CO{sub 2} SEQUESTRATION POTENTIAL OF TEXAS LOW-RANK COALS
The objectives of this project are to evaluate the feasibility of carbon dioxide (CO{sub 2}) sequestration in Texas low-rank coals and to determine the potential for enhanced coalbed methane (CBM) recovery as an added benefit of sequestration. There were three main objectives for this reporting period, which related to obtaining accurate parameters for reservoir model description and modeling reservoir performance of CO{sub 2} sequestration and enhanced coalbed methane recovery. The first objective was to collect and desorb gas from 10 sidewall core coal samples from an Anadarko Petroleum Corporation well (APCL2 well) at approximately 6,200-ft depth in the Lower Calvert Bluff Formation of the Wilcox Group in east-central Texas. The second objective was to measure sorptive capacities of these Wilcox coal samples for CO{sub 2}, CH{sub 4}, and N{sub 2}. The final objective was to contract a service company to perform pressure transient testing in Wilcox coal beds in a shut-in well, to determine permeability of deep Wilcox coal. Bulk density of the APCL2 well sidewall core samples averaged 1.332 g/cc. The 10 sidewall core samples were placed in 4 sidewall core canisters and desorbed. Total gas content of the coal (including lost gas and projected residual gas) averaged 395 scf/ton on an as-received basis. The average lost gas estimations were approximately 45% of the bulk sample total gas. Projected residual gas was 5% of in-situ gas content. Six gas samples desorbed from the sidewall cores were analyzed to determine gas composition. Average gas composition was approximately 94.3% methane, 3.0% ethane, and 0.7% propane, with traces of heavier hydrocarbon gases. Carbon dioxide averaged 1.7%. Coal from the 4 canisters was mixed to form one composite sample that was used for pure CO{sub 2}, CH{sub 4}, and N{sub 2} isotherm analyses. The composite sample was 4.53% moisture, 37.48% volatile matter, 9.86% ash, and 48.12% fixed carbon. Mean vitrinite reflectance was 0.54%. Coal rank was high-volatile C to B bituminous. Comparison of the desorbed gas content (395 scf/ton, as received) at reservoir pressure (2,697 psi) with the sorption isotherm indicates that Lower Calvert Bluff coal at this well site is oversaturated, but lost gas may have been overestimated. This high gas content suggests that little or no depressurization would be required to initiate methane production. Sorption isotherms results indicate that the sorptive capacity of CO{sub 2} is about 2.5 times that of CH{sub 4} at 1,000 psia. This ratio is similar to that of higher rank bituminous coals from other basins (e.g., Carroll, and Pashin, 2003), and it is very low in comparison to results of other low-rank coals and to the values that we used in our preliminary reservoir modeling. If this value from the APCL2 well is representative, Wilcox coals in this area will sequester less CO{sub 2} on a per ton basis than we had earlier inferred. However, because measured methane contents are higher, enhanced coalbed methane production potential is greater than we earlier inferred. Pressure transient testing for determining coal fracture permeability will be conducted soon by Pinnacle Technologies. The data from these analyses will be used to finalize our coal model for the reservoir simulation phase of the project.
- Research Organization:
- Texas Engineering Experiment Station (US)
- Sponsoring Organization:
- (US)
- DOE Contract Number:
- FC26-02NT41588
- OSTI ID:
- 837839
- Resource Relation:
- Other Information: PBD: 1 Feb 2005
- Country of Publication:
- United States
- Language:
- English
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