Coal Bed Methane (black coal, green future.)

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Dwight Baldwin
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Global coal distribution Coal Bed Methane (black coal, green future.) What is CMB?

anaerobic bacteria in the early stage of coalification - Kohleflözmethan (ger) In the old days was

(coal mine gas Grubengas) Thermogenic methane is formed mainly during coalification at temperatures

Conventional natural gas Rock formations important to oil and gas: Source rock formation that

1 Global coal distribution Coal Bed Methane (black coal, green future.) What is CMB? Formation of Also know as: - Coalbed gas - Coal seam gas (CSM) Biogenic methane is produced by anaerobic bacteria in the early stage of coalification - Kohleflözmethan (ger) In the old days was mainly a safety risk! (coal mine gas Grubengas) Thermogenic methane is formed mainly during coalification at temperatures of C Canary in a coal mine. Conventional natural gas Rock formations important to oil and gas: Source rock formation that contains the organic matter Reservoir rock formation with pore volume capable of containing commercial quantities of hydrocarbons Cap rock impermeable formation that inhibits flow of fluids and gases Conventional natural gas Schematic view of a conventional gas deposit 1

Conventional natural gas Conventinal gas vs unconventional gas Conventional gas = Unconventional gas Reservoir rock: porous sandstone

source rock into the reservoir rock Coal is the source rock and the reservoir rock = unconventional gas Methane is adsorbed to the coal

not occur as free gas in the pore space of coal (only 1 2 %) does not conform to the ideal gas law (pv=nrt) Adsorption/desorption of gas

aqueous concentration (or gaseous partial pressure), Γ = amount adsorbed Γ max = maximum amount adsorbed as c increases = unconventional

2 Conventional natural gas Conventinal gas vs unconventional gas Conventional gas = Unconventional gas Reservoir rock: porous sandstone porosity 10-20% Unconventional gas: Shale gas Methane clathrate Oil shale gas Tight gas = unconventional gas did not migrate from the source rock into the reservoir rock Coal is the source rock and the reservoir rock = unconventional gas Methane is adsorbed to the coal matrix Coal can store around 6 to 7 times more methane than the equivalent volume of rock in a conventional reservoir The methane does not occur as free gas in the pore space of coal (only 1 2 %) does not conform to the ideal gas law (pv=nrt) Adsorption/desorption of gas to/from the surface of a solid can be described by the Langmuir Isotherm Γ = Γ max (K c/1+ K c) K = Langmuir equilibrium constant, c = aqueous concentration (or gaseous partial pressure), Γ = amount adsorbed Γ max = maximum amount adsorbed as c increases = unconventional gas Face cleats Butt cleats Desorption from internal coal surfaces Diffusion through the matrix and micropores Fluid flow into natural fracture network 2

Face cleats Butt cleats Cleats form an interconnected network in the coal, normal

cleats is normally less than 25 mm and the aperture is 0.

intrinsic tensile force (shrinkage), fluid pressure and tectonic stress Tectonic

Permeabilty ratio face cleats : butt cleats may range from 1:1 to 17:1 production

php production Two factors are important for production Gas content / Adsorption

3 Face cleats Butt cleats Cleats form an interconnected network in the coal, normal to bedding Angle between face cleats and butt cleats is around 90 Spacing between cleats is normally less than 25 mm and the aperture is mm Butt cleats (shorter) terminate at a face cleat Cleats are formed due to intrinsic tensile force (shrinkage), fluid pressure and tectonic stress Tectonic stress controls the geometric pattern of the cleats (face cleats parallel to S H ) Permeabilty ratio face cleats : butt cleats may range from 1:1 to 17:1 production production Two factors are important for production Gas content / Adsorption capacity Gas content and adsorption capacity of the coal Hydraulic permeability of the coal Gas content / Adsorption capacity Gas content / Adsorption capacity 3

4 Example from San Juan Basin: Total OGIP 28.2 BCF (790 mio m 3 ) Gas content / Adsorption capacity 65 m/ 8.9 BCF 7 m/ 180 MMCF 134 m/ 16.9 BCF Peak production: 10.5 MMCF/d 130 psia/9 bar 1091 psia/75 bar 1819 psia/125 bar Drilling of an exploratory borehole Drilling of an exploratory borehole Permeability testing Permeability testing Assembling of packer Installation of packer 4

5 What is a packer? Expandable rubber sleeve Permeability testing Installation of packer Central tube (mandrel) Steel ends Couplings Permeability testing with a packer Mostly using a double packer to isolate a borehole test section Type of tests Injection-falloff test Inject / produce water into / from the test section Pressure and flow in test zone 5

Type of tests Falloff ( after injection test) Injection Falloff Type of tests Flow [l/min] 12 8 4 0 9000 DST (Drill Stem Test) Consists of a drawdown phase and a buildup phase Pressure [kpa] 8500

6 Type of tests Falloff ( after injection test) Injection Falloff Type of tests Flow [l/min] DST (Drill Stem Test) Consists of a drawdown phase and a buildup phase Pressure [kpa] Elapsed Time [s] Understanding pressure diagrams of DSTs Position of gauges: Pressure in test string above valve Type of tests DST (Drill Stem Test) Pressure (psi) Pressure in test string Pressure in test interval Pressure below packer Pressure in test section 100 Pressure below lower packer Elapsed time (hrs) 8 10 Hydraulic fracturing Hydraulic Fracturing Technique: Hydraulic fracturing is a technique to measure rock stress. Water is injected in a packed-off test section using a high pressure pump. In oil and gas industry: to increase the permeability of the rock - sometimes in combination with injection of propants. Injection of water under high pressure in a packed-off borehole section Theory: Fracturing the rock perpendicular to the direction of the minimum principal stress 6

Potential problems with Water management of pumped water

Use of land for exploration UCG Underground coal

and steam Extraction of syngas Gasification process

by natural gas) UCG Underground coal gasification Set-up

drilling UCG-CCS Underground coal gasification / carbon

7 Potential problems with Water management of pumped water Impact on groundwater level/quality Noise from compressors Use of land for exploration UCG Underground coal gasification Principle of UCG Injection of oxygen (55%) and steam Extraction of syngas Gasification process Production of synthetic gas from coal (town gas replaced by natural gas) UCG Underground coal gasification Set-up of injection wells and production well Directional drilling UCG-CCS Underground coal gasification / carbon capture and storage UCG-CCS Underground coal gasification / carbon capture and storage 7

8 E Enhanced coal bed methane Idea of CCS (Carbon Capture and Storage) CCS involves: Carbon capture Capture of CO 2 at larger sources Transport of CO 2 Injection of CO 2 Storage of CO 2 in deep saline reservoir rock Storage of CO 2 in deep geological formations 1. Immobilization of CO2 forming tiny droplets in small pores. 2. Dissolution in brine 3. Reaction with minerals in aquifer. Formation of solid matter. 8

Sleipner West: the first commercial-scale project In operation since 1996

inspection of the packer Injection into Utsira formation (brine saturated

$2 sequestration Hydraulic fracturing for CO 2 sequestration Installation of packer$ $of the cap rock Hydraulic fracturing for CO 2 sequestration of the cap rock Large$

9 Sleipner West: the first commercial-scale project In operation since 1996 Separation of CO 2 Permeability testing for CO 2 sequestration Preparation and inspection of the packer Injection into Utsira formation (brine saturated sandstone, thickness 250 m) 1 x 10 6 t of CO 2 per year Permeability testing for CO 2 sequestration Hydraulic fracturing for CO 2 sequestration Installation of packer Extended Leakoff Test (hydraulic fracturing test) Aim: Determine the frac pressure of the cap rock Hydraulic fracturing for CO 2 sequestration Extended Leakoff Test (hydraulic fracturing test) Aim: Determine the frac pressure of the cap rock Large scale water injection 9

Coalbed Methane- Fundamental Concepts

Coalbed Methane- Fundamental Concepts By: K. Aminian Petroleum & Natural Gas Engineering Department West Virginia University Introduction This article is the first in a series of articles that will discuss