Experimental Research on Structural Casing Soaking Time in Deepwater Drilling

Abstract

Abstract Structural casing is defined as the first string of casing installed in the well construction process. It provides structure and support for all the casing strings, the subsea christmas tree, and BOP stact. In the deep water drilling process, the soaking time of structural casing has directly influence on the bearing capacity and drilling period, and that is crucial in deep water drilling design. Jetting of structural casing has become the preferred method of installation in most deep-water drilling. In order to decrease the risk of deep water surface drilling work, and to shorten the drilling period, this paper gives a simulation experiment on soil-pile interaction to get the change rule between soaking time and bearing capacity. Once the structural casing string has been jetted successfully to final depth, a period of soak time is employed to allow the skin friction to increase and improve the soil to casing adhesion. Based on field experiments and mechanical analyses, the paper builds up a calculate method on wellhead load in different situations. Considering the structural casing safe driving depth and drilling efficiency, it gives a design method of soaking time window of deep-water structural casing in different formation. Soak period of two to three hours is prudent insurance against casing subsidence after running tool release in clay strata, and one to two hours in sand and mud interbed strata. This method optimized the setting depth of structural casing, improved the drilling efficiency, and saved more than 12 h per well on average with the ensurance of deep water drilling safety. It turns out a great application results in South China Sea deep-water drilling practice.