No abstract

Wettability of two types of sandstone cores, Berea (permeability on the order of 600 md), and a reservoir rock (permeability on the order of 10 md), is altered from liquid-wetting to intermediate gas-wetting at a high temperature of 140°C. Previous work on wettability alteration to intermediate gas-wetting has been limited to 90°C. In this work, chemicals previously used at 90°C for wettability alteration are found to be ineffective at 140°C. New chemicals are used that alter wettability at high temperatures. The results show that: (1) wettability could be permanently altered from liquid-wetting to intermediate gas-wetting at high reservoir temperatures, (2) wettability alteration has a substantial effect on increasing liquid mobility at reservoir conditions, (3) wettability alteration results in improved gas productivity, and (4) wettability alteration does not have a measurable effect on the absolute permeability of the rock for some chemicals. We also find the reservoir rock, unlike Berea, is not strongly water-wet in the gas/water/ rock system. ity alteration to examine the effect of treatment on gas productivity. In the following, we describe the rocks and fluids used, and present the experimental setup and procedures.

The dynamics of asphaltene molecules is highly impacted by both the nature of the solvent and the physical conditions of the system. We performed molecular simulation to investigate the dynamic behavior of asphaltene during gas flooding. We also consulted the experimental observations for validation purposes when available. Two structures representing the archipelago and continental types are used, whose aggregation and interactions are studied in methane (C1), propane (C3), carbon dioxide (CO2), heptane (C7), and toluene as pure solvents, binary mixtures of toluene and either C1, C3, or CO2, and a representative oil composition. The continental structure is used afterward to evaluate the impact of temperature, pressure, and resin content on the aggregation dynamics in CO2 mixtures. Interestingly, the solvating power of CO2 is dependent on the asphaltene structure where inhibitor-like behavior is observed for the continental structure and precipitator-like behavior is observed for the archipelago structure. The solvent quality is highly correlated with the solvent s ability to replace the interactions among asphaltene molecules with interactions between asphaltene and solvent. The aggregate size is reduced by temperature and enhanced by pressure in CO2. However, limited effect is reported for resins on asphaltene dynamics in CO2. The aggregation of asphaltene is impacted by the physical state of CO2 as its solvating power to asphaltene is significantly enhanced in its supercritical state. Nonetheless, this impact is limited when CO2 is introduced to a representative oil mixture.

No abstract

Spontaneous imbibition is one of the mechanisms proposed to reveal the fate of fluids used during fracturing operations in shale reservoirs. However, the influence of salinity and mineralogy on the imbibition kinetics is not yet well understood. We performed imbibition experiments on samples collected from Woodford and Caney shale outcrops with slick water having salinities up to 15 wt % KCl. The impact of salinity on the imbibition rate and capacity shows a different trend for samples of varying mineralogy. A correlation between the carbonate/clay ratio and the imbibition rate is observed. This ratio and the illite content were linked to be factors affecting the impact of salinity on imbibition. This correlation suggests a maximum volume of imbibition at a ratio of 1.5. The impact of salinity on the formation strength seems to correlate with the amount of siderite and anhydrite present in the rock. It is worth noting that the swelling of the expansive clay minerals could mask the imbibition signature of the samples, where the apparent weight is used to estimate the liquid uptake. This is mainly apparent in the later stages when the bulk volume expansion can outweigh the liquid uptake; however, this effect does not reach the level of impacting the trends and correlations observed in this study.