Method for Controlling Fluid Pressure in a Borehole Using 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 from the borehole to a reservoir to clean the drilling fluid for reuse. An 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. A formation fluid pressure is predicted at a depth below a lowermost depth to which the borehole is drilled and the aperture is adjusted to maintain a selected pressure in the borehole in response to the predicted formation fluid pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting annular pressures and formation pore and fracture pressures.

FIGS. 2A and 2B are plan views of two different embodiments of the apparatus that can be use with a method according to the invention.

FIG. 3 is a block diagram of the pressure monitoring and control system used in the embodiment shown in FIG. 2.

FIG. 4 is a functional diagram of the operation of the pressure monitoring and control system.

FIG. 5 is a graph showing the correlation of predicted annular pressures to measured annular pressures.

FIG. 6 is a graph showing the correlation of predicted annular pressures to measured annular pressures depicted in FIG. 5, upon modification of certain model parameters.

FIG. 7 is a graph showing how the DAPC system may be used to control variations in formation pore pressure in an overbalanced condition;

FIG. 8 is a graph depicting DAPC operation as applied to at balanced drilling.

FIGS. 9A and 9B are graphs depicting how the DAPC system may be used to counteract annular pressure drops and spikes that accompany pump off/pump on conditions.

FIG. 10 shows another embodiment of a DAPC system that uses only rig mud pumps for providing selected fluid pressure to both the drill string and the annulus.

Claims

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;predicting a formation fluid pressure at a depth below a lowermost depth to which the borehole is drilled; andadjusting the aperture to maintain a selected pressure in the borehole in response to the predicted formation fluid pressure.

2. The method of claim 1 wherein the predicting comprises measuring d-exponent.

3. The method of claim 1 wherein the predicting comprises measuring formation acoustic velocity.

4. The method of claim 1 wherein the predicting comprises measuring formation electrical resistivity.

5. The method of claim 1 wherein the predicting comprises performing seismic velocity analysis.

6. 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, the selected fluid pressure calculated by an hydraulics model;measuring fluid pressure in the annular space at a plurality of depths; andcalibrating the hydraulics model based on the measured fluid pressures.

7. The method of claim 6 wherein the calibrating comprises correcting the model for changes in shape of the borehole.

8. The method of claim 6 wherein the calibrating comprises correcting the model for variations in temperature along the borehole.

9. The method of claim 6 wherein the calibrating comprises detecting circulation in the annular space of fluid entered into the borehole from an Earth formation adjacent the borehole.