No abstract

Foams have been used as hydraulic fracturing fluids to reduce water usage and minimize the potentially deleterious impact on water-sensitive formations. Traditionally, carbon dioxide (CO2) and nitrogen (N2) have been used as the internal phase in these foamed fluids. Hydraulic fracturing with natural gas (NG) is a relatively inexpensive option, particularly if NG produced from the wellhead can be used without significant processing. In an ongoing program sponsored by the US Department of Energy (DOE), an alternative fracturing process is being developed that uses NG-based foam. Previously, the optimal thermodynamic pathway was identified to transform wellhead NG into pressurized NG suitable for use as the internal phase in a foamed fracturing fluid. Recent work has focused on preparing a NG-based foam at surface conditions typically encountered in hydraulic fracturing and measuring the stability and rheological properties of the foam. In addition, the transient response of the foam during fracture initiation was simulated using a fast-acting solenoid valve. A single base-fluid mixture was prepared by combining a commercially available viscosifier and foaming surfactant with water. The base fluid was then injected into a tee using a water pump. Simultaneously, liquefied natural gas (LNG) was pressurized using a cryogenic pump, vaporized using a heat exchanger, and injected into the tee to mix with the base fluid and generate foam. The foam then flowed through approximately 300 ft of 0.312-in. inside diameter (ID) tubing equipped with pressure transducers at several locations. The test fixture included a sight glass to visually inspect the quality of the foam. This paper reports on findings related to foam stability and rheology and compares these results to previous studies on foamed fracturing fluids.

No abstract

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.

No abstract