carried out by using the sessile drop (5) Chalbaud, C.; Robin, M.; Egermann, P. Interfacial Tension Data and Correlations of Brine/CO2 Systems Under Reservoir Conditions. Proceedings of SPE (Society of Petroleum Engineers) Annual Technical Conference and Exhibition, San Antonio, TX, September 24–27, 2006; paper SPE 102918. (6) Juanes, R.; Spiteri, E. J.; Blunt, M. J. Impact of Relative Permeability Hysteresis on Geological CO2 Storage. Water Resour. Res. 2006, 42, W12418. (7) Arendt, B.; Dittmar, D.; Eggers, R. Interaction of Interfacial Convection and Mass Transfer Effects in the System CO2-Water. Int. J. Heat Mass Transfer 2004, 47, 3649–3657. (8) Morrow, N. R. Wettability and Its Effect on Oil Recovery. J. Pet. Technol. 1990, 42, 1476–1484. (9) Amott, E. Observations Relating to the Wettability of Porous Rock. Trans., AIME 1959, 216, 156–162. (10) Donaldson, E. C.; Thomas, R. D.; Lorenz, P. B. Wettability Determination and Its Effect on Recovery Efficiency. SPE J. 1969, 9, 13– 20. (11) Anderson, W. G. Wettability Literature Survey-Part 2: Wettability Measurement. J. Pet. Technol. 1986, 37, 1246–1262.
10.1021/ef700383x CCC: $40.75 2008 American Chemical Society Published on Web 11/30/2007
Wettability of ReserVoir Brine-ReserVoir Rock
method,11–16 modified sessile drop method,17 axisymmetric drop shape analysis (ADSA) technique,18,19 captive-drop technique,20 analysis of capillary profile around a cylinder technique,21 dualdrop-dual-crystal technique,22 and Wilhelmy plate method.15 It has been found that the contact angle is not only the most universal measure of the wettability of a solid surface, but also has been widely used to characterize wettability phenomenon of the complicated crude oil–water-rock systems at high pressures and elevated temperatures.8,11–14,23 In the literature, the reservoir rock is categorized to be water-wet, intermediatewet, and oil-wet when the advancing contact angle of water on a reservoir rock surface is in the range of 0–75°, 75–105°, and 105–180°, respectively.11,12 Traditionally, the contact angle is measured by photographing a sessile drop and then measuring the contact angles from the negative films with a goniometer.11–15,22 Recently, an advanced shape analysis technique, known as the ADSA technique,18,19 has been developed to accurately measure the contact angle of a fluid-liquid–solid system. In the ADSA technique, an objective function is constructed to express the discrepancy between the theoretically predicted Laplacian curve and the experimentally observed sessile drop profile. Then, this objective function is minimized numerically to determine the contact angle and the interfacial tension simultaneously. The output data also include the contact radius, volume, and surface area of the sessile brine drop. This technique only requires the local gravity and the density difference between the two bulk phases involved as the input data. In comparison with the other existing methods, the ADSA technique for the sessile drop case is accurate for the contact angle measurement (( 0.1°), fully automatic, and completely free of the operator’s subjectivity. Most importantly, the ADSA technique can be used to automatically and accurately measure the contact angle versus time, i.e., the dynamic contact angle. In this paper, an experimental technique is developed to determine the wettability of the CO2-reservoir brine-reservoir rock system at high pressures and elevated temperatures. On the basis of the ADSA technique for the sessile drop case, this new technique makes it possible to measure the contact angles (12) Morrow, N. R. Interfacial Phenomena in Petroleum RecoVery; Marcel Dekker, Inc.: New York, 1991. (13) McCaffery, F. G. Measurement of Interfacial Tensions and Contact Angles at High Temperature and Pressure. J. Can. Pet. Technol. 1972, 11, 26–32. (14) McCaffery, F. G.; Mungan, N. Contact Angle and Interfacial Tension Studies of Some Hydrocarbon-Water-Solid Systems. J. Can. Pet. Technol. 1970, 9, 185–196. (15) Adamson, A. W. Physical Chemistry of Surfaces, 6th ed.; John Wiley and Sons, Inc.: New York, 1996. (16) Dickson, J. L.; Gupta, G.; Horozov, T. S.; Binks, B. P.; Johnston, K. P. Wetting Phenomena at the CO2/Water/Glass Interface. Langmuir 2006, 22, 2161–2170. (17) Treiber, L. E.; Owens, W. W. Laboratory Evaluation of the Wettability of Fifty-Five Oil Producing Reservoirs. SPE J. 1972, 12, 531– 540. (18) Rotenberg, Y.; Boruvka, L.; Neumann, A. W. Determination of Surface Tension and Contact Angle from the Shapes of Axisymmetric Fluid Interfaces. J. Colloid Interface Sci. 1983, 93, 169–183. (19) Cheng, P.; Li, D.; Boruvka, L.; Rotenberg, Y.; Neumann, A. W. Automation of Axisymmetric Drop Shape Analysis for Measurement of Interfacial Tensions and Contact Angles. Colloids Surf. 1990, 43, 151– 167. (20) Chiquet, P.; Broseta, D.; Thibeau, S. Wettability Alteration of Caprock Minerals by Carbon Dioxide. Geofluids 2007, 7, 112–122. (21) Gu, Y.; Li, D.; Cheng, P. A Novel Contact Angle Measurement Technique by Analysis of Capillary Rise Profile Around A Cylinder (ACRPAC). J. Colloid Interface Sci. 1996, 180, 212–217. (22) Rao, D. N.; Girard, M. G. A New Technique for Reservoir Wettability Characterization. J. Can. Pet. Technol. 1996, 35, 31–39. (23) Wagner, O. R.; Leach, R. O. Improving Oil Displacement Efficiency by Wettability Adjustment. Trans., AIME 1959, 216, 65–72.
Energy & Fuels, Vol. 22, No. 1, 2008 505 Table 1. Physical and Chemical Properties of the Weyburn Reservoir Brine calcium, mg/L magnesium, mg/L sodium, mg/L potassium, mg/L iron, mg/L barium, mg/L manganese, mg/L chloride, mg/L sulfate, mg/L pH @ 23 °C conductivity @ 25 °C, S/m density, g/cm3 @ 15 °C @ 20 °C @ 60 °C refractive index @ 25 °C total dissolved solids, mg/L @ 110 °C @ 180 °C
1600.00 348.00 20350.00 532.00 0.22 2.60
