Drivability analysis and performance of plugged conductors for deepwater offshore platforms

The use of a drivable plug in conductors being installed on deepwater offshore oil platforms promises several benefits both to the marine contractor performing the installation and to the oil company for whom the platform is being installed. The first benefit of plugging the conductors is to make the net weight manageable. With a nonporus plug in the conductor tip, buoyancy is used to minimize the conductor string weight such that the jacket framing can support multiple strings without any additional temporary load frames. Offshore drilling contractors can also use the plug to their advantage because a conductor installed with a plug has its interior void and easy to map, making it easier to plan a drilling program.;One final benefit comes from an unexpected source--conductor drivability. The primary hindrance for using plugged conductors has been the lack of drivability definition. This research shows that plugged conductors/piles driven in silty-clayey soils will drive easier than open-ended pipe when using the same equipment to achieve the same depth of penetration. Both the final driving resistance and the slope of the resistance curve with depth are significantly less for plugged conductors than that encountered by open-ended conductors.;This research analyzes the technical issues of plugged conductor utilization so that the benefits listed above can be achieved during installations of conductors for offshore platforms. Current soil theories that model the plugged pile behavior are applied to the soil data at selected installation sites in the Gulf of Mexico. The modified soil parameters are used to generate a recommended set of input parameters for analyzing the drivability of plugged conductors in silty-clay soils. Data from actual conductor installations, including electronic instrumentation, were also obtained for this research. The recorded data provide the validation of analytical procedures used to model both open and plugged conductor driving. An additional benefit of the recorded data is correlation between the electronic data and the more typical blow count data. The result is validation of the state-of-practice for the analysis and tabulation of open conductor installations and recommended modifications to the typical input parameters for widely available pile driving programs that are applicable for plugged conductors at other deepwater locations in the Gulf of Mexico.