Oral Session-023: Understanding processes associated with chronic hydrocarbon releases from natural and accidental sources
When: Thu, February 7th, 8:30 AM – 12:00 PM
Where: GoMOSES, Hyatt Regency
Scientists working on the MC-20 incident will be presenting at the Gulf of Mexico Oil Spill & Ecosystem Science conference in New Orleans on Thursday, February 7, 2019.
Their presentations will take place during “Oral Session-023: Understanding processes associated with chronic hydrocarbon releases from natural and accidental sources,” and include:
Application of Physical, Chemical, Biological and Geological Constraints on Petroleum Seepage at MC20
In 2004 Hurricane Ivan induced a regional submarine slope failure that inundated block 20 of the Mississippi Canyon protraction unit. The flow transported and then toppled Taylor Energy’s MC20 platform, which became partially buried by the 40-foot emplacement of new sediment, and came to rest 550 feet downslope from its original location. Prior to the Hurricane the platform was producing ~1000 barrels of oil per day, with >99.5% of production potential coming from nine wells; the remaining 16 wells had been produced in the preceding decades to the point they no longer flowed oil without stimulation. Following the Hurricane, oil freely leaked from a subset of wells, focused at two seafloor locations: the former location of the platform which retained the buried well heads, and near to the fallen platform where the conductor pipes (the pipes that connect the platform to well heads) had severed and become buried. By 2011 nine intervention wells had been completed for the producing wells mentioned above, which eliminated seafloor discharge at multiple locations including the site over the wellheads, but a persistent oil sheen remains in the vicinity of the platform. The contemporary surface sheen appears to emanate from the area near to the platform that overlies the severed conductor pipes. This area has developed into a large scour pit from which oil and gas seep. The focus of this talk is on placing holistic constraints on the processes active at this site, including biological, chemical, physical and geological processes that define the immediate source of seeping petroleum and the rates at which such processes occur.
Insights from the long-term Taylor Energy response at the Mississippi Canyon Block 20: A review of several decades of chemical data
Following the 2004 toppling and burial of the Taylor Energy Company’s platform in the northern Gulf of Mexico at Mississippi Canyon block 20 (MC-20) by a massive hurricane-induced submarine slide, the wreckage field has hosted a pervasive surface sheen. However, the immediate source feeding the sheens and the rate of release are uncertain and the focus of ongoing response activities. We conducted a forensic investigation of analytical data from 1986 to 2018 to assess the likelihood of a single dominant source (e.g., a leaking well) feeding the contemporary slick, which we compared to sediment samples and slick samples from the site. Our results show a plurality of biodegraded slick oils sufficiently complex that a single source is excluded. A forensic comparison of sheens collected at different times with sediments indicates multiple oils feeding the sheens with contributions that vary in space and time. Collectively, the heterogeneity in surface sheen, the degree of biodegradation in both surface sheens and sediment oils, and the extent of sediment oiling indicate the contemporary sheen at the MC20 site derives primarily from a plural assortment of residual oil from the saturated sediments near the downed jacket. These results are inconsistent with surface sheens being from an ongoing release and are difficult to reconcile with recent remote sensing-based reports that claim flow rates in excess of 39.71 to 110.83 cubic meters per day. The distinction between residual oil in sediment and active ongoing discharge is important because it dictates response options that are viable and appropriate for the site, a topic of active consideration.
Two decades of in-situ observation guiding MC20 response operations: what we have learned and why it matters
Forensic analysis of the MC20 platform’s destruction indicates that the hurricane-induced turbidity flow which toppled it was unlike anything previously encountered or contemplated by US regulatory policy. The unusual characteristics of this disaster, combined with the natural complexity of this shelf break region has required careful planning and execution of response operations in order to minimize environmental impact and safety risks. Over the past two decades numerous in-situ surveys have been conducted at the MC20 site to inform these response operations using an array of advanced in-situ technologies operated from surface ships, remotely operated vehicles, autonomous underwater vehicles, seafloor tethered platforms, and saturation divers. Under the auspices of the Unified Incident Command, results from these operations have been used to develop a composite 4-dimmensional model of the site in order to aid situational awareness, with particular emphasis on understanding the persistent oil sheen, along with the potential utility, risks, and consequences of specific response actions. This talk presents an overview of the in-situ technologies and methods used to inform response operations, examines the 4D model developed from these studies and its use in guiding response operations, as well as the physical and chemical evolution of the MC20 site over the past 14 years.
Character and Dynamics of Surface Sheens at MC20
A seafloor collapse during hurricane Ivan sheared the legs of the MC20 platform, moved the platform approximately 550 feet, bent well piping, and buried damaged wells below newly deposited mud. This unforeseen event and associated extraordinary damage to the MC20 structure has resulted in the presence of a persistent surface sheen at the site. Under the Unified Command, a workgroup was chartered to “assist in identifying the seabed location(s) of the hydrocarbon source(s) causing the continue sheening in MC20”. Data collection included: water column velocity measurements (profiles); time-stamped, georeferenced aerial observations of sheen origination(s); forensic analysis of discrete samples of recently surfaced residual oil (rosebuds); time-stamped, georeferenced locations of surface observations of rosebuds and dry gas bubbles at the origin of the sheen and locations along the surfacing trajectory; conductivity, temperature, and speed of sound depth profiles; and acoustic multi-beam imagery of water column anomalies and bathymetry. This talk presents information on characteristics of surfacing material and dynamics of surface expressions including models of upward trajectory of hypothetical releases and subsequent comparison of model output to observations at the surface and multibeam imagery of acoustic water column anomalies.
View the program here: