Bartin-Amasra coal field was found convenient for enhanced coalbed methane (ECBM) recovery among the other fields in Zonguldak Coal Basin, Turkey. The lithologic information were examined and the depths of the coal seams and the locations of the wells were visualized to perform a reliable correlation between 63 coal layers existed in the area.
The initial methane in place found in the coal layers both in free and adsorbed states were estimated using probabilistic simulations resulted in possible reserve (P10) of 72.97 billion scf, probable reserve (P50) of 47.74 billion scf and proven reserves (P90) of 30.46 billion scf. Since the Amasra coal reservoir is not saturated with water, almost 10% of the total gas in place was found to be in the cleats as free gas.
ECBM recovery was simulated with CMG-GEM module using Coal Layer #26 which has more initial gas in place, average thickness of 1.8 m and depth of 545 m. The effects of adsorption, compressibility, density, permeability, permeability anisotropy, and porosity and water saturation parameters were examined. Cumulative methane production was enhanced with the injection of CO2 approximately 23% more than that of CBM recovery. Injected CO2 amount of 5192 tonnes/year in layer #26 was only capable to sequester only 0.3% of the yearly CO2 emission of Zonguldak Catalagzi Power Plant nearby. Considering the gas in place capacity of the coal layer #26 as 15% of the resource area-A, it can be said that the project aiming ECBM recovery rather than CO2 sequestration would be successful.
Long-term storage of CO2 can be accomplished by separating CO2 from flue gases and subsequently injecting it into active or depleted oil and gas fields with enhanced oil recovery (EOR), deep saline aquifers, gas-rich shales, methane hydrate formations, salt caverns, unmineable coalbeds, other geological formations, or the ocean. Among these sequestration options, those that allow the production of a value-added product such as methane (CH4) or petroleum are the options that are the most attractive and will likely be developed first. One of these value-added processes is the sequestration of CO2 in gassy coalbeds with the simultaneous recovery of methane1.
CBM reservoirs hold gas primarily as a sorbed phase at liquid-like densities within the micro-porous matrix of the coal, not as free gas in conventional gas reservoirs. In CBM some free gas exists in the natural fractures or cleats of the coal, but this gas represents only a small fraction of the total gas. CBM recovery is, therefore, primarily recovery of desorbing gas2. Primary production of CBM recovers only 20%-60% of original gas in place (GIP). New technologies have been proposed to recover a larger fraction of GIP. Injected CO2 is preferentially adsorbed (and remains sequestered within the seam) at the expense of the coalbed methane. The key reservoir screening criteria for successful application of CO2-ECBM include laterally continuous and permeable coal seams, concentrated seam geometry, and minimal faulting and reservoir compartmentalization3.
