Management of Coalbed Methane and Coal Mine Produced Water for Beneficial Use in Damodar Basin of India

Abstract

In India, coalbed methane (CBM) is rapidly emerging source of natural gas with current production levels of about 1.35 million metric standard cubic metres per day (mmscm/day) and expected to rise to 7 mmscm/day by 2020. CBM extraction associated with pumping of large amount of formation water to reduce hydrostatic pressure existing on gas-bearing coalbeds. At this time out of 32 awarded CBM blocks, only 6 blocks have commenced recovery of methane gas from about 200 wells, with water producing rate more than 20 m3 per well per day. Out of 424 underground coal mines, only 10–20 places, mine water is being used for domestic, washing of coal and other industrial uses with or without treatment. The high cost of water disposal and lack of efficient technology for treatment are barriers to advance development of CBM reserves in the country. If large amount of CBM and mine-produced water handled economically and treated efficiently to make it acceptable for different uses or surface discharge, it may become a source of fresh water. Produced water samples were collected from CBM production wells and different coal mines water disposal heads in various locations of Damodar basin and analysed using ICPMS and water analysis kit for the assessment of water quality. In CBM water the physical parameters like pH, electrical conductivity, TDS and alkalinity observed in the range of 7.23–8.72, 1678–5436 µs/cm, 1124.26–3642.26 mg/L and 1650–2150 mg/L respectively, whereas in coal mine water, it varies from 6.78 to 8.58, 623–1513 µs/cm, 417.41–1013.71 mg/L and 100–800 mg/L respectively. CBM water is mainly of Na–HCO3 type and coal mine water is Ca–Mg–SO4 and HCO3–Cl–SO4 type. Much of the produced water has total dissolve solids (TDS) content <3000 mg/L and can potentially be put to beneficial use within and outside the CBM industry. Sodium adsorption ratio (SAR) was calculated for each sample using concentration of sodium to the sum of the concentrations of calcium and magnesium. The higher the SAR, the greater the potential for reduced permeability, which reduces infiltration, reduces hydraulic conductivity, and causes surface crusting. Trace metal concentrations have a very similar range of distribution in both CBM and coal mine water. With minimal processing, much of this water may be used for a variety of industrial and agricultural purposes controlling pH, electrical conductivity, alkalinity, bicarbonate, sodium, fluoride, metals and SAR values. Drinking water availability is the major issue in Damodar basin; however the large quantity of water generated from CBM production wells can be potential freshwater sources for various applications, including potable consumption after RO treatment. This investigation employs CBM and mine water management strategies considering the spectrum of geologic, hydrologic and geochemical parameters to ensure environmental protection, foster beneficial use, treatment options of produced waters and improving reservoir performance. The CBM-produced water is derived from virgin multiple deep aquifer system having higher concentrations of Na+ and HCO3 −, while mine water is of shallow aquifer continuously flushed by seasonal rain water percolation and water drainage system employed in underground coal mine. It also reviews specific water treatment options and associated economics for managing CBM-produced water in Damodar basin.