Simulation of CO_2 process for enhanced Coalbed Methane (ECBM) recovery at early stage of Production- a case study from Jharia Coalfield, India

摘要

Coalbed methane (CBM) or Coalbed gas has gained considerable ground as an unconventional source of energy in the recent past. Due to incremental demand for conventional fossil fuel both in industrial and domestic sector, coupled with dwindling reserves of oil and gas, hunt for unconventional sources of energy has gained momentum world over. Gas production in coal bed methane reservoir requires the pressure to drop sufficiently for gas to desorb from coal matrix and flow through natural fracture system of cleats. The complexity in the storage and transport mechanism warrant reservoir simulation which is an important tool in performance analysis of coal bed methane reservoirs.In the present study the coal samples were collected from Jharia Coalfield, Jharkhand (near Parbatpur, latitude 23°41'31.28" N and longitude 86°20'56.20" E and covered in the Survey of India toposheet No. 731/6). Numerical modelling and simulation studies for primary and CO_2 enhanced coal bed methane (ECBM) recovery have been carried out and depth of coalbed considered for present study ranges from 2969.16 to 3177.49ft. The adsorption isotherm parameters were evaluated as per Langmuir Adsorption model (Pl values for both CO_2 and CH_4 are 360 psia and 611 psia respectively, and V_L values for both CO_2 and CH_4 are 924 scf/ton and 578 scf/ ton respectively). Non-equilibrium two-phase black oil model was used for simulating the system. Using 5 spot pattern, efficiency of CO_2 injection was analysed and the optimum well spacing are determined. Sensitivity analysis using optimum well spacing were performed on dominant factor of production such as initial water saturation, sorption time and injection pressure for optimization of different operational parameters using ECLIPSE simulator.The studies suggest that CO_2 injection is very effective for enhancing the recovery of methane and reduces the dewatering period. Simulation study shows that CO_2 injection at the early stage also reduces total project duration, thus it may make the CBM project an economic one in the present CBM field.