Failures related to casing connectors jump-out have occurred, causing flat time of deep water drilling rigs, which generates great losses due to very high daily rate of these rigs. The objective of this paper is to show a methodology for performing post analysis of this type of failure. In order to do the analysis, it is mandatory to obtain the mechanical properties and dimensions of the casing connector. It is important to raise the stress-strain curve of samples extracted from the connector. In case of proprietary connectors, the dimensions should be obtained with the manufacturer, once it is necessary detailed dimensions.
Aiming to verify the structural integrity of the casing connector, a proper definition of the load scenario prior to failure must be done. Provided the meteocean condition during the analyzed operation, a dynamic finite element analysis of the whole casing string is performed. The string is treated as beam elements and bending moments and axial stresses are tracked. Varying wave parameters it is possible to define a load envelope. Due to the geometric and material complexity of casing connectors, axisymmetric and 3D finite element models were developed to reproduce the problem domain and load scenarios. Based on an excessive displacement and plasticity criteria, a strength envelope was evaluated. Combining load and strength conditions, it was possible to access some issues that may have caused the connector failure.
In deep water drilling operation with floating rigs, while running in offshore surface casing, sometimes jump-out of connectors has been observed. This problem usually causes big losses and, therefore, it is very important to find out the reasons in order to avoid them.
The main objective of this study is to determine the possible causes of jump-out of casing connectors while running these pipes into a well in offshore floating rigs.
Since 2002 Petrobras has been using connectors welded to the surface casing X-56, 20?? × 5/8??, 131.5 ppf. This connector has tension strength approximately 40% lower than the pipe body. The length of the joint is 12m (40ft). The connection makeup is done with ¾ of turn and a key seat must be used to guarantee the connection will be safe.
In August 4th, 2011, it was initiated the operation of running a 20?? surface casing into the well. After 7 (seven) joints have been assembled using an auxiliary table, the casing string was moved to the main table with a trolley (Figure 1). The casing was lifted up to the main table and the trolley stayed below the rotary table functioning as a guide.