How Difficult Is Offshore Drilling?

Offshore drilling in the oilfield can be done with 3 types of "vehicles" or Oil Drilling Rig, depending on the depth of water

1. Offshore drilling For depth of 7 - 15 ft (shallow sea) is often used type of oil rig "Swamp Barge." How to mobilize the oil rig to the location of the wells? after the rig was drowned by filling the tanks Ballast with water. After the rig sitting on the base and the Spud Can be fixed into its sea floor, we can start the offshore drilling. To prevent the oil rig from the sea flow , The oil rig is stabilized first by attaching it to the poles. If they are not stable and the position of rig is moving, there will be a serious problem, especially the well.

2. Offshore drilling for depth 15 - 250 ft, is usually used jack-up rig (typically 3 or 4 feet, and the independent legs with spud legs on its leg. There is also a non-independent leg with type "mat foundation" . The oil riglegs with a mat foundation is usually used in the sea that have soft seabed .
Jack-up oil rig can be used to drill exploration wells in the oilfield . The most critical time is when moving the oil rig aproaching to the platform, because the rig should be close to a certain distance from the platform. It should be done carefully, The oil rig might hit the platform and can cause significant damage. The distance between the oil rig and platform has been determined according to the design,so oil rig floor and derrick located on the cantilever on the deck that can moved so those all can reach the well slots on the platform . One platform can contain 4, 6, 9, 12 or more slots depending on the size of the well platform. Platform for approaching oil rig is guided by 2 or 3 towing boats, and supported by 2 or 4 anchors in the rig. After the rig in the final locked position, the rig legs are given the initial burden with water. The Oil Rig hull is increased slightly above sea surface until the rig legs is not going down at 100% preload. Usually after the oil rig is stable for three hours the "initial burden" is removed and the rig can be jacked up to the height of a certain mode position for Drilling on the platform. That's how the offshore drilling done for water depth 15 - 250 ft.

3. Offshore drilling for depth (> 250 ft), used drillships (floater) or semi-submersible.
This Floater Drilling Rig is usually used for drilling well since this type can be attached to developments wells.This type of oil rig is usually equipped with 8 anchors, which are spread around the rig. After the rig is in the position of the wells, all anchors are deployed and given tension (pretension) to 300000lbs for each anchor. Similar to 'preloading' in type jack-up oil rig, 'pretension' during mooring operations is very important to be done to floaters oil rig ,so it can be stable at the Drilling mode. In addition, the rig is also equipped with "motion compensator" system to overcome the problem heave, pitch and roll, so the relative position of the hole is stable all the times. After all these steps are done,we are ready to do offshore drilling. That's how the offshore drilling done for water depth more than 250 ft