Method for excavating mud line cellar for subsea well drilling
A method for excavating a well cellar includes lowering an excavating apparatus having a cellar liner therein to a bottom of a body of water. The well cellar is excavated while contemporaneously lowering the cellar liner into the well cellar until a top of the cellar liner is substantially level with the bottom of the body of water. A pilot well is excavated below a bottom of the cellar. A well head support pipe is inserted into the pilot well. The bottom of the well cellar and a top of the cellar liner are covered.
1. A method for excavating a well cellar, comprising:
lowering an excavating apparatus having a cellar liner therein to a bottom of a body of water, the excavating apparatus comprising pads mounted to articulated arms, the arms extendable and retractable to selectively lock the excavating apparatus in place inside the cellar liner, a first motor coupled to a drill bit, the first motor mounted to the excavating apparatus by a pivoting element operable so that an angle of the first motor with respect to a longitudinal axis of the excavating apparatus is controllable during use, means to move the excavating apparatus upwardly and downwardly, and a second motor attached to excavating apparatus enable rotation of the first motor about the longitudinal axis;
excavating the well cellar by operating the excavating apparatus, while contemporaneously lowering the cellar liner into the well cellar until a top of the cellar liner is substantially level with the bottom of the body of water;
excavating a pilot well below a bottom of the cellar using the excavating apparatus; and
inserting a well head support pipe into the pilot well.
2. The method of claim 1 further comprising inserting an extension pipe into the wellhead support pipe, the extension pipe extending through a cover on the top of the cellar liner.
3. The method of claim 2 further comprising covering the extension pipe with a cap having a locating beacon affixed thereto.
4. The method of claim 3 further comprising:
removing the cap;
drilling a surface well to a selected depth;
removing the extension pipe; and
inserting a surface casing in the surface well to the selected depth and cementing the surface casing in the surface well.
5. The method of claim 4 further comprising removing the cover from the top of the cellar liner and affixing a well pressure control apparatus to an upper end of the surface casing.
6. The method of claim 4 wherein the removing the cap, drilling the surface well, removing the extension pipe and inserting and cementing the surface casing is performed from a drilling unit moved to a location of the well cellar.
7. The method of claim 1 wherein the cellar liner comprises concrete.
8. The method of claim 1 wherein the excavating apparatus and cellar liner are lowered to the bottom of the body of water from a transport vessel.
9. The method of claim 8 further comprising moving the transport vessel from a location of the well cellar after covering the bottom of the well cellar and the top of the cellar liner.
10. The method of claim 9 further comprising moving the transport vessel to a location different than the location of the well cellar and repeating the lowering an excavating apparatus having a cellar liner therein to a bottom of a body of water, excavating the well cellar while contemporaneously lowering the cellar liner into the well cellar until a top of the cellar liner is substantially level with the bottom of the body of water, excavating a pilot well below a bottom of the cellar, inserting a well head support pipe into the pilot well and covering the bottom of the well cellar and a top of the cellar liner at the different location.
11. The method of claim 1 further comprising covering the bottom of the well cellar and a top of the cellar liner.