APPLICATIONS OF GEOPHYSICAL SURVEYS IN THE CONSTRUCTION OF A PIPELINE

Planning, designing, routing and construction of a petroleum condensate pipeline requires careful planning based on knowledge of the subsurface conditions of the site the pipeline is to be built upon. The purpose of this project was to assess for geologic hazards such as active landslides, potentially unstable regions, and areas that required the use of horizontal directional drilling (HDD). The scope of this project was fifty miles of pipeline that navigated steep topography, unstable rock types such as the Conemaugh group shale, old mine spoil, abandoned mine shafts, preexisting pipelines, highways and roads. Resources used for this project included aerial photographs, Google Earth files, topographic overlays, and a full desktop geotechnical report.

Risk factors of landslides considered for this project included areas that were at a 0.4 gradient or steeper, and sections of pipeline that were to be placed parallel to the slope angle. As detailed in the geotechnical report, other risk areas included shallow depth to bedrock, old mine spoil, mine subsidence, and possible HDD installation difficulties such as attempting to drill through unconsolidated gravel. Once risk areas were identified, recommended geophysical surveys were determined for each site, which were to be either refraction microtremor (ReMi) or electrical resistivity tomography (ERT). Lines were placed on aerial photographs to suggest the scope and orientation of onsite survey lines. Areas of pipeline that required HDD were the most survey intensive, as much deeper ERT penetration would be required to characterize the drilling conditions.

The next phase of the project is to apply the created survey maps to the field sites. The created maps will be used as references for what risks are being examined in each location, and to guide the collection of geophysical data such as that from ReMi and ERT. Data sets will be collected and processed in the field, allowing for modification of the survey design in real time. Recorded data will be inverse modeled in a 2D/3D format using Advance Geosciences Inc. EarthImager 2D software so it can be visually interpreted into results. The results of the geophysical methods used will be compared, and the strengths and weaknesses of each will be determined with the intent of developing the best methods of data collection and analysis.