Carbon dioxide reforming of methane (CDRM) was studied over a variety of ZrO 2 -, ceria-doped ZrO 2 -, and CeO 2 -ZrO 2 -supported Ni catalysts. Different techniques were used to prepare supports material having different physicochemical properties, and a correlation was established to show the importance of a robust support material. Various characterization of the catalyst further established that the coking behavior of the catalyst depends on the support preparation techniques. Compared to zirconia and ceria-doped zirconia, the use of ceria-zirconia (Ce x Zr 1-x O 2 ) solid solution as a support prepared by using a surfactant was found to be the most stable for low-temperature CDRM. It seems the inhibition of reactions leading to carbon deposition is prominent in systems having ZrO 2 . Temperature-programmed oxidation (TPO) experiments indicated excellent resistance toward carbon formation for Ni supported on Ce x Zr 1-x O 2 compared with other catalysts studied. H 2 -TPR (temperature-programmed reduction) analyses also showed that the stability of Ce x Zr 1-x O 2 solid solution is a function of its enhanced reducibility at lower temperatures as compared to either pure ceria or ceria-doped ZrO 2 . Based on all the catalysts studied, 5% Ni Ce 0.6 Zr 0.4 O 2 was found to be the best catalyst as activity was stable for up to 100 h at 650 and 700 °C, while at 800 °C the catalyst activity remained stable for more than 200 h.

A series of ceria-zirconia mixed oxide supports with nominal composition "Ce 0.6 Zr 0.4 O 2 " were synthesized by two different routes, namely, a surfactant-assisted route and a coprecipitation route. Among the supports obtained by the surfactant-assisted route, different surfactant/metal molar ratios (namely, 1.25, 0.8, and 0.5) were employed to study the influence of the surfactant amount on the catalyst performance. A nominal 5 wt % Ni was impregnated on the supports by a wet impregnation method. These catalysts were evaluated for CO 2 reforming of CH 4 in both the presence and absence of steam. The textural, structural, and physicochemical characteristics of the catalysts were thoroughly investigated with the help of various bulk and surface characterization techniques. The activity results indicate the superior nature of the catalysts obtained by the surfactant-assisted route over the one obtained by coprecipitation. Also, within the limits of the surfactant ratios used, the amount of surfactant employed during the course of support preparation seems to affect the activity, with catalysts prepared with the higher surfactant/metal molar ratio exhibiting better activity and enhanced stability. Structure-activity relationships (SARs) were formulated for some of the characteristics in order to explain the marked difference in activity between the catalysts obtained by the surfactant-assisted and coprecipitation methods and between the catalysts prepared by the surfactant-assisted route but with different surfactant/metal molar ratios. The SARs helped to identify that high oxygen storage capacity, high surface area, high reducibility, higher nickel surface area, better nickel dispersion, and higher surface nickel content are necessary for good performance in the CO 2 reforming of CH 4 . On the whole, catalysts obtained by the surfactant-assisted route exhibit a reasonably good performance in the CO 2 reforming reaction but were prone to deactivation in the presence of steam. The inherent hydrophilic nature of the ceria-zirconia support is the main cause for the apparent deactivation in the presence of steam.

Carbon dioxide reforming of methane (CDRM) to synthesis gas was studied over various Ni-based catalysts. It is shown that the mixed oxide supports CeO 2 -ZrO 2, CeO 2 -Al 2 O 3 , and La 2 O 3 -Al 2 O 3 , prepared using surfactant, exhibit a high catalytic activity and stability for CDRM. Temperature program reduction (TPR) results demonstrate that the presence of CeO 2, ZrO 2 , or La 2 O 3 leads to the enhancement of the Ni reducibility compared to Al 2 O 3 , which is an important indicator of high activity and stability of these Ni catalysts for CDRM. Our thermodynamic calculations indicate that CeO 2 could react with CH 4 to produce synthesis gas, and then CO 2 might reoxidize CeO 2-x to its oxidation state. Furthermore, CeO 2 might help in gasification of deposited carbon to inhibit the carbon formation and therefore improve catalyst stability. The presence of alumina tends not to affect the stability of the catalyst as well.

An improved viscoelastic surfactant (VES) based self-diverting acid system has been developed for matrix treatment of carbonate formations. The self-diverting acid contains a novel viscoelastic surfactant that undergoes an increase in viscosity as the fluid penetrates carbonate formations. The decrease in acid concentration as the acid reacts with the carbonate rocks promotes the transformation of spherical micellar structure into a worm-like structure that imparts high viscosity to the fluid. The highly viscous fluid acts as a temporary barrier to reduce further fluid loss into the wormholes and allows complete stimulation of all treating zones. After acid treatment, the viscous fluid is broken by either formation hydrocarbons or pre-flush fluids. The VES based self-diverting acid contains no solids, so there is no bridging when it is pumped through tubing. Rheological studies showed that the acid rapidly developed viscosity as the acid was spent with CaCO3, and the spent fluid was stable up to 300°F. Diversion tests using multiple-core flood equipment showed effective wormholing in both high permeability and low permeability cores. The effectiveness of the new system in diversion and stimulation was confirmed in more than 70 field applications, both through increased well production and /or injection and production logs. Introduction During matrix acidizing treatment of carbonate reservoirs, acids are injected into the formation below the fracturing pressure. When acids reach the formation, they will follow the path of least resistance and enter zones with the highest injectivity, which are high permeability zones or zones with the least damage. Acids dissolve carbonate minerals as they enter the formation creating highly conductive flow channels called wormholes resulting in a further increase in injectivity. Consequently, most treatment acids will flow through the same wormholes leaving other zones of interest unstimulated. Diversion, therefore, is required to ensure stimulation of the entire interval. Over the years, many chemicals including polymer gels, foams, oil soluble resins and rock salts1,2 have been developed as diverting agents. Field application of those diverting agents generally requires pumping multiple stages of alternating acid and diverting agent. A self-diverting acid is therefore highly desirable to simplify the process. Polymer based acid systems have been applied successfully in the field as self-diverting fluid3. The systems rely on in-situ increase in viscosity when the pH of the fluid rises as a result of acid spending. The in-situ increase in viscosity creates resistance to flow into the high injectivity zones allowing subsequent acids to enter zones with lower injectivity. The viscosity of the fluid then breaks down with further increase in pH as acids are completely spent with carbonates. However, there have been concerns about the potential damage to the formation as the system contains polymeric materials4,5. Recently, Chang et al reported the laboratory development of a VES based self-diverting acid for carbonate acidizing treatments6. The reduction of acid concentration as the acid reacts with the carbonate rocks promotes the transformation of spherical structure into a worm-like structure that imparts high viscosity to the fluid (Figure 1). The highly viscous fluid reduces the chance of further acid loss into the wormholes, thereby enabling complete acidizing of all zones. After acid treatment, the viscous fluid breaks down upon contact with formation hydrocarbons. The VES acid system contains no solids, so there is no bridging when it is pumped through tubing. However, this VES self-diverting acid system has upper temperature limit of 200°F.

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