Microbubbles as proxies for oil spill delineation in field tests

To overcome the environmental impacts of releasing oil into the ocean for testing acousticmethods in field experiments using autonomous underwater vehicles (AUVs), environmentallyfriendly gas bubble plumes with low rise velocities are proposed in this research to be used as proxiesfor oil. An experiment was conducted to test the performance of a centrifugal-type microbubble generator in generating microbubble plumes and their practicability to be used in field experiments. Sizesof bubbles were measured with a Laser In-Situ Scattering and Transmissometry sensor. Residencetime of bubble plumes was estimated by using a Ping360 sonar. Results from the experiment showedthat a larger number of small bubbles were found in deeper water as larger bubbles rose quickly tothe surface without staying in the water column. The residence time of the generated bubble plumesat the depth of 0.5 m was estimated to be over 5 min. The microbubble generator is planned to beapplied in future field experiments, as it is effective in producing relatively long-endurance plumesthat can be used as potential proxies for oil plumes in field trials of AUVs for delineating oil spills

Evaluation of offshore drilling cuttings management technologies using multicriteria decision-making

This thesis presents an evaluation of drilling cuttings management technologies. A deterministic multicriteria decision-making approach was applied to help assess eight drilling cuttings management alternatives based on twenty five criteria. The eight evaluated technologies included a vertical centrifuge, horizontal centrifuge, thermal desorption, incineration, grinding, stabilization/sodification, bioreactor, and re-injection. The criteria included one threshold criterion of conformity with regulations and four categories of decision-making criteria: technical feasibility, rig compatibility, environmental impacts, and costs. The alternatives evaluated include existing technologies that are currently used offshore and those used onshore but with potential for offshore applications. The criteria were assigned weights corresponding to their importance. The total weights for each of the major aspects, technical, environmental, and cost, were approximately equal. The eight options were scored under each corresponding criterion according to the technologies' information obtained from various sources such as journal papers, personal communication with industry personnel, and questionnaires. To score the options, quantitative and qualitative scoring schemes were used. Quantitative data were used to qualitatively measure the option. The overall values of each option were then calculated using the Additive Value Model. Uncertainty analysis was also conducted to reflect uncertainty associated with the final results. -- From the evaluation, the three optimum drilling cuttings management technologies are the vertical centrifuge, horizontal centrifuge, and re-injection. In the present study, the fourth-ranked bioreactor technology is considered the most promising onshore technology for offshore applications. However, due to lack of availability of data for bioreactor, this option is associated with larger uncertainties compared with the three optimum options. Sensitivity analysis, where weight distribution of criteria was varied, was also conducted. The three optimum options remained as the best scored options regardless of the changes in criteria weights. In addition, the dominating criteria in this evaluation were determined to be costs, energy consumption, treatment capacity, treatment efficiency, size, and weight. These are considered the most influential properties in selecting a management technology to be used offshore. The least significant criteria included the associated solid wastes, ease of repair and maintenance, impacts on other operations, and chemical requirement of the technology. Further, this study also reviewed some innovative technologies including microemulsion, supercritical extraction, and silica microencapsulation in terms of their general process, status of development, and potential for offshore applications

Well modeling incorporating compositional and non-isothermal effects

This study proposed a methodology to predicting asphaltene precipitation in wells with advanced completions. A fundamental comprehensive two-phase flow model was proposed to predict asphaltene precipitation in horizontal production wells. The main objective of the research was to incorporate compositional and non-isothermal effects into an isothermal physical flow model and to investigate conditions that promote asphaltene precipitation. The precipitation induced by flow restriction found in equipment installed as parts of advanced well completion was the main focus. The proposed model consisted of a black-oil network model and a compositional asphaltene model allowing investigation of both physical and phase behaviour of flowing fluids in non-isothermal environment. The original network model was an isothermal model. In order to take into account heat transport in wellbores, an approach to predict wellbore temperature profile using a network-type model was proposed. This enabled the proposed network model to predict pressure, temperature, flow rate, and phase fractions of the produced fluid in different parts of the well. Local asphaltene precipitation predictions were able to be conducted at locations where asphaltene formation was likely to occur. In this research an asphaltene model was proposed. The model was developed based on a pseudo-three-phase solid-type asphaltene model. An isenthalpic flash was used to reflect the characteristics of flows through restrictions. By using the proposed asphaltene model, asphaltene onset conditions can be predicted and asphaltene phase behaviour at the conditions of interest can be determined. -- In this study the proposed methodology was used and successfully predicted flow behaviour in example well networks. It was found that different completion schemes have different effects on fluid conditions in the well and, in turn, asphaltene precipitation behaviour. The example simulations suggested that the drastic pressure drop induced by the valve restriction can cause asphaltene to precipitate. In the example cases the precipitation occurred inside the restriction thus downstream and upstream conditions were not sufficient for evaluation of asphaltene precipitation. In addition temperature also has effects on asphaltene precipitation prediction. The isothermal assumption for production systems, where the temperature in the well is always constant and equal to the reservoir temperature, may not be sufficient to accurately describe the asphaltene phase behaviour in the well. An increase in fluid temperature inside the restricted flow path also has effects on prediction of the asphaltene onset pressure. The extent of these temperature effects depend on the shift in the predicted onset pressure compared with the prevailing pressure drops in the entire well network

A Backseat Control Architecture for a Slocum Glider

Adaptive sampling provides an innovative and favorable method of improving the effectiveness of underwater vehicles in collecting data. Adaptive sampling works by controlling an underwater vehicle by using measurements from sensors and states of the vehicle. A backseat driver system was developed in this work and installed on a Slocum glider to equip it with an ability to perform adaptive sampling tasks underwater. This backseat driver communicated with the main vehicle control system of the glider through a robot operating system (ROS) interface. The external control algorithms were implemented through ROS nodes, which subscribed simulated sensor measurements and states of the glider and published desired states to the glider. The glider was set up in simulation mode to test the performance of the backseat driver as integrated into the control architecture of the glider. Results from the tests revealed that the backseat driver could effectively instruct the depth, heading, and waypoints as well as activate or deactivate behaviors adaptively. The developed backseat driver will be tested in future field experiments with sensors included and safety rules implemented before being applied in adaptive sampling missions such as adaptive oil spill sampling