Nitrogen (N2) and Carbon Dioxide (CO2) foams have been used as hydraulic fracturing fluids for several decades to reduce water usage and minimize damage in water-sensitive reservoirs. These foam treatments require gases to be liquefied and transported to site. An alternative approach would be to use natural gas (NG) that is readily available from nearby wells, pipelines, and processing facilities as the internal, gaseous phase to create a NG-based foam. Hydraulic fracturing with NG foam is a relatively inexpensive option, makes use of an abundant and often wasted resource, and may even provide production benefits in certain reservoirs. As part of an ongoing development project sponsored by the Department of Energy (DOE), the surface process to create NG foam is being developed and the properties of NG foam are being explored. This paper presents recent results from a rigorous pilot-scale demonstration of NG foam over a range of operating scenarios relevant to surface and bottomhole conditions with a variety of base-fluid mixtures. The Pilot-scale Foam Test Facility (PFTF) used in these investigations is first described. The PFTF is capable of generating foamed fluids at pressures up to 7,500 psig and at temperatures in excess of 300°F. Then, results from several investigations aimed at proving NG foam at conditions relevant to the field are presented. NG foam was characterized using rheology measurements and flow visualization techniques. Experiments were performed to investigate the texture and stability of NG foam generated by two different mixing methods: one using a custom designed tee to match mixing velocities in the field where the gas phase is jetted into the aqueous stream, and another to ensure comprehensive mixing for laboratory analysis. Parametric studies were conducted to explore the effects of flow rate, foam quality, and temperature on the stability of NG foam. Moreover, different fluid preparations were used to investigate the effect of base fluid and additive concentrations on the stability of NG foams. Additional laboratory studies that investigated foam stability with produced water and multicomponent NG mixtures are also reported. The NG foams explored in these investigations exhibited typical, shear-thinning behavior observed in rheological studies of N2- and CO2-based foams. The measured viscosity and observed stability indicate that NG foams are well suited for fracturing applications. Like other foams, NG foam exhibits sensitivity to operating temperature characterized by a decrease in apparent viscosity as temperature increases. Rapid foam breakdown was observed at significantly elevated temperatures exceeding 290°F. In addition to fluid characterization, these investigations also yielded several key lessons that should be applied to future field demonstrations of NG foam.

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Demand is constantly increasing for high-fidelity models that execute quickly. To increase the fidelity of aircraft engine simulations, low-fidelity thermodynamic models are often interfaced with high-fidelity models used for capturing 2D and 3D effects. Unfortunately, interfaces and high-fidelity models are typically slow compared to rapid lower-fidelity thermodynamic models. This paper presents an approach for managing the interface between a low-fidelity model and high-fidelity model that, under certain circumstances, significantly reduces simulation time. The typical solver in a thermodynamic engine simulation sequentially iterates through each component in the system until a converged solution is reached. This type of communication pattern is also known as synchronous communication. Alternatively, an asynchronous communication pattern partitions the model into independent groups of components. Each partition contains its own solver, and each partition converges independently of the others. By partitioning a high-fidelity subsystem model, which was developed in an external tool, along with its associated interface, the solver variables associated with the subsystem model can be separated from the main solver. This implementation can reduce the number of calls to the high-fidelity subsystem and reduce overall simulation time. To demonstrate the asynchronous communication pattern, and to explore the approach’s impact on simulation time, a turbine-based combined cycle (TBCC) engine performance model was developed using the Numerical Propulsion System Simulation (NPSS) software. The NPSS model was interfaced with a high-fidelity afterburner model that was developed in an external tool. Using an asynchronous communication pattern, the engine performance model converged roughly 2.2x faster than using the conventional synchronous communication pattern for the same model. However, it was also shown that the asynchronous communication pattern is not beneficial in all scenarios, because it requires more total solver iterations. In this paper, the authors discuss the implementation and application of the asynchronous communication pattern, results, and conclusions.