Method of preventing drill string overflow

A method of preventing drilling fluid overflow when adding or removing drill pipe sections to or from a drill string disposed in a well bore comprising the steps of:

• introducing pressurized air into said drill string until a predetermined volume thereof is introduced therein;
• introducing drilling fluid into said drill string after introducing air therein until a predetermined volume thereof is introduced at a predetermined pressure thereby displacing drilling fluid originally contained in said drill string downwardly within said drill string and upwardly within the annulus between said drill string and said well bore to lower the level of said drilling fluid in said drill string a distance such that upon releasing the pressurized air and drilling fluid from said drill string and removing drilling fluid and air therefrom, the resulting level of drilling fluid in said drill string is below the level at which said drill pipe sections are added to or removed from said drill string;
• releasing said pressurized air and drilling fluid from said drill string whereby said air and drilling fluid flow upwardly through said drill string and drilling fluid and air are removed therefrom;
• and then
• adding or removing drill pipe sections to or from said drill string.

A method of preventing aqueous drilling fluid overflow when adding or removing drill pipe sections to or from a drill string disposed in a well bore, the upper end of the drill string being attached to a kelly which is in turn attached to a swivel and a drilling fluid conduit system for introducing drilling fluid into the kelly and drill string comprising the steps of:

• introducing air into said kelly and drill string by way of said drilling fluid conduit system until a predetermined volume thereof is introduced therein;
• introducing drilling fluid into said kelly and drill string by way of said drilling fluid conduit system after introducing said air until a predetermined volume thereof is introduced therein and said air is pressurized thereby displacing drilling fluid originally contained in said kelly and drill string downwardly within said kelly and drill string and upwardly within the annulus between said drill string and said well bore to lower the level of said drilling fluid in said kelly and drill string a distance such that upon releasing the pressurized air and introduced drilling fluid from said kelly and drill string and removing drilling fluid and air therefrom, the resulting level of drilling fluid in said kelly and drill string is below the point of disconnection of said kelly from said drill string;
• releasing said pressurized air and introduced drilling fluid from said kelly and drill string whereby said air and drilling fluid flow upwardly through said kelly and drill string into said conduit system and drilling fluid and air are removed therefrom;
• removing said kelly from said drill string;
• and
• adding or removing pipe sections to or from said drill string.