HOUSTON–As deepwater oil and gas exploration expands around the world, well cementing is a critical aspect of well construction with unique considerations because of the deepwater environment and downhole conditions. To minimize risks, well construction costs and nonproductive time, it is important to understand the constraints for deepwater cementing and essential good cementing practices, and to carefully plan for contingencies that may arise when working in locations where cement must be placed properly the first time, every time.
Two of the most frequently asked questions regarding offshore operations are what makes deepwater drilling so challenging, and what is the major difference from drilling on the Shelf? To answer this question, one must understand that deepwater drilling rigs float thousands of feet above the surface location. They are kept on station either by anchors attached by miles of gigantic cables or by an automated dynamic positioning system that operates the rig’s thrusters based on very precise data from global positioning satellites. Both of these systems have limits, but they have propelled oil and gas exploration into water depths greater than 10,000 feet.
Deepwater semisubmersibles deploy two-story-high stacks of blowout preventers that sit on the seafloor and are exposed to extreme cold and external pressure. The floating rigs also carry small unmanned, remotely operated vehicles that monitor operations at the seafloor and use robotic arms to assist when necessary. These technological wonders and dozens more, developed and built by the service industry especially for the challenges of deepwater drilling, add to a huge capital investment by oil and gas exploration and production companies. The cost of developing a deepwater field can exceed $1 billion, and increases with increasing water depth.
The mechanics of drilling a deepwater well are also much different from drilling on land or on the Shelf. In deep water, the first two to three strings of pipe are installed without a connection back to the rig. Riserless drilling essentially eliminates any means of placing pressure on the well, other than the pressure exerted by the well fluids and the natural column of sea water. This means that mud and cement companies must have very specialized systems and training in order to counteract and control the problems associated with riserless drilling.
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