No abstract

A computational modeling effort was undertaken to combine finite element analysis (FEA) and computational fluid dynamics (CFD) methods to simulate the closing of the blind shear rams of a blowout preventer (BOP) under flowing conditions. The objective of this effort was to develop a high-fidelity fluid-structure interaction (FSI) simulation methodology that reliably assesses the combined mechanical and hydrodynamic forces acting on BOP shear rams that could potentially impact the rams’ ability to safely shut-in a well. BOP shear ram designers typically consider the material properties and geometry of the drill pipe to be sheared and the hydrostatic flowing pressure during ram closure. Fluid hydrodynamic effects on the rams are difficult to simulate and currently cannot be produced in a laboratory setting due to complexity and personnel safety in conducting such tests under high transient conditions, and thus are often neglected. To determine the best computational approach in terms of complexity and accuracy, a novel simulation methodology was developed by coupling the fluid interaction with the BOP as it shears a drill pipe using LS-DYNA® and ANSYS® Fluent®. The conditions and assumptions made for this analysis are presented herein, and initial simulation cases are compared against validation data to confirm model accuracy. For a high-pressure, high-flow well scenario in the Gulf of Mexico (GOM), a one-way coupling of the FEA and CFD simulations was determined to be the best approach for modeling the closing of blind shear rams under flowing conditions. This investigation also confirms that as long as the fluid is single phase, the ram forces due to fluid flow effects are small in comparison to the mechanical shearing force. It is noted, that highly dynamic flow events such as slugging flow or the potential erosive effects of sands or solid particles present additional risks, and the analysis methodology described here can serve as the basis for additional investigations into more complicated flow scenarios.

Planar laser induced fluorescence (PLIF) is a measurement technique that can be used to provide a laboratory reference for validating the performance of field instrumentation that either directly measures mixture density or infers it from a combination of ancillary techniques. PLIF density measurements offer high-speed response and the ability to resolve minute flow features in transient flow patterns. Fundamentally, PLIF can also be used to verify multiphase flow models and predictive tools that are used for designing production piping. The use of PLIF to determine an instantaneous mixture density of two-phase flows has been successfully accomplished in previous fundamental laboratory studies found in literature. However, the use of this technique to determine the mixture density of three-phase flows for field-related scenarios has not been previously evaluated. To assess PLIF as a potential reference measurement system, a testing effort was undertaken to measure the instantaneous mixture density from a comingled oil-gas, water-oil, and oil-water-gas flow that was subjected to slug, churn, and bubble transient flow conditions inside of vertical piping. The objective of this work was to compare and validate the results obtained using the PLIF measurement approach against a commercially available gamma densitometer and tomography system for a variety of flowing conditions. The PLIF technique was able to resolve transient flow features and density values for both two-phase and three-phase flows through the piping. Distinct slug flow features such as the slug head, gas pocket, pocket collapse, and the tail were captured by PLIF and were observable in the raw image sequence captured by a high-speed camera. Additionally, the results for a variety of water-oil-gas flowing conditions were within 3% difference of a mixture density model that was calculated from liquid and gas flow measurements utilized in the test facility. The comparison of the PLIF results to the reference instrumentation indicates that this technique is successful at obtaining a mixture density for steady and transient oil, water, and gas comingled flows.

Improvement of cryogenic fluid storage and transfer technology for in-space propulsion and storage systems is required for long-term space missions. Screened channel liquid acquisition devices (LADs) have long been used with storable propellants to deliver vapor-free liquid during engine restart and liquid transfer processes. The use of LADs with cryogenic fluids is problematic due to low temperatures associated with cryogenic fluids. External heat leaks will cause vapor bubbles to form within the LADs that are difficult to remove in the existing designs. A tapered LAD channel has been proposed to reliably remove vapor bubbles within the device without costly thrusting maneuvers or active separation systems. A model has been developed to predict bubble movement within tapered LAD channels, and subsequent ground testing was completed with a simulant fluid to provide model validation data. Suborbital microgravity testing of tapered LAD technology was recently completed with two different simulant fluids and demonstrated that the concept can passively expel vapor bubbles within the channel. Two additional suborbital flights have been funded to further develop this technology by investigating the performance of larger scale versions of the design.

In gas processing, boosting, and gathering applications, gas-liquid separator equipment (typically referred to as a scrubber) is placed upstream of each reciprocating compressor stage to remove water and hydrocarbon condensates. However, field experience indicates that liquids are often still present downstream of the separation equipment. When liquids are ingested into the reciprocating compressor, machinery failures, some of which are severe, can result. While it is generally understood that liquid carryover and condensation can occur, it is less clear how the multiphase fluid moves through equipment downstream of the scrubber. In this paper, mechanisms responsible for liquid formation and carryover into reciprocating compressors are explored. First, the effects of liquid ingestion on reciprocating compressors reported in the open literature are reviewed. Then, the role of heat and pressure loss along the gas flow path is investigated to determine whether liquid formation (i.e., condensation) is likely to occur for two identical compressors with different pulsation bottle configurations. For this investigation, conjugate heat transfer (CHT) models of the suction pulsation bottles are used to identify regions where liquid dropout is likely to occur. Results of these investigations are presented. Next, liquid carryover from the upstream scrubber is considered. Multiphase models are developed to determine how the multiphase fluid flows through the complex flow path within the pulsation bottle. Two liquid droplet size distributions are employed in these models. Descriptions of the modeling techniques, assumptions, and boundary conditions are provided.