Unconventional (oil and gas) reservoirs, or unconventional resources (resource plays) are accumulations where oil and gas phases are tightly bound to the rock fabric by strong capillary forces, requiring specialized measures for evaluation and extraction.[1]
^SPE (2018). Petroleum Resource Management System (revised June 2018) (1.01 ed.). Society of Petroleum Engineers. p. 52. ISBN978-1-61399-660-7.