Wettability alteration of caprock minerals by carbon dioxide

Abstract

One of the critical factors that control the efficiency of CO 2 geological storage process in aquifers and hydrocarbon reservoirs is the capillary-sealing potential of the caprock. This potential can be expressed in terms of the maximum reservoir overpressure that the brine-saturated caprock can sustain, i.e. of the CO 2 capillary entry pressure. It is controlled by the brine/CO 2 interfacial tension, the water-wettability of caprock minerals, and the pore size distribution within the caprock.By means of contact angle measurements, experimental evidence was obtained showing that the water-wettability of mica and quartz is altered in the presence of CO 2 under pressures typical of geological storage conditions. The alteration is more pronounced in the case of mica. Both minerals are representative of shaly caprocks and are strongly water-wet in the presence of hydrocarbons.A careful analysis of the available literature data on breakthrough pressure measurements in caprock samples confirms the existence of a wettability alteration by dense CO 2 , both in shaly and in evaporitic caprocks. The consequences of this effect on the maximum CO 2 storage pressure and on CO 2 storage capacity in the underground reservoir are discussed. For hydrocarbon reservoirs that were initially close to capillary leakage, the maximum allowable CO 2 storage pressure is only a fraction of the initial reservoir pressure.

Direct Measurement of Static and Dynamic Contact Angles Using a Random Micromodel Considering Geological CO2 Sequestration

“…Figure 2a. Results show that the advancing contact angle is considerably higher than the receding contact angle in the same pore throat, consistent with previous studies [18,22,[43][44][45]. The difference between ACA and RCA is attributed to the blemishes on non-ideal surfaces which results in pinning the interfaces to the solid surface [46].…”

“…Average contact angles on flat surface inside micromodel at pressure of one and eight megapascals are 62° ± 7° and 49° ± 21°, respectively, in agreement with Kim et al [58] observations showing a wide range of contact angles from 40° to 80° inside a uniform micromodel. Contact angles on a flat surface in this study are higher than those shown in previous sessile drop or captive bubble tests with large droplet of water or bubble of CO2 (i.e., 8° to 45° on silica or glass surface) [18,22,43,[50][51][52]. This could be due to the micro-scaled CO2 bubble size on a flat surface inside the micromodel of [18,22,43,[50][51][52].…”

“…Contact angles on a flat surface in this study are higher than those shown in previous sessile drop or captive bubble tests with large droplet of water or bubble of CO2 (i.e., 8° to 45° on silica or glass surface) [18,22,43,[50][51][52]. This could be due to the micro-scaled CO2 bubble size on a flat surface inside the micromodel of [18,22,43,[50][51][52]. This could be due to the micro-scaled CO 2 bubble size on a flat surface inside the micromodel of the present study in comparison with the other studies with larger dimension of bubble ranging from a few to tens of millimeter.…”

“…Because of different level of relaxation of the interfaces, various mode of interfaces before stoppage (i.e., receding or advancing), and pinning effect originated from solid surface imperfection, SCA shows wide range of values for the two different tests and also for each test in any throat sizes. The range of SCA at each pore throat size is higher than that of equilibrium contact angle (ECA) measured with CO 2 or water droplet on flat surface (i.e., 8 • to 45 • on silica or glass surface) [18,22,43,[50][51][52]. Static contact angle during drainage and imbibition processes.…”

“…Values of in-situ contact angles and local capillary pressure are not distinguishable [9]. In a different approach, static and dynamic contact angles have been vastly measured on a flat surface representing a specific mineral surface (i.e., silica, mica, or natural rock) using various methods such as sessile drop, captive bubble, Wilhelmy plate, and dual-drop dual-crystal (DDDC) methods [18][19][20][21][22][23][24][25][26][27][28][29]. High discrepancies in contact angles measured in literature have been observed.…”