Adsorption Studies of Natural Gas Storage in Devonian Shales
- Xiao-Chun Lu (Texas A and M U.) | Fan-Chang Li (Texas A and M U.) | A.T. Watson (Texas A and M U.)
- Document ID
- Society of Petroleum Engineers
- SPE Formation Evaluation
- Publication Date
- June 1995
- Document Type
- Journal Paper
- 109 - 113
- 1995. Society of Petroleum Engineers
- 5.1.1 Exploration, Development, Structural Geology, 5.4.2 Gas Injection Methods, 4.6 Natural Gas, 5.8.2 Shale Gas, 5.2.1 Phase Behavior and PVT Measurements, 5.6.4 Drillstem/Well Testing, 5.6.1 Open hole/cased hole log analysis, 5.10.2 Natural Gas Storage, 5.6.9 Production Forecasting, 5.5.8 History Matching, 5.5 Reservoir Simulation
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Significant amounts of natural gas exist as an adsorbed, or condensed, phase in Devonian shale formations and other unconventional gas resources. The amount of the adsorbed phase depends on the pressure and temperature. The Langmuir isotherm has been used to describe the pressure dependence. However, temperature dependence has not been explored. This is important to evaluate thermal stimulation as a recovery method and to extrapolate laboratory measurements to reservoir conditions. We investigate adsorption as a function of both pressure and temperature. We found that the effects of temperature are significant and that the Langmuir model does not describe adsorption adequately. We reconciled the data with bi-Langmuir models.
Large amounts of natural gas accumulations exist in the Devonian shale formations of the Appalachian, Michigan, and Illinois basins. Several thousand trillion cubic feet of gas are estimated to be contained in this area.The gas storage mechanisms in Devonian shale formations are quite different from those in conventional gas reservoirs. Natural gas is believed to be stored as an "adsorbed" phase on the shale matrix and organic materials, and as conventional "free" gas in the porous space. Experimental measurements have indicated that more than 50% of the total gas storage in the Devonian shales may exist as an adsorbed phase.
Modeling the adsorbed phase can effect selection of stimulation techniques as well as production forecasts. Adsorption generally cannot be determined accurately from history matching production data alone. A well-test design has been developed for that purpose, but it has yet to be demonstrated in the field. The laboratory testing of actual shale samples from reservoir cores is important for characterizing adsorption.
Previous laboratory studies have reported data from measurements at single temperatures, and the measured data have been represented by Langmuir isotherms. While there is evidence that such representations can describe the dependence of pressure on adsorption adequately, the effect of temperature on adsorption has not been explored. Knowledge of the effect of temperature on adsorption in shales is important for several reasons. First, thermal stimulation could be used if the effects of temperature on desorption are sufficiently large. Second, the use of isotherms at reservoir temperatures that do not match the specific temperature for which they are used may result in poor predictions of reservoir behavior. Suitable representation of temperature effects can lead to methods for extrapolation or interpolation of measured data to reservoir conditions. Third, representations for adsorption should be adequately tested as functions of pressure and temperature if they are to be used with confidence in reservoir simulation.
In this work, we report experimental adsorption measurements for shale samples at various temperatures. We investigate the representation of adsorption behavior as a function of both temperature and pressure. We use the measured data to develop other basic thermodynamic quantities important for gas/shale adsorption.
|File Size||1 MB||Number of Pages||5|