Subsea Chemical Dispersant Research - SL 2014_Belore-44-Subsea...Subsea Chemical Dispersant Research...

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Transcript of Subsea Chemical Dispersant Research - SL 2014_Belore-44-Subsea...Subsea Chemical Dispersant Research...

  • Subsea Chemical Dispersant Research

    Randy Belore SL Ross Environmental Research Limited

    Ottawa, ON, Canada randy@slross.com

    Abstract

    The primary objective of this work was to determine if the presence of natural gas or methane in a subsea oil and gas discharge would reduce the effectiveness of a dispersant injected into the gas-oil mixture. The underlying concern is that some of the dispersant might be attracted to the hydrocarbon gas bubble-water interface and not be available to attach to the oil-water interface and thus reduce the effectiveness of the applied dispersant. Tests were conducted with air (non-hydrocarbon) or methane (hydrocarbon) with all other parameters kept constant and the resulting oil drop size distributions compared. The significance of dispersant to oil ratio (DOR), gas to oil ratio (GOR), oil type and orifice diameter were also evaluated in the test program. The size of the oil drops generated in the subsea release, specifically the volume medium drop diameter (VMD) metric of the oil drop size distribution, was used as the criteria for comparison of dispersant effectiveness. Tests were conducted both at the SL Ross laboratory facilities in Ottawa and at the BSEE operated National Oil Spill Response Research & Renewable Energy Test Facility (Ohmsett) in Leonardo, New Jersey. The tests utilized a horizontal jet release to segregate the rising oil drops and gas bubbles to allow direct measurement of the oil drops using a laser in-situ particle size analyzer (LISST). Air pressurized supply tanks and precision needle valves for flow control were implemented for the oil and dispersant delivery systems. Gas flow was controlled using a rotameter flow meter.

    The effect of methane in the flow stream on dispersant effectiveness was not consistent throughout all tests. For two of the oils tested a slight reduction in dispersant effectiveness was identified, as measured by an increase in the oil drop size distribution VMD by about 20 to 30 microns, when methane as opposed to air was present in the flow stream. Terra Nova crude oil, in the small orifice tests conducted at SL Ross, and Endicott crude oil in the large orifice tests conducted at Ohmsett exhibited a slight reduction in effectiveness. For the Dorado oil tested at Ohmsett there was no apparent loss in effectiveness when methane was present in the discharge in either the small or large orifice tests conducted.

    The dispersant to oil ratio (DOR) had a significant effect on dispersant effectiveness in all of the tests conducted, as would be expected. DORs of at least 1:100 were needed to achieve dispersions with oil drop VMDs of less than about 100 microns for the various conditions tested.

    The orifice size used in the testing appeared to have an effect on the dispersant effectiveness with better dispersant efficiency generally achieved in the larger orifice tests.

    The effect of gas to oil ratio (GOR) on the dispersant effectiveness was inconclusive. This study did not address the issue of deep water releases, gas properties under high

    pressure, complex natural gas mixtures, or hydrate formation under high pressure conditions and is applicable only to shallow well blowout situations.

    1 Introduction

    The BP Macondo subsea blowout in the Gulf of Mexico was the first oil spill response that included the injection of chemical dispersants into a subsea oil and gas plume. The effect of

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    mailto:randy@slross.com

  • this countermeasure on the ultimate fate of the oil was difficult to quantify during the spill event, but the operation generally was deemed to be effective in breaking the oil into smaller drops that resulted in less oil reaching the surface and an increase in the rate of bio-degradation of the oil. As such, there is considerable interest by both spill response organizations and regulatory agencies to 1) develop methods to measure the characteristics of the oil and gas plumes generated before and after chemical injection, 2) confirm that the injection of dispersants in a subsea plume is indeed effective, and 3) develop equipment and procedures to maximize the potential of the countermeasure under various spill and environmental conditions.

    Because this is a very new approach to the use of chemical dispersants, there are many questions that need to be answered before a full understanding of the processes will be gained. Many of these questions include the development of plume measurement methods, nozzle design, study of injection location effects, application rates, the effects of temperature and pressure and the presence of gases and sediments. The research conducted in this project investigates the issue of the effect of natural gas, oil type, dispersant to oil ratio, and gas to oil ratio on the subsea chemical dispersion process.

    The primary objective of this work was to determine if the presence of natural gas or methane in a subsea oil and gas discharge would reduce the effectiveness of a dispersant injected into the gas-oil mixture. The underlying concern was that some of the dispersant might be attracted to the hydrocarbon gas bubble-water interface and not be available to attach to the oil-water interface and thus reduce the effectiveness of the applied dispersant. Tests were conducted with air (non-hydrocarbon) or methane (hydrocarbon) with all other parameters kept constant and the resulting drop size distributions compared. The significance of dispersant to oil ratio (DOR), gas to oil ratio (GOR), oil type and orifice diameter were also evaluated in the test program. The size of the oil drops generated in the subsea release, specifically the volume medium drop diameter (VMD) metric of the oil drop size distribution, was used as the criteria for comparison of dispersant effectiveness.

    2 Project Description

    Tests were conducted both at the SL Ross laboratory facilities in Ottawa and at the BSEE operated National Oil Spill Response Research & Renewable Energy Test Facility (Ohmsett) in Leonardo, New Jersey. The small scale work at SL Ross provided convenient and cost-effective test environments to evaluate methods for liquid and gas delivery to the underwater nozzle and methods for the measurement of the resulting oil and gas plumes. The liquid and gas delivery systems and successful oil drop size measurement techniques developed and tested in the small scale testing were then implemented in the larger scale tests conducted at Ohmsett. The laser in-situ particle size analyzer (LISST) was the primary tool used to measure the dispersed oil drop sizes in the discharge plume in the small scale tank tests at SL Ross and in the large scale tests at Ohmsett. The processing of digital video imagery for the measurement of the larger oil drops present in the untreated oil and gas plumes was investigated but a suitable method was not identified and further work in this area is required. The preliminary small-scale testing conducted at SL Ross is not presented in this paper due to space restrictions.

    This paper focuses on the results of the Ohmsett large-scale tank testing. The full project report can be requested form the U.S. Bureau of Safety and Environmental Enforcement (BSEE), the project funders. Contact information for BSEE can be found at http://www.bsee.gov/.

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  • 3 Large-Scale Ohmsett Testing Large scale testing was conducted at the Ohmsett facility in Leonardo New Jersey. A

    photo of the test tank is provided in Figure 1. The tank is 18 meters wide, 61 meters long with a water depth of 2.4 meters. The tests in this program were completed next to one of the viewing windows on the west side of the tank. The main bridge, identified as the tow bridge in Figure 1, was used as the main base of operations during the on-tank testing. All tests were completed with no wave action with water temperatures ranging from 24 C to 27 C. The salinity and interfacial tension of the water with mineral oil at the time of the tests were 31 ppt and 38.5 dynes/cm, respectively. The high interfacial tension value indicates that the test water was clear of surfactants at the time of the testing. The tests were conducted outdoors with relatively small methane flow rates that were allowed to dissipate under natural diffusion processes. The research participants on site were made aware of the use of the methane and precautions were taken to ensure that no ignition sources were present during the methane release.

    Figure 1 Ohmsett - The National Oil Spill Response Research & Renewable Energy Test

    Facility

    4 Test Apparatus The experience and methods gained from the small-scale testing phases of the project

    were transferred to the larger scale testing conducted at the Ohmsett facility. The dispersant, oil and gas delivery and measuring methods used in the small scale testing were deployed in the large scale work. One improvement to the setup was the implementation of underwater remotely activated solenoid valves in the dispersant, oil and gas flow lines placed near the discharge header to provide more precise control over the flow start and stop conditions. Figure 2 shows the equipment cage used to hold the LISST-100x drop size analyzers, video cameras, acoustic drop size measurement equipment and outlet nozzles. The acoustic equipment, high definition underwater camera and one of the GoPro cameras was deployed and managed by Applied Research Associates to gather data for further refinement of their oil drop size measurement system. Two LISST devices were mounted directly above the horizontal discharge nozzle. The LISST devices were fitted with light path reduction modules (80 and 90%) to permit recording in

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  • high oil concentrations. One underwater GoPro camera (1440x864 pixel resolu