Pressure Safety System for Use With a Dynamic Annular Pressure Control System

Abstract

A method for controlling formation pressure during the drilling of a borehole through a subterranean formation includes selectively pumping a drilling fluid through a drill string extended into a borehole, out a drill bit at the bottom end of the drill string, and into an annular space between drill string and the borehole. The drilling fluid is discharged to a reservoir to clean the drilling fluid for reuse. Annular space fluid pressure is selectively increased to maintain a selected fluid pressure proximate the bottom of the borehole by applying fluid pressure to the annular space. The selective increasing includes controlling an aperture of an orifice operatively coupled between the annular space and the reservoir. Fluid from the annular space is discharged other than through the orifice when the annular space fluid pressure exceeds a selected value, or drops below a selected value.

1 . A method for controlling formation pressure during the drilling of a borehole through a subterranean formation, comprising:
 selectively pumping a drilling fluid through a drill string extended into a borehole, out a drill bit at the bottom end of the drill string, and into an annular space between drill string and the borehole;   discharging the drilling fluid to a reservoir to clean the drilling fluid for reuse;   selectively increasing annular space fluid pressure to maintain a selected fluid pressure proximate the bottom of the borehole by applying fluid pressure to the annular space, the selective increasing including controlling an aperture of an orifice operatively coupled between the annular space and the reservoir; and   discharging fluid from the annular space other than through the orifice when the annular space fluid pressure exceeds a selected value or drops below a selected value.   
   
   
       2 . The method of  claim 1  wherein the discharging comprises opening a pressure relief valve when the fluid pressure in the annular space exceeds a preselected fraction of a formation integrity test pressure. 
   
   
       3 . The method of  claim 2  wherein the preselected fraction is between about 80 to 90 percent of the formation integrity test pressure. 
   
   
       4 . The method of  claim 1  further comprising operating a safety valve if the fluid pressure in the annular space falls below a selected value. 
   
   
       5 . The method of  claim 4  wherein the operating the safety valve comprises stopping fluid flow to the orifice. 
   
   
       6 . The method of  claim 4  wherein the operating the safety valve comprises diverting fluid flow from the orifice to a backup selectively controllable orifice. 
   
   
       7 . A method for controlling formation pressure during the drilling of a borehole through a subterranean formation, comprising:
 selectively pumping a drilling fluid through a drill string extended into a borehole, out a drill bit at the bottom end of the drill string, and into an annular space between drill string and the borehole;   discharging the drilling fluid to a reservoir to clean the drilling fluid for reuse;   selectively increasing annular space fluid pressure to maintain a selected fluid pressure proximate the bottom of the borehole by applying fluid pressure to the annular space, the selective increasing including controlling an aperture of an orifice operatively coupled between the annular space and the reservoir; and   operating a safety valve if the fluid pressure in the annular space falls below a selected value.   
   
   
       8 . The method of  claim 7  wherein the operating the safety valve comprises stopping fluid flow to the orifice. 
   
   
       9 . The method of  claim 7  wherein the operating the safety valve comprises diverting fluid flow from the orifice to a backup selectively controllable orifice. 
   
   
       10 . The method of  claim 7  further comprising causing fluid to flow other than through the orifice if the fluid pressure in the annular space increases above a selected value. 
   
   
       11 . The method of  claim 10  wherein the causing fluid flow comprises opening a pressure relief valve. 
   
   
       12 . The method of  claim 11  wherein the pressure relief valve is caused to operate when the fluid pressure reaches a preselected fraction of a formation integrity test pressure. 
   
   
       13 . The method of  claim 12  wherein the preselected fraction is between about 80 to 90 percent of the formation integrity test pressure.