Hydrogeology of a shallow coalbed methane play: A case study of Ardley coal in west- central, Alberta S.M. Harrison, M.Sc., P.Geol., P.Geo. SH Consulting Services In association with NLR Associates Inc.
Outline PART I Overview and Well Data Location Stratigraphy / Hydrostratigraphy Well Drilling / Completion / Testing Data Pressure Transmissivity (permeability) Water Chemistry PART II Production / Development / Regulatory Testing implications for well spacing Local Water Well Use Quantity / Quality Produced Water PART III - Regional Considerations Regional Pressure Regional Chemistry Synthesis Other
Study Location
Stratigraphic / Hydrostratigraphic Chart
Schematic Cross-section section 2000 A Cadomin X Disturbed Belt Schematic Cross-section central Alberta B Edmonton A B C C 1000 0 Coalspur Brazeau Paskapoo Scollard Wapiti Horseshoe Canyon X Lea Park & Colorado Belly River Mannville -1000 Paleozoic -2000 Precambrian 0 30 0 90 Horizontal Scale (km) A to B Vertical Exag. A to B = 25 B to C B to C x 75 Distribution of coal Plains Area (section view; modified AGS-EUB) EUB)
Data Coal Testholes (red) High number of testholes Data used for various mapping themes (e.g. structure contour map showing the distribution of Ardley coal
Data Hydrochemistry (DST) 8-10-047-04 W5M Some DST s show a-typical water chemistry. e.g. Anomalous DIC (bicarbonate or HCO 3 ) western part of area Indicator of biogenic gas?? Associated sulphate (200 mg/l) Higher gas content in parts of study area
0 Gamma Ray API 150 8-10-47-4 W5M KB = 859 m asl Target 25 50 8-10-47-4 W5M KB = 859 m asl 0 Gamma Ray API 150 75 100 125 Paskapoo Fm 150 Scollard Fm 200 Coal Zone Paskapoo Fm (lower) Coal Zone approx. 9 m thick 175 200 Scollard Fm (Ardley Coal Zone) 225 250 Gamma Ray 0 API 150 1900 Bulk Density kg/m 3 450 Density Correction -50 kg/m 3 2900 Photoelectric Effect 0.0 10.0 Caliper 275 Gamma Ray 0 API 150 1900 Bulk Density kg/m 3 450 Density Correction -50 kg/m 3 2900 Photoelectric Effect 0.0 10.0
Well Data what we wanted to What: evaluate and why Pressure Permeability Water Chemistry / Water Quality Why: Wet or dry coal Biogenic gas present Producibility Regulatory
Well 103 Field Methods Drilling / Completion Testing / Data Collection
Field Methods: Drilling Surface casing set Air/mud-drilled drilled to target Intermediate casing cemented at the top of coal target isolating coal Coal air drilled and reamed Liner set No well stimulation Well purged of fluid and allowed to equilibrate for 80 hours
Field Methods: Well Set-up and Testing Well 103 and obs. well Downhole sondes Pump rate in 103 = 26 m 3 /day @120 minutes pump gas locks (i.e. end of pump-off test) Build-up period
Well Data: Pressure Build-up up Data Build-up up period approx. 3500 minutes Static pressure head 1470 kpa (150 m or 50 m btop) Gas Lock @ 120 min (125 m of drawdown)
Well Data: Permeability gas/water? Cooper-Jacob Semi-log method or Theis recovery Late time data where water phase is assumed dominant Definitely permeability <5 md (likely <1 md)
Well Data Water Chemistry/Quality Routine: Na-HCO 3 type water, TDS = 1920 mg/l Na = 836 mg/l Cl = 250 mg/l SO 4 = <5 mg/l HCO 3 = 1650 mg/l Trace Metals (dissolved): Low dissolved and total dissolved metals (only Fe and Mn above CCME DWQ guidelines) Hydrocarbon (regulated): No hydrocarbon (e.g. BTEX) Sodium Adsorption Ratio (SAR) EC 58 (restricts use as irrigation water, for example, without upgrade) 3140 µs/cm
Isotopes: Isotope Geochemistry (water and dissolved gas) δ CDIC enriched +22 δ CCH4CH4 depleted -46 to -51 δ O/δ 2 H meteoric 3 H non-tritiated (test-well) δ 2 H CH4 /δ 2 H H2O suggest CO 2 reduction pathway
Part I: Summary and Conclusions Detailed compilation of well data pertaining specifically to the ACZ (part) hydraulic regime: Chemistry fresh water <2,000 mg/l TDS; relatively high sodium (Na); high HCO 3 (Na-HCO 3 type water) Isotope Geochem Meteoric; biogenic gas present Pressure near normal hydrostatic pressure (water) Permeability low; likely on the order of 1 md or less
Part II Production / Development and Regulatory Data are important to evaluate reservoir character/flow system as it pertains to, for example, development / production (e.g. quantity/quality of water, well spacing, etc.); CO 2 sequestration Relationship to water wells within the area?? Code of Practice vs. Water Act
Results Review: Recall permeability is relatively low (to water) must move water (i.e. depressurize) to attain gas flow 100 m Downhole sondes Pump rate in 103 = 26 m 3 /day @120 minutes pump gas locks (i.e. end of test) No interference effect
Production / Development Well Array: Yellow circle = 800 m radius Blue = water wells Red = prodn well (vertical)
Water Act may be applicable CBM Working Group / Alberta Environment EUB: 1. Code of Practice 2. Div. Approval 3. No Reporting Required <5m 3 /day no reporting required
Water Well Distn. Blue = water wells Test-well Within a 600 m radius test Yellow circle 800 m radius
Pressure vs. Depth (Test-well 103) 0 50 Paskapoo/Drift Hydrostatic gradient Well 103 Linear (Hydrostatic gradient) Depth (m) 100 150 Data Gap 200 250 0 500 1000 1500 2000 2500 Pressure (kpa)
s Piper Plot (water wells and 103) S3 Paskapoo / Drift observation well 60 4 20 + C l 40 60 Na + K Mg SO 80 80 60 40 40 80 S3 80 80 60 20 40 CO Ca + M g 20 20 sea water fresh-water 9 10 7 6 11 2 3 1 4 5 8 60 3 HCO 3 80 60 S O 4 40 40 20 S3 20 80 60 20 40 60 80 Ca 40 20 C l
Part III: Regional Considerations Regional Pressure Pressure vs. Depth Hydraulic Head vs. Elevation Hydraulic Head vs. Topo Cross-section section Regional Chemistry Piper δ 18 O vs. δ 2 H δ 2 H H2O vs. δ 2 H CH4 Synthesis Summary and interpretation of data Framework Flow Data Requirements
Pressure / Hydraulic Head lowermost Paskapoo - Ardley - Scollard Hydraulic Head distribution Cross- section line B-B
Topo vs. Hydraulic Head Topography (KB elevation) vs. Hydraulic Head Hydraulic Head (m 1200 1000 800 600 400 103 y = 0.457x + 401.5 R 2 = 0.5912 Group 1 Group 2 Linear (Group 1) correlation with topography possibly reflecting gravity or topo driven flow 200 0 0 200 400 600 800 1000 1200 1400 Topography (m asl)
Hydrostratigraphic Section B-B B Section B-B' 1200 Elevation (m asl) 1000 800 600 400 200 Well 103 Topography Test Interval Group 1 Hydraulic Head Group 1 Test Interal Group 2 Hydraulic Head Group 2 0-0.25 0.25 0.75 1.25 1.75 2.25 2.75 Distance (relative) Cross-section section illustrating relative head differences in lowermost Paskapoo Ardley Scollard (Groups 1 and 2); break in hydraulic regime shown as dashed line
Chemistry Piper Diagram lowermost Paskapoo - Ardley - Scollard Well 103 is Na- HCO 3 type water Obs well shown for comparison (reflects higher sulphate) Water wells are Ca-Mg HCO 3 type
18 O vs δ 2 H regional δ 18 Water-line (solid) for Edmonton Station with GMWL (dashed) Well 103 plots along line suggesting meteoric origin
δ 2 H vs. H2O δ 2 HCH4 δ 2 H CH4 ( ) VSMOW CO 2 Reduction 0-50 -100-150 -200-250 -300-350 -400 CO2 reduction trend line δ 2 Η CΗ 4 = δ 2 Η H2O - 160 +/- 10 Coleman et al. 1988 Aravena et al. 1995 Aravena et al. 2003 Aravena et al. 2003 This Study S3 Martini et al. 2003-200 -150-100 -50 0 δ 2 Η H 2 O ( ) VSMOW CO 2 reduction appears to be the methanogenic pathway Contribution of biogenic gas
SYNTHESIS Cross-section section B-B B Hydraulic head distribution Cross- section line B-B
Synthesis 1200 18 O/ 2 H meteoric Section B-B' 1000 Well 103 Elevation (m asl) 800 600 400 200 Underpressured? Gas Prone? CO 2 reduction Topography Test Interval Group 1 Hydraulic Head Group 1 Test Interal Group 2 Hydraulic Head Group 2 0-0.25 0.25 0.75 1.25 1.75 2.25 2.75 Distance (relative) Recharging meteoric waters represented by Group 1 ( Paskapoo( Water System ) Regional flow system with local flow components normal or near-normal normal pressure Biogenic gas (methanogenesis( methanogenesis) ) generation within carbon-rich rich facies (coal) leading to high DIC (i.e. high HCO 3 concentrations enriched in 13 C) Gas-prone lower system?? - significantly underpressured
Flow SW Disturbed Belt 00/05-30-042-09 18 O/ 2 H meteoric Impact?? 00/11-01-044-08 18 O/ 2 H meteoric Subcrop NE local flow line 02/11-33-046-06 00/12-33-046-06 Impact?? regional flow line 511.37 497.9 Paskapoo 520.5 568 Paskapoo Scollard well 103 660 m asl 08-10-47-04 Gas Prone? ACZ Scollard Gas Prone? Flow details?? Local vs. intermediate vs. regional Additional data
Well Log (Detailed View) Detailed View of the Coal Zone Haynes Member (?) H = 805 m TDS = 1920mg/L Gas/Water Perm = 1mD Isotopes ( 2 H, 18 O, 13 C) 200 coal zone Scollard?
Summary and Conclusions Detailed compilation of well data pertaining specifically to the ACZ (part) hydraulic regime: Chemistry Na-HCO 3 type water Pressure near normal pressure Permeability low likely <1 md Synthesis and interpretation of data within regional context suggests at least parts of the Ardley lie within the Paskapoo Water System and have a component of biogenic gas Data are important to evaluate reservoir character/flow system as it pertains to, for example, production (quantity/quality of water, well spacing, potential for CO 2 sequestration) Flow system?????
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