Offshore geotechnical engineering

Offshore geotechnical engineering is a sub-field of geotechnical engineering. It is concerned with foundation design, construction, maintenance and decommissioning for human-made structures in the sea. Oil platforms, artificial islands and submarine pipelines are examples of such structures. The seabed has to be able to withstand the weight of these structures and the applied loads. Geohazards must also be taken into account. The need for offshore developments stems from a gradual depletion of hydrocarbon reserves onshore or near the coastlines, as new fields are being developed at greater distances offshore and in deeper water, with a corresponding adaptation of the offshore site investigations. Today, there are more than 7,000 offshore platforms operating at a water depth up to and exceeding 2000 m. A typical field development extends over tens of square kilometers, and may comprise several fixed structures, infield flowlines with an export pipeline either to the shoreline or connected to a regional trunkline. An offshore environment has several implications for geotechnical engineering. These include the following: Ground improvement (on the seabed) and site investigation are expensive. Soil conditions are unusual (e.g. presence of carbonates, shallow gas). Offshore structures are tall, often extending over above their foundation. Offshore structures typically have to contend with significant lateral loads (i.e. large moment loading relative to the weight of the structure). Cyclic loading can be a major design issue. Offshore structures are exposed to a wider range of geohazards. The codes and technical standards are different from those used for onshore developments. Design focuses on ultimate limit state as opposed to deformation. Design modifications during construction are either unfeasible or very expensive. The design life of these structures often ranges between 25–50 years. The environmental and financial costs in case of failure can be higher.

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Submarine pipeline

A submarine pipeline (also known as marine, subsea or offshore pipeline) is a pipeline that is laid on the seabed or below it inside a trench. In some cases, the pipeline is mostly on-land but in places it crosses water expanses, such as small seas, straits and rivers. Submarine pipelines are used primarily to carry oil or gas, but transportation of water is also important. A distinction is sometimes made between a flowline and a pipeline.

Offshore drilling

Offshore drilling is a mechanical process where a wellbore is drilled below the seabed. It is typically carried out in order to explore for and subsequently extract petroleum that lies in rock formations beneath the seabed. Most commonly, the term is used to describe drilling activities on the continental shelf, though the term can also be applied to drilling in lakes, inshore waters and inland seas. Offshore drilling presents environmental challenges, both offshore and onshore from the produced hydrocarbons and the materials used during the drilling operation.

Offshore geotechnical engineering

Geotechnical Studies: Preliminary Investigations CIVIL-306: Geotechnical engineering

Explores the significance of preliminary geotechnical studies and the tools used for data collection.