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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
Developing a new field with CGC
– Selecting target coals
– Living with reservoir heterogeneity
Identifying sweet spots for dewatering.
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CGC uses Raman spectroscopy (discovered 1928).
Raman is a vibrational spectroscopy.
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.
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.
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.
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
CGC science is well established.
Technology used CGC can assist in • Targeting the right coals • Scoping coal heterogeneity • Planning where to start producing.
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