Movable wellbay assembly

A method for constructing a new, or retrofitting and/or repurposing an existing drilling unit for service as a production facility capable of drilling, evaluating, completing, maintaining, improving, or producing from wells penetrated into a subsurface (subterranean) oil and gas reservoir located beneath a body of water, the drilling unit comprising a drilling derrick and an opening in a deck of the facility that allows vertical access to and passage of components therethrough, the drilling derrick secured to a drilling deck over the opening at a single location, the method comprising:

• a) for constructing a new drilling unit, building and/or installing a structural assembly that is located at least partially in the opening, wherein the entire structural assembly is configured to be laterally and transversely movable at least for aligning at the single location a top end of first one riser of a set of two or more risers and then aligning at the single location a different riser of the set of risers below the drilling derrick, wherein the structural assembly has at least two riser holders, and wherein each riser holder is designed and built to hold a top-tensioned riser that is stretched between the riser holder and components at or near a seabed for production of hydrocarbons from the subterranean oil and gas reservoir;
• b) for retrofitting and/or repurposing an existing drilling unit having any one or more of the following 1) a marine drilling riser and tensioner system, 2) a subsea blowout preventer (BOP) and cart transport system, 3) marine drilling riser storage and handling equipment, and 4) a power generation and management system, if any one or more of (1)-(4) are present, then removing them, but if (1)-(4) are not present, then proceeding with step (c);
• and
• (c) building and/or installing a structural assembly that is located at least partially in the opening of the existing drilling unit, wherein the entire structural assembly is configured to be laterally and transversely movable at least for aligning at the single location a top end of first one riser of a set of two or more risers and then aligning at the single location a different riser of the set of risers below the drilling derrick, wherein the structural assembly has at least two riser holders, and wherein each riser holder is designed and built to hold a top-tensioned riser that is stretched between the riser holder and components at or near a seabed for production of hydrocarbons from the subterranean oil and gas reservoir.

A facility for oil and gas well drilling, evaluation, completion, improvement, maintenance, intervention or production, comprising:

• a structure having an opening in a deck of the facility that allows vertical access to and passage of components therethrough, wherein the structure has deck structures, and wherein the structure has an upper drilling deck that surrounds the opening, the opening having an area and a centerline;
• a drilling derrick with a primary operating device;
• and
• a wellbay assembly located at least partially in the opening, wherein the wellbay assembly comprises a grid defining an array of two or more structurally distinct slots, each slot having one set of a corresponding two or more sets of riser tensioners therein, and wherein each of the corresponding two or more sets of riser tensioners is designed and built to hold one of a set of two or more risers in tension;
• wherein the structure has a pair of supports, wherein the grid rests on the pair of supports and is configured to be only laterally movable on the pair of supports along a first axis laterally along the area of the opening, wherein the structure has a pair of beams or rails, wherein the drilling derrick and primary operating device are received on the pair of beams or rails and are only movable orthogonally along a second axis to either side of the centerline of the opening on the pair of beams and rails;
• whereby any one of the set of two or more risers can be accessed directly for the oil and gas well drilling, evaluation, completion, improvement, maintenance, intervention and/or production.