Recovery of gas from drilling fluid returns in underbalanced drilling

• US 5,775,442 A
• Filed: 10/29/1996
• Issued: 07/07/1998
• Est. Priority Date: 10/25/1996
• Status: Expired due to Term

• Current Assignee: Weatherford Canada Partnership (Weatherford International PLC)
• Original Assignee: Northland Production Testing Limited
• Inventors: Speed, David
• Primary Examiner(s): Suchfield, George A.
• Application Number:
  US08/741,201
• Time in Patent Office: 616 Days
• Field of Search: 166/267, 175/48, 175/66, 175/69, 175/71, 175/206, 175/207, 175/212, 175/217, 175/218, 55/346, 55/349, 55/459.1, 95/268, 95/269, 95/271, 96/188, 210/788
• US Class Current: 175/48
• CPC Class Codes: E21B 21/067 Separating gases from drilling fluids
• CPC Class Codes: E21B 21/085 Underbalanced techniques, i.e. where borehole fluid pressure is below formation pressure
• CPC Class Codes: E21B 21/14 using liquids and gases, e.g. foams
• CPC Class Codes: E21B 41/005 Waste disposal systems

Abstract

The drilling fluid returns from underbalanced drilling are introduced into a separator and a separate gas stream is recovered. The gas stream is cleaned at the well site to remove entrained liquid and particulate solids, to produce gas suitable to be fed to a compressor. The cleaned gas is compressed to re-injection pressure and recycled to the well.

Claims

1. A method for treating pressurized drilling fluid returns from a well having a returns outlet and inlet means for introducing drilling fluid and added gas to the well, said well undergoing underbalanced drilling, said returns comprising a liquid component, a particulate solids component and a gas component comprising added gas, said method comprising:

providing a pressure-containing loop circuit extending between and connected with the returns outlet and inlet means, said circuit comprising a separator vessel, a circuit for cleaning gas and a compressor;

introducing the returns into the separator vessel, separating the solids, liquid and gas components in the vessel and producing separate solids, liquid and gas streams from the vessel, said gas stream containing minor amounts of entrained solids and liquid;

separating sufficient entrained solids and liquid from the gas stream in the cleaning circuit to produce cleaned gas acceptable as compressor feed; and

compressing cleaned gas in the compressor to well re-injection pressure and recycling it to the well as added gas.

2. A method for treating pressurized drilling fluid returns from a well having a returns outlet and inlet means for introducing drilling fluid and added gas to the well, said well undergoing underbalanced drilling, said returns comprising a liquid component, a particulate solids component and a gas component comprising added gas, said method comprising:

providing a pressure-containing loop circuit extending between and connected with the returns outlet means and inlet means, said circuit comprising a separator vessel, said vessel having a returns inlet and outlets for producing separate liquid, solids and gas streams, means for separating minor amounts of entrained solids and liquid from the gas stream, said separating means having an inlet and outlet, a compressor having an inlet and outlet, a flare stack, a first line connecting the well outlet means with the vessel returns inlet, second and third lines connecting the vessel gas outlet with each of the separating means inlet and the flare stack, a fourth line connecting the separating means outlet with the compressor inlet, a fifth line connecting the compressor outlet and the well inlet means, means for monitoring the flow rate of the gas stream leaving the vessel, valve means controlling each of the second and third lines, a source of make-up added gas, a sixth line connecting the make-up gas source with the circuit and valve means for controlling the sixth line;

introducing the returns through the first line into the vessel inlet, separating the solids, liquid and gas components in the vessel and producing separate solids, liquid and gas streams through the vessel outlets, said gas containing minor amounts of entrained solids and liquid;

monitoring the pressure of the gas stream leaving the vessel and opening the valve means controlling the third line to vent gas through the flare stack when a predetermined flow rate value is exceeded and closing the third line valve means when the pressure diminishes beneath the predetermined value;

conveying produced gas from the vessel outlet through the second line to the separating means and separating sufficient entrained solids and liquid to produce cleaned gas acceptable as compressor feed;

conveying the cleaned gas from the separating means to the compressor inlet through the fourth line and compressing the cleaned gas to re-injection pressure; and

conveying the compressed cleaned gas through the fifth line and reinjecting it into the well through the inlet means.

3. The method as set forth in claim 2 comprising:

opening the valve means controlling the sixth line to add make-up added gas to the cleaned gas when the flow rate of the gas stream leaving the vessel falls below a predetermined value.