Riserless Casing Seat Optimization

Riserless Casing Seating Optimization is a design method for the installation of riserless casing strings in Deepwater drilling environments.

The conventional Deepwater well design model fails to take advantage of the early and progressive growth of the subsurface fracture gradient immediately below the mud line, due to perceived requirement to set an another casing string above anticipated shallow drilling hazards. This results in the inability to supply sufficient and safe ³leak-off² for the drilling of subsequent holes and casing installations, adequately mitigate shallow hazards, and avoid ³wasting² casing diameters in the riserless hole sections and thus subsequent sections to total vertical well depth. This method provides for the installation of at the minimum two riserless casing strings, beginning with the structural conductor, which is conventionally installed by ³jetting² operations.

The proposal is for the dual purpose use of the structural conductor in that it is installed at deeper depth so that it takes advantage of the early growth of the fracture gradient, and then becomes a true structural casing being able to support the axial loads of the BOP¹s and subsequent casing strings. Furthermore this ensures sufficient leak-off protection for next string and the safe drilling of subsequent shallow hazards.

Article: Riserless CasingSeat Optmization: a Big Bore Liner Drilling Application

Riserless CasingSeat Op0miza0on: a Big Bore Liner Drilling Applica0on

By David M. Pritchard, P.E.(Texas & LA) & Kenneth J. Kotow, P. Eng. (Alberta)

Abstract:

Unique patented well design process for placement of casing strings in the riserless well sections. Uses pore pressure/fracture gradient geological properties to select optimum casing seats. Patent No. US2011/0036587A1.