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.

Evaluation of underground hydraulic fracturing using transient electromagnetic method.

The effective area of hydraulic fracturing is the core index to evaluate its effects. Through conducting transient electromagnetic tests, this paper deals with the influential range of the underground hydraulic fracturing as well as water-cut detection and gas extraction in the fracturing area. The resistivity response law of the coal seam in hydraulic fracturing process is explored, and the water-bearing area is determined. The obtained results from the tests show that the water-cut areas of the coal seam, measured by anti-interference transient electromagnetic instrument after fracturing, are commonly placed in the low-resistance area of the transient test. Further, the variations of amplitude of the low-resistance area in various directions of the test line are different. According to the variation law of the apparent resistivity of the coal seam before and after fracturing, the effective influential area of the hydraulic fracturing is defined, and the influence range is evaluated to be 35 m. The water cut and the gas extraction tests of the coal seam before and after fracturing are performed. The results reveal that the growth of water content in the coal seam is inversely proportional to the distance from the hydraulic fracturing borehole. The effective fracturing zone with the increment of the water content reaching 0.2% is the effective fracturing zone, and the effective fracturing zone of #9 and #10 is 38 m. After hydraulic fracturing, the gas extraction concentration would be in the range of 25.4-75.4%, with the average of 70.22%, which is 21.22% higher than that of the original coal body. The net amount of the gas extraction after fracturing is about eight times of that before fracturing. The effective fracturing range, which is determined by transient electromagnetic, is verified successfully. Exploring the effective fracturing regions of the hydraulic fracturing process would be very helpful in improving the evaluation system of the hydraulic fracturing effect.

High temperature/pressure MAS-NMR for the study of dynamic processes in mixed phase systems.

A new MAS-NMR rotor (the WHiMS rotor) has been developed which can reach pressures of 400 bar at 20 °C or 225 bar at 250 °C. These rotors are ideal for mixed phase systems such as a reaction using a solid catalyst with a liquid/supercritical solvent topped with high pressure gas in the head space. After solid and liquid portions of the sample are loaded, the rotor is capped with an o-ring equipped polymer bushing that snaps into a mating groove in the rotor. The bushings incorporate a check valve into the sealing mechanism which allows for pressurization without mechanical manipulation - they will allow gas to flow in but not out. This WHiMS rotor design has enabled experiments on a wide variety of biotic and abiotic mixed-phase systems. Geochemical systems have also been studied, for example, adsorption and confinement studies of supercritical methane/CO2 in clays and other minerals which display pressure dependent 13C chemical shifts. Example data from other mixed-phase chemical and microbial systems are reported. These include monitoring metabolite conversion of extremophilic bacteria found in subsurface systems at elevated pressures and real-time operando reactions in catalysis systems - with liquid-quality resolution for 1H and 13C NMR spectra.

Complex Fluids and Hydraulic Fracturing.

Nearly 70 years old, hydraulic fracturing is a core technique for stimulating hydrocarbon production in a majority of oil and gas reservoirs. Complex fluids are implemented in nearly every step of the fracturing process, most significantly to generate and sustain fractures and transport and distribute proppant particles during and following fluid injection. An extremely wide range of complex fluids are used: naturally occurring polysaccharide and synthetic polymer solutions, aqueous physical and chemical gels, organic gels, micellar surfactant solutions, emulsions, and foams. These fluids are loaded over a wide range of concentrations with particles of varying sizes and aspect ratios and are subjected to extreme mechanical and environmental conditions. We describe the settings of hydraulic fracturing (framed by geology), fracturing mechanics and physics, and the critical role that non-Newtonian fluid dynamics and complex fluids play in the hydraulic fracturing process.