Location: Sakhalin Island, Russia
Client: Exxon Neftegas Limited
In 2008, MEG Consulting Limited (M+EG) was contracted by Exxon Neftegas Limited to perform a liquefaction assessment for the foundation soils at the Odoptu North Well Site located at the central coastal section Sakhalin Island, Russia. Subsequently in 2009, M+EG was requested to provide site supervision for the geotechnical program that was being performed for the proposed haul road alignments that will be constructed to allow construction access as the development of the onshore facilities is progressed.
A drill pad is to be built at the onshore facilities location that will be used to directional drill out to the reservoir some 8-10 km offshore. ExxonMobil has had particular success in this area achieving records for directionally-drilled wells.
The scope of work that is to be provided by M+EG for the project considers the following:
- Site supervision of drilling and sampling activities over a 4-month period in 2009;
- Analysis of the susceptibility of the non-frozen granular soils to liquefaction under the design earthquake conditions;
- Evaluation of the liquefaction potential for the presently-frozen soils that are expected to thaw during the lifetime of production operations at the Odoptu Site;
- Based on the results of the liquefaction analyses, the potential for both vertical and horizontal ground deformations was assessed.
- The site investigation work was completed over the period August 2008 to January 2009. Conditions along the proposed haul road alignment were particularly severe during the main winter months;
- Environmental controls were important in the sensitive habitat;
- One important objective of the field investigation was to determine the location of permafrost areas, particularly in the plant site area. Thaw-back of the permafrost will induce thaw-settlement in the frozen granular soils and is a source of potential foundation problems. A range of thaw settlements were estimated in order to assess the susceptibility of the presently-frozen granular soils to liquefaction and resulting vertical settlements.
- Even in good foundation areas, piled foundations were necessary to limit potential foundation settlement. The potential ground movements around the drill rig were of significant concern.