| Description |
Unconventional resources (shale resources) have played a key role in increasing oil production in the past decade in the U.S. The sizes of pores in shales storing the oil are believed to be on the order of nanometers. It is believed that the fluids present in such small nanometer-scale pores have different properties compared to properties measured in the bulk. Fluid bubble points at given temperatures in the nano-sized pores are affected by the influence of pore walls in the vicinity of the fluid molecules. Bubble points affect the proportion of liquid or gas extracted from a given well and, thus, impact the economic viability of oil production. Hence, an accurate measure of a bubble point is important. Most studies on phase behavior of confined fluid systems have focused on modeling pore size dependence upon critical properties with no direct experimental evidence. In this work, direct bubble point measurements of hydrocarbon mixtures in several porous materials are provided. Two different synthesized mesoporous silica materials, SBA-15 and SBA-16, having nano-sized pores of about 4 nm, were used. Mesoporous monoliths with only nano-sized pores and no macro pores were also synthesized using a unique procedure developed in this study. Finally, to see the industrial application of this work, the Niobrara rock which is from one of the famous shale reservoirs in the U.S. was used. These porous materials were characterized well by X-ray diffraction (XRD), nitrogen adsorption/desorption isotherm (BET), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Binary mixtures of hydrocarbons (decane-methane, octane-methane) with 90:10 mole ratio were employed. The phase diagrams of those hydrocarbon mixtures were modeled using a commercial thermodynamic simulator. The bubble point of bulk (no porous medium) mixtures of decane-methane and octane-methane, and the bubble point with porous materials (SBA-15, SBA-16, and mesoporous monoliths) were measured experimentally. Experiments were also performed with micrometer-sized sand particles and the Niobrara rock. The bubble point results of the hydrocarbon mixtures in the porous materials and the Niobrara rock were lower than those in the bulk, while the bubble points with sand were closer to those with bulk measurements. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) results showed that the boiling points of pure decane and decane saturated in the monolith were different, possibly due to the confinement effect. This study shows the phase behavior of hydrocarbons in a confined system is different from that in the bulk system. |
