Method for correcting the measured concentrations of gas components in drilling mud

• US 8,011,238 B2
• Filed: 10/09/2008
• Issued: 09/06/2011
• Est. Priority Date: 10/09/2008
• Status: Expired due to Fees

• Current Assignee: Chevron USA Incorporated (Chevron Corp.)
• Original Assignee: Chevron USA Incorporated (Chevron Corp.)
• Inventors: Hanson, Scott A.
• Primary Examiner(s): Fitzgerald; John
• Application Number:
  US12/248,620
• Publication Number:
  US 20100089120A1
• Time in Patent Office: 1,062 Days
• Field of Search: 73/190.2, 73/190.9, 731/520.4, 731/521.8, 731/521.9, 702/6, 702/9
• US Class Current: 73/152.04
• CPC Class Codes: E21B 49/005 Testing the nature of borehole walls or the formation by using drilling mud or cutting data
• CPC Class Codes: G01N 2030/8854 involving hydrocarbons
• CPC Class Codes: G01N 33/2823 raw oil, drilling fluid or polyphasic mixtures hydrocarbon content of earth materials G01N33/241; prospecting G01V; drilling per se E21B

Abstract

A method of characterizing formation fluid present in a subsurface earth formation during drilling using methods for correcting the measured concentrations of gas components in drilling mud. Gas trap values for the gas components of interest, light hydrocarbons, are measured during mud logging and are corrected using relative response factors, determined from laboratory fluid analysis values and relative extraction efficiency values. The relative response factors for each gas component of interest can be used for correcting additional gas trap values measured in the same well or for correcting gas trap values measured in surrounding wells utilizing a similar drilling fluid. The corrected gas trap values for each of the gas components of interest can be utilized to calculate gas/oil ratios for characterizing the formation fluid from the volume of drilling mud.

Claims

1. A method for characterizing formation fluid present in a subsurface earth formation, the method comprising:

extracting a plurality of gas components from a volume of drilling mud comprising formation fluid and gases, while drilling;

measuring a gas trap value for each gas component of interest;

determining a gas trap response factor for each gas component of interest by dividing the gas trap value by a laboratory fluid analysis value for each gas component of interest;

determining a relative response factor for each gas component of interest by dividing the gas trap response factor for each gas component of interest by the gas trap response factor for the gas component of interest with the lowest molecular weight; and

calculating the corrected gas trap value for each gas component of interest by dividing the gas trap value by the relative response factor for each gas component of interest;

wherein the corrected gas trap value for each gas component of interest is utilized to calculate gas/oil ratios for characterizing the formation fluid from the volume of drilling mud.

2. A method in accordance with claim 1, wherein the plurality of gas components are extracted from the volume of drilling mud using a gas trap.

3. A method in accordance with claim 1, wherein the plurality of gas components comprises methane, ethane, propane, butane, and/or pentane.

4. A method in accordance with claim 1, wherein the gas components of interest are chosen from the group of methane, ethane, propane, butane, and/or pentane.

5. A method in accordance with claim 1, wherein the gas trap values are measured using gas chromatography or gas chromatography-mass spectrometry.

6. A method in accordance with claim 1, wherein the laboratory fluid analysis value is measured using gas chromatography or gas chromatography-mass spectrometry.

7. A method in accordance with claim 1, wherein the corrected gas trap values are used to calculate gas to oil ratios to characterize the formation fluid.

8. A method in accordance with claim 1, wherein the determined relative response factors are utilized to correct gas trap values measured in the same well at various depths.

9. A method in accordance with claim 1, wherein the determined relative response factors are utilized to correct gas trap values measured in surrounding wells utilizing a similar drilling fluid.

10. A method for using previously determined relative response factors for correcting gas trap values for gas components in a drilling mud, comprising:

extracting a plurality of gas components from a volume of drilling mud comprising formation fluid and gases, while drilling;

measuring a gas trap value for each gas components of interest; and

calculating the corrected gas trap value for each of the gas components of interest by dividing each gas trap value by a previously determined relative response factor for each of the gas components of interest;

wherein, the corrected gas trap value for each of the gas components of interest is utilized to calculate gas/oil ratios for characterizing formation fluids from the volume of drilling mud.

11. The method in accordance with claim 10, wherein the previously determined relative response factor for each gas component of interest is utilized to correct gas trap values for each of the gas components of interest measured in surrounding wells utilizing a similar drilling fluid.

12. A system for automatically correcting a plurality of gas trap values, comprising:

a data storage device having non-transitory computer readable data including mud logging data relating to the plurality gas trap values;

a processor, configured and arranged to execute machine executable instructions stored in a processor accessible memory for performing a method comprising;

acquiring a gas trap value for each gas component of interest;

determining a gas trap response factor for each gas component of interest by dividing the gas trap value by a laboratory fluid analysis value for each gas component of interest;

determining a relative response factor for each gas component of interest by dividing the gas trap response factor for each gas component of interest by the gas trap response factor for the gas component of interest with the lowest molecular weight;

correcting the gas trap value for each gas component of interest by dividing the gas trap value by the relative response factor for each gas component of interest; and

utilizing the corrected gas trap value for each gas component of interest to calculate gas/oil ratios for characterizing formation fluids.

13. A system as in claim 12, further comprising a user interface configured and arranged to allow a user to adjust parameters used in correcting the gas trap value for each gas component of interest.

14. A system as in claim 12, further comprising a user interface configured and arranged to allow a user to adjust parameters used in the calculation gas/oil ratios.

15. A system as in claim 12, further comprising a display, configured and arranged to display a layer structure of a subsurface region from which the formation fluid and gases were taken, based, at least in part, on the gas trap values.