SYSTEM AND METHOD FOR INHIBITING AN EXPLOSIVE ATMOSPHERE IN OPEN RISER SUBSEA MUD RETURN DRILLING SYSTEMS

摘要

A method for inhibiting an explosive atmosphere in a wellbore drilling system, including a riser (12) connected to a wellbore above a top thereof wherein the riser has a fluid outlet (17) below a surface of a body of water in which the wellbore is drilled, and wherein the fluid outlet is connected to a subsea pump to return drilling fluid to a drilling platform on the water surface and wherein a space in the riser (12) above the drilling fluid level filled with air includes pumping drilling fluid into a drill string (15) extending from the drilling platform into the wellbore. Fluid (27) is introduced proximate an upper end of the riser (12). A rate of introducing the fluid (27) is selected to inhibit an explosive atmosphere in the space in the riser above the drilling fluid level. The subsea pump to remove fluid from the riser outlet is operated at a rate selected to maintain the fluid level or to maintain a selected wellbore pressure.

主权项

1. A method for inhibiting an explosive atmosphere in a wellbore drilling system including a riser connected to a wellbore above a top thereof, the riser having a fluid outlet below a surface of a body of water in which the wellbore is drilled, the fluid outlet connected to a subsea pump to return drilling fluid to a drilling platform on the water surface, the pump operated to maintain a selected drilling fluid level in the riser or a selected wellbore pressure, a space in the riser above the drilling fluid level filled with air, the method comprising:
pumping drilling fluid into a drill string extending from the drilling platform into the wellbore; introducing fluid proximate an upper end of the riser, a rate of introducing the fluid selected to generate sufficient downward velocity of fluid in the riser so as to substantially stop upward movement of gas in the riser, thereby inhibiting an explosive atmosphere in the space in the riser above the drilling fluid level; and operating the subsea pump to remove fluid from the riser outlet at a rate selected to maintain the fluid level or the selected wellbore pressure.