Subsurface methane leakage in unconventional shale gas reservoirs: A review of leakage pathways and current sealing techniques

Shale gas extraction is seen to be a bridge fuel to the future due to lower GHG emissions compared to oil. However, it is also one of the most controversial topics due to the involvement of fracking in their production. Based on the analysis performed in this review we found that despite hydraulic fracture propagation being a possible conduit of methane leakage, the major cause of gas leakage is through leaking wells within the vicinity of fracturing sites. Remedial attempts have revealed promising yet inconsistent results, with no concrete method established for the methane leakage mitigation from shale gas wells.