Numerical investigation of coupled anomalous diffusion and heat transfer during thermal displacement process in porous media under local thermal equilibrium

Heterogeneities are acknowledged to exist on many different length scales in geological media and outcrops, leading to a huge range of fluid velocities, porosities, and effective thermal conductivities. In this regard, existing continuum-based non-isothermal simulation models may not always be accurate for predicting transport behavior in highly heterogeneous reservoir rocks, or fractured rocks with fractal geometry. In the present study, the fractional calculus theory is adopted to simulate anomalous fluid and heat transport in porous media under non-isothermal flow conditions. The resulting coupled mathematical model is developed under the assumption of local thermal equilibrium (LTE) and is handled numerically by employing existing finite difference and finite volume numerical discretization methods. Numerical experiments performed indicate that transport behavior of the anomalous non-isothermal model differs significantly from the classical non-isothermal formulation which is based on Darcy flux and Fourier-flux constitutive relations. The simulation results indicate that the sub-diffusive regime leads to a higher pressure-drop through the porous media. In addition, the rate of heat propagation in the porous media is noted to be retarded when the order of fractional differentiation deviates from unity. This study demonstrates the use of fractional calculus as a tool to characterize complex transport behavior observed in heterogeneous porous media

Mass and Heat Transfer of Thermochemical Fluids in a Fractured Porous Medium

The desire to improve hydraulic fracture complexity has encouraged the use of thermochemical additives with fracturing fluids. These chemicals generate tremendous heat and pressure pulses upon reaction. This study developed a model of thermochemical fluids’ advection-reactive transport in hydraulic fractures to better understand thermochemical fluids’ penetration length and heat propagation distance along the fracture and into the surrounding porous media. These results will help optimize the design of this type of treatment. The model consists of an integrated wellbore, fracture, and reservoir mass and heat transfer models. The wellbore model estimated the fracture fluid temperature at the subsurface injection interval. The integrated model showed that in most cases the thermochemical fluids were consumed within a short distance from the wellbore. However, the heat of reaction propagated a much deeper distance along the hydraulic fracture. In most scenarios, the thermochemical fluids were consumed within 15 ft from the fracture inlet. Among other design parameters, the thermochemical fluid concentration is the most significant in controlling the penetration length, temperature, and pressure response. The model showed that a temperature increase from 280 to 600 °F is possible by increasing the thermochemical concentration. Additionally, acid can be used to trigger the reaction but results in a shorter penetration length and higher temperature response

Experimental investigation of carbonate wettability as a function of mineralogical and thermo-physical conditions

Precise characterization of carbonate wettability is challenging and is broadly debated in recent past. While carbonates are known to be oil-wet, the influence of complex mineralogy, surface chemistry, and surface topographic features (e.g. surface roughness) on carbonate wettability did not receive much attention. Furthermore, despite scores of publications analyzing the influence of operating pressure and temperature on carbonate wettability, there are several contradictory trends. Therefore, to address these uncertainties associated with carbonate rock wettability, we report experimental observations of contact angles (θ) for carbonate/crude-oil/brine systems on five different carbonate samples (four real carbonate rocks and a pure calcite mineral) as a function of pressure, temperature, as well as variable mineralogy. In addition, the RMS (root mean square) surface roughness and the pertinent 2D and 3D surface topographic profiles of these rock samples were analyzed and correlated with the observed wetting behaviors. We find that increase in pressure results in an increase in θ in the low-pressure range, while relatively stable θ in high-pressure range. However, the observed θ values, follow both increasing and distinct trends with respect to temperature. Further, surface chemistry of samples suggest that calcite-based samples are relatively more hydrophilic compared to dolomitic carbonates. In addition, the RMS roughness and the corresponding 3D topographic profiles suggest that the samples with abundance of peaks demonstrated much higher θ values. These results may lead to a better understanding of the wider variability associated with the wettability behavior of carbonate rocks

Preliminary study of in-situ combustion in diatomites: SUPRI TR-32

Diatomaceous sediments of California host large reserves of oil and gas but are incompletely exploited. The matrix of these sediments is comprised largely of the frustules of diatoms (microscopic marine plants). Punctae in the frustules are responsible for the high porosities characteristic of diatomites (up to 70 vol. %), but because of the very small size of the pores, permeabilities are low (commonly around 1 md). Furthermore, the oil contained in the reservoirs is often either immature or heavily biodegraded, hence viscous. In order to test the feasibility of applying in-situ combustion techniques to diatomaceous reservoirs, a laboratory test was conducted for a section of core taken in the south plunge of the anticline in the Lost Hills field of the San Joaquin Valley in California. During the experiment, a fast steam plateau, good oxygen utilization, and an unusual front were observed. Fingering caused formation of a second front downstream. This finger stabilized and later became very hot (1600/sup 0/F). Velocity of front movement through the core almost doubled after the two fronts joined. API gravity of the oil extracted from the core ranged between 28 and 45, compared to the original value of 28/sup 0/ API. Tests were conducted to compare the cores before and after combustion, using scanning microscopy, power x-ray diffraction, and extraction techniques. After burning, the sediments changed from dark brown to red in color as a result of oxidation of organic and iron phases. Small numbers of diatom frustules were transformed from amorphous opal to quartz, with accompanying occlusion of pore spaces. With the exception of the color change, however, the sediments remained largely unaltered