No abstract

Biomarker thermal maturity is widely used to study burial heating of sediments over millions of years. Heating over short timescales such as during earthquakes should also result in measurable increases in biomarker thermal maturity. However, the sensitivity of biomarker thermal maturity reactions to short, higher-temperature heating has not been established. We report on hydrous pyrolysis experiments that determine the kinetic parameters of methylphenanthrene maturation at timescales and temperatures relevant to earthquake heating. Samples of Woodford Shale were heated at temperatures up to 343°C over 15-150 min. The thermal maturity of the samples as measured by the methylphenanthrene index-1 (MPI-1) increased with heating time and temperature. We find that MPI-1 increases with time and temperature consistent with a first-order kinetic model and Arrhenius temperature relationship. Over the timescales tested here, MPI-1 is strongly affected by maximum temperature and less sensitive to heating duration. Production of new phenanthrene isomers and expulsion of a liquid pyrolyzate also occurred. Differential expulsion of methylphenanthrene isomers affected the apparent maturity of the rock at lower temperatures and may need to be considered for organic-rich fault rocks. Our results demonstrate that the overall MPI-1 reaction extent in both the rock and pyrolyzate are a useful measure of thermal maturity and reflect temperature history during rapid heating.

This paper describes the methodology and technical solutions employed to address earthquake loading challenges on the Berkut topsides, including design and operational considerations. The Berkut platform is part of the Sakhalin-I development in offshore Russia, which is located in an area of high seismicity. Offshore platforms in the region require highly specialized designs to balance the competing requirements resulting from earthquake, wave and ice loading. Design strategies used in the region to protect structures from earthquakes include a tuned mass damper to protect the drilling derrick on the Orlan platform and Friction Pendulum seismic isolation on the Lunskoye-A and Piltun-Astokhskoye-B platforms.The Berkut structure consists of a four-shaft gravity based structure (GBS) with a topsides operating weight of approximately 50,000 tonnes. Seismic isolation devices called Friction Pendulum Bearings (FPBs) are placed between the GBS shafts and the topsides to reduce horizontal load transfer and accelerations. A performance-based design approach was developed to derive load and resistance factors providing a specified probability of non-performance (2% in 50 years with a minimum 90% level of confidence). This approach, which can be applied to a broad range of extreme environmental design criteria, enabled the seismic design for Berkut to be completed with a more consistent level of reliability than would have been achieved using traditional methods. Seismic analyses were carried out using nonlinear time history analyses of a fully coupled analytical model containing topsides, GBS and soil. This was complemented by finite element analysis for local design.A seismic event of smaller magnitude than the design event can impact production unless Operations personnel can confirm that no safety-critical components have been compromised by earthquake loading. A custom structural monitoring system has been configured to monitor accelerations and FPB displacements; and an earthquake-response strategy has been implemented to enable Operations personnel to make prudent decisions following an event.