Oman-India Pipeline Route Survey
Authors: Mullee J.E. 
Published: October 2008

Paper describes the geological setting in the Arabian Sea For a proposed 28-inch gas pipeline from Oman to India Reaching 3,500-m water depths. Covers planning, Execution, quality control and results of geophysical, Geotechnical and oceanographic surveys. Outlines theory And application of pipeline stress analysis on board survey Vessel for feasibility assessment, and specifies equipment used.

INTRODUCTION

In the fall of 1993, the Oman Oil Company sought to Establish the technical feasibility of laying a submarine Gas pipeline from Oman to India. Figure 1 shows the Project area. The pipeline would have to be laid in water Depths up to 3,500 meters 4 times the existing limitand would require marine survey techniques not Available at the time. Several known and suspected Natural hazards lay in wait on the seabed.

The challenge of surveying the route and proving Pipe way feasibility was accepted with enthusiasm by a Team of companies operating on the leading edges of Their respective technologies.

BASELINE STUDY

The first step was to carry out a Baseline Study (desktop Study). This provided valuable information for planning Field work and guiding on-the-spot decisions on board the Survey vessel (Refs. 1 through 5).

The tectonic setting of the project region is shown on Figure 2. The Gulf of Aden is being opened by the Carlsberg Ridge, which has an offset at the Owen Fracture Zone. This is believed to be connected to the Murray Ridge, which runs NE across the pipeline route.

The bathymetric expression of these features is shown On Figure 3. The Murray Ridge dominates the central Section of the pipeline route, while the Omani and Indian Continental Slopes fall sharply to the Abyssal Plain on Both sides. Seamounts in the Murray Ridge rise to within 300 meters of the surface from the surrounding, flat Seabed, 3,500m deep. The Dalrymple Trougha long Fault graven running along the Murray Ridge would also Have to be crossed by the pipeline.

The Indus River 11th largest in the world has a 70-km-wide fan which has deposited sediments up to, 100m thick (Figure 4). Here the study revealed a Complex system of large submarine channels reaching Lengths of 500km. The channels have been formed by Turbidity currents flowing across the fan over periods Measured in millions of years. Turbidity currents are Bodies of water move laden with sediment that periodically Down slope in otherwise still conditions.

The study indicated that the pipeline could not avoid Crossing highly sinuous channels up to 8 km wide and With 275-m-high levees. The levees were built up by Successive overtopping of the channel sides by the Sediment flows. Seabed samples taken by previous Surveys indicated that turbidity currents had probably not Flowed in the region of the planned pipeline route for Several thousand years.

The study also provided valuable information on the Probable onset and intensity of the SW and NE Monsoon Storm periods, and the likelihood of interference from Fishing and other vessels Overview covering such a large, Relatively unknown terrain in one survey season was a Major challenge.