Abstract
Coalbed methane (CBM) recovery is associated with production of large quantity of groundwater. The coal seams are depressurized by pumping of water for regular and consistent gas production. Usually, CBM operators need to pump >10 m3 of water per day from one well, which depends on the aquifer characteristics, drainage and recharge pattern. In India, 32 CBM blocks have been awarded for exploration and production, out of which six blocks are commercially producing methane gas at 0.5 million metric standard cubic feet per day. Large amount of water is being produced from CBM producing blocks, but no specific information or data are available for geochemical properties of CBM-produced water and its suitable disposal or utilization options for better management. CBM operators are in infancy and searching for the suitable solutions for optimal management of produced water. CBM- and mine-produced water needs to be handled considering its physical and geochemical assessment, because it may have environmental as well as long-term impact on aquifer. Investigations were carried out to evaluate geochemical and hydrogeological conditions of CBM blocks in Raniganj Basin. Totally, 15 water samples from CBM well head and nine water samples from mine disposal head were collected from Raniganj Basin. The chemical signature of produced water reveals high sodium and bicarbonate concentrations with low calcium and magnesium, and very low sulphate in CBM water. It is comprehend that CBM water is mainly of Na–HCO3 type and coal mine water is of Ca–Mg–SO4 and HCO3–Cl–SO4 type. The comparative studies are also carried out for CBM- and mine-produced water considering the geochemical properties, aquifer type, depth of occurrence and lithological formations. Suitable options like impounding, reverse osmosis, irrigation and industrial use after prerequisite treatments are suggested. However, use of this huge volume of CBM- and mine-produced water for irrigation or other beneficial purposes may require careful management based on water pH, EC, TDS, alkalinity, bicarbonate, sodium, fluoride, metals content and SAR values.
Highlights
In India, Coalbed methane (CBM) recovery is increasing day-by-day and expected to rise from current 0.5 to 7 mmscmd by 2020
It is comprehend that CBM water is mainly of Na–HCO3 type and coal mine water is of Ca– Mg–SO4 and HCO3–Cl–SO4 type
This paper presents the basic information on various physical and geochemical aspects of CBM- and coal mineproduced water
Summary
In India, CBM recovery is increasing day-by-day and expected to rise from current 0.5 to 7 mmscmd by 2020. Production of CBM is associated with pumping of large quantity of aquifer. CBM wells, in comparison with conventional oil and gas wells, produce large volume of water early in their life, and the water volume declines over time (Khatib and Verbeek 2003). Management of CBM-produced water is associated with challenges, and it is very expensive for operators. Understanding about produced water characteristics can help in increasing the production and knowledge of its chemical constituents; operators can determine the proper application of scale inhibitors and well treatment chemicals as well as identify potential wellbore or reservoir problem areas (Breit et al 1998). The geochemical properties of CBM-produced water vary with the original depositional environment, depth of burial and coal type, and it vary significantly across production areas (Jackson and Myers 2002). The suitability of CBM-produced water for agricultural purposes generally irrigation or stock watering, will depend on the quality of the produced water and on the conditions of the receiving areas (ALL 2003)
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