METHOD OF DRILLING A SUBTERRANEAN BOREHOLE

• US 20150107898A1
• Filed: 05/03/2013
• Published: 04/23/2015
• Est. Priority Date: 05/03/2012
• Status: Active Grant

• Current Assignee: Grant Prideco Incorporated (NOV, Inc.)
• Original Assignee: Managed Pressure Operations Pte. Ltd. (Akastor ASA)
• Inventors: Leuchtenberg, Christian
• Granted Patent: US 10,138,693 B2
• Time in Patent Office: Days
• US Class Current: 175/25
• CPC Class Codes: E21B 21/08 Controlling or monitoring pressure or flow of drilling fluid, e.g. automatic filling of boreholes, automatic control of bottom pressure valve arrangements therefor E21B21/10
• CPC Class Codes: E21B 21/106 Valve arrangements outside the borehole, e.g. kelly valves valves specifically for maintaining circulation of drilling fluid while connecting or disconnecting tubular joints E21B21/019
• CPC Class Codes: E21B 44/00 Automatic control systems specially adapted for drilling operations, i.e. self-operating systems which function to carry out or modify a drilling operation without intervention of a human operator, e.g. computer-controlled drilling systems; Systems specially adapted for monitoring a plurality of drilling variables or conditions
• CPC Class Codes: E21B 47/06 Measuring temperature or pressure
• CPC Class Codes: E21B 47/107 using acoustic means

Abstract

A method of drilling a subterranean wellbore using a drill string comprising the steps of: a. injecting a drilling fluid into the well bore via the drill string and removing said drilling fluid from an annular space around the drill string (the annulus) via an annulus return line, b. oscillating the pressure of the fluid in the annulus, c. determining the wellbore storage volume and wellbore storage coefficient for each fluid pressure oscillation, d. using the wellbore storage volume and wellbore storage coefficient to determine the proportion by volume of gas and proportion by volume of liquid in the annulus during that pressure oscillation.

Claims

1. A method of drilling a subterranean wellbore using a drill string comprising the steps of:

a. injecting a drilling fluid into the well bore via the drill string and removing said drilling fluid from an annular space around the drill string (the annulus) via an annulus return line,

b. oscillating the pressure of the fluid in the annulus,

c. determining the wellbore storage volume and wellbore storage coefficient for each fluid pressure oscillation,

d. using the wellbore storage volume and wellbore storage coefficient to determine the proportion by volume of gas and proportion by volume of liquid in the annulus during that pressure oscillation.

2. A method according to claim 1 wherein the wellbore storage volume and wellbore storage coefficient are determined by monitoring the rate of flow of fluid along the annulus return line.

3. A method according to claim 1 wherein the wellbore storage volume and wellbore storage coefficient are determined by monitoring the fluid pressure at the top of the annulus.

4. A method according to claim 1 wherein the volume percentage of gas in the annulus and the fluid pressure in the annulus are used to obtain an estimate of the maximum pressure of the gas when the gas enters the annulus return line.

5. A method according to claim 4 wherein drilling is stopped and a blowout preventer closed around the drill string if it is determined that the estimated maximum pressure of the gas when the gas enters the annulus return line exceeds a predetermined value.

6. A method according to claim 1 wherein a main control choke is provided in the annulus return line, and the oscillation of the pressure in the annulus is achieved by oscillating the main choke so that the degree to which the choke restricts fluid flow along the annulus return line is alternately decreased and increased.

7. A method according to claim 1 wherein a main control choke is provided in the annulus return line, and an auxiliary choke is provided in a branch line which extends from the annulus return line upstream of the main control choke to the annulus return line downstream of the main control choke, the oscillation of the pressure in the annulus is achieved by oscillating the auxiliary choke so that the degree to which the choke choke restricts fluid flow along the branch line is alternately decreased and increased.

8. A method according to claim 6 further including the steps of monitoring the fluid pressure at the bottom of the wellbore, and controlling the main choke to maintain the fluid pressure at the bottom of the wellbore at a predetermined level.

9. A method according to claim 8 wherein the main choke is operated to increase its restriction of fluid flow along the annulus return line immediately after the presence of gas in the annulus is detected.

10. A method according to claim 6 further including the step of controlling the gain setting of the main choke in accordance with the proportion by volume of gas in the annulus.

11. A method according to claim 1 wherein an estimate of the position of any gas in the annulus is determined by analysing the shift in the frequency of the returning pressure pulse compared with the frequency of the applied pressure pulse.

12. (canceled)

13. (canceled)