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Downhole Geochemical Analysis of Gas Content

And Critical Desorption Pressure for Carbonaceous Reservoirs*

By

Robert A. Lamarre1

 

Search and Discovery Article #40217 (2006)

Posted October 20, 2006

 

*Oral presentation at AAPG Annual Convention, Houston, Texas, April 9-12, 2006

 

Click to view presentation in PDF format.

 

1Consultant, Laramie, Wyoming ([email protected])

 

Overview of New Technology 

Critical Gas Content (CGC) service

–        Underlying science

–        Downhole analysis

 

Developing a new field with CGC

–        Selecting target coals

–        Living with reservoir heterogeneity

Identifying sweet spots for dewatering.

 

 

uOverview

uSelected figures

uScience

uDownhole analysis

uCGC Technology

uReservoir

uConclusions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uOverview

uSelected figures

uScience

uDownhole analysis

uCGC Technology

uReservoir

uConclusions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uOverview

uSelected figures

uScience

uDownhole analysis

uCGC Technology

uReservoir

uConclusions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Selected Figures

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Underlying Science 

CGC uses Raman spectroscopy (discovered 1928).

  • Well-suited to water environments

Raman is a vibrational spectroscopy.

  • Sensitive to molecular bonding and structure

  • Identifies, quantifies molecular species

  • Very specific

Methane peak is distinct and unique.

Dissolution of methane shifts peak to lower frequency and broadens it.

Methane peak area can be calibrated to concentration.

Methane concentration can readily be converted to methane partial pressure via solubility law.

Methane partial pressure can be derived from concentration.

 

Downhole Analysis 

Tool analyzes wellbore fluid.

Service analysis requires reservoir fluid.

Internal controls identify when these fluids are not the same.

Knowing solution gas concentration enables accurate measurement of desorption pressure and gas content.

 

CGC Technology 

Convert partial pressure to gas content via adsorption isotherm.

 

Analyzing and Selecting the Reservoir 

Wellbore hydrostatic pressure “holds” solution gas in dissolved state.

If wellbore pressure is reduced below methane partial pressure, gas is released from solution.

If wellbore pressure is above methane partial pressure, gas remains in solution.

  • CGC test accurately reflects reservoir.

When other fluids are resident in the wellbore, the effects are obvious.

 

Selecting target coals--homogeneous and heterogeneous, living with reservoir heterogeneity , identifying sweet spots for dewatering

 

Conclusions 

CGC science is well established.

Technology used downhole extensively

CGC can assist in

•         Targeting the right coals

•         Scoping coal heterogeneity

•         Planning where to start producing.        

 

Downhole geochemical analysis is a better way to test your coals.

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