Project reports
26 April 2014 |   ByO Kozaci
Fugro Author

China National Petroleum Corporation (CNPC), one of the world’s largest oil companies, recently initiated the design and construction of a natural gas pipeline extending from China to the border between Turkmenistan and Uzbekistan.

The pipeline alignment through Uzbekistan, Tajikistan and Kyrgyzstan crosses one of the most active tectonic regions of the world. Fugro provided consultancy for a quick turn-around feasibility-level geohazards investigation and detailed topographical and geophysical data acquisition.

To meet CNPC’s ambitious project schedule, an integrated data acquisition and interpretation plan was implemented utilising airborne data acquisition and remote sensing data interpretation services. The project commenced in May 2013 with all field activities completed by November 2013 and consultancy reports submitted in stages throughout the project. 

Obigarm_Tajikistan

The results of Fugro’s lidar and EM aerial survey along with the geohazard investigation meet the basic requirements for the detailed design of the next step. It has helped to accelerate the process of project implementation and has provided a basis for future large, long distance pipeline digital construction and maintenance.
Mr Zhang Chi, Trans-Asia Gas Pipeline Project Manager, CNPC

The planned 900-kilometre pipeline route extends from west to east through a corridor bound by the Pamir Mountains and Tien Shan, also known as “The Roof of the World”; associated tunnels form part of the project. The initial project phase started in Tajikistan and extended into Kyrgyzstan while later phases extended into Uzbekistan.

Airborne Data Acquisition

Airborne platforms acquired topographic and geophysical data in Tajikistan and Kyrgyzstan, while lidar was used to acquire high resolution (1:2,000 scale) topographic information and EM survey methods collected geophysical data along the planned pipeline route. These data support ongoing construction planning and additional detailed geohazard characterisation. 

Mounting the FLI-MAP® system on Russian Mi-8 helicopters for LiDAR surveys in Tajikistan and Kyrgyzstan presented one of several new challenges. Fugro’s engineers worked on site and adapted the laser equipment to this new platform using local resources for cost and schedule savings. Adapting the FLI-MAP® system to the Mi-8 helicopter will considerably increase the potential for use of the airborne laser scanning system, opening doors for surveying completely new territories. Fugro also established 80 pairs of concrete markers and 250 topographic markers and undertook river bathymetry surveys at planned pipeline crossings.

For the Tajikistan and Kyrgyzstan segments  of the pipeline route a heliborne EM survey was implemented. Acquired data were processed daily in near real-time to provide estimates of soil thickness over bedrock and soil properties with depth along the alignment. The EM data was then integrated with desktop geohazard mapping to refine interpretations and guide borehole layout planning efforts.

Geohazards

Desktop geohazard screening included performing 1:50,000 scale mapping of geohazards (faults, landslides and liquefaction) within a five kilometre-wide corridor centred on the proposed pipeline route as part of a fatal flaw desktop screening study. Geohazard maps, including Quaternary geologic units, active faults and slope failures, were prepared for CNPC as a near real-time interim deliverable to guide and make necessary modifications to pipeline alignment, including proposed lidar and EM flight routes based on the initial identification of hazards. In addition, ‘traffic light-style’ landslide and liquefaction susceptibility maps were produced to provide guidance for route refinement for hazard mitigation.

As part of the phased approach, a geologic field verification study was performed to review and field check the desktop geohazard screening study findings along selected portions of the pipeline corridor. Experienced Fugro geologists undertook field reconnaissance and mapping in Tajikistan and Kyrgyzstan which resulted in refinements to the definition and extent of geohazards delineated in the desktop study, through increased geohazard mapping detail at key locations. This in turn improved confidence and specification of recommendations to CNPC on needs for further site-specific investigations.

A probabilistic seismic hazard assessment (PSHA) was completed by establishing a project-specific seismotectonic model characterising rates, magnitudes and style of faulting that impact the project area. PSHA calculations provided acceleration response spectra to guide design along the pipeline route for 475-, 975- and 2475-year return periods. The seismic hazard results were deaggregated to identify the key contributors to the hazard in terms of earthquake magnitude and distances to, and types of, seismogenic sources.

Borehole Drilling Programme

Fugro provided a geohazard-focused borehole layout to optimise sampling of different geologic units and potential hazards. Recommendations for geotechnical borehole locations along Tajikistan and Kyrgyzstan segments utilised the desktop Quaternary geologic mapping as a datadriven framework to optimise the borehole drilling programme for subsurface data collection and correlation. Potential locations for critical infrastructure that required refined estimates of site response for seismic loading were also identified.

The borehole programme recommendations considered future needs for geotechnical sampling methods and locations based on Fugro’s understanding of the variety of geologic conditions and potential hazards that may need further characterisation to fully assess pipeline constructability and reliability. Integrating the geohazard mapping results with the EM data reduced the number of boreholes required (compared to an evenly spaced drilling approach) while increasing the informational value of each borehole location. This in turn produced significant schedule and cost efficiencies for CNPC, while maintaining a sound scientific approach to satisfy engineering input requirements.

Key To Success

Key to the success of this geographically and logistically challenging project was the close collaboration among CNPC, Fugro teams and local government authorities, including Tajik Air, Fazo (Tajik Land Survey Authority), Supreme Air and Geoconsult Survey Agency in Kyrgyzstan.

 

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